阅读说明：本技术 光掩模坯料及光掩模的制造方法、以及显示装置的制造方法 (Photomask blank, method for manufacturing photomask, and method for manufacturing display device ) 是由 安森顺一 浅川敬司 田边胜 于 2021-03-23 设计创作，主要内容包括：本发明的目的在于提供可以制造遮光膜图案的精度优异、并且具有通过曝光转印图案时可以实现高图案精度的光学特性的光掩模的光掩模坯料。为此,本发明的光掩模坯料是在制作显示装置制造用光掩模时使用的光掩模坯料,其具有：透明基板、和设置于透明基板上的遮光膜,遮光膜从透明基板侧起具备第1反射抑制层、遮光层及第2反射抑制层,第1反射抑制层从透明基板侧起依次具备氧相对于氮的比例相对较少的第1低度氧化铬层、和氧相对于氮的比例相对较多的第1高度氧化铬层,第2反射抑制层从透明基板侧起依次具备氧相对于氮的比例相对较少的第2低度氧化铬层、和氧相对于氮的比例相对较多的第2高度氧化铬层。(The present invention aims to provide a photomask blank which can manufacture a photomask having excellent precision of a light shielding film pattern and optical characteristics capable of realizing high pattern precision when a pattern is transferred by exposure. Therefore, the photomask blank of the present invention is a photomask blank used in manufacturing a photomask for manufacturing a display device, and comprises: the light-shielding film includes a 1 st reflection suppression layer, a light-shielding layer, and a 2 nd reflection suppression layer from the transparent substrate side, the 1 st reflection suppression layer includes, in order from the transparent substrate side, a 1 st low-degree chromium oxide layer in which a ratio of oxygen to nitrogen is relatively small, and a 1 st high-degree chromium oxide layer in which a ratio of oxygen to nitrogen is relatively large, and the 2 nd reflection suppression layer includes, in order from the transparent substrate side, a 2 nd low-degree chromium oxide layer in which a ratio of oxygen to nitrogen is relatively small, and a 2 nd high-degree chromium oxide layer in which a ratio of oxygen to nitrogen is relatively large.)

1. A photomask blank used for manufacturing a photomask for manufacturing a display device,

the photomask blank has:

a transparent substrate formed of a material substantially transparent to exposure light, and

a light shielding film disposed on the transparent substrate and formed of a material that is substantially opaque to the exposure light,

the light shielding film is provided with, from the transparent substrate side: a 1 st reflection suppressing layer, a light shielding layer and a 2 nd reflection suppressing layer,

the 1 st reflection suppression layer includes, in order from the transparent substrate side: a 1 st chromium oxide layer containing chromium, oxygen and nitrogen, and having a smaller proportion of oxygen than nitrogen; and a 1 st high chromium oxide layer containing chromium, oxygen and nitrogen, and having a larger proportion of oxygen than nitrogen,

the 2 nd reflection suppression layer includes, in order from the transparent substrate side: a 2 nd low-degree chromium oxide layer containing chromium, oxygen and nitrogen, and having a smaller proportion of oxygen than nitrogen; and a 2 nd high chromium oxide layer containing chromium, oxygen and nitrogen, and having a larger proportion of oxygen than nitrogen,

the composition and film thickness of at least the 1 st reflection suppression layer, the light shielding layer, and the 2 nd reflection suppression layer are set so that the reflectance of the front surface and the back surface of the light shielding film with respect to the exposure wavelength of 300nm to 436nm of the exposure light is 15% or less, and the optical density is 3.0 or more, respectively.

2. The photomask blank of claim 1, wherein,

the light-shielding layer is formed of a chromium-based material having a chromium content of 97 at% or more and 100 at% or less.

3. The photomask blank of claim 1 or 2, wherein,

the ratio of oxygen to nitrogen in the 2 nd-level chromium oxide layer is 2.5 or more and 10 or less.

4. The photomask blank according to any one of claims 1 to 3, wherein,

the ratio of oxygen to nitrogen in the 1 st-height chromium oxide layer is 2.5 or more and 10 or less.

5. The photomask blank according to any one of claims 1 to 4, wherein,

the 1 st reflection suppression layer contains carbon.

6. The photomask blank according to any one of claims 1 to 5, wherein,

the 2 nd reflection suppression layer contains carbon.

7. The photomask blank according to any one of claims 1 to 6, wherein,

a chromium content of 25 at% to 75 at%, an oxygen content of 15 at% to 45 at%, and a nitrogen content of 2 at% to 30 at% in the 1 st reflection suppressing layer,

the 2 nd reflection suppression layer has a chromium content of 25 at% or more and 75 at% or less, an oxygen content of 15 at% or more and 60 at% or less, and a nitrogen content of 2 at% or more and 30 at% or less.

8. The photomask blank according to any one of claims 1 to 7, wherein,

the 1 st and 2 nd reflection suppressing layers each have a region in which the content of at least one element of oxygen and nitrogen changes continuously or stepwise in the film thickness direction.

9. The photomask blank according to any one of claims 1 to 8, wherein,

a composition gradient region in which elements constituting the 1 st reflection suppression layer, the light-shielding layer, and the 2 nd reflection suppression layer continuously have a composition gradient is provided between the transparent substrate and the 1 st reflection suppression layer, between the 1 st reflection suppression layer and the light-shielding layer, and between the light-shielding layer and the 2 nd reflection suppression layer.

10. The photomask blank according to any one of claims 1 to 9, wherein,

the surface of the light-shielding film has an in-plane uniformity of reflectance with respect to an exposure wavelength of the exposure light of 3% or less.

11. The photomask blank according to any one of claims 1 to 10, wherein,

a semi-transparent film is further provided between the transparent substrate and the light-shielding film, and the optical density of the semi-transparent film is lower than that of the light-shielding film.

12. The photomask blank according to any one of claims 1 to 10, wherein,

a phase shift film is further provided between the transparent substrate and the light shielding film.

13. A method of manufacturing a photomask, the method comprising:

a step of preparing a photomask blank according to any one of claims 1 to 12; and

and forming a light shielding film pattern on the transparent substrate by forming a resist film on the light shielding film and etching the light shielding film using a resist pattern formed from the resist film as a mask.

14. A method of manufacturing a photomask, the method comprising:

a step of preparing a photomask blank according to any one of claims 1 to 12;

forming a resist film on the light-shielding film, and etching the light-shielding film using a resist pattern formed of the resist film as a mask to form a light-shielding film pattern on the transparent substrate; and

and etching the semi-transparent film by using the light shielding film pattern as a mask to form a semi-transparent film pattern on the transparent substrate.

15. A method of manufacturing a photomask, the method comprising:

a step of preparing a photomask blank according to any one of claims 1 to 12;

forming a resist film on the light-shielding film, and etching the light-shielding film using a resist pattern formed of the resist film as a mask to form a light-shielding film pattern on the transparent substrate; and

and etching the phase shift film using the light shielding film pattern as a mask to form a phase shift film pattern on the transparent substrate.

16. A method of manufacturing a display device, the method comprising:

an exposure step of placing the photomask obtained by the method for manufacturing a photomask according to any one of claims 13 to 15 on a mask stage of an exposure apparatus, and exposing and transferring at least one light-shielding film pattern of the light-shielding film pattern, the semi-light-transmitting film pattern, and the phase shift film pattern formed on the photomask to a resist formed on a display device substrate.

Technical Field

The present invention relates to a photomask blank, a method for manufacturing a photomask, and a method for manufacturing a display device.

Background

In recent years, not only large screens and wide viewing angles but also high definition and high speed Display have been rapidly performed on Display devices such as FPDs (Flat Panel displays) represented by LCDs (Liquid Crystal displays). In order to achieve high definition and high speed display, it is one of the necessary elements to fabricate electronic circuit patterns such as fine and highly dimensionally accurate elements and wirings. Photolithography is often used for patterning electronic circuits for display devices. Therefore, a photomask for manufacturing a display device, in which a fine and highly precise pattern is formed, is required.

A photomask for manufacturing a display device is manufactured from a photomask blank. A photomask blank is formed by providing a light-shielding film made of a material opaque to exposure light on a transparent substrate made of synthetic quartz glass or the like. For example, as disclosed in patent document 1, in a photomask blank or a photomask, in order to suppress the reflection of light from a transferred object on the surface of the photomask and the re-reflection of the light on the transferred object again when the panel of the transferred object is exposed using the photomask, antireflection films are provided on both front and back surfaces of a light-shielding film, and the photomask blank is formed of a film in which a back surface antireflection film, a light-shielding film, a reflection-attenuation film, and an antireflection film are laminated in this order from the transparent substrate side, for example. A photomask is manufactured by patterning each film constituting a photomask blank by wet etching or the like to form a predetermined light-shielding film pattern.

Documents of the prior art

Patent document

Patent document 1: korean granted patent No. 10-1473163 publication

Disclosure of Invention

Problems to be solved by the invention

However, when a photomask blank is formed by patterning a light-shielding film by etching, the light-shielding film pattern of the photomask blank is required to have high accuracy. This is because, if the accuracy of the light shielding film pattern is low, the line width of the transferred pattern and the size of the hole pattern become uneven when the light shielding film pattern is transferred to the object by using the photomask, and the CD Uniformity (CD Uniformity) of the pattern formed on the object is impaired.

In addition, when a photomask blank is subjected to exposure treatment of a transfer object using a photomask, the light-shielding film surface is also required to have a low reflectance so that a highly accurate transfer pattern can be transferred. If the surface of the light-shielding film pattern formed on the photomask has a high reflectance, the light reflected from the object to be transferred repeats reflection with the surface of the light-shielding film pattern of the photomask during exposure processing, and so-called flare (flare) may occur. For example, the light reflected by the back surface of the light-shielding film pattern of the photomask from the exposure device is reflected again by the optical system of the exposure device (transfer device) and enters the photomask again, and so-called return light may be generated. These flare spots and return light may impair the pattern accuracy of a transfer pattern formed using a photomask.

Accordingly, an object of the present invention is to provide a photomask blank having optical characteristics such that a highly accurate light-shielding film pattern can be obtained when a photomask is manufactured by patterning a light-shielding film in the photomask blank by etching, and pattern accuracy of a transfer target is improved when the transfer pattern is transferred to the transfer target using the photomask.

Means for solving the problems

(scheme 1)

A photomask blank used for manufacturing a photomask for manufacturing a display device,

the photomask blank has:

a transparent substrate formed of a material substantially transparent to exposure light, and

a light shielding film formed of a material which is provided on the transparent substrate and is substantially opaque to the exposure light,

the light shielding film includes, from the transparent substrate side: a 1 st reflection suppressing layer, a light shielding layer and a 2 nd reflection suppressing layer,

the 1 st reflection suppressing layer includes, in order from the transparent substrate side: a 1 st chromium oxide layer containing chromium, oxygen and nitrogen, and having a smaller proportion of oxygen than nitrogen; and a 1 st high chromium oxide layer containing chromium, oxygen and nitrogen, and having a larger proportion of oxygen than nitrogen,

the 2 nd reflection suppressing layer includes, in order from the transparent substrate side: a 2 nd low-degree chromium oxide layer containing chromium, oxygen and nitrogen, and having a smaller proportion of oxygen than nitrogen; and a 2 nd high chromium oxide layer containing chromium, oxygen and nitrogen, and having a larger proportion of oxygen than nitrogen,

at least the 1 st reflection suppression layer, the light shielding layer, and the 2 nd reflection suppression layer have compositions and film thicknesses set so that the reflectivities of the front surface and the back surface of the light shielding layer with respect to the exposure wavelength of 300nm to 436nm of the exposure light are 15% or less, respectively, and the optical density is 3.0 or more.

(scheme 2)

The photomask blank of scheme 1, wherein,

the light-shielding layer is formed of a chromium-based material having a chromium content of 97 at% or more and 100 at% or less.

(scheme 3)

The photomask blank according to scheme 1 or 2, wherein,

the ratio of oxygen to nitrogen in the 2 nd-level chromium oxide layer is 2.5 or more and 10 or less.

(scheme 4)

The photomask blank according to any of claims 1 to 3, wherein,

the ratio of oxygen to nitrogen in the 1 st-height chromium oxide layer is 2.5 or more and 10 or less.

(scheme 5)

The photomask blank according to any of schemes 1 to 4, wherein,

the 1 st reflection suppression layer contains carbon.

(scheme 6)

The photomask blank according to any one of claims 1 to 5, wherein,

the 2 nd reflection suppressing layer contains carbon.

(scheme 7)

The photomask blank according to any one of claims 1 to 6, wherein,

the first reflection suppressing layer 1 has a chromium content of 25 at% to 75 at%, an oxygen content of 15 at% to 45 at%, and a nitrogen content of 2 at% to 30 at%,

the 2 nd reflection suppressing layer has a chromium content of 25 at% to 75 at%, an oxygen content of 15 at% to 60 at%, and a nitrogen content of 2 at% to 30 at%.

(scheme 8)

The photomask blank according to any one of claims 1 to 7, wherein,

the 1 st reflection suppression layer and the 2 nd reflection suppression layer each have a region in which the content of at least one element of oxygen and nitrogen changes continuously or stepwise in composition along the film thickness direction.

(scheme 9)

The photomask blank according to any of claims 1 to 8, wherein,

a composition gradient region in which elements constituting the 1 st reflection suppression layer, the light shielding layer, and the 2 nd reflection suppression layer continuously have a composition gradient is provided between the transparent substrate and the 1 st reflection suppression layer, between the 1 st reflection suppression layer and the light shielding layer, and between the light shielding layer and the 2 nd reflection suppression layer.

(scheme 10)

The photomask blank according to any one of claims 1 to 9, wherein,

the surface of the light-shielding film has an in-plane uniformity of reflectance with respect to an exposure wavelength of the exposure light of 3% or less.

(scheme 11)

The photomask blank according to any of claims 1 to 10, wherein,

a semi-transparent film is further provided between the transparent substrate and the light-shielding film, and the optical density of the semi-transparent film is lower than that of the light-shielding film.

(scheme 12)

The photomask blank according to any of claims 1 to 10, wherein,

a phase shift film is further provided between the transparent substrate and the light shielding film.

(scheme 13)

A method of manufacturing a photomask, the method comprising:

preparing a photomask blank according to any one of claims 1 to 12; and

and forming a light-shielding film pattern on the transparent substrate by forming a resist film on the light-shielding film and etching the light-shielding film using a resist pattern formed of the resist film as a mask.

(scheme 14)

A method of manufacturing a photomask, the method comprising:

preparing a photomask blank according to any one of claims 1 to 12;

forming a resist film on the light-shielding film, and etching the light-shielding film using a resist pattern formed of the resist film as a mask to form a light-shielding film pattern on the transparent substrate; and

and etching the semi-transparent film using the light-shielding film pattern as a mask to form a semi-transparent film pattern on the transparent substrate.

(scheme 15)

A method of manufacturing a photomask, the method comprising:

preparing a photomask blank according to any one of claims 1 to 12;

forming a resist film on the light-shielding film, and etching the light-shielding film using a resist pattern formed of the resist film as a mask to form a light-shielding film pattern on the transparent substrate; and

and etching the phase shift film using the light-shielding film pattern as a mask to form a phase shift film pattern on the transparent substrate.

(scheme 16)

A method of manufacturing a display device, the method comprising:

an exposure step of placing the photomask obtained by the method for manufacturing a photomask according to any one of claims 13 to 15 on a mask stage of an exposure apparatus, and exposing and transferring at least one light-shielding film pattern of the light-shielding film pattern, the semi-light-transmitting film pattern, and the phase-shift film pattern formed on the photomask to a resist formed on a display device substrate.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, it is possible to obtain a photomask blank capable of manufacturing a photomask having optical characteristics such that a highly accurate light-shielding film pattern can be obtained when the photomask blank is manufactured by patterning a light-shielding film in the photomask blank by etching, and the pattern accuracy of a transfer target is improved when the transfer pattern is transferred to the transfer target using the photomask.

Drawings

Fig. 1 is a cross-sectional view showing a schematic configuration of a photomask blank according to an embodiment of the present invention.

Fig. 2 is a graph showing the results of composition analysis in the film thickness direction in the photomask blank of example 1.

Fig. 3 is a graph showing a reflectance spectrum of the front and back surfaces for the photomask blank of example 1.

Fig. 4 is a graph showing the results of composition analysis in the film thickness direction in the photomask blank of reference example 1.

Fig. 5 is a graph showing a reflectance spectrum of the front and back surfaces with respect to the photomask blank of reference example 1.

Description of the symbols

1 photomask blank

11 transparent substrate

12 light shielding film

13 st reflection inhibitor layer

13a 1 st low degree chromium oxide layer

13b layer of 1 st highly chromium oxide

14 light-shielding layer

15 nd 2 nd reflection suppressing layer

15a 2 nd low chromium oxide layer

15b layer of high order 2 chromium oxide

Detailed Description

< Studies by the present inventors >

The present inventors have studied a light-shielding film in a photomask blank in which a 1 st reflection suppression layer, a light-shielding layer, and a 2 nd reflection suppression layer are sequentially stacked from the transparent substrate side, in order to improve the optical characteristics thereof. However, it has been confirmed that: only by reducing the reflectance of the front and back surfaces of the light-shielding film in the photomask blank, the transfer pattern transferred to the object cannot be transferred with high accuracy.

As a result of examining the main causes thereof, it has been found that: the main cause of the deterioration of the transfer pattern accuracy of the transferred object is the in-plane unevenness of the reflectance of the front and back surfaces of the light-shielding film of the photomask blank (large in-plane variation of reflectance). In the light-shielding film, the 1 st and 2 nd reflection suppression layers are oxidized in order to reduce the reflectance thereof, but the degree of oxidation tends to vary within the plane. In addition, when the light-shielding layer is nitrided, the degree of nitridation tends to vary within the plane. The degree of oxidation of the 1 st and 2 nd reflection suppressing layers and the degree of nitridation of the light-shielding layer vary in the plane, and therefore, the reflectance of the light-shielding layer on the front surface and the reflectance of the light-shielding layer on the back surface are not uniform in the plane.

In addition, in order to further reduce the reflectance of the front surface and the back surface of the light-shielding film, the 1 st reflection suppression layer and the 2 nd reflection suppression layer need to be oxidized more strongly, but defects are likely to occur during film formation.

In a photomask, since the reflectance of the front and back surfaces of the light-shielding film pattern becomes nonuniform in the plane (in-plane variation in reflectance becomes large), the light-shielding film pattern of the photomask cannot be accurately transferred to a transfer target, and the CD uniformity of the transfer pattern of the obtained transfer target is impaired.

On the other hand, the factors that lower the pattern accuracy of the light-shielding film pattern obtained when etching the light-shielding film of the photomask blank include the inconsistency in the etching rate or etching time of each layer constituting the light-shielding film. If the etching rate and the etching time of each layer constituting the light-shielding film are greatly deviated, etching residue is likely to occur particularly in the region on the transparent substrate side of the 1 st reflection suppressing layer when the light-shielding film is etched to form the light-shielding film pattern. If etching residue occurs, the cross-sectional shape of the light-shielding film pattern is less likely to become vertical, and therefore the line width of the light-shielding film pattern differs between the front side and the back side, resulting in a decrease in the accuracy of the light-shielding film pattern of the photomask.

Based on the above, the present inventors have studied a method for making the reflectance of the front surface and the reflectance of the back surface of the light-shielding film in a photomask blank uniform in the plane. The 1 st and 2 nd reflection suppression layers in the photomask blanks so far are generally each composed of a single layer of a highly oxidized layer. However, when the 1 st and 2 nd reflection suppression layers are formed of a single highly oxidized layer, the variation in the degree of oxidation of the 1 st and 2 nd reflection suppression layers becomes more significant in the photomask blank surface, and the variation in the in-plane reflectance of the front and back surfaces of the light-shielding film is considered to be greatly influenced. Further, defects are likely to occur by highly oxidizing the 1 st and 2 nd reflection suppressing layers.

Therefore, the present inventors have focused on the 1 st and 2 nd reflection suppressing layers having a laminated structure of two layers having different degrees of oxidation, i.e., a layer having a low degree of oxidation and a layer having a high degree of oxidation. As a result, it was found that the reflectance of the front surface and the back surface of the light-shielding film can be made more uniform within the photomask blank surface or defects in the light-shielding film can be reduced, as compared with the case where the 1 st and 2 nd reflection suppression layers are formed of only a single highly oxidized layer. Further, it was found that by constituting the 1 st reflection suppression layer by a layer having a low degree of oxidation and a layer having a high degree of oxidation in this order from the transparent substrate side, etching residue at a portion of the 1 st reflection suppression layer on the transparent substrate side can be suppressed, and as a result, the cross-sectional shape of the light shielding film pattern can be made good, and a highly accurate light shielding film pattern can be obtained.

It has further been found that: from the viewpoint of making the reflectance of the front and back surfaces of the light-shielding film more uniform in the surface of the photomask blank, it is preferable to form the light-shielding layer of the light-shielding film as close as possible to a metal film that is not oxidized or nitrided. Heretofore, from the viewpoint of controlling the etching rate (etching time) of the light-shielding film, the light-shielding layer is composed of a metal film containing nitrogen (metal nitride film). However, if nitrogen is contained in the light-shielding layer, variation (unevenness) in the nitrogen content may occur in the surface of the photomask blank. Further, since the 1 st and 2 nd reflection suppression layers located above and below the light shielding layer contain oxygen, the 1 st and 2 nd reflection suppression layers also cause variation (unevenness) in the oxygen content in the photomask blank surface. In addition, the variation (non-uniformity) of the nitrogen content in the light-shielding layer in the surface of the photomask blank and the variation of the oxygen content in the 1 st and 2 nd reflection suppressing layers in the surface of the photomask blank cooperate with each other to increase the in-plane variation (non-uniformity) of the reflectance on the front and back surfaces of the light-shielding layer. In order to reduce the in-plane variation in reflectance of the front and back surfaces of the light-shielding film, it is more effective to reduce the variation in nitrogen in the front surface of the photomask blank contained in the light-shielding layer, and therefore, by reducing the content of nitrogen contained in the light-shielding layer (without adding nitrogen), the in-plane variation in reflectance of the front and back surfaces of the light-shielding film can be reduced.

The present invention is based on the above findings.

< one embodiment of the present invention >

Hereinafter, one embodiment of the present invention will be described. The following embodiments are merely one embodiment of the present invention, and the present invention is not limited to the embodiments. In the drawings, the same or corresponding portions are denoted by the same reference numerals, and the description thereof may be simplified or omitted. In the present specification, the numerical range expressed by the term "to" means a range including the numerical values described before and after the term "to" as the lower limit value and the upper limit value.

(1) Photomask blank

First, a photomask blank according to an embodiment of the present invention will be described. The photomask blank of the present embodiment is used for manufacturing a photomask for use in manufacturing a display device by exposing light having a single wavelength selected from a wavelength range of 300nm to 436nm, or light having a plurality of wavelengths (for example, j-line (wavelength 313nm), wavelength 334nm, i-line (wavelength 365nm), h-line (405nm), and g-line (wavelength 436 nm)).

Fig. 1 is a cross-sectional view showing a schematic configuration of a photomask blank according to an embodiment of the present invention. The photomask blank 1 includes a transparent substrate 11 and a light-shielding film 12. Hereinafter, a photomask blank in which a light-shielding film pattern (transfer pattern) of a photomask is a binary type of light-shielding film pattern will be described as one embodiment of the present invention.

(transparent substrate)

The transparent substrate 11 is not particularly limited as long as it is formed of a material substantially transparent to exposure light and has light transmittance. As the transmittance with respect to the exposure wavelength, a substrate material of 85% or more, preferably 90% or more can be used. Examples of the material for forming the transparent substrate 11 include: synthetic quartz glass, soda lime glass, alkali-free glass, low thermal expansion glass.

The size of the transparent substrate 11 is not particularly limited, and may be appropriately changed according to the size required for the photomask. For example, in the case of a photomask for manufacturing a display device, a rectangular transparent substrate 11 having a short side of 330mm to 1620mm in length can be used as the transparent substrate 11. As the transparent substrate 11, for example, substrates having a size of 330mm × 450mm, 390mm × 610mm, 500mm × 750mm, 520mm × 610mm, 520mm × 800mm, 800 × 920mm, 850mm × 1200mm, 850mm × 1400mm, 1220mm × 1400mm, 1620mm × 1780mm, and the like can be used. In particular, the length of the short side of the substrate is preferably 850mm or more and 1620mm or less. By using such a transparent substrate 11, photomasks for manufacturing display devices of G7 to G10 can be obtained.

(shading film)

The light shielding film 12 is formed of a material substantially opaque to exposure light, and is configured by laminating a 1 st reflection suppression layer 13, a light shielding layer 14, and a 2 nd reflection suppression layer 15 in this order from the transparent substrate 11 side. In the present specification, the light-shielding film 12 side of the two surfaces of the photomask blank 1 is referred to as the front surface, and the transparent substrate 11 side is referred to as the back surface.

The composition and film thickness of at least the 1 st reflection suppression layer 13, the light shielding layer 14, and the 2 nd reflection suppression layer 15 are set so that the reflectance of the front surface and the back surface of the light shielding film 12 with respect to the exposure wavelength of 300nm to 436nm of the exposure light is 15% or less, and the optical density is 3.0 or more. In addition, at least the composition ratio and the film thickness of the 1 st low-degree chromium oxide layer 13a and the 1 st high-degree chromium oxide layer 13b in the 1 st reflection suppression layer 13 may be adjusted so that the representative wavelength 365nm to 436nm of the exposure light from the back surface side of the light shielding film 12 becomes 10% or less.

(1 st reflection suppressing layer)

The 1 st reflection suppression layer 13 is provided on the surface of the light shielding layer 14 close to the transparent substrate 11 side of the light shielding layer 12, and is disposed close to an exposure apparatus (exposure light source) when pattern transfer is performed using a photomask manufactured using the photomask blank 1. When exposure processing is performed using a photomask, exposure light is irradiated from the transparent substrate 11 side (back side) of the photomask, and a pattern transfer image is transferred to a resist film formed on a substrate for a display device as a transfer target. At this time, the reflected light of the exposure light reflected on the back surface side of the light shielding film pattern enters the optical system of the exposure apparatus and enters again from the transparent substrate 11 side of the photomask, which becomes stray light of the light shielding film pattern and becomes a factor of deterioration of the transfer pattern such as formation of a ghost image and increase of flare. According to the 1 st reflection suppressing layer 13, when pattern transfer is performed using a photomask, reflection of exposure light on the back surface side of the light shielding film 12 can be suppressed, and therefore, deterioration of a transfer pattern can be suppressed, and transfer characteristics can be improved.

As described above, in the present embodiment, in order to reduce defects, reduce the reflectance of the back surface of the light-shielding film 12, and improve the uniformity of reflectance within the photomask blank surface (in order to suppress in-plane variations in reflectance), the 1 st reflection suppression layer 13 is configured by stacking the 1 st low-degree chromium oxide layer 13a, which is relatively less oxidized, and the 1 st high-degree chromium oxide layer 13b, which is relatively more oxidized, in this order from the transparent substrate 11 side.

The 1 st low-degree chromium oxide layer 13a is formed so that the degree of oxidation becomes small.

As described later, the 1 st low-degree chromium oxide layer 13a has a smaller proportion of oxygen (O) to nitrogen (N), that is, a higher content of N, than the 1 st high-degree chromium oxide layer 13b, and therefore, the etching time can be shortened as compared with the 1 st high-degree chromium oxide layer 13 b. Therefore, when etching the photomask blank 1, the etching residue of the 1 st low-degree chromium oxide layer 13a can be prevented, and the sectional shape of the light shielding film pattern can be made closer to vertical.

Further, since the 1 st low-degree chromium oxide layer 13a has a small oxidation degree and a large N content, even when a fine light-shielding film pattern is formed by etching the light-shielding film 12, adhesion to the transparent substrate 11 can be secured, and film peeling of the light-shielding film pattern can be prevented.

With respect to the 1 st-height chromium oxide layer 13b, the degree of oxidation is improved in such a manner that the back surface reflectance of the light-shielding film 12 (the back surface reflectance of the 1 st reflection suppression layer 13) attains a given characteristic.

(light-shielding layer)

The light-shielding layer 14 is provided between the 1 st reflection suppression layer 13 and the 2 nd reflection suppression layer 15 in the light-shielding film 12. The light-shielding layer 14 has a function of adjusting the optical density of the light-shielding film 12 so as to be substantially opaque to the exposure light. Here, the substantially opaque exposure light means a light-shielding property of 3.0 or more in terms of optical density, and the optical density is preferably 4.0 or more, and more preferably 4.5 or more from the viewpoint of transfer characteristics.

(No. 2 reflection suppressing layer)

The 2 nd reflection suppression layer 15 is provided on the surface of the light shielding layer 14 on the side away from the transparent substrate 11 in the light shielding layer 12. The 2 nd reflection suppressing layer 15 has the following functions: when a resist film is formed thereon and drawing light (laser light) by a drawing device (e.g., a laser drawing device) forms a given resist pattern in the resist film, reflection of the above-described drawing light on the surface side of the light-shielding film 12 can be suppressed. This can improve the CD uniformity of the resist pattern and the light-shielding film pattern formed on the basis of the resist pattern. On the other hand, when the photomask is used, the 2 nd reflection suppressing layer 15 is disposed on the transfer object side, and suppresses light reflected by the transfer object from being reflected again on the surface side of the light shielding film 12 of the photomask and returning to the transfer object. This can suppress deterioration of the transfer pattern, and contributes to improvement of transfer characteristics.

The 2 nd reflection suppression layer 15 is composed of two chromium oxide layers having different degrees of oxidation, as in the 1 st reflection suppression layer 13. Specifically, in order to reduce defects, reduce the surface reflectance of the light-shielding film 12, and improve the uniformity of the surface reflectance within the photomask blank surface (in order to suppress in-plane variations in the surface reflectance), the 2 nd reflection suppressing layer 15 is formed by laminating a 2 nd low-degree chromium oxide layer 15a having relatively little oxidation and a 2 nd high-degree chromium oxide layer 15b having relatively much oxidation in this order from the light-shielding layer 14 side.

The 2 nd low-degree chromium oxide layer 15a is formed to have a smaller degree of oxidation in the same manner as the 1 st low-degree chromium oxide layer 13 a.

With the 2 nd-height chromium oxide layer 15b, the degree of oxidation is increased in such a manner that the surface reflectance of the light-shielding film 12 (the reflectance of the surface of the 2 nd reflection suppression layer 15) attains a given characteristic. Further, the high degree of oxidation of the 2 nd-level chromium oxide layer 15b contributes to improvement in chemical resistance against a cleaning solution such as an acid or an alkali used in cleaning a photomask blank or a photomask, and high adhesion to a resist film when the resist film is formed on the 2 nd-level chromium oxide layer 15 b.

(Material for light-shielding film)

Next, the materials for forming the 1 st reflection suppression layer 13, the light shielding layer 14, and the 2 nd reflection suppression layer in the light shielding layer 12 will be described.

The material of each of the 1 st reflection suppression layer 13, the light shielding layer 14, and the 2 nd reflection suppression layer is not particularly limited as long as the above-described optical characteristics can be obtained in the photomask blank 1, and from the viewpoint of obtaining the above-described optical characteristics, it is preferable to use the following materials for each layer.

The 1 st reflection suppression layer 13 is preferably made of a chromium-based material containing chromium, oxygen, and nitrogen. Oxygen (O) mainly has a function of reducing the reflectance of the 1 st reflection suppression layer 13. The nitrogen (N) mainly has a function of reducing the reflectance of the 1 st reflection suppression layer 13, increasing the etching rate of the 1 st reflection suppression layer 13, and shortening the etching time. In view of controlling the etching characteristics, the 1 st reflection suppression layer 13 may further contain carbon (C) and fluorine (F), and carbon (C) is particularly preferably contained. By including C in the 1 st reflection suppression layer 13, the etching rates of the 1 st reflection suppression layer 13 and the light shielding layer 14 can be easily made uniform, and the cross-sectional shape of the light shielding film pattern can be made more favorable.

The 1 st reflection suppression layer 13 is composed of a 1 st low-degree chromium oxide layer 13a and a 1 st high-degree chromium oxide layer 13b having different degrees of oxidation. The degree of oxidation represents a ratio of oxygen to nitrogen (hereinafter also referred to as an O/N ratio), the 1 st-level chromium oxide layer 13a is formed of a chromium-based material having a relatively small ratio of O to N, and the 1 st-level chromium oxide layer 13b is formed of a chromium-based material having a relatively large ratio of O to N.

The light-shielding layer 14 is made of a chromium-based material. The light-shielding layer 14 may contain O, N, C, F or the like in addition to chromium (Cr). From the viewpoint of making the surface reflectance and the back surface reflectance of the light-shielding film 12 more uniform over the surface of the photomask blank, it is preferable that the light-shielding layer 14 is a chromium film substantially not containing O, N, F. Making the light-shielding layer 14 a chromium film substantially free of O, N, F means that the chromium film is not intentionally added, except for the case where the chromium film is inevitably included. More specifically, the chromium film substantially not containing O, N, F means a chromium film in which the total content of these elements is 3 at% or less, and further means a chromium film in which the total content of these elements is 2 at% or less. As described above, in the light-shielding layer 14, the nitrogen content cannot be made uniform in the plane, and the difference in refractive index between the light-shielding layer 14 and the 1 st reflection suppression layer 13 and the 2 nd reflection suppression layer 15 is excessively large or small, which may cause variations in the back surface reflectance and the surface reflectance of the photomask blank 1 in the plane. In this regard, when the light-shielding layer 14 is a chromium film substantially not containing O, N, F, the surface reflectance and the back surface reflectance of the light-shielding film 12 can be made more uniform on the photomask blank surface.

The 2 nd reflection suppressing layer 15 is preferably made of a chromium-based material containing chromium, oxygen, and nitrogen. In the 2 nd reflection suppressing layer 15, oxygen (O) not only reduces the reflectance of exposure light and drawing light, but also has a function of improving adhesion to the resist film and suppressing side etching due to permeation of an etchant from the interface between the resist film and the light shielding film 12. Nitrogen (N) may decrease the reflectivity of the 2 nd reflection inhibitor layer 15 and may increase the etching rate of the 2 nd reflection inhibitor layer 15, thereby shortening the etching time. From the viewpoint of controlling etching characteristics, carbon (C) and fluorine (F) may be further contained, and carbon (C) is particularly preferably contained. By including C in the 2 nd reflection suppression layer 15, the etching rates of the 2 nd reflection suppression layer 15 and the light shielding layer 14 can be easily made uniform, and the cross-sectional shape of the light shielding film pattern can be made more favorable.

(composition of shading film)

Next, the composition of each layer in the light-shielding film 12 will be specifically described. The content of each element described later is a value measured by X-ray photoelectron spectroscopy (XPS).

The chromium-based material forming the 1 st-order low-chromium oxide layer 13a preferably contains chromium (Cr), oxygen (O), and nitrogen (N), and the ratio of O to N is 0.1 or more and less than 2.5. The 1 st-degree chromium oxide layer 13a preferably contains 25 to 95 atomic% of chromium (Cr), 5 to 45 atomic% of oxygen (O), and 2 to 35 atomic% of nitrogen (N), respectively, in the following content ratios, and the ratio of O to N is 0.1 or more and less than 2.5.

The chromium-based material forming the 1 st-height chromium oxide layer 13b preferably contains chromium (Cr), oxygen (O), and nitrogen (N), and the ratio of O to N is 2.5 or more and 10 or less. The 1 st high-chromium oxide layer 13b contains 30 to 95 atomic% of chromium (Cr), 7 to 50 atomic% of oxygen (O), and 2 to 25 atomic% of nitrogen (N), and the ratio of O to N is 2.5 to 10.

The content of Cr contained in the 1 st low-degree chromium oxide layer 13a and the 1 st high-degree chromium oxide layer 13b is preferably lower than that contained in the light-shielding layer 14. Further, the total content of O and N contained in the 1 st low-chromium oxide layer 13a and the 1 st high-chromium oxide layer 13b is preferably 7 to 75 atomic%.

The chromium material forming the light-shielding layer 14 mainly contains Cr, and preferably contains 97 at% to 100 at% Cr. O, N, C, F, etc. may be contained in addition to Cr, and the total content thereof is preferably 3 atomic% or less.

The chromium-based material forming the 2 nd low-degree chromium oxide layer 15a preferably contains chromium (Cr), oxygen (O), and nitrogen (N), and the ratio of O to N is 0.1 or more and less than 2.5. Further, it is preferable that the 2 nd-level chromium oxide layer 15a contains 25 to 95 atomic% of chromium (Cr), 5 to 45 atomic% of oxygen (O), and 2 to 35 atomic% of nitrogen (N), and the ratio of O to N is 0.1 or more and less than 2.5.

The chromium-based material forming the 2 nd-level chromium oxide layer 15b preferably contains chromium (Cr), oxygen (O), and nitrogen (N), and the ratio of O to N is 2.5 or more and 10 or less. Further, it is preferable that the 2 nd high chromium oxide layer 15b contains 30 to 70 atomic% of chromium (Cr), 15 to 60 atomic% of oxygen (O), and 2 to 30 atomic% of nitrogen (N), and the ratio of O to N is 2.5 to 10.

The content of Cr contained in the 2 nd low-degree chromium oxide layer 15a and the 2 nd high-degree chromium oxide layer 15b is preferably lower than that contained in the light-shielding layer 14. Further, the total content of O and N contained in the 2 nd low-chrome oxide layer 15a and the 2 nd high-chrome oxide layer 15b is preferably 7 to 75 atomic%.

The 1 st reflection suppression layer 13 and the 2 nd reflection suppression layer 15 each preferably have a region in which the content of at least one element of O and N changes continuously or stepwise in composition along the film thickness direction.

Further, a composition gradient region in which elements constituting the 1 st reflection suppression layer 13, the light shielding layer 14, and the 2 nd reflection suppression layer 15 continuously have a composition gradient may be formed between the transparent substrate 11 and the 1 st reflection suppression layer 13, between the 1 st reflection suppression layer 13 and the light shielding layer 14, and between the light shielding layer 14 and the 2 nd reflection suppression layer 15.

(regarding film thickness)

The thickness of each of the 1 st reflection suppression layer 13, the light shielding layer 14, and the 2 nd reflection suppression layer 15 in the light shielding layer 12 is not particularly limited, and may be appropriately adjusted according to the optical density and reflectance required for the light shielding layer 12.

From the viewpoint of achieving both the suppression of defects in the 1 st reflection suppression layer 13 and the reduction in the back surface reflectance, the thicknesses of the 1 st low-order chromium oxide layer 13a, the 1 st high-order chromium oxide layer 13b, and the like are preferably 10nm or more and 35nm or less, respectively, and the thickness of the 1 st reflection suppression layer 13 obtained by adding these layers is preferably 20nm or more and 70nm or less. The ratio of the thicknesses of the 1 st-level chromium oxide layer 13a and the 1 st-level chromium oxide layer 13b is preferably 1:7 to 1:1 of the 1 st-level chromium oxide layer to 1 st-level chromium oxide layer, and more preferably 1:5 to 1:2 of the 1 st-level chromium oxide layer to 1 st-level chromium oxide layer.

The thickness of the light-shielding layer 14 can be changed as appropriate in accordance with the required optical density of the light-shielding film 12. For example, if the optical density is 3 or more, the thickness of the light-shielding layer 14 may be 50nm to 200 nm.

The thickness of the 2 nd reflection suppression layer 15 is adjusted so that predetermined optical characteristics (surface reflectance) can be obtained with respect to exposure light or drawing light from the surface side of the light shielding film 12. Specifically, the thicknesses of the 2 nd low-degree chromium oxide layer 15a and the 2 nd high-degree chromium oxide layer 15b in the 2 nd reflection suppression layer 15 are adjusted so that the typical wavelength (for example, 365nm to 436nm) of the exposure light from the back surface side of the light shielding film 12 becomes 10% or less. From the viewpoint of achieving both the suppression of defects in the 2 nd reflection suppressing layer 15 and the reduction in the surface reflectance, it is preferable that the thickness of the 2 nd low-degree chromium oxide layer 15a and the thickness of the 2 nd high-degree chromium oxide layer 15b are each 10nm to 35nm, and the thickness of the 2 nd reflection suppressing layer 15 obtained by adding these layers is preferably 20nm to 70 nm. The ratio of the thicknesses of the 2 nd to 2 nd low-degree chromium oxide layers 15a and 15b is preferably 1:7 to 1:1 of the 2 nd high-degree chromium oxide layer to the 2 nd low-degree chromium oxide layer, and more preferably 1:5 to 1:2 of the 2 nd high-degree chromium oxide layer to the 2 nd low-degree chromium oxide layer.

(optical characteristics of photomask blank)

The photomask blank 1 has optical characteristics as described below.

In the reflectance spectrum of the surface of the light-shielding film 12 obtained when the surface of the light-shielding film 12 of the photomask blank 1 is irradiated with exposure light and subjected to light drawing, the surface reflectance is preferably 15% or less, more preferably 12% or less, and still more preferably 10% or less at a representative wavelength in the range of the exposure wavelength 300nm to 436 nm. The light-shielding film 12 preferably has a surface reflectance of 15% or less, more preferably 12% or less, and still more preferably 10% or less in a reflection spectrum of the surface within a range of an exposure wavelength of 300nm to 436 nm. Alternatively, the reflectance of the surface of the light-shielding film 12 is preferably 10% or less, more preferably 7.5% or less, and even more preferably 5% or less, at a representative wavelength in the range of 365nm to 436 nm. The reflectance spectrum of the surface of the light-shielding film 12 is preferably within a range of an exposure wavelength of 365nm to 436nm, and the surface reflectance is preferably 10% or less, more preferably 7.5% or less, and still more preferably 5% or less.

In the reflectance spectrum of the rear surface of the light-shielding film 12 obtained by irradiating the rear surface of the light-shielding film 12 of the photomask blank 1 with exposure light, the rear surface reflectance is preferably 15% or less, more preferably 12% or less, and still more preferably 10% or less at a representative wavelength in the range of the exposure wavelength 300nm to 436 nm. The light-shielding film 12 preferably has a reflection spectrum of the rear surface in the range of an exposure wavelength of 300nm to 436nm, and a rear surface reflectance of preferably 15% or less, more preferably 12% or less, and still more preferably 10% or less. The reflectance spectrum of the rear surface of the light-shielding film 12 is preferably 10% or less, more preferably 7.5% or less, and even more preferably 5% or less of the rear surface reflectance at a representative wavelength in the range of 365nm to 436nm as the exposure wavelength. The light-shielding film 12 preferably has a reflection spectrum of the rear surface in the range of 365nm to 436nm of the exposure wavelength, and a rear surface reflectance of preferably 10% or less, more preferably 7.5% or less, and still more preferably 5% or less.

The light-shielding film 12 of the photomask blank 1 has a small wavelength dependence of the reflectance of the front and back surfaces thereof on the exposure wavelength of 300nm to 436nm or 365nm to 436 nm. The wavelength dependence means that the reflectance changes depending on the exposure wavelength, and a small wavelength dependence means that the difference between the maximum value and the minimum value of the reflectance is small, that is, the amount of change (fluctuation range) of the reflectance is small. Specifically, the wavelength dependence of the reflectance of the front and back surfaces of the light-shielding film 12 is preferably 12% or less, more preferably 10% or less, in the range of the exposure wavelength 300nm to 436 nm. Alternatively, the wavelength dependence of the reflectance of the front and back surfaces of the light-shielding film 12 is preferably 5% or less, more preferably 3% or less, in the range of the exposure wavelength 365nm to 436 nm.

In addition, in the photomask blank 1, the variation in the reflectance of the front and back surfaces of the light-shielding film 12 (surface reflectance, back surface reflectance) in the plane can be suppressed, and the in-plane uniformity of the reflectance of the front and back surfaces can be improved.

Specifically, the surface reflectance of the light-shielding film 12 can be suppressed to 3% or less (statistical range). The in-plane uniformity of the surface reflectance of the light shielding film 12 is calculated as follows: the surface reflectance was measured at 121 points 11 × 11 on the surface of the photomask blank 1 except for the edge portion 50mm using a reflectance measuring instrument, and calculation was performed based on the result.

In addition, the back surface reflectance of the light shielding film 12 can be suppressed to 5% or less (statistical range). The in-plane uniformity of the back surface reflectance of the light shielding film 12 is calculated as follows: the 1 st reflection suppression layer 13, the light shielding layer 14, and the 2 nd reflection suppression layer 15 constituting the light shielding film 12 are formed on a plurality of pieces of model substrates (for example, 6 inches × 6 inches) laid over the surface of the photomask blank 1 in place of the photomask blank 1, the reflectance of the back surface of the light shielding film 12 formed on the model substrates is measured using a reflectance measuring instrument, and calculation is performed based on the obtained results of the back surface reflectance.

The in-plane uniformity of the reflectance means a difference between a maximum value and a minimum value of the reflectance at arbitrary plural points of the mask blank.

< method for producing photomask blank >

Next, a method for manufacturing the photomask blank 1 will be described.

(preparation Process)

A transparent substrate 11 substantially transparent to exposure light is prepared. The transparent substrate 11 may be subjected to any processing step such as a grinding step or a polishing step as necessary to obtain a flat and smooth main surface. After polishing, the surface of the transparent substrate 11 may be cleaned to remove foreign matters and contaminants. As the cleaning, for example: sulfuric acid, sulfuric acid/hydrogen peroxide (SPM), ammonia/hydrogen peroxide (APM), OH radical cleaning water, ozone water, warm water, and the like.

(step of Forming reflection suppressing layer 1)

Next, the 1 st reflection suppression layer 13 is formed on the transparent substrate 11. In the present embodiment, the 1 st reflection suppression layer 13 is formed by laminating the 1 st low-degree chromium oxide layer 13a and the 1 st high-degree chromium oxide layer 13b in this order from the transparent substrate 11 side.

In the formation of the 1 st reflection suppression layer 13, the film is formed by reactive sputtering using a sputtering target containing Cr, a reactive gas containing an oxygen-based gas and a nitrogen-based gas, and a sputtering gas containing a rare gas. At this time, as the film formation condition, a flow rate at which the reactive gas contained in the sputtering gas is in the metal mode is selected.

In reactive sputtering, when a sputtering target is discharged while introducing a reactive gas such as an oxygen-based gas or a nitrogen-based gas, the state of discharge plasma changes according to the flow rate of the reactive gas, and the film formation rate changes accordingly. In the metal mode, by reducing the ratio of the reactive gas, the adhesion of the reactive gas to the surface of the sputtering target can be reduced, and the film formation rate can be increased. In the metal mode, since the supply amount of the reactive gas is small, for example, a film having a lower content of at least either of the oxygen content (O content) and the nitrogen content (N content) than that of a film having a stoichiometric composition can be formed.

From the viewpoint of suppressing defects in the 1 st reflection suppression layer 13, it is preferable to reduce the applied power to the sputtering target in the film formation conditions. If the power applied to the sputtering target is reduced, micro-arcs and abnormal discharge occurring in the sputtering target can be suppressed in reactive sputtering in which an oxygen-based gas and a nitrogen-based gas are introduced, and the occurrence of defects in the 1 st reflection suppression layer 13 can be suppressed. As the conditions of the metal mode for forming the 1 st reflection suppression layer 13, for example, the flow rate of the oxygen-based gas is 1 to 45sccm, the flow rate of the nitrogen-based gas is 30 to 60sccm, the flow rate of the hydrocarbon-based gas is 1 to 15sccm, and the flow rate of the rare gas is 20 to 100 sccm. In addition, the power applied to the target can be set to 1.0 to 6.0 kW.

The sputtering target may contain chromium, and for example, a chromium-based material such as chromium oxide, chromium nitride, or chromium oxynitride may be used in addition to chromium. As the oxygen-based gas, for example: oxygen (O)₂) Carbon dioxide (CO)₂) Nitrogen oxide gas (N)₂O、NO、NO₂) And the like. As the nitrogen-based gas, nitrogen (N) may be used₂) And the like. As the rare gas, for example: helium, neon, argon, krypton, xenon, and the like. In addition to the above reactive gas, a hydrocarbon gas may be supplied, and for example, methane gas, butane gas, or the like may be used.

In the present embodiment, the reactive gas flow rate and the power applied to the sputtering target are set to the conditions of the metal mode, and the film formation process by the reactive sputtering is performed using the sputtering target containing Cr. Thus, on the transparent substrate 11, first, a 1 st low-degree chromium oxide layer 13a in which the ratio of O to N is relatively small is formed, and a 1 st high-degree chromium oxide layer 13b in which the ratio of O to N is relatively large is formed thereon, thereby forming a 1 st reflection suppression layer 13. The 1 st low-degree chromium oxide layer 13a is formed in a metallic mode at a low power so that the O content is lower than that of the 1 st high-degree chromium oxide layer 13 b. The 1 st high-degree chromium oxide layer 13b is formed in a metallic mode at a low power so that the O content is higher than that of the 1 st low-degree chromium oxide layer 13 a. The film forming conditions in the metal mode can be set, for example, with reference to japanese patent application laid-open No. 2019-20712.

In the film formation of the 1 st low-degree chromium oxide layer 13a to the 1 st high-degree chromium oxide layer 13b, the kind and flow rate of the reactive gas, the ratio of the oxygen-based gas and the nitrogen-based gas in the reactive gas, and the like may be appropriately changed so as to change the O content and the N content. Further, the arrangement of the gas supply ports, the gas supply method, and the like may be changed. The film formation time may be appropriately changed according to the thickness of each layer.

(Process for Forming light-shielding layer)

Next, the light-shielding layer 14 is formed on the 1 st reflection suppression layer 13. In this formation, film formation is performed by sputtering using a sputtering target containing Cr and a sputtering gas containing a rare gas. At this time, as the film formation condition, a flow rate at which the reactive gas contained in the sputtering gas is in the metal mode is selected.

The sputtering target may contain chromium. A sputtering target made of chromium is preferable from the viewpoint of improving the in-plane uniformity of the reflectance of the front surface and the back surface of the light shielding film 12. As the rare gas, for example: helium, neon, argon, krypton, xenon, and the like. In addition to the above rare gas, an oxygen-based gas, a nitrogen-based gas, or a hydrocarbon-based gas may be supplied within a range not departing from the effects of the present invention.

In the present embodiment, the flow rate of the reactive gas and the sputtering target application power are set to the conditions of the metal mode, and sputtering is performed using a sputtering target containing Cr. Thereby, the light-shielding layer 14 mainly containing Cr is formed on the 1 st reflection suppression layer 13.

The deposition condition of the light-shielding layer 14 may be, for example, a flow rate of the rare gas of 60 to 200 sccm. The power applied to the target may be 3.0 to 10.0 kW.

(step 2 of Forming reflection suppressing layer)

Next, the 2 nd reflection suppression layer 15 is formed on the light shielding layer 14. In this formation, similarly to the 1 st reflection suppression layer 13, film formation by reactive sputtering is performed using a sputtering target containing Cr under such conditions that the flow rate of the reactive gas and the applied power to the sputtering target are set to be in the metal mode. Thereby, a 2 nd low-degree chromium oxide layer 15a having a relatively small ratio of O to N is formed on the light shielding layer 14, and a 2 nd high-degree chromium oxide layer 15b having a relatively large ratio of O to N is formed thereon, thereby forming the 2 nd reflection suppressing layer 15. The 2 nd low-degree chromium oxide layer 15a is formed in a metallic mode at a low power so that the O content is lower than that of the 2 nd high-degree chromium oxide layer 15 b. The 2 nd high-degree chromium oxide layer 15b is formed in a metallic mode at a low power so that the O content is higher than that of the 2 nd low-degree chromium oxide layer 15 a.

As the conditions of the metal mode for forming the 2 nd reflection suppression layer 15, for example, the flow rate of the oxygen-based gas is 1 to 45sccm, the flow rate of the nitrogen-based gas is 30 to 60sccm, the flow rate of the hydrocarbon-based gas is 1 to 15sccm, and the flow rate of the rare gas is 20 to 100 sccm. In addition, the power applied to the target can be set to 1.0 to 6.0 kW.

In the film formation of the 2 nd low-chrome oxide layer 15a to the 1 st high-chrome oxide layer 13b, the kind and flow rate of the reactive gas, the ratio of the oxygen-based gas and the nitrogen-based gas in the reactive gas, and the like may be appropriately changed in the same manner as the 1 st reflection suppressing layer 13. Further, the arrangement of the gas supply ports, the gas supply method, and the like may be changed.

Thus, the photomask blank 1 of the present embodiment can be obtained.

The layers of the light-shielding film 12 can be formed in-situ by using an in-line sputtering apparatus. In the case where the film formation is not in-line, the transparent substrate 11 needs to be taken out of the apparatus after the film formation of each layer, and the transparent substrate 11 is exposed to the atmosphere, which may cause surface oxidation and surface carbonization of each layer. As a result, the reflectance of the light shielding film 12 with respect to the exposure light and the etching rate may be changed. In this regard, if the in-line type is employed, since each layer can be formed continuously without taking out the transparent substrate 11 to the outside of the apparatus and exposing it to the atmosphere, introduction of an unwanted element into the light-shielding film 12 can be suppressed.

Further, when the light-shielding film 12 is formed by using an in-line type sputtering apparatus, since each of the 1 st reflection suppression layer 13, the light-shielding layer 14, and the 2 nd reflection suppression layer 15 has a composition gradient region (transition layer) in which a composition gradient continuously exists between the layers, a light-shielding film pattern formed by etching (particularly wet etching) using a photomask blank has a smooth cross section and can be made nearly vertical, which is preferable.

< method for manufacturing photomask >

Next, a method for manufacturing a photomask using the photomask blank 1 will be described.

(Process for Forming resist film)

First, a resist is applied to the 2 nd reflection suppressing layer 15 in the light-shielding film 12 of the photomask blank 1 and dried to form a resist film. As the resist, an appropriate resist needs to be selected according to the drawing apparatus to be used, and a positive or negative resist can be used.

(Process for Forming resist Pattern)

Next, a given pattern is drawn on the resist film using a drawing device. In general, a laser drawing apparatus is used when a photomask for manufacturing a display device is manufactured. After the drawing, development and rinsing are performed on the resist film, thereby forming a given resist pattern.

In this embodiment, since the 2 nd reflection suppressing layer 15 is configured to have a low reflectance, reflection of drawing light (laser light) can be reduced when a pattern is drawn on the resist film. Thus, a resist pattern with high pattern accuracy can be formed, and a light-shielding film pattern with high dimensional accuracy can be formed.

(Process for Forming light-shielding film Pattern)

Next, the light-shielding film 12 is etched using the resist pattern as a mask, thereby forming a light-shielding film pattern. The etching may be wet etching or dry etching. In general, a photomask for manufacturing a display device is wet-etched, and as an etching solution (etchant) used for the wet etching, for example, a chromium etching solution containing cerium ammonium nitrate and perchloric acid can be used.

In the present embodiment, since the composition of each layer is adjusted so that the etching rates of the 1 st reflection suppression layer 13, the light-shielding layer 14, and the 2 nd reflection suppression layer 15 are made uniform in the thickness direction of the light-shielding layer 12, the cross-sectional shape at the time of wet etching, that is, the cross-sectional shape of the light-shielding layer pattern can be made nearly perpendicular to the transparent substrate 11, and high CD uniformity can be obtained.

(peeling step)

Next, the resist pattern is peeled off to obtain a photomask in which a light-shielding film pattern (light-shielding film pattern) is formed on the transparent substrate 11.

As described above, the photomask of the present embodiment can be obtained.

< method for manufacturing display device >

Next, a method for manufacturing a display device using the photomask will be described.

(preparation Process)

First, a substrate with a resist film, in which a resist film is formed on a substrate of a display device, is prepared. Next, the photomask obtained by the above-described manufacturing method is placed on a mask stage of an exposure apparatus so as to face a resist film of a substrate with a resist film, with a projection optical system of the exposure apparatus interposed therebetween.

(Exposure step (Pattern transfer step))

Next, a resist exposure step of irradiating the photomask with exposure light and transferring a pattern to a resist film formed on a substrate of the display device is performed.

The exposure light is, for example, light having a single wavelength (j line (wavelength 313nm), wavelength 334nm, i line (wavelength 365nm), h line (wavelength 405nm), g line (wavelength 436nm), etc.) selected from a wavelength range of 300nm to 436nm, or composite light including light having a plurality of wavelengths (for example, j line (wavelength 313nm), wavelength 334nm, i line (wavelength 365nm), h line (405nm), g line (wavelength 436 nm)). In the case of using a large-sized photomask, the exposure light may be composed of the composite light from the viewpoint of the amount of light.

In this embodiment, the light-shielding film pattern (light-shielding film pattern) has a reduced reflectance on the front and back surfaces, and a display device (display panel) is manufactured using a photomask having high in-plane uniformity of the reflectance.

< Effect of the present embodiment >

According to the present embodiment, one or more of the following effects can be exhibited.

(a) In the photomask blank 1 of the present embodiment, the 1 st reflection suppression layer 13 is formed by laminating the 1 st low-degree chromium oxide layer 13a, which is relatively less oxidized, and the 1 st high-degree chromium oxide layer 13b, which is relatively more oxidized, in the light shielding film 12. This reduces defects in the 1 st reflection suppression layer 13, thereby reducing the reflectance of the rear surface of the light shielding film 12. In addition, in the photomask blank 1, in-plane variations in the back surface reflectance can be suppressed, and uniformity in the back surface reflectance can be improved.

(b) The 2 nd reflection suppression layer 15 is formed by laminating a 2 nd low-degree chromium oxide layer 15a that is relatively less oxidized and a 2 nd high-degree chromium oxide layer 15b that is relatively more oxidized. Thereby, defects in the 2 nd reflection suppression layer 15 can be reduced, thereby reducing the reflectance of the surface of the light shielding film 12. Further, in the photomask blank 1, in-plane variations in surface reflectance can be suppressed, and uniformity in surface reflectance can be improved.

(c) Preferably, the 1 st-degree chromium oxide layer 13a contains 25 to 95 atomic% of Cr, 5 to 45 atomic% of O, and 2 to 35 atomic% of N, respectively, and the ratio of O to N is less than 2.5, the 1 st-degree chromium oxide layer 13b contains 30 to 95 atomic% of Cr, 7 to 50 atomic% of O, and 2 to 25 atomic% of N, respectively, and the ratio of O to N is 2.5 to 10. Preferably, the 2 nd-level chromium oxide layer 15a contains 25 to 95 atomic% of Cr, 5 to 45 atomic% of O, and 2 to 35 atomic% of N, respectively, and the content of O relative to N is less than 2.5, the 2 nd-level chromium oxide layer 15b contains 30 to 70 atomic% of Cr, 15 to 60 atomic% of O, and 2 to 30 atomic% of N, respectively, and the content of O relative to N is 2.5 to 10. By constituting each layer with such a composition, the reflectance (10% or less with respect to the representative wavelength of the exposure light) of the front surface and the back surface of the light-shielding film 12 can be reduced, and defects can be reduced. Further, the etching rates of the respective layers of the light-shielding film 12 can be made uniform, and therefore, the sectional shape of the light-shielding film pattern can be made closer to vertical.

(d) The 1 st reflection suppression layer 13 and the 2 nd reflection suppression layer 15 preferably have regions in which the content of at least one of O and N changes continuously or stepwise in composition along the film thickness direction. By changing the composition of each of the 1 st reflection suppression layer 13 and the 2 nd reflection suppression layer 15, the difference in etching rate between the respective layers can be reduced, and the cross-sectional shape of the light-shielding film pattern can be made more vertical.

(e) The chromium content of the light-shielding layer 14 is preferably 97 atomic% to 100 atomic%. By forming the light-shielding layer 14 of chromium containing substantially no O, N, F, variation in-plane composition due to the O, N, F content can be suppressed. This makes it possible to make the surface reflectance and the back surface reflectance of the light-shielding film 12 more uniform on the photomask blank surface.

(f) In the 1 st reflection suppression layer 13, the ratio of O to N in the 1 st-height chromium oxide layer 13b is preferably 2.5 to 10. By configuring such that the O/N ratio is achieved, the reflectance of the 1 st reflection suppression layer 13 can be reduced, and the difference in etching rate with other layers (light-shielding layer: particularly, chromium content of 97 to 100 atomic%) can be reduced.

(g) In the 2 nd reflection suppression layer 15, the ratio of O to N in the 2 nd high-order chromium oxide layer 15b is preferably 2.5 to 10. By configuring to achieve the above O/N ratio, the reflectance of the 2 nd reflection suppression layer 15 can be reduced. In addition, the adhesiveness with the resist film formed on the surface of the 2 nd low-degree chromium oxide layer 15a can be improved, and the cross-sectional shape of the light-shielding film pattern can be made more stable and nearly vertical.

(h) Preferably, at least one of the 1 st reflection suppression layer 13 and the 2 nd reflection suppression layer 15 further contains C. This can reduce the difference in etching rate between the 1 st and 2 nd reflection suppressing layers 13 and 15 and the light shielding layer 14. In particular, when the chromium content of the light-shielding layer 14 is 97 atomic% to 100 atomic%, the above difference can be further reduced.

(i) The photomask blank 1 has the following optical characteristics by including the light-shielding film 12 described above: the reflectance of both the front and back surfaces in the exposure wavelength range of 300nm to 436nm is 15% or less, and the wavelength dependence of the front and back surface reflectances in the above wavelength range is 12% or less. The photomask blank 1 is improved to have the light-shielding film 12 described above and has the following optical characteristics: the reflectance of the front and back surfaces in the range of the exposure wavelength from 365nm to 436nm is 10% or less, and the wavelength dependence of the front and back surface reflectances in the above wavelength range is 5% or less. According to such a photomask blank 1, when exposure light is irradiated as a photomask, the light-shielding film 12 can suppress the reflection of light on the front and back surfaces in the entire wavelength range of the exposure wavelength from 300nm to 436nm or the entire wavelength range of the exposure wavelength from 365nm to 436nm, and therefore, the total amount of reflected light on the front and back surfaces can be reduced. In particular, since the wavelength dependence of the back surface reflectance of the light-shielding film 12 can be set to 5% or less, the back surface reflectance can be reduced on average over the entire wavelength range, and thus the return light to the back surface of the photomask can be suppressed. As a result, it is possible to suppress a decrease in the accuracy of the transfer pattern due to reflection of light on the front and back surfaces of the photomask when the display device is manufactured using the photomask.

(j) Preferably, photomask blank 1 has a back surface reflectance smaller than a surface reflectance over the entire range of exposure wavelengths 300nm to 436 nm. Alternatively, it is preferable that the photomask blank 1 has a back surface reflectance smaller than a surface reflectance in the entire range of exposure wavelengths from 365nm to 436 nm. This can suppress reflection of the exposure light in a wide wavelength range, and further reduce the total amount of reflected exposure light.

(k) Preferably, photomask blank 1 has a wavelength dependence of the reflectance of the back surface smaller than that of the reflectance of the surface in the range of exposure wavelength 300nm to 436 nm. Alternatively, it is preferable that the photomask blank 1 has a wavelength dependence of the reflectance of the back surface smaller than that of the reflectance of the surface over the entire range of the exposure wavelength from 365nm to 436 nm. That is, in the wavelength range, the amount of change in the back surface reflectance is preferably smaller than the amount of change in the surface reflectance. This can further suppress the return light on the back surface of the photomask, and can further reduce the degradation of the transfer pattern accuracy.

(l) According to the photomask blank 1, the surface reflectance of the light-shielding film 12 on the surface side is low, and therefore, when a resist film is provided on the light-shielding film 12 and a resist pattern is formed by the drawing/developing step, reflection of drawing light on the surface of the light-shielding film 12 can be reduced. Thus, the dimensional accuracy of the resist pattern can be improved, and the dimensional accuracy of the light-shielding film pattern of the photomask formed therefrom can be improved. Specifically, the CD uniformity of the light-shielding film pattern can be improved, and a light-shielding film pattern with high accuracy of 75nm or less can be formed.

(m) the photomask produced from the photomask blank 1 has a light-shielding film pattern with high accuracy, and has a small reflectance on the front and back surfaces of the light-shielding film pattern and high in-plane uniformity of reflectance, so that high transfer characteristics can be obtained when transferring a pattern to a transfer target.

< other embodiments >

While one embodiment of the present invention has been specifically described above, the present invention is not limited to the above embodiment, and can be appropriately modified within a range not departing from the gist thereof.

In the above-described embodiment, the case where the light shielding film 12 is directly provided on the transparent substrate 11 has been described, but the present invention is not limited thereto. For example, a photomask blank may be provided with a semi-transparent film having a lower optical density than the light-shielding film 12 between the transparent substrate 11 and the light-shielding film 12. In the photomask blank having the translucent film and the light-shielding film 12 formed on the transparent substrate 11, it is also preferable that the reflectance of the translucent film with respect to the back surface of the exposure light is 15% or less and the reflectance of the light-shielding film with respect to the front surface of the exposure light is 15% or less in the range of the exposure wavelength of 300nm to 436 nm. In the photomask blank having the translucent film and the light-shielding film 12 formed on the transparent substrate 11, it is preferable that the reflectance of the translucent film with respect to the back surface of the exposure light is 10% or less and the reflectance of the light-shielding film with respect to the front surface of the exposure light is 10% or less in the range of the exposure wavelength 365nm to 436 nm. The photomask blank can be used as a photomask blank for a gray tone mask or a gray scale mask having an effect of reducing the number of photomasks used in manufacturing a display device. The light-shielding film pattern in the gray tone mask or the gray tone mask is a semi-light-transmitting film pattern and/or a light-shielding film pattern.

Alternatively, a phase shift film capable of shifting the phase of transmitted light may be provided between the transparent substrate 11 and the light-shielding film 12 instead of the semi-transmissive film. In the photomask blank having the phase shift film and the light-shielding film 12 formed on the transparent substrate 11, it is also preferable that the back surface reflectance of the phase shift film with respect to the exposure light is 15% or less and the surface reflectance of the light-shielding film with respect to the exposure light is 15% or less in the range of the exposure wavelength of 300nm to 436 nm. In the photomask blank having the phase shift film and the light-shielding film 12 formed on the transparent substrate 11, it is preferable that the back surface reflectance of the phase shift film with respect to the exposure light is 10% or less and the surface reflectance of the light-shielding film with respect to the exposure light is 10% or less in the range of the exposure wavelength of 365nm to 436 nm. The photomask blank may be used as a phase shift mask having the effect of high pattern resolution based on the phase shift effect. The light shielding film pattern in the phase shift mask is a phase shift film pattern, or a phase shift film pattern and a light shielding film pattern.

A material having etching selectivity to a chromium-based material as a material constituting the light-shielding film 12 is suitable for the semi-transparent film and the phase shift film. As such a material, a metal silicide-based material containing molybdenum (Mo), zirconium (Zr), titanium (Ti), tantalum (Ta), and silicon (Si) can be used, and a material further containing at least one of oxygen, nitrogen, carbon, and fluorine is preferable. For example, metal silicides such as MoSi, ZrSi, TiSi, TaSi, MoZrSi, motiisi, and MoTaSi, oxides of metal silicides, nitrides of metal silicides, oxynitrides of metal silicides, carbonitrides of metal silicides, oxycarbides of metal silicides, and oxycarbonitrides of metal silicides are suitable. The semi-transparent film and the phase shift film may be a laminated film composed of the above-mentioned films as functional films.

In the above-described embodiment, an etching mask film made of a material having etching selectivity to the light-shielding film 12 may be formed on the light-shielding film 12.

In the above-described embodiment, an etching stopper film made of a material having etching selectivity to the light-shielding film may be formed between the transparent substrate 11 and the light-shielding film 12. The etching mask film and the etching stopper film may be made of a material having etching selectivity to a chromium-based material as a material constituting the light shielding film 12. Examples of such a material include molybdenum (Mo) and zirconium (Zr)) Titanium (Ti), tantalum (Ta), and silicon (Si), Si, SiO₂、SiON、Si₃N₄And the like.

Examples

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

< example 1 >

In this example, a photomask blank having a light-shielding film was produced by using an in-line sputtering apparatus and laminating a 1 st low-chromium oxide layer, a 1 st high-chromium oxide layer, a light-shielding layer, a 2 nd low-chromium oxide layer, and a 2 nd high-chromium oxide layer in this order on a transparent substrate having a substrate size of 1220mm × 1400mm as shown in fig. 1 by the method shown in the above-described embodiment.

The film forming conditions of the 1 st low chromium oxide layer and the 2 nd high chromium oxide layer are as follows: a Cr sputtering target is used as a sputtering target, and the flow rate of a reactive gas is set to be a metal mode, wherein the flow rate of an oxygen gas is selected from the range of 1-45 sccm, the flow rate of a nitrogen gas is selected from the range of 30-60 sccm, the flow rate of a hydrocarbon gas is selected from the range of 1-15 sccm, the flow rate of a rare gas is selected from the range of 20-100 sccm, and the target applied power is set within the range of 1.0-6.0 kW.

The light-shielding layer was formed under the following conditions: the Cr sputtering target material is used as a sputtering target material, the flow rate of the rare gas is set within the range of 60-200 sccm, and the target material application power is set within the range of 3.0-10.0 kW.

The film forming conditions of the 2 nd low chromium oxide layer and the 2 nd high chromium oxide layer are as follows: a Cr sputtering target is used as a sputtering target, and the flow rate of a reactive gas is set to be a metal mode, wherein the flow rate of an oxygen gas is selected from the range of 1-45 sccm, the flow rate of a nitrogen gas is selected from the range of 30-60 sccm, the flow rate of a hydrocarbon gas is selected from the range of 1-15 sccm, the flow rate of a rare gas is selected from the range of 20-100 sccm, and the target applied power is set within the range of 1.0-6.0 kW.

The composition of the light-shielding film of the obtained photomask blank in the film thickness direction was measured by X-ray photoelectron spectroscopy (XPS), and it was confirmed that each layer in the light-shielding film had the composition distribution shown in fig. 2. Fig. 2 is a graph showing the results of composition analysis in the film thickness direction in the photomask blank of example 1, in which the horizontal axis represents the film thickness and the vertical axis represents the content of the element [ atomic% ]. The film thickness represents the depth [ nm ] from the surface of the light-shielding film.

In fig. 2, a region containing about 15 atomic% of carbon (C) near the surface of the light-shielding film is a surface native oxide layer. The region, excluding the surface native oxide layer and having a depth of about 1.3nm to about 14nm from the surface of the light-shielding film, in which the ratio of oxygen (O) to nitrogen (N) is 2.5 or more is a 2 nd-height chromium oxide layer. A region having a ratio of oxygen (O) to nitrogen (N) of less than 2.5, excluding the surface native oxide layer, and having a depth of about 15nm to about 43nm from the surface of the light-shielding film is a 2 nd-order low-chromium oxide layer. The region apart from the surface native oxide layer and having a depth of about 44nm to about 66nm from the surface of the light-shielding film is a transition layer. The region, excluding the surface native oxide layer and having a depth of about 67nm to about 156nm from the surface of the light-shielding film, in which the content of chromium (Cr) is 97 atomic% or more is a light-shielding layer. The region which is apart from the surface natural oxide layer and is about 157nm to about 164nm deep from the surface of the light shielding film is a transition layer. A region having a ratio of oxygen (O) to nitrogen (N) of 2.5 or more excluding the surface native oxide layer and having a depth of about 165nm to about 188nm from the surface of the light-shielding film is a 1 st-height chromium oxide layer. The region, excluding the natural oxide layer on the surface and having a depth of about 189nm to 195nm from the surface of the light-shielding film, in which the ratio of oxygen (O) to nitrogen (N) is less than 2.5 is a 1 st low-degree chromium oxide layer. The region where the ratio of oxygen (O) to silicon (Si) reaches about 2 is the transparent substrate, and the region between the transparent substrate and the above-described 1 st low-degree chromium oxide layer is the transition layer.

As shown in FIG. 2, the 1 st low chromium oxide layer is a CrCON film containing 54.2 to 56.5 atomic% of Cr, 12.0 to 14.2 atomic% of N, 14.8 to 15.1 atomic% of O, and 2.7 to 4.3 atomic% of C. The ratio of O to N (O/N ratio) is 1.9 to 2.4.

The 1 st high chromium oxide layer is a CrCON film containing 57.1 to 90.7 atomic% of Cr, 2.0 to 11.3 atomic% of N, 7.3 to 28.3 atomic% of O, and 0 to 3.3 atomic% of C. The ratio of O to N (O/N ratio) is 2.5 to 3.6.

The light shielding layer is a CrO film containing 97.4 to 99.1 atomic% of Cr and 0.9 to 2.6 atomic% of O.

The 2 nd low chromium oxide layer is a CrCON film containing 49.3 to 76.9 atomic% of Cr, 6.2 to 18.9 atomic% of N, 24.4 to 32.5 atomic% of O, and 2.9 to 5.2 atomic% of C. The ratio of O to N (O/N ratio) is 1.3 to 2.4.

The 2 nd high chromium oxide layer is a CrCON film containing Cr 42.3-49.0 atomic%, N8.7-12.4 atomic%, O35.3-44.8 atomic%, and C2.2-4.2 atomic%. The ratio of O to N (O/N ratio) is 2.9 to 5.2.

(evaluation of photomask blank)

The photomask blank of example 1 was evaluated for the optical density of the light-shielding film and the reflectance of the light-shielding film on the front and back surfaces by the following methods.

The optical density of the light-shielding film was measured with a spectrophotometer ("SolidSpec-3700" manufactured by shimadzu corporation) of the photomask blank of example 1, and as a result, it was 5.0 or more in g-line (wavelength 436nm) which is the wavelength range of the exposure light. The reflectance of the light-shielding film was measured on the front and back surfaces thereof by a spectrophotometer ("SolidSpec-3700", Shimadzu corporation). Specifically, the reflectance (surface reflectance) of the light-shielding film on the 2 nd reflection suppression layer side and the reflectance (back surface reflectance) of the light-shielding film on the transparent substrate side were measured with a spectrophotometer, respectively. As a result, a reflectance spectrum shown in fig. 3 was obtained. Fig. 3 shows a reflectance spectrum of the front and back surfaces of the photomask blank of example 1, with the horizontal axis representing wavelength [ nm ] and the vertical axis representing reflectance [% ].

As shown in fig. 3, it was confirmed that the photomask blank of example 1 can greatly reduce the reflectance for light of a wide range of wavelengths. Specifically, the light-shielding film has a surface reflectance of 15.0% or less (12.2% (wavelength 300nm), 10.9nm (wavelength 313nm), 8.2% (wavelength 334nm), 4.3% (wavelength 365nm), 1.8% (wavelength 405nm), 1.7% (wavelength 413nm), and 2.0% (wavelength 436nm)) at a wavelength of 300 to 436nm, and a surface reflectance of 10.0% or less (4.3% (wavelength 365nm), 1.8% (wavelength 405nm), 1.7% (wavelength 413nm), and 2.0% (wavelength 436nm)) at a wavelength of 365 to 436 nm. The light-shielding film has a back surface reflectance of 7.5% or less (7.4% (wavelength 300nm), 6.2% (wavelength 313nm), 3.9% (wavelength 334nm), 1.7% (wavelength 365nm), 0.9% (wavelength 405nm), and 2.1% (wavelength 436nm) at wavelengths of 350nm to 436nm and 365nm to 436 nm.

The dependency of the surface reflectance of the light-shielding film on the exposure wavelength in the range of 300nm to 436nm was 10.6%, and the dependency of the back surface reflectance was 6.6%. Further, the dependency of the surface reflectance of the light-shielding film in the exposure wavelength range of 365nm to 436nm was 2.7%, and the dependency of the back surface reflectance was 1.3%, which was good.

In the entire wavelength range of 300nm to 500nm, the surface reflectance was 436nm and the back surface reflectance was 415.5nm for a wavelength (peak bottom wavelength) corresponding to the minimum value (peak bottom) of the surface reflectance and the back surface reflectance.

(evaluation of light-shielding film pattern)

A light-shielding film pattern was formed on a transparent substrate using the photomask blank of example 1. Specifically, a novolak positive resist film was formed on a light-shielding film on a transparent substrate, and then laser drawing (wavelength 413 nm)/development treatment was performed to form a resist pattern. Then, the resist pattern was used as a mask, and wet etching was performed with a chromium etching solution, thereby forming a light-shielding film pattern on the transparent substrate. The light-shielding film pattern was evaluated by forming a line-and-space pattern (line-and-space pattern) of 2.5 μm and observing the cross-sectional shape of the light-shielding film pattern with a Scanning Electron Microscope (SEM). As a result, it was confirmed that the angle formed between the side surface of the light shielding film pattern and the transparent substrate was 77 °. This confirmed that the light shielding film pattern could be formed to have a cross-sectional shape close to vertical.

(in-plane uniformity of reflectance)

The in-plane uniformity of the surface reflectance of the light-shielding film of the obtained photomask blank was measured. The surface reflectance was measured at 121 points in the substrate surface except for the edge portion 50mm of the substrate by 11 × 11 using a reflectance measuring instrument, and the in-plane uniformity of the surface reflectance was calculated based on the obtained evaluation results, and the result was 2.0% (statistical range). As described above, the in-plane uniformity of the back surface reflectance of the light-shielding film using the model substrate was calculated, and the result was 3.5% (statistical range).

As in example 1 above, the light-shielding film of the photomask blank was configured such that the 1 st reflection suppression layer, the light-shielding layer, and the 2 nd reflection suppression layer were stacked from the transparent substrate side and each layer had a predetermined composition, thereby realizing a cross-sectional shape in which the light-shielding film pattern was vertically formed when patterning was performed by wet etching. Further, it was confirmed that the defects can be reduced by providing the 1 st reflection suppression layer and the 2 nd reflection suppression layer with a laminated structure of a low-degree chromium oxide layer and a high-degree chromium oxide layer from the transparent substrate side, and further, the layers can be configured to have a predetermined composition, and therefore, the in-plane uniformity of the reflectance of the front surface and the back surface of the light shielding film is high.

(production of photomask)

Next, a photomask was produced using the photomask blank of example 1.

First, a novolak-type positive resist is formed on the light-shielding film of the photomask blank. Then, a pattern of a circuit pattern for a TFT panel was drawn on the resist film using a laser drawing apparatus, and further development and rinsing were performed, thereby forming a predetermined resist pattern (the minimum line width of the circuit pattern was 0.75 μm).

Then, the light-shielding film was patterned by wet etching using a chromium etching solution with the resist pattern as a mask, and finally the resist pattern was peeled off by a resist-peeling solution, thereby obtaining a photomask in which a light-shielding film pattern (light-shielding film pattern) was formed on a transparent substrate. The photomask had an aperture ratio of a light-shielding film pattern (light-shielding film pattern) formed on a transparent substrate, that is, an exposure ratio of the transparent substrate on which the light-shielding film pattern was not formed to the entire surface of the photomask on which the light-shielding film pattern was formed was 45%.

When the light shielding film pattern of the photomask was observed by a Scanning Electron Microscope (SEM), the cross-sectional shape of the light shielding film pattern was 77 ° which was good. The CD uniformity of the light shielding film pattern of the photomask was measured by Seiko Instruments Nanotechnology "SIR 8000". Measurement of CD uniformity the CD uniformity was measured at 11 × 11 spots for an area of 1100 × 1300mm except for the edge area of the substrate. As a result, the CD uniformity was less than 60nm, and the obtained photomask had good CD uniformity.

(production of LCD Panel)

The photomask produced in example 1 was set on a mask stage of an exposure apparatus, and a transfer object having a resist film formed on a substrate for a display device (TFT) was subjected to pattern exposure to produce a TFT array. As the exposure light, composite light including i-line having a wavelength of 365nm, h-line having a wavelength of 405nm, and g-line having a wavelength of 436nm was used.

The thus-produced TFT array was combined with a color filter, a polarizing plate, and a backlight to produce a TFT-LCD panel. As a result, a TFT-LCD panel free from display unevenness was obtained. This is considered to be because, when pattern exposure is performed using a photomask, reflection of light on the front and back surfaces is suppressed, the total amount of reflected light is reduced, and in-plane uniformity of reflectance is improved.

(reference example 1)

A photomask blank was produced in the same manner as in example 1, except that in reference example 1, the 1 st reflection suppression layer was a single-layer chromium oxide layer, the 2 nd reflection suppression layer was a laminated structure of a high-degree chromium oxide layer and a low-degree chromium oxide layer from the transparent substrate side, and the light-shielding layer was CrON.

The film formation conditions of the 1 st reflection suppression layer were: a Cr sputtering target is used as a sputtering target, the flow rate of an oxygen gas is selected from the range of 5-45 sccm, the flow rate of a nitrogen gas is selected from the range of 30-60 sccm, the flow rate of a rare gas is selected from the range of 60-150 sccm, and the target applied power is set within the range of 2.0-6.0 kW, so that the flow rate of a reactive gas is in a metal mode.

The light-shielding layer was formed under the following conditions: a Cr sputtering target is used as a sputtering target, the flow rate of a nitrogen-based gas is selected from the range of 1-60 sccm, the flow rate of a rare gas is selected from the range of 60-200 sccm, and the target applied power is set in the range of 3.0-7.0 kW, so that the flow rate of a reactive gas is in a metal mode.

The film formation conditions of the 2 nd reflection suppressing layer were: a Cr sputtering target is used as a sputtering target, the flow rate of an oxygen gas is selected from the range of 8-45 sccm, the flow rate of a nitrogen gas is selected from the range of 30-60 sccm, the flow rate of a rare gas is selected from the range of 60-150 sccm, and the target applied power is set in the range of 2.0-6.0 kW, so that the flow rate of a reactive gas is in a metal mode.

The light-shielding film of the obtained photomask blank was measured for composition in the film thickness direction by XPS in the same manner as in example 1, and it was confirmed that each layer in the light-shielding film had a composition distribution shown in fig. 4. Fig. 4 is a graph showing the results of composition analysis in the film thickness direction in the photomask blank of reference example 1, in which the horizontal axis represents the film thickness and the vertical axis represents the content of element [ atomic% ]. The film thickness represents the depth [ nm ] from the surface of the light-shielding film.

In fig. 4, a region containing about 21 atomic% of carbon (C) near the surface of the light-shielding film is a surface native oxide layer. The region, excluding the surface native oxide layer, in which the ratio of oxygen (O) to nitrogen (N) is less than 2.5 and which is at a depth of about 5nm to about 15nm from the surface of the light-shielding film is a low-degree chromium oxide layer. A region having a ratio of oxygen (O) to nitrogen (N) of 2.5 or more, excluding the surface native oxide layer, and having a depth of about 16nm to about 34nm from the surface of the light-shielding film is a high chromium oxide layer. The region, excluding the surface native oxide layer, at a depth of about 35nm to about 89nm from the surface of the light-shielding film is a transition layer. The region apart from the surface native oxide layer and having a depth of about 90nm to about 208nm from the surface of the light-shielding film is the light-shielding layer. The region, excluding the surface native oxide layer, at a depth of about 209nm to about 227nm from the surface of the light-shielding film is a transition layer. The region excluding the surface native oxide layer and having a depth of about 228nm to about 251nm from the surface of the light-shielding film is the 1 st reflection suppression layer. A region where the ratio of oxygen (O) to silicon (Si) reaches about 2 is a transparent substrate, and a region between the transparent substrate and the 1 st reflection suppression layer is a transition layer.

As shown in FIG. 4, the 1 st reflection suppressing layer is a CrCON film containing 51.4 to 57 atomic% of Cr, 13.5 to 18.2 atomic% of N, 22.6 to 31.6 atomic% of O, and 2.8 to 4.8 atomic% of C. The light shielding layer is a CrON film containing 85.4 to 91.9 atomic% of Cr, 7.4 to 9.3 atomic% of N, and 0.5 to 6.0 atomic% of O. The 2 nd reflection suppression layer is composed of a high-degree chromium oxide layer and a low-degree chromium oxide layer. The high chromium oxide layer is a CrCON film containing 49.0 to 50.6 atomic% of Cr, 9.1 to 13.0 atomic% of N, 33.7 to 39.4 atomic% of O, and 2.2 to 2.9 atomic% of C. The low-degree chromium oxide layer is a CrCON film containing 50.0 to 51.1 atomic% of Cr, 13.5 to 14.1 atomic% of N, 31.8 to 33.4 atomic% of O, and 2.5 to 3.5 atomic% of C.

(evaluation of photomask blank)

The photomask blank of reference example 1 was measured for the optical density of the light-shielding film in the same manner as in example 1, and found to be 5.0 or more in g-line (wavelength 436nm) which is the wavelength range of the exposure light. The reflectance of the front and back surfaces of the light-shielding film was measured by a spectrophotometer, and the reflectance spectrum shown in fig. 5 was obtained. Fig. 5 shows a reflectance spectrum of the front and back surfaces of the photomask blank of comparative example 1, with the horizontal axis representing wavelength [ nm ] and the vertical axis representing reflectance [% ]. As shown in fig. 5, it was confirmed that the photomask blank of reference example 1 can significantly reduce the reflectance with respect to light having a wide range of wavelengths, as in example 1. Specifically, the light-shielding film has a surface reflectance of 15.0% or less (15.0% (wavelength 300nm), 13.3% (wavelength 313nm), 7.7% (wavelength 365nm), 1.8% (wavelength 405nm), 1.1% (wavelength 413nm), 0.3% (wavelength 436nm)) at a wavelength of 300nm to 436nm, and a surface reflectance of 10.0% or less (7.7% (wavelength 365nm), 1.8% (wavelength 405nm), 1.1% (wavelength 413nm), 0.3% (wavelength 436nm)) at a wavelength of 365nm to 436 nm. The light-shielding film has a back surface reflectance of 15.0% or less (12.2% (wavelength 300nm), 10.4% (wavelength 313nm), 6.2% (wavelength 365nm), 4.7% (wavelength 405nm), 4.8% (wavelength 436nm)) at a wavelength of 300nm to 436nm, and a back surface reflectance of 7.5% or less (6.2% (wavelength 365nm), 4.7% (wavelength 405nm), 4.8% (wavelength 436nm)) at a wavelength of 365nm to 436 nm. The reflectance of the light-shielding film at a wavelength of 350nm to 436nm on the front and back surfaces thereof can be reduced to 15% or less, or the reflectance of the light-shielding film at a wavelength of 365nm to 436nm on the front and back surfaces thereof can be reduced to 10% or less, and it has been confirmed that the reflectance particularly with respect to light having a wavelength of 436nm can be set to 0.3% on the front surface and 4.8% on the back surface.

The in-plane uniformity of the surface reflectance of the light-shielding film of the obtained photomask blank was measured. The surface reflectance was measured at 121 points in the substrate surface except for the edge portion 50mm of the substrate by 11 × 11, and the in-plane uniformity of the surface reflectance was calculated based on the obtained evaluation results, and the result was 3.9% (statistical range). The back surface reflectance was calculated from the in-plane uniformity of the back surface reflectance of the light-shielding film using the model substrate as described above, and as a result, the in-plane uniformity exceeded 5.0% (statistical range), and the unevenness in reflectance was observed by visual observation.

(evaluation of light-shielding film pattern)

A light-shielding film pattern was formed on the photomask blank of the reference example in the same manner as in example 1, and evaluated. The light-shielding film pattern was observed by SEM, and it was confirmed that the cross-sectional shape of the light-shielding film pattern was inclined with respect to the vertical and tapered. The angle formed by the side surface of the light-shielding film pattern and the transparent substrate was measured and was found to be 54 °.

Next, a photomask was produced using the photomask blank of the reference example in the same manner as in example 1. The CD uniformity of the light-shielding film pattern of the photomask thus obtained was measured, and as a result, a defect of 100nm was obtained. As described above, the mask blanks of the reference examples can reduce the reflectance of the front and rear surfaces, but cannot form a mask pattern with high accuracy.