阅读说明：本技术 反射性掩模坯料的制造方法、反射性掩模坯料和反射性掩模的制造方法 (Method for manufacturing reflective mask blank, and method for manufacturing reflective mask ) 是由 寺泽恒男 金子英雄 稻月判臣 高坂卓郎 于 2020-09-11 设计创作，主要内容包括：本发明涉及一种反射性掩模坯料的制造方法、反射性掩模坯料和反射性掩模的制造方法。具体涉及一种反射性掩模坯料,其包括衬底、从衬底侧依次形成在衬底的一个主表面上的用于EUV光反射的多层反射膜、保护膜和用于EUV光吸收的吸收体膜以及导电膜。在衬底的其他主表面上形成坐标参比标记时,在另一主表面上形成坐标参比标记。(The present invention relates to a method for manufacturing a reflective mask blank, and a method for manufacturing a reflective mask. And more particularly to a reflective mask blank comprising a substrate, a multilayer reflective film for EUV light reflection, a protective film, and an absorber film and a conductive film for EUV light absorption formed on one main surface of the substrate in this order from the substrate side. When the coordinate reference mark is formed on the other main surface of the substrate, the coordinate reference mark is formed on the other main surface.)

1. A method of manufacturing a reflective mask blank comprising a substrate, and a multilayer reflective film for EUV light reflection, a protective film and an absorber film for EUV light absorption formed on one main surface of the substrate in this order from the substrate side, and a conductive film formed on the other main surface of the substrate, the method comprising the steps of:

(A1) forming a conductive film on the other main surface,

(A2) a coordinate reference mark is formed on the other main surface side,

(B1) forming a multilayer reflective film and a protective film on the one main surface,

(B2) inspecting the multilayer reflective film and the protective film formed in the step (B1) for defects, obtaining positional information of the detected defects based on coordinates defined with reference to a coordinate reference mark, and saving the positional information to a recording medium,

(C1) after the step (B2), forming an absorbent film on the protective film, and

(C2) the defect in the absorber film formed in step (C1) is inspected, position information of the detected defect is obtained based on the coordinates defined with reference to the coordinate reference mark, and the position information is saved to a recording medium.

2. The method according to claim 1, wherein in step (A2), a coordinate reference mark is formed on the conductive film formed in step (A1).

3. The method of claim 1, further comprising the step of measuring the flatness of the substrate after step (B1) and before step (B2).

4. The method of claim 1, further comprising the step of measuring the flatness of the substrate after step (C1) and before step (C2).

5. The method of claim 1, wherein when a defect is detected in step (B2), the step (B2) comprises the steps of: a processing order for the defect is created and saved to the recording medium together with the position information.

6. The method of claim 5, wherein a processing order is a priority order for processing defects, the priority order determined based on printability of detected defects.

7. A reflective mask blank comprising a substrate, a multilayer reflective film for EUV light reflection, a protective film and an absorber film for EUV light absorption formed on one main surface of the substrate in this order from the substrate side, and a conductive film formed on the other main surface of the substrate, wherein

A coordinate reference mark is formed on the conductive film.

8. A set of a reflective mask blank and a recording medium,

the reflective mask blank comprises, as main components, a substrate, and a multilayer reflective film for EUV light reflection, a protective film and an absorber film for EUV light absorption formed on one main surface of the substrate in this order from the substrate side, and a conductive film formed on the other main surface of the substrate, on which a coordinate reference mark is formed,

the recording medium records position information of the defect based on coordinates defined with reference to the coordinate reference mark.

9. The reflective mask blank of claim 8, wherein the recording medium further records a prioritization for handling defects, the prioritization determined based on printability of detected defects.

10. A method of manufacturing a reflective mask, comprising the steps of:

a kit for preparing the reflective mask blank and recording medium of claim 9,

setting a coordinate system with reference to a coordinate reference mark formed on the reflective mask blank, and determining a position of a defect of the reflective mask blank in the coordinate system with reference to position information of the defect stored in the recording medium,

the drawing pattern data is prepared by patterning the absorber film to form an absorber pattern,

sequentially evaluating the possibility of processing the defect by retaining the absorber film as the absorber pattern according to the priority stored in the recording medium, and

an absorber pattern is formed by etching and removing a portion of the absorber film of the reflective mask blank so that the absorber pattern remains at a location of the defect that has been evaluated as treatable from the location of the defect in the coordinate system.

Technical Field

The present invention relates to a reflective mask blank and a method of manufacturing the same, and more particularly, to a reflective mask blank suitable for manufacturing a reflective mask having reduced phase defects, and a method of manufacturing the same. The invention also relates to a method of manufacturing a reflective mask with reduced phase defects using the reflective mask blank.

Background

In a manufacturing process of a semiconductor device, an optical lithography technique is used in which a circuit pattern formed on a transfer mask is transferred onto a semiconductor substrate (semiconductor wafer) through a reduction projection optical system that irradiates exposure light to the mask. Currently, the predominant wavelength of exposure light is 193nm by an argon fluoride (ArF) excimer laser. By employing a process called multi-patterning in combination with a multi-exposure process and a multi-process (etching) process, a pattern having a size smaller than the exposure wavelength can be finally formed.

However, since it is necessary to form a finer pattern, an EUV lithography technique using extreme ultraviolet light (hereinafter referred to as "EUV") having a shorter wavelength than an ArF excimer laser as exposure light is promising. EUV light is light having a wavelength of about 0.2 to 100nm, more specifically, about 13.5 nm. The EUV light has very low transmittance for substances and cannot be used for a conventional transmissive projection optical system or mask, and therefore, a reflective optical element is applied. Therefore, a reflective mask has also been proposed as a mask for pattern transfer. The reflective mask has a multilayer reflective film formed on a substrate and reflecting EUV light, and a patterned absorber film formed on the multilayer reflective film and absorbing the EUV light. On the other hand, the material before patterning the absorber film is referred to as a reflective mask blank and is used as the material of the reflective mask.

In the manufacturing process of the reflective mask, a pattern is formed by etching the absorber film of the reflective mask blank, and then the pattern is generally inspected. When a defect is detected, the defect is repaired. However, in the case of the reflective mask, in addition to defects derived from the absorber film and the absorber pattern in some cases, there are defects in which the reflectance is reduced due to structural disorder of the multilayer reflective film, so-called phase defects. In addition, it is difficult to directly align phase defects in the multilayer reflective film after the absorber pattern is formed.

In this context, many studies have been made on techniques for detecting phase defects in reflective mask blanks. For example, JP-a 2003-. Further, JP-A H6-349715 (patent document 2) discloses a technique of utilizing a bright field in an X-ray microscope as a method of detecting a phase defect inside a multilayer reflective film by using EUV. These methods accurately detect phase defects in multilayer reflective films. In particular, in the dark field detection method using EUV light described in patent document 1, a phase defect peculiar to a reflective mask blank having a multilayer reflective film can be detected as a bright spot signal having high sensitivity. Therefore, this is a very effective method for determining the presence or absence of a phase defect after the formation of the multilayer reflective film.

On the other hand, as a method of finally completing reduction of phase defects at the manufacturing stage of the reflective mask even if phase defects remain in the reflective mask blank, for example, JP-a 2002-. In this method, after the absorber pattern is formed, it is necessary to accurately obtain the position of the phase defect in the multilayer reflective film based on the coordinates of the absorber pattern. However, it is difficult to accurately determine the position of the phase defect after the patterning.

Further, WO 2014/129527a1 (patent document 4) discloses a technique of patterning an absorber film by avoiding the position of a phase defect as follows: a reference mark is formed on the absorber film, the position of the phase defect is obtained in the multilayer reflective film as the position of the unevenness on the surface of the absorber film on the multilayer reflective film, and converted into position information of the defect with respect to the reference mark, and the rendering data is further modified for patterning the absorber film based on the defect position information. In this method, it is not necessary to engrave a reference mark into the multilayer reflective film, and therefore the risk of particle generation due to engraving of the reference mark can be reduced. However, in some phase defects, as the irregularities on the surface of the multilayer reflective film, the structural disorder in the multilayer reflective film that reduces the reflectance hardly occurs. Therefore, in the inspection of the absorber film, it is difficult to accurately obtain the positional information of all the phase defects. Therefore, the reflective mask blank obtained by this method cannot draw an absorber pattern while avoiding all relevant phase defects, and therefore this method cannot avoid phase defects with high accuracy when forming the absorber pattern.

List of citations

Patent document 1: JP-A2003-114200

Patent document 2: JP-AH 6-349715

Patent document 3: JP-A2002-532738

Patent document 4: WO 2014/129527A1

Patent document 5: JP-A2007-200953

Disclosure of Invention

For example, as a method for detecting and avoiding a phase defect with high accuracy, it is considered to provide a concave or convex mark on a substrate to serve as a reference mark for configuring a coordinate system. According to the method, a multilayer reflective film can be formed on a reference mark formed on a substrate, and the position of a phase defect in the multilayer reflective film is determined with reference to the reference mark in a subsequent phase defect inspection. Further, when the absorber film is formed on the multilayer reflective film on the reference mark, the pattern drawing position for forming the absorber pattern is determined based on the position of the phase defect in the multilayer reflective film determined with reference to the reference mark, and the absorber pattern can be formed while avoiding the phase defect by using the same reference mark.

However, when the respective layers constituting the multilayer reflective film are stacked on the reference mark and an absorber film is further stacked thereon, the total thickness of the film stack is generally more than 300 nm. In the case where the reference mark is buried deep in the film, high-precision position determination cannot be expected. Alternatively, the reference mark may be engraved in the multilayer reflective film after the multilayer reflective film is formed and before the absorber film is formed. However, preferably, the multilayer reflective film and the absorber film are formed continuously. In particular, if the reference mark is formed in the multilayer reflective film by engraving at this stage, the risk of particle defects in the resulting reflective mask blank increases.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a reflective mask blank and a manufacturing method thereof, which can accurately grasp the position of a defect (particularly a fine defect) in a multilayer reflective film after forming the multilayer reflective film on a substrate and after forming an absorber film on the multilayer reflective film, with respect to defects such as phase defects which affect a reflective mask manufactured from the reflective mask blank; and to provide a reflective mask blank and a method for manufacturing the same, which can efficiently form an absorber pattern that reduces the influence of defects in a multilayer reflective film and can avoid the defects with high accuracy. Further, the present invention provides a method of manufacturing a reflective mask, which can efficiently form an absorber pattern that alleviates the effect of defects in a multilayer reflective film, while avoiding defects from such a reflective mask blank with high accuracy.

In order to solve the above-described problems, the inventors found that, with a reflective mask blank including a substrate and a multilayer reflective film for EUV light reflection, a protective film, and an absorber film for EUV light absorption formed on one main surface of the substrate and a conductive film formed on the other main surface of the substrate, when a coordinate reference mark is formed on the other main surface side, particularly on the conductive film, without burying the coordinate reference mark in a thick film formed on one main surface of the substrate, the position of a defect such as a phase defect in the multilayer reflective film can be determined with high accuracy.

Further, the inventors found that a reflective mask blank in which coordinate reference marks are formed on the other major surface side was manufactured by: inspecting defects in the multilayer reflective film and the absorber film once in a stage where the multilayer reflective film and the absorber film have been formed; obtaining position information of the detected defect based on coordinates defined with reference to the coordinate reference mark and saving the position information to a recording medium; then, an absorber film is formed, defects in the absorber film are inspected, positional information of the detected defects is obtained based on coordinates defined with reference to a coordinate reference mark, and the positional information is saved to a recording medium. According to this method, the position of the defect can be accurately grasped from the information stored in the recording medium. Further, by efficiently forming an absorber pattern that mitigates the influence of defects in the multilayer reflective film based on the positional information of the defects stored in the recording medium, it is possible to obtain a reflective mask from a reflective mask blank while avoiding defects such as phase defects with high accuracy.

In one aspect, the present invention provides a method of manufacturing a reflective mask blank including a substrate, and a multilayer reflective film for EUV light reflection, a protective film, and an absorber film for EUV light absorption formed on one main surface of the substrate in this order from the substrate side, and a conductive film formed on the other main surface of the substrate, the method comprising the steps of:

(A1) a conductive film is formed on the other main surface,

(A2) a coordinate reference mark is formed on the other main surface side,

(B1) a multilayer reflection film and a protection film are formed on the one main surface,

(B2) inspecting the multilayer reflective film and the protective film formed in the step (B1) for defects, obtaining positional information of the detected defects based on coordinates defined with reference to a coordinate reference mark, and saving the positional information to a recording medium,

(C1) after the step (B2), forming an absorbent film on the protective film, and

(C2) the defect in the absorber film formed in step (C1) is inspected, position information of the detected defect is obtained based on the coordinates defined with reference to the coordinate reference mark, and the position information is saved to a recording medium.

Preferably, in the step (a2), a coordinate reference mark is formed on the conductive film formed in the step (a 1).

Preferably, the method further comprises the steps of: measuring the flatness of the substrate after step (B1) and before step (B2) and/or measuring the flatness of the substrate after step (C1) and before step (C2).

Preferably, when the defect is detected in the step (B2), the step (B2) includes the steps of: a processing order of the defects is created and saved to the recording medium together with the position information, typically the processing order is a priority of processing the defects, the priority being determined according to the printability of detecting the defects.

In another aspect, the present invention provides a reflective mask blank comprising: a substrate, a multilayer reflective film for EUV light reflection, a protective film and an absorber film for EUV light absorption formed on one main surface of the substrate in this order from the substrate side, and a conductive film formed on the other main surface of the substrate, wherein

A coordinate reference mark is formed on the conductive film.

In another aspect, the invention provides a set (set) of a reflective mask blank and a recording medium,

as main components, a reflective mask blank includes a substrate, and a multilayer reflective film for EUV light reflection, a protective film, and an absorber film for EUV light absorption, which are formed on one main surface of the substrate in this order from the substrate side, and a conductive film formed on the other main surface of the substrate, and a coordinate reference mark is formed on the conductive film,

the recording medium records position information of the defect based on coordinates defined with reference to the coordinate reference mark.

Preferably, the recording medium is further recorded with a priority order for handling the defects, the priority order being determined based on printability of the detected defects.

In another aspect, the present invention provides a method of manufacturing a reflective mask, the method comprising the steps of:

a set of a reflective mask blank and a recording medium is prepared,

configuring a coordinate system with reference to coordinate reference marks formed on the reflective mask blank, and determining a position of a defect of the reflective mask blank in the coordinate system with reference to position information of the defect stored in the recording medium,

the drawing pattern data is prepared by patterning the absorber film to form an absorber pattern,

sequentially evaluating the possibility of processing the defect by retaining the absorber film as the absorber pattern according to the priority stored in the recording medium, and

an absorber pattern is formed by etching and removing a portion of the absorber film of the reflective mask blank, thereby maintaining the absorber pattern at a position of the defect that has been evaluated as treatable from the position of the defect in the coordinate system.

Advantageous effects of the invention

According to the present invention, with respect to defects such as phase defects that affect a reflective mask manufactured from a reflective mask blank, after a multilayer reflective film is formed on a substrate, further after an absorber film is formed on the multilayer reflective film, the position of the defects (particularly even fine defects) in the multilayer reflective film can be accurately grasped. Further, a reflective mask blank can be manufactured by efficiently forming an absorber pattern that can mitigate the influence of defects in the multilayer reflective film while avoiding defects with high accuracy.

Brief description of the drawings

Fig. 1A and 1B show an example of a reflective mask, fig. 1A being a plan view of an outline from a surface side of the reflective mask on which an absorber pattern is formed, and fig. 1B being an enlarged cross-sectional view of a device pattern region of the reflective mask in fig. 1A.

As illustrative diagrams, fig. 2A to 2C show phase defects of a reflective mask, fig. 2A is a sectional view illustrating a state of a phase defect existing in a multilayer reflective film before an absorber film is formed, fig. 2B is a sectional view for illustrating a state of an exposed phase defect, and fig. 2C is a sectional view illustrating a state of a phase defect covered by an absorber pattern.

Fig. 3A to 3C show examples of planar shapes of coordinate reference marks, and fig. 3A, 3B, and 3C are cross marks, longitudinal line marks, and transverse line marks, respectively.

Fig. 4 is a bottom view of a reflective mask blank with a coordinate reference mark formed on a conductive film.

Fig. 5A to 5E are views for explaining each step of manufacturing the reflective mask blank of the present invention, fig. 5A is a sectional view of a substrate, fig. 5B is a sectional view of a state where a conductive film is formed, fig. 5C is a sectional view of a state where a coordinate reference mark is formed on the conductive film, fig. 5D is a sectional view of a state where a multilayer reflective film and a protective film are formed, and fig. 5E is a sectional view of a state where an absorber film is formed.

Fig. 6 is a conceptual diagram of an inspection tool including an optical system for detecting a film defect and an optical system for detecting a coordinate reference mark.

Fig. 7 is an explanatory diagram showing a state of warpage or bending of the main surface of the substrate by a quadratic curve.

Fig. 8 is a sectional view showing a state where the substrate having the film formed thereon is locally inclined at an angle θ.

Fig. 9 is a flowchart of an example of a method of manufacturing a reflective mask by patterning an absorber film of a reflective mask blank.

Fig. 10A and 10B are conceptual views illustrating positions of phase defects existing in an absorber pattern of a reflective mask and a multilayer reflective film, respectively.

Detailed Description

The reflective mask blank of the present invention comprises: the EUV light-absorbing film includes a substrate, and a multilayer reflective film for EUV light reflection, a protective film (for multilayer reflective film), and an absorber film for EUV light absorption formed on one main surface (front side) of the substrate in this order from the substrate side, and a conductive film formed on the other main surface (back side) of the substrate, which is the opposite side of the one main surface. A conductive film is formed to electrostatically hold the reflective mask on a mask stage of an exposure tool. The thickness of the conductive film is usually 10 to 40 nm. In the above description, one main surface of the substrate is defined as a front side or upper side, and the other main surface is defined as a back side or lower side. However, for convenience, a front side and a rear side or an upper side and a lower side are defined in both surfaces. The two main surfaces (film formation surfaces) are one main surface and the other main surface, respectively. The front and back sides or the upper and lower sides may be replaced. Meanwhile, the reflective mask is formed by patterning the absorber film of the reflective mask blank to form an absorber pattern (pattern of the absorber film).

Fig. 1A and 1B show an example of a reflective mask for EUV exposure as a typical reflective mask of the present invention. Fig. 1A is a plan view of an outline from the surface side of a reflective mask on which an absorber pattern is formed, and fig. 1B is an enlarged cross-sectional view of a device pattern region of the reflective mask in fig. 1A. As shown in fig. 1A and 1B, a device pattern region MDA, which constitutes a circuit pattern of a semiconductor integrated circuit device, is formed at a predetermined position located in a central portion of one main surface side of the substrate 101 of the reflective mask RM. Alignment mark regions MA1, MA2, MA3, MA4 including marks for alignment of the reflective mask or wafer alignment marks are formed in the peripheral portion other than the device pattern region MDA. Further, a multilayer reflective film 102 for EUV light reflection, a protective film 103, and an absorber pattern 114 for EUV light absorption are formed on one main surface of the substrate 101 (in this order from the substrate 101 side), and a conductive film 105 is formed on the other main surface of the substrate 101.

It is preferable to use a substrate composed of a low thermal expansion material and having a sufficiently flat surface. For example, the substrate preferably has a thermal expansion coefficient of. + -. 3X 10^-8Within. + -. 1X 10 ℃ more preferably^-8Within/° c. The surface roughness (RMS value) of the main surface of the substrate is preferably at most 0.1nm, more preferably at most 0.05 nm. In particular, the surface roughness may be satisfied at least on one region on which an absorber pattern (e.g., device pattern region MDA in fig. 1A) is formed in the main surface on which the absorber film is formed, preferably at the entire main surface on which the absorber film is formed. Such a surface roughness can be obtained by polishing the substrate.

The multilayer reflective film is a multilayer filmThe multilayer film is composed of alternately stacked layers composed of a material of low refractive index and layers composed of a material of high refractive index. For example, for EUV light having an exposure wavelength of 13 to 14nm (typically a wavelength of about 13.5 nm), a Mo/Si laminated film including a molybdenum layer (Mo) as a low refractive index material and a silicon (Si) layer as a high refractive index material may be alternately laminated for about 40 cycles (40 layers each). The thickness of the multilayer reflective film is usuallyLeft and right.

The protective film is referred to as a cover layer, and is provided to protect the multilayer reflective film when forming an absorber pattern or a collimating absorber pattern provided on the protective film. As a material of the protective film, for example, silicon (Si), ruthenium (Ru), or a ruthenium (Ru) compound to which niobium (Nb) and/or zirconium (Zr) is added can be used. The thickness of the protective film is typically about 2 to 5 nm.

The absorber pattern is a mask pattern that absorbs EUV light, and is formed by patterning the absorber film. For example, a compound containing tantalum (Ta) as a main component or a compound containing chromium (Cr) as a main component can be used as a material of the absorber film. The absorbent film can be composed of a single layer or multiple layers. The thickness of the absorber film is typically about 70 to 90 nm.

The reflective mask blank may have a hard mask film on the absorber film to assist in patterning of the absorber film. The hard mask film is generally removed after the absorber pattern is formed, and the hard mask film does not remain in the reflective mask. Further, a resist film (photoresist film) for patterning the absorber film may be formed in the reflective mask blank.

In some cases of reflective masks, there is a defect called a phase defect in which the reflectance is reduced due to structural disorder in the multilayer reflective film. Hereinafter, a phase defect generated in the multilayer reflective film will be described. Fig. 2A to 2C are diagrams illustrating phase defects in a reflective mask for EUV exposure. Fig. 2A is a sectional view illustrating a phase defect state existing in the multilayer reflective film before forming the absorber film, fig. 2B is a sectional view for illustrating a phase defect state exposed on the multilayer reflective film, and fig. 2C is a sectional view illustrating a phase defect state covered by the absorber pattern.

Fig. 2A shows the following state: wherein when the multilayer reflection film 102 is formed on the surface of the substrate 101, the convex phase defect 120 is formed through the multilayer reflection film 102 to the protection film 103 formed on the defect because the multilayer reflection film 102 is formed on the main surface of the substrate on which there is a fine convex portion. Reference numeral 105 denotes a conductive film. Although fig. 2A shows a case where there are fine protrusions on the main surface of the substrate 101, when there are fine recesses on the main surface of the substrate 101, concave phase defects 120 will be formed. Even if fine concave or convex portions are present on the main surface of the substrate 101, when the concave or convex shape is gently flattened by a smoothing action in the process of forming each layer of the multilayer reflective film 102, it may sometimes be difficult in some cases to exhibit the concave or convex shape on the finally obtained surface of the multilayer reflective film 102 or the protective film 103. However, even in this case, if there is a fine concave or convex shaped portion in the multilayer reflective film 102, the portion serves as a phase defect that causes a certain phase shift to the reflected light and reduces the reflectance.

When the reflective mask blank is manufactured by: if an absorber film is formed on the protective film 103 in a state where a phase defect 120 is present (as shown in fig. 2A), and then an absorber pattern is formed by patterning the absorber film, if there is an exposed phase defect 120 (as shown in fig. 2B) between adjacent absorber patterns 114, the height of the convex portion or the depth of the concave portion is, for example, at least about 2 to 3nm, the phase of reflected light is disturbed and the reflectance is lowered, so that a defect occurs in the pattern projection image. On the other hand, when the phase defect 120 is covered by the absorber pattern 114 and the reflectivity of the phase defect 120 portion is sufficiently low, no defect occurs in the projected image of the pattern of the reflective mask. Therefore, when the circuit pattern is formed to cover the portion where the phase defect exists with the absorber pattern when the reflective mask is manufactured, a defect in the pattern projection image caused by the phase defect can be avoided. For this reason, it is important to be able to accurately determine the location (coordinates) of the phase defects present in the reflective mask blank. In addition, it is important to be able to accurately grasp the position (coordinates) of the phase defect, which corresponds to the coordinates of the drawing pattern for forming the absorber pattern, when patterning the absorber film.

In the reflective mask blank of the present invention, the coordinate reference mark is formed on the other substrate main surface side (back side) on the opposite side of the one main surface side (front side) on which the multilayer reflective film, the protective film, and the absorber film are formed. The coordinate reference mark is a reference (coordinate reference) on a two-dimensional coordinate or a three-dimensional coordinate for determining the position of a specific place, for example, a place where a defect exists in a reflective mask blank or a reflective mask obtained from the reflective mask blank. Thus, the coordinate reference mark is typically formed in at least two locations, preferably at least three locations, more preferably at least four locations. The coordinate reference mark may have a convex shape. However, the concave shape is convenient and is preferably engraved on a substrate or film to form the mark. In particular, in the case where the other main surface side is a suction surface for applying an electrostatic chuck, it is more preferable to form the coordinate reference mark in a concave shape.

The planar shape of the coordinate reference mark is not particularly limited as long as the position thereof can be detected by the inspection light of the optical inspection tool. A cross mark 106a shown in fig. 3A, a longitudinal line mark 106B composed of a plurality of spaced lines (six lines in this case) shown in fig. 3B, and a transverse line mark 106C composed of a plurality of spaced lines (six lines in this case) shown in fig. 3C are exemplified. The size of the mark is not particularly limited. For example, the width may be 50nm to 10 μm and the length may be 50 to 200 μm.

In the reflective mask blank of the present invention, it is preferable that a coordinate reference mark is formed on the conductive film. In general, a conductive film is formed on the other main surface side of the substrate so that an electrostatic chuck can be applied to the reflective mask obtained from the reflective mask blank when the reflective mask is loaded onto an exposure tool. The coordinate reference mark may be formed directly on the substrate. However, in view of the handleability of the coordinate reference mark, it is advantageous to form the coordinate reference mark by processing the conductive film. In addition, when the reflective mask is mounted on the exposure tool, even if the coordinate reference mark is formed on the conductive film, the function of the conductive film is not damaged. This is an advantage of forming a coordinate reference mark on the conductive film. In general, a concave reference mark is formed on a conductive film by engraving a part of the conductive film, particularly a part of the outer periphery of the conductive film. Typically, the coordinate reference marks are not used to load the reflective mask onto the exposure tool.

Fig. 4 is a bottom view of a reflective mask blank in which a coordinate reference mark is formed on a conductive film. In this case, the conductive film 105 is formed on the other main surface side of the substrate 101, and four concave coordinate reference marks 106 formed by engraving are formed in each part of the outer periphery of the conductive film 105 (in this case, specifically in each of the four mark forming regions 116 near the four corners).

The coordinate reference mark formed on the opposite side to the side where the circuit pattern is to be formed is used as a common reference, a position reference for inspecting defects such as phase defects existing in the multilayer reflective film, a position reference for drawing an absorber pattern, a position reference for defect inspection, and other references, without laminating layers for forming the circuit pattern, such as the multilayer reflective film, the protective film, the absorber film, and other films, on the coordinate reference mark. Further, since the coordinate reference mark is buried deep in each film without laminating a thick film on the coordinate reference mark, high accuracy can be obtained in determining the position. Further, unlike the method of forming the absorber film after forming the coordinate reference mark on the multilayer reflective film or protective film, the coordinate reference mark is formed on the opposite side to the side where the circuit pattern is to be formed. Therefore, it is not necessary to perform a process of making a coordinate reference mark having a risk of generating particles after forming the multilayer reflective film or protective film.

Next, a method for manufacturing the reflective mask blank of the present invention will be described. In the present invention, a reflective mask blank is suitably manufactured by a method comprising the steps of:

(A1) forming a conductive film on the other main surface,

(A2) a coordinate reference mark is formed on the other main surface side,

(B1) forming a multilayer reflective film and a protective film on the one main surface,

(B2) inspecting the multilayer reflective film and the protective film formed in the step (B1) for defects, obtaining positional information of the detected defects based on coordinates defined with reference to a coordinate reference mark, and saving the positional information to a recording medium,

(C1) after the step (B2), forming an absorbent film on the protective film, and

(C2) the defect in the absorber film formed in step (C1) is inspected, position information of the detected defect is obtained based on the coordinates defined with reference to the coordinate reference mark, and the position information is saved to a recording medium.

The method is described in detail with reference to the accompanying drawings. Fig. 5A to 5E are diagrams for explaining each step of manufacturing the reflective mask blank of the present invention. Fig. 5A is a cross-sectional view of a substrate. Fig. 5B is a sectional view of a state where a conductive film is formed on the other main surface of the substrate. Fig. 5C is a sectional view of a state where a coordinate reference mark is formed on the conductive film. Fig. 5D is a sectional view of a state where a multilayer reflective film and a protective film are formed in this order on one main surface of a substrate. Fig. 5E is a sectional view of a state where an absorber film is formed on the protective film.

In step (a1), as shown in fig. 5A, the substrate 101 is prepared. As the substrate 101, a substrate having one main surface and the other main surface with a predetermined surface roughness is prepared. Next, as shown in fig. 5B, a conductive film 105 is formed over the other main surface of the substrate 101.

In step (a2), a coordinate reference mark is formed on the other major surface side. In the case shown in fig. 5C, a coordinate reference mark is formed at a predetermined position in the outer periphery of the conductive film 105. The coordinate reference mark may be formed by etching and removing a portion of the conductive film 105. As the shape of the coordinate reference mark, a quasi-line mark or a fiducial (fiducial) mark of the same shape commonly used in a reflective mask may be applied. In particular, after the conductive film and the coordinate reference mark are formed, it is necessary to keep one main surface of the substrate clean. Therefore, if necessary, the substrate may be cleaned after the conductive film or the coordinate reference mark is formed. Even if one main surface of the substrate has been contaminated at the same time as the formation of the coordinate reference mark, the surface of the substrate itself is easily cleaned by the cleaning process. Therefore, steps (a1) and (a2) are preferably performed before step (B1).

In step (B1), as shown in fig. 5C, the multilayer reflective film 102 and the protective film 103 are formed on one main surface of the substrate 101. The multilayer reflective film and the protective film may be formed by an ion beam sputtering method, a CD sputtering method, or an RF sputtering method, respectively. Fig. 5C shows an example of forming the convex phase defect 120 in the multilayer reflective film 102 and the protective film 130.

In step (B2), defects in the multilayer reflective film 102 and the protective film 103 are inspected, position information of a detected defect (in this case, a phase defect) is obtained based on coordinates defined with reference to the coordinate reference mark 106, and the position information is saved to a recording medium. A specific method of inspecting defects in this step is described later. In such defect inspection, it is preferable to obtain information of the detection signal level of the defect and position information and save them in the recording medium. In addition, a step of measuring the flatness of the substrate may be included after the step (B1) and before the step (B2). The flatness can be measured, for example, by detecting a coordinate reference mark using a function for focusing in the optical system of the inspection tool shown in fig. 6, and will be described later.

In step (C1), as shown in fig. 5E, the absorber film 104 is formed on the protective film 103. The absorber film can also be formed by ion beam sputtering, CD sputtering, or RF sputtering. In fig. 5E, the absorber film 104 has a convex shape at the position of the phase defect 120 resulting from the formation of the convex phase defect 120 formed in the multilayer reflective film 102 and the protective film 103. Fig. 5E also shows an example in which the particles 121 are attached on the surface of the absorber film 104.

In step (C2), the formed absorber film is inspected for defects including phase defects, grain defects, and other defects in the multilayer reflective film, position information of the detected defects is obtained based on the coordinates defined with reference to the coordinate reference mark 106, and the position information is saved to a recording medium. Defect inspection can be performed in this step by a conventionally known method. For example, as shown in fig. 5E, when particles are attached on the surface of the absorber film, the defect is detected as a particle defect. Position information of the detected defect is obtained and saved to the recording medium. In addition, a step of measuring the flatness of the substrate may be included after the step (C1) and before the step (C2).

After the step (C2), a step of forming a resist film (photoresist film) on the absorber film may be included. According to this method, a reflective mask blank RMB shown in fig. 5E is obtained, and a reflective mask shown in fig. 2C is manufactured, for example, by patterning an absorber film of the reflective mask blank.

Next, a suitable defect inspection method for steps (B2) and (C2) is described. Fig. 6 is a conceptual diagram of an inspection tool including an optical system for detecting a defect of a film formed on one main surface side of a substrate (a defect of a multilayer reflective film, particularly a phase defect in step (B2), or a defect of an absorber film in step (C2)) and an optical system for detecting a coordinate reference mark on the other main surface side of the substrate. The inspection tool 200 includes: a support member SPT for supporting the film formation substrate FFS, a mask stage STG, a stage driving unit 201, an optical system 202 for defect inspection, an imaging and control unit 203 for defect inspection, an optical system 204 for detecting a coordinate reference mark, an imaging and control unit 205 for detecting a coordinate reference mark, and a control device 206 for controlling the entire defect detection. In steps (B2) and (C2), the object (object) of the film-forming substrate FFS is typically an intermediate product or a reflective mask blank in the process of manufacturing the reflective mask blank. However, an intermediate product in the process of manufacturing the reflective mask or the reflective mask may be used as the object.

Although not shown, the optical system 202 for defect inspection and the optical system 204 for detection coordinate reference mark include an illumination optical system and a focusing system for irradiating inspection light, respectively. The inspection light used in the optical system 202 for defect inspection may be inspection light having a wavelength of 190 to 540nm that is generally applied, and further EUV light having a wavelength of 13 to 15nm may also be applied. When EUV light is applied, a reflection mirror is used in an illumination optical system and an optical system for inspection. For example, as an optical system for detecting a coordinate reference mark formed on the other main surface side of the substrate, an optical system in which a wafer substrate is an object disclosed in JP-a 2007-200953 (patent document 5) is known, and the optical system can also be used.

In the case of the inspection tool shown in fig. 6, the optical system 202 for defect inspection and the optical system 204 for detection coordinate reference mark are disposed so that the axes of the lenses are coaxially aligned. When a defect of the film is detected by the optical system 202 for defect inspection after the coordinate reference mark 106 formed on the other main surface side of the film formation substrate FFS is detected, the position of the defect can be obtained as position information determined based on the reference coordinate reference mark, and the obtained position information is saved or recorded in a recording medium. Further, information of the detected defect signal level may be obtained along with the position information of the defect. In this case, information of the detected defect signal level may be saved or written to the recording medium together with the position information of the defect. The coordinate system may be a two-dimensional coordinate system or a three-dimensional coordinate system.

In particular, when a defect, in particular a phase defect, is detected, it is preferable to create a processing order for the defect and save or record the processing order together with the position information into the recording medium. The processing order may be a priority order for processing the defects, the priority order being determined based on printability of detecting the defects. For example, in the step (B2), when a phase defect is detected in the multilayer reflective film, the influence of a decrease in reflectance (printability of a defect in use of a reflective mask) caused by the phase defect of the multilayer reflective film can be evaluated from the signal level information of the detected phase defect. Also, a processing order may be created so as to give priority to defects evaluated as defects having a large influence on reflectance reduction. In this case, the processing order may be a priority for processing the defects, for example, a priority for covering the defects with the absorber pattern by patterning the absorber film to form the absorber pattern when the reflective mask is manufactured.

In the case of the inspection tool shown in fig. 6, the support member SPT does not have a structure in which the film formation substrate FFS is fixed with pressurization. The film formation substrate FFS is simply supported by the support member SPT, and any pressure that deforms its shape is not applied to the film formation substrate FFS.

By forming films such as a multilayer reflective film, a protective film, an absorber film, and other films, the substrate warps due to stress. When a film formation substrate is simply supported as an inspection tool shown in fig. 6 and inspected, the substrate has a bend, and inspection is performed in a state having the bend. In many cases, the shape of the warp or bend may be represented by a quadratic curve as shown in fig. 7, for example. In fig. 7, a curve P-P' shows a state of the main surface of the substrate having warpage or curvature. The symbol "L" represents a distance from one of opposite corners of the substrate to the center of the substrate (i.e., "2 × L" corresponds to a distance of the diagonal line), and the symbol "H" represents an amount of warpage or bending (height) at the center of the substrate. From these values, the radius of curvature R (distance from the symbol "O" expressed as the center of curvature) can be calculated assuming that the shape of the main surface of the substrate is a quadratic surface. The distance L and the height H can be obtained by measuring the flatness of the substrate.

In the defect inspection, a local inclination of the film formation substrate causes a positional difference between one main surface and the other main surface of the substrate. Therefore, it is preferable to grasp the warp or bend of the substrate on which the multilayer reflective film, the protective film, the absorber film, and the other films are formed, and to calibrate the influence of the local tilt caused by the warp or bend. Fig. 8 is a sectional view schematically showing a state of a local inclination angle θ of a substrate on which a film is formed. In this case, when the total thickness of the substrate 101, the multilayer reflective film 102, the protective film 103, and the conductive film 105 is "T", a positional difference expressed as "T × sin θ" occurs in the coordinates between the one and other main surfaces. Thus, the difference can be calibrated. The angle θ may be calculated from the shape of the warp or bend drawn by the quadric and the approximate location of the detected defect. Further, the angle θ can be directly calculated based on the method described in JP-a 2007-200953 (patent document 5).

The calibration value may be calculated, for example, as follows. In a two-dimensional coordinate system defined with reference to the coordinate reference mark, when the radius of curvature of the quadric surface and the coordinates of the defect with respect to the origin (x is 0, y is 0) are "R" and "x, y", respectively, the calibration value "Δ x" in the x direction and the calibration value "Δ y" in the y direction due to the inclination of the angle θ are Δ x ═ T/R) x and Δ y ═ T/R) y, respectively. When such calibration is applied, information for calibrating the position of the defect may be saved or recorded in the recording medium together with the position information of the defect.

The position information of the defect in the reflective mask blank is saved or recorded in the recording medium together with information of the signal level of the detected defect, the processing order (priority order), information for calibrating the position of the defect, and the like. The reflective mask blank of the present invention can be provided as a set of a reflective mask blank (main component) and a recording medium. According to the reflective mask blank combined with the recording medium, when the reflective mask is manufactured from the reflective mask blank, the position and the processing order of the defect can be determined from the information saved or recorded in the recording medium when the absorber film is patterned.

Next, a method of manufacturing the reflective mask is described. Referring to the flowchart shown in fig. 9, an example of a method of manufacturing a reflective mask by patterning an absorber film of a reflective mask blank is described.

First, a reflective mask blank and a recording medium or a set including the reflective mask blank and the recording medium is prepared (step S101). The reflective mask blank includes, as main components, prescribed films formed on one main surface and the other main surface of the substrate, and coordinate reference marks formed on the other main surface of the substrate. The recording medium stores or records position information of defects such as phase defects, information of signal levels of detected defects, processing order (priority order), information for calibrating defect positions, and the like, based on coordinates defined with reference to a coordinate reference mark. Examples of the recording medium include a medium on which information is electrically or magnetically recorded. The recording medium may be a paper medium in which information is written. Next, a coordinate system is configured with reference to coordinate reference marks formed on the reflective mask blank, and the position of the defect in the reflective mask blank is determined in the coordinate system with reference to the position information of the defect stored in the recording medium (step S102). The coordinate system may be a two-dimensional coordinate system or a three-dimensional coordinate system.

Next, drawing pattern data is prepared to form an absorber pattern by patterning the absorber film (step S103). Next, the positions of the drawn patterns are compared with the positions of the defects, and the possibility of handling the defects by leaving the absorber film as the absorber pattern, typically the possibility of covering the defects with the absorber pattern, is sequentially evaluated according to the priority order stored in the recording medium (step S104). At this stage, if the evaluation result determines that there is no defect that can be handled, or the number of defects is relatively small, the entire drawing pattern forming the absorber pattern can be rearranged by moving in a predetermined direction. Then, the process returns to step S103, and the drawing position at which the pattern is drawn can be optimized by performing step S104 again. In this way, the drawing position of the drawing pattern can be optimized to cover the defect having a high priority order, which has a high fatality and should be preferentially covered by the absorber pattern among the defects, to the maximum extent. Further, regarding the influence of the local tilt due to the warp or bend of the substrate, the drawing position of the drawn pattern may be calibrated in the same manner as the calibration of the defect position with respect to the local tilt of the film formation substrate.

The drawing pattern may be set based on coordinates defined with reference to the coordinate reference mark. For this purpose, the tool for writing the drawn pattern preferably has the function of detecting a coordinate reference mark. If the drawing tool does not have a function for detecting the coordinate reference mark, or cannot detect the coordinate reference mark, an auxiliary mark may be formed around the absorbent film by the drawing tool in advance to be used for the setting. The fiducial mark may be used as an auxiliary mark. In this case, a coordinate system defined by the reference coordinate reference mark via the auxiliary mark may be configured by obtaining a relationship between the coordinate reference mark and the auxiliary mark using, for example, an inspection tool shown in fig. 6.

Next, an absorber pattern is formed by patterning the absorber film (step S105). In particular, the absorber pattern may be formed by etching and removing a portion of the absorber film of the reflective mask blank, thereby leaving the absorber pattern at a location of the defect that has been evaluated as treatable according to the location of the defect in the coordinate system.

By such a manufacturing method of a reflective mask, an absorber pattern can be formed so that the influence of a defect (phase defect) is mitigated as much as possible, and a reflective mask having a controlled defect influence can be manufactured. Furthermore, when a reflective mask can be manufactured by this method, it is not necessary to completely eliminate defects of the reflective mask blank, such as phase defects, to zero. Therefore, by this method, the yield of the reflective mask blank usable for manufacturing the reflective mask can be effectively improved, and the reflective mask blank can be provided with good productivity.

In general, a reflective mask obtained by patterning an absorber film to form an absorber pattern is provided for inspecting the absorber pattern for pattern defects (step S106). If necessary, repair or shape calibration of the absorber pattern is performed. Conventionally known methods can be used for these, and the coordinates defined with reference to the coordinate reference mark of the present invention are preferably used for checking defects of the absorber pattern, or repair or shape calibration of the absorber pattern.

For example, after the pattern defect of the absorber pattern is inspected, as shown in fig. 9, the possibility of a fatal defect, particularly a fatal phase defect, remaining in the reflective mask is evaluated with reference to the defect information of the inspected absorber pattern, the position information of the defect stored in the recording medium, and the position information of the drawn pattern (step S107). Next, if a fatal defect remains, a calibration amount is calculated to calibrate the shape of the absorber pattern (step S108), and the need to repair the absorber pattern according to the defect information to detect the absorber pattern and the need to calibrate the absorber pattern shape for the fatal defect are evaluated (step S109). On the other hand, when it is evaluated in step S107 that the absorber pattern has no fatal defect, step S109 is directly performed (without step S108), and the need to repair the absorber pattern according to the defect information of the inspected absorber pattern is evaluated. Next, when it is evaluated that it is necessary to repair the absorber pattern or calibrate the shape of the absorber pattern for the fatal defect based on the defect information of the inspected absorber pattern, repair or shape calibration of the absorber pattern is performed (step S110).

Here, the shape calibration of the absorber pattern is described using an absorber pattern showing the reflective mask and the positions of phase defects present in the multilayer reflective film. Fig. 10A and 10B are conceptual views illustrating positions of phase defects existing in an absorber pattern of a reflective mask and a multilayer reflective film, respectively. In both fig. 10A and 10B, the phase defect 120A having a high priority order is completely covered by the absorber pattern 114, and the phase defect 120A having a high priority order is in a state where the phase defect is not projected as a defect when a reflective mask is used. On the other hand, for example, in some cases, the phase defect 120b which is low in priority and not covered by the absorber pattern 114 may remain. If the number of defects is large, the possibility of remaining the phase defect 120b not covered by the absorber pattern 114 increases. Further, if a position error is caused when the absorber film pattern is formed, the phase defect 120b not covered by the absorber pattern 114 may remain.

When the residual phase defect is a phase defect existing between adjacent absorber patterns, for example, the influence in the projection mask pattern by the exposure tool can be reduced by a method disclosed in JP-a 2002-.

Examples

Examples of the invention are given below by way of illustration and not by way of limitation.

Example 1

First, a substrate was prepared, and a conductive film (20nm thick) made of a Cr-based material was formed on the other main surface of the substrate. Next, a cross mark as shown in fig. 3A is formed as a coordinate reference mark in each of the four mark forming regions of the conductive film shown in fig. 4. The coordinate reference mark is a concave mark formed to a depth of 20nm by etching and removing the conductive film by photolithography. The width of the lines was 2 μm and the length of the crossing lines was 100 μm, respectively.

Next, after cleaning the substrate, a multilayer reflective film (280nm thick) including 40 molybdenum (Mo) layers and 40 silicon (Si) layers alternately stacked was formed on one main surface of the substrate. Further, a protective film (2.5nm thick) made of a material containing ruthenium as a main component was formed on the multilayer reflective film.

Next, the substrate on which the multilayer reflective film and the protective film are formed is subjected to defect inspection by an inspection tool shown in fig. 6. First, the origin of two-dimensional x-y coordinates (x is 0, y is 0) is set at the central portion of the other main surface of the substrate. Next, before inspecting defects of the multilayer reflective film and the protective film, warpage or bending of the substrate is measured as flatness by a function of focusing of an optical system to detect a coordinate reference mark. As a result, it was found that the center of the substrate warped upward compared to the outer periphery of the substrate. The measured substrates had a length L of 106mm and a height H of 400nm, respectively, as shown in FIG. 7. Thus, the radius of curvature R of the warp is 1.4045 × 10⁷mm。

In this defect inspection, first, a phase defect in the multilayer reflective film is inspected, and the position of the defect is obtained on the two-dimensional x-y coordinates of the other main surface. The position of the defect is calibrated with the obtained radius of curvature R to change the warp or bend of the substrate, and the position information of the defect is saved to the recording medium together with the information of the signal level of the detected defect. Next, after the multilayer reflective film is inspected in the entire predetermined area, the priority order of processing is determined based on the information of the defects stored in the recording medium, and the priority order is also saved into the recording medium.

Next, an absorber film (70nm thick) composed of a material containing tantalum (Ta) as a main component was formed on the protective film.

Next, the inspector shown in FIG. 6 is usedThe defect inspection is performed on the substrate on which the absorber film is formed. First, before defect inspection of the absorber film, warpage or bending of the substrate is measured as flatness by a function of focusing of an optical system to detect a coordinate reference mark. As a result, the center of the substrate was found to warp upward than the outer periphery of the substrate. The substrate was measured to have a length L of 106mm and a height H of 550nm, respectively, as shown in FIG. 7. Thus, the radius of curvature R of the warp is 1.0214 × 10⁷mm。

In this defect inspection, first, a phase defect in the absorber film is inspected, and the position of the defect is obtained on the two-dimensional x-y coordinates of the other main surface. The position of the defect is calibrated with the obtained radius of curvature R to change the warp or bend of the substrate, and the position information of the defect is saved to the recording medium together with the information of the signal level of the detected defect. By this method, a reflective mask blank is obtained.

Next, a reflective mask is manufactured according to the procedure in the flowchart described in fig. 9. First, a set of a reflective mask blank (as a main component) and a recording medium is prepared, an electron beam resist is coated on the surface of the blank, and then the blank is mounted on a mask stage of an electron beam drawing tool. Next, the coordinate position of the defect stored in the recording medium is determined with reference to the coordinate reference mark. Next, drawing pattern data for the absorber film is prepared, and drawing positions of the absorber pattern are optimized to cover the maximum number of defects according to the priority stored in the recording medium. Then, the optimally arranged drawing pattern is drawn as an absorber pattern onto the electron beam resist, and the absorber pattern is formed by a conventional manner.

In this case, since the manufacturing from the reflective mask blank to the reflective mask is performed by commonly using the coordinate reference marks formed on the other main surface of the substrate, the position of the defect can be determined with high accuracy. Therefore, the error of position detection is within 10 nm.

Comparative example 1

After the same conductive film as in example 1 was formed on the other main surface of the substrate, the same coordinate reference mark as in example 1 was formed on one main surface of the substrate by a general photolithography method without forming the coordinate reference mark in the conductive film. Next, a multilayer reflective film, a protective film, and an absorber film similar to those of example 1 were formed on one main surface of the substrate, to obtain a reflective mask blank. In the production of a reflective mask from the obtained reflective mask blank in the same manner as in example 1, measurement of flatness (correction of warp or bend) and defect inspection were performed.

In this case, a film having a total thickness of about 280nm is formed on the coordinate reference mark at a stage after the multilayer reflection film and the protection film are formed, and a film having a total thickness of about 350nm is formed on the coordinate reference mark at a stage after the absorber film is further formed. Since a resist film is formed on the absorber film when the reflective mask is manufactured, the accuracy of determining the position of the defect is low as compared with example 1. Therefore, position detection errors within 10nm are not obtained.