阅读说明：本技术 光掩膜坯料关联基板的评价方法 (Evaluation method of photomask blank related substrate ) 是由 木下隆裕 于 2019-06-19 设计创作，主要内容包括：技术问题：提供一种光掩膜坯料关联基板的评价方法,在光掩膜坯料关联基板中,能够简便地评价其表面状态(例如,形成于透明基板上的光学膜等的透射率、光学常数以外的膜质)。解决方案：在光掩膜坯料关联基板的评价方法中,拍摄所述光掩膜坯料关联基板的表面而获取表面图像,并从该获取的表面图像中获取该表面图像的对比度,并利用该获取的表面图像的对比度来评价所述光掩膜坯料关联基板。(The technical problem is as follows: provided is a method for evaluating a photomask blank-related substrate, which can easily evaluate the surface state (for example, the transmittance of an optical film or the like formed on a transparent substrate, and the film quality other than the optical constant) of the photomask blank-related substrate. The solution is as follows: in the method for evaluating a photomask blank-related substrate, a surface image is acquired by imaging a surface of the photomask blank-related substrate, a contrast of the surface image is acquired from the acquired surface image, and the photomask blank-related substrate is evaluated using the contrast of the acquired surface image.)

1. A method for evaluating a photomask blank-related substrate,

taking an image of the surface of the photomask blank-related substrate to obtain a surface image,

the contrast of the surface image is acquired from the acquired surface image,

evaluating the photomask blank-related substrate using the contrast of the acquired surface image.

2. The method of evaluating a photomask blank-related substrate according to claim 1,

when evaluating the photomask blank-related substrate, performing:

a standard contrast acquisition step of preparing a photomask blank-related substrate as a standard in advance, and acquiring a contrast of a surface image of the standard photomask blank-related substrate as a standard contrast;

an evaluation target contrast acquiring step of preparing a photomask blank related substrate to be evaluated different from the standard photomask blank related substrate, and acquiring a contrast of a surface image of the photomask blank related substrate to be evaluated as an evaluation target contrast with the same optical system as the standard contrast acquiring step; and

and a contrast comparison step of comparing the evaluation target contrast with the standard contrast to evaluate the evaluation target photomask blank-related substrate.

3. The method of evaluating a photomask blank-related substrate according to claim 2,

in the contrast comparison step, the contrast ratio is compared,

and when the evaluation object contrast is within a specified value% of the standard contrast, the evaluation object photomask blank related substrate is used as a qualified product.

4. The method of evaluating a photomask blank-related substrate according to claim 2,

in the contrast comparison step, the contrast ratio is compared,

and when the evaluation object contrast is within +/-10% of the standard contrast, taking the evaluation object photomask blank related substrate as a qualified product.

5. The method of evaluating a photomask blank-related substrate according to claim 3,

in the contrast comparison step, the contrast ratio is compared,

and when the evaluation object contrast is within +/-10% of the standard contrast, taking the evaluation object photomask blank related substrate as a qualified product.

6. A method for evaluating a photomask blank-related substrate,

taking an image of the surface of the photomask blank-related substrate to obtain a surface image,

the contrast of the surface image is acquired from the acquired surface image,

a contrast magnification for making the contrast of the acquired surface image a predetermined value is calculated,

the photomask blank-related substrate is evaluated using the calculated contrast ratio.

7. The method of evaluating a photomask blank-related substrate according to claim 6,

when evaluating the photomask blank-related substrate, performing:

a standard contrast ratio calculation step of preparing a photomask blank-related substrate as a standard in advance, and calculating a contrast ratio of a surface image of the standard photomask blank-related substrate as a standard contrast ratio;

an evaluation target contrast ratio calculation step of preparing a photomask blank-related substrate as an evaluation target different from the standard photomask blank-related substrate, and calculating a contrast ratio of a contrast of a surface image of the evaluation target photomask blank-related substrate as an evaluation target contrast ratio using the same optical system as the standard contrast ratio calculation step; and

and a contrast ratio comparison step of comparing the evaluation target contrast ratio with the standard contrast ratio to evaluate the evaluation target photomask blank-related substrate.

8. The method of evaluating a photomask blank-related substrate according to claim 7,

in the contrast ratio amplification ratio comparing step,

and when the evaluation target contrast magnification is within a specified value% of the standard contrast magnification, the evaluation target photomask blank-related substrate is regarded as a qualified product.

9. The method of evaluating a photomask blank-related substrate according to claim 7,

in the contrast ratio amplification ratio comparing step,

and when the evaluation object contrast magnification is within ± 10% of the standard contrast magnification, the evaluation object photomask blank-related substrate is regarded as a non-defective product.

10. The method of evaluating a photomask blank-related substrate according to claim 8,

in the contrast ratio amplification ratio comparing step,

and when the evaluation object contrast magnification is within ± 10% of the standard contrast magnification, the evaluation object photomask blank-related substrate is regarded as a non-defective product.

11. The method of evaluating a photomask blank-related substrate according to any one of claims 1 to 10,

when the surface of the photomask blank-related substrate is photographed to obtain a surface image, the photographing is performed in a bright field by a confocal optical system.

Technical Field

The present invention relates to a photomask blank used for manufacturing a photomask (transfer mask) used for manufacturing a semiconductor device (semiconductor device) or the like, a photomask blank intermediate product, or a photomask glass substrate (hereinafter, these are also referred to as a photomask blank-related substrate).

Background

A semiconductor device is manufactured by using a photolithography technique in which an exposure beam is irradiated to a mask for pattern transfer such as a photomask on which a circuit pattern is drawn, and the circuit pattern formed on the mask is transferred onto a semiconductor substrate via a reduction optical system. With the miniaturization of circuit patterns of semiconductor devices, the wavelength of a mainstream exposure beam is 193nm using an argon fluoride (ArF) excimer laser, and a pattern having a size sufficiently smaller than the exposure wavelength can be formed by a multi-patterning process that combines an exposure process and a processing process a plurality of times.

A pattern transfer mask is produced by forming a circuit pattern on a photomask blank having an optical film formed on a light-transmissive substrate (photomask glass substrate). Such an optical film is generally a film containing chromium or a film containing molybdenum, and is a film functioning as a light-shielding film, a film functioning as a phase-shift film, or the like (see patent document 1), and thus can be used as a photomask blank, and further, a hard mask or an etching stopper film can be formed for the purpose of processing an optical film with high precision, and can also be used as a photomask blank.

In order to achieve finer features, the surfaces of the photomask blank and the photomask glass substrate are required to be smoother.

Further, before forming a film on a glass substrate for a photomask to be a photomask blank, a step of laminating each optical film as described above is required, and an intermediate product (a photomask blank intermediate product) thereof is also required to be smooth.

Disclosure of Invention

Technical problem to be solved

In the production process of a photomask blank, for example, a sputtering method is used for film formation, but even if the film thickness, optical constant, and the like of optical films are the same, the film quality may be different (even if the same film type is produced, the optical characteristics and film thickness of the films are predetermined values, but the state of the films may change due to a failure in the production process), and a method for easily managing the film quality in addition to the film thickness and optical constant is required.

If the film quality is different (film quality changes), the processability changes, and a desired pattern shape may not be formed.

As a method for controlling the film quality, for example, surface roughness is considered. Here, since the photomask blank is smoothed to have an Ra (arithmetic mean roughness) of 0.5nm or less, measurement is generally performed using an AFM (atomic force microscope). However, the measurement by AFM is a damage inspection, and the photomask blank-related substrate itself used for manufacturing the photomask cannot be measured.

Further, as miniaturization progresses, the photomask blank-related substrate needs to detect defects such as finer foreign substances and pinholes, and the sensitivity of the detector needs to be improved, but there is a problem that a pseudo defect is generated in which a portion that is not a defect is recognized as a defect during inspection in order to detect a fine defect, or the detector is occupied for a long time in order to detect a plurality of pseudo defects.

The suspected defect is identified, for example, because the surface roughness is coarse and it is difficult to distinguish the height from the height of the defect.

The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a method for evaluating a photomask blank-related substrate, which can easily evaluate the surface state (the transmittance of an optical film or the like formed on a transparent substrate, and the film quality other than the optical constant) of the photomask blank-related substrate.

(II) technical scheme

In order to achieve the above object, the present invention provides a method for evaluating a photomask blank-related substrate, comprising the steps of obtaining a surface image by imaging a surface of the photomask blank-related substrate, obtaining a contrast of the surface image from the obtained surface image, and evaluating the photomask blank-related substrate using the contrast of the obtained surface image.

Here, the contrast of the surface image means a difference in light intensity between the brightest portion and the darkest portion of an image obtained within a predetermined range of the photomask blank-related substrate in an image obtained by irradiating light to the surface of the photomask blank-related substrate and reflecting the light. That is, when the intensity of the reflected light of the brightest portion of the image is Imax and the weakest portion is Imin, the contrast Δ is defined by (Imax-Imin)/(Imax + Imin).

The inventors of the present invention have conducted extensive studies and found that the contrast Δ is related to the surface roughness shape of a photomask blank-related substrate, and by measuring the contrast Δ, it is possible to obtain an index of the surface state (film surface state, hereinafter also referred to as film quality, in the case where a film is formed on the surface) of the mask blank reflecting the surface roughness, undulation, and the like. The present invention is also directed to a method for evaluating a photomask blank-related substrate using such a new index, which enables easy evaluation of film qualities other than transmittance and optical constant without breaking.

Further, by performing this evaluation method before defect inspection, for example, it is possible to remove in advance a photomask blank-related substrate in which a plurality of suspected defects exist. This prevents the defect detector from being occupied for a long time by a plurality of pseudo defects as in the conventional case. Therefore, the efficiency of defect inspection can be improved.

Further, according to the evaluation method of the present invention, it is possible to stably provide a high-quality photomask blank-related substrate by eliminating, for example, a product having an abnormal film quality.

In this case, when evaluating the photomask blank-related substrate, the method may further include: a standard contrast acquisition step of preparing a photomask blank-related substrate as a standard in advance, and acquiring a contrast of a surface image of the standard photomask blank-related substrate as a standard contrast; an evaluation target contrast acquiring step of preparing a photomask blank related substrate to be evaluated different from the standard photomask blank related substrate, and acquiring a contrast of a surface image of the photomask blank related substrate to be evaluated as an evaluation target contrast with the same optical system as the standard contrast acquiring step; and a contrast comparison step of comparing the evaluation target contrast with the standard contrast to evaluate the evaluation target photomask blank-related substrate.

By preparing a photomask blank-related substrate as a standard in this manner and comparing the substrates as standard samples, the film quality can be evaluated more accurately.

In the contrast comparison step, when the evaluation target contrast is within a predetermined value% of the standard contrast, the evaluation target photomask blank-related substrate may be regarded as a non-defective product.

In particular, in the contrast comparison step, when the evaluation target contrast is within ± 10% of the standard contrast, the evaluation target photomask blank-related substrate may be regarded as a non-defective product.

Through these steps, a product with normal film quality and an abnormal product can be more reliably discriminated, and a non-defective product can be determined from the evaluation target. Therefore, a photomask blank-related substrate having stable quality can be provided.

The present invention also provides a method for evaluating a photomask blank-related substrate, comprising the steps of obtaining a surface image by imaging a surface of the photomask blank-related substrate, obtaining a contrast of the surface image from the obtained surface image, calculating a contrast ratio for setting the contrast of the obtained surface image to a predetermined value, and evaluating the photomask blank-related substrate using the calculated contrast ratio.

The magnification (γ) of the contrast of the surface image referred to herein is a magnification (magnification) when the contrast is set to a predetermined level. That is, when a predetermined contrast is set to α, the contrast magnification γ is defined by γ ═ α/Δ.

By the evaluation method of the present invention, film qualities other than transmittance and optical constant can be easily evaluated without breaking.

Further, by performing the inspection before the defect inspection, etc., it is possible to exclude the photomask blank-related substrate having a plurality of suspected defects in advance. In addition, the method can eliminate products with abnormal surface states and is helpful for manufacturing high-quality photomask blank related substrates.

In this case, when evaluating the photomask blank-related substrate, the method may further include: a standard contrast ratio calculation step of preparing a photomask blank-related substrate as a standard in advance, and calculating a contrast ratio of a surface image of the standard photomask blank-related substrate as a standard contrast ratio; an evaluation target contrast ratio calculation step of preparing a photomask blank-related substrate as an evaluation target different from the standard photomask blank-related substrate, and calculating a contrast ratio of a contrast of a surface image of the evaluation target photomask blank-related substrate as an evaluation target contrast ratio using the same optical system as the standard contrast ratio calculation step; and a contrast ratio comparison step of comparing the evaluation target contrast ratio with the standard contrast ratio to evaluate the evaluation target photomask blank-related substrate.

By preparing a photomask blank-related substrate as a standard in this manner and comparing the prepared photomask blank-related substrate as a standard sample, the film quality can be evaluated more accurately.

In the contrast ratio comparison step, when the evaluation target contrast ratio is within a predetermined value% of the standard contrast ratio, the evaluation target photomask blank-related substrate may be regarded as a non-defective product.

In particular, in the contrast ratio comparison step, when the evaluation target contrast ratio is within ± 10% of the standard contrast ratio, the evaluation target photomask blank-related substrate may be regarded as a non-defective product.

According to these steps, the quality of the film, the quality of the product in which the glass substrate for a photomask is normal, and the quality of the product in which the glass substrate for a photomask is abnormal can be more reliably determined, and the quality can be determined from the evaluation target. Therefore, a photomask blank-related substrate having stable quality can be provided.

In addition, when the surface of the photomask blank-related substrate is imaged to obtain a surface image, the imaging may be performed in a bright field by a confocal optical system.

It is preferable to use a confocal optical system as the optical system because a change in contrast with a change in the height direction can be more significantly expressed. In particular, in a confocal optical system using a laser beam, a height shift is likely to be expressed as a difference in reflection intensity.

Further, by providing a bright field, contrast can be more reliably obtained even if there are not so many surface irregularities.

(III) advantageous effects

As described above, according to the present invention, the surface state, which is a characteristic other than the transmittance and the optical constant, of the photomask blank-related substrate can be easily evaluated without breaking. Further, the defect detector can be prevented from being occupied for a long time due to the presence of the suspected defect, and it is possible to stably produce a high-quality product having a good surface state.

Drawings

Fig. 1 shows an example of an evaluation flow of the present invention using contrast in manufacturing a photomask blank-related substrate.

Fig. 2 is an explanatory diagram showing an example of the correlation between the film surface state and the contrast of the photomask blank. The contrast Δ a is a contrast without defect, and the contrast Δ b is a contrast when the surface roughness is larger than usual.

FIG. 3 is a graph showing AFM results of STD and LOT (E) standard substrates in example 1. Wherein (a) is Ra and (b) is Rq.

FIG. 4 is a graph of example 1, in which (a) is a comparison of STD and LOT (E) of the standard substrates with respect to Δ Ra_AVEThe graph (b) is a graph comparing the Δ of STD and LOT (E) of the standard substrates with respect to Rq_AVEA graph of (a).

Fig. 5 is an explanatory diagram showing an example of the correlation between the film surface state of the photomask blank and the contrast magnification. Wherein (a) is a contrast magnification γ of a defect-free portion_aAnd (b) a contrast magnification gamma in the case where the surface roughness is larger than usual_b。

FIG. 6 is a graph of example 2, in which (a) is γ which compares STD and LOT (E) of the standard substrates with Ra_AVEThe graph (b) is a graph comparing the gamma of STD and LOT (E) of the standard substrates with respect to Rq_AVEA graph of (a).

Detailed Description

Embodiments of the present invention will be described in more detail below with reference to the accompanying drawings, but the present invention is not limited thereto.

(first embodiment)

First, a case where contrast is used as an index for evaluating the surface state of a photomask blank-related substrate will be described.

In the evaluation method of the present invention, the steps may include capturing an image of the surface of the photomask blank-related substrate to obtain a surface image, obtaining a contrast of the surface image from the obtained surface image, and evaluating the photomask blank-related substrate using the contrast of the obtained surface image. The foregoing equation is used in acquiring the contrast.

The above-described process may be performed only on the photomask blank-related substrate to be evaluated, but as described below, the above-described process may be performed on both standard photomask blank-related substrates in addition to the photomask blank-related substrate to be evaluated, and the obtained contrasts may be compared with each other to perform evaluation. By preparing a standard photomask blank-related substrate as a standard sample and comparing the samples, the surface state of the film quality and the like can be evaluated more accurately.

The more specific process flow will be described below.

< Standard contrast obtaining Process >

First, a standard photomask blank-related substrate is prepared. In the case of a transparent substrate (glass substrate for a photomask), a photomask blank intermediate product, or a photomask blank, the same material as the substrate related to a photomask blank to be evaluated, such as the material of an optical film to be further formed thereon, may be prepared.

The photomask blank-related substrate to be evaluated is applicable to a transparent substrate (a glass substrate for a photomask), and also applicable to a photomask blank intermediate product that is an intermediate product when a photomask blank on which a Cr-containing film, a MoSi-containing film, or the like, which is generally used for a photomask, is formed and each optical film is laminated, and in the case of a photomask blank or a photomask blank intermediate product, there is no particular limitation on the film structure, the film thickness, or the like. The structure may be one in which a halftone film containing MoSi is formed as a film structure of a photomask blank, a Cr-containing film as a light-shielding film is formed thereon, a hard mask containing Si is further formed thereon, a Cr-containing film, a MoSi-shielding film, and a C-containing film are sequentially formed on a halftone film containing MoSi, or a Cr-containing film is formed, a Si-containing film is formed thereon, and a Cr-containing film is further formed thereon. The film forming method is also not limited, and for example, a sputtering method is applicable.

Next, the surface of the prepared standard photomask blank-related substrate is photographed to obtain a surface image. As long as it is a device capable of photographing in such a manner that contrast can be acquired from the acquired surface image later, for example, a defect inspection apparatus capable of acquiring a surface image may be used.

In this case, by using the confocal optical system, the change in contrast with respect to the change in the height direction can be more greatly expressed. Further, it is preferable to use a bright field because contrast can be more reliably obtained even if there are not so many irregularities on the surface to be imaged. It is particularly preferable to perform photographing in a bright field with a confocal optical system.

Further, the imaging range may be a region free from defects such as foreign matter, dents, and pinholes on the surface.

The wavelength used for imaging is preferably 600nm or less, for example. The lower limit is not particularly limited, and is preferably not less than 150nm, for example, because the wavelength is short and the sensitivity to defects and fine unevenness can be reflected. In particular, in a generation with a half pitch of 10nm or less, 400nm or less is preferable.

Then, the contrast of the surface image is acquired from the acquired surface image. And this is taken as the standard contrast.

In addition, as the surface image, an image in which the surface state is further emphasized by an image processing algorithm such as differential processing may be used.

< evaluation object contrast acquisition step >

Next, a photomask blank-related substrate to be actually evaluated, which is different from the standard photomask blank-related substrate, is prepared. Then, a surface image is acquired by the same optical system as in the standard contrast acquisition step, and the contrast of the surface image is acquired. And this is taken as the evaluation target contrast.

< contrast comparison Process >

Subsequently, the obtained evaluation target contrast is compared with the standard contrast, thereby evaluating the photomask blank-related substrate to be evaluated.

The reference for the comparative evaluation is not particularly limited, and for example, a reference within ± 10% of the standard contrast may be set. That is, when the evaluation target contrast is within ± 10% of the standard contrast, the evaluation target photomask blank-related substrate can be treated as a non-defective product. If the standard is such as this, the quality of the film or the product having an abnormality in the photomask glass substrate can be more reliably determined from the normal product, and the non-defective product to be evaluated can be determined with high accuracy. The quality can be stabilized.

The standard contrast is not limited to within ± 10%, and may be set to within a predetermined value% of the standard contrast according to a desired evaluation criterion.

According to the evaluation method of the present invention as described above, unlike the conventional damage inspection using, for example, AFM, the surface state of the photomask blank-related substrate can be evaluated easily without damage. Further, by performing the inspection before the defect inspection, etc., it is possible to prevent the defect inspection due to the suspected defect from being performed for a long time, and to achieve high efficiency. In addition, since the product having an abnormal surface state can be eliminated, a high-quality photomask blank-related substrate can be provided.

The present invention can be used for detecting errors and abnormalities in a process, in addition to evaluating and inspecting products. For example, the method can also be used for process monitoring in a film forming process. In addition, the method can be used for monitoring the change of the surface roughness and undulation of the glass substrate for the photomask caused by the change of the polishing condition.

In the case where the evaluation method of the present invention is performed before the defect inspection is performed as described above, when the evaluation target contrast is equal to or higher than the predetermined value, the defect that does not actually exist in the defect inspection is highly likely to be recognized as the existence of the defect, and therefore the inspection result may be NG or the inspection may be interrupted.

For example, when the defect inspection process is controlled in the next process, the present invention can be implemented by the following flow.

Fig. 1 shows an example of a process of an evaluation flow of the present invention using contrast in manufacturing a photomask blank-related substrate.

The evaluation device may use a defect inspection device capable of acquiring a surface image.

First, a program is constructed in such a manner that a series of steps of surface image acquisition, contrast acquisition, and acceptance/rejection determination (contrast comparison) are automatically executed.

Next, a standard substrate (standard photomask blank-related substrate) is produced, a surface image is acquired, and a standard contrast Δ is calculated_STD. Here, Δ is calculated from the average of four points at the corner and five points at the center, for example_STD。

Finally, Δ is set in the evaluation device_STDWithin + -10% is considered as the threshold value of normal products.

After the above setting is completed, the photomask blank-related substrate to be evaluated (mask blank-related substrate to be evaluated) is inspected. In the image acquisition step, a surface image of coordinates specified in advance is acquired, in the contrast acquisition step, the contrast is automatically measured from the acquired image, in the acceptance/rejection determination step, the contrast of the test piece is compared with a preset reference value, and only when it is determined that the contrast is within ± 10%, the next step is performed. Here, the inspection is stopped for the photomask blank-related substrate determined to be abnormal, and an alarm is issued.

According to this inspection flow, it is possible to quickly detect an abnormality on the film surface, which has been difficult to determine whether the film is acceptable or not, and to quickly improve the process.

(second embodiment)

Next, a case where a contrast magnification is used as an index for evaluating the surface state of the photomask blank-related substrate will be described.

In the evaluation method of the present invention, the steps may include acquiring a surface image by imaging the surface of the photomask blank-related substrate, acquiring the contrast of the surface image from the acquired surface image, calculating a contrast magnification for setting the contrast of the acquired surface image to a predetermined value, and evaluating the photomask blank-related substrate using the calculated contrast magnification. The foregoing equation is used in calculating the contrast magnification.

That is, in comparison with the first embodiment, the contrast ratio is acquired, and then the contrast ratio is calculated and evaluated using the contrast ratio instead of the contrast ratio.

More specifically, for example, first, a standard contrast magnification calculation step is performed in which a standard photomask blank-related substrate is prepared in advance, and a contrast magnification of the contrast of the surface image is calculated as a standard contrast magnification.

Next, an evaluation target contrast ratio calculation step of preparing an evaluation target photomask blank-related substrate and calculating a contrast ratio of the contrast of the surface image of the evaluation target photomask blank-related substrate as an evaluation target contrast ratio using the same optical system as the standard contrast ratio calculation step is performed.

Then, a contrast ratio comparison step of comparing the standard contrast ratio and the evaluation target contrast ratio is performed to evaluate the photomask blank-related substrate to be evaluated.

In this way, the photomask blank-related substrate can be evaluated easily without breaking, and the various effects described above can be achieved in the same manner as in the first embodiment.

Other elements (for example, the conditions of the confocal optical system and the bright field, the reference in the contrast magnification ratio comparison step: within a predetermined value% of the standard contrast magnification ratio (in particular, within ± 10%), and the like) may be the same as those in the first embodiment.