Evaluation method for a substrate associated with a photomask blank

Abstract

Technical problem: To provide a method for evaluating a substrate related to a photomask blank, in which the surface state (for example, the transmittance of an optical film formed on a transparent substrate, the film quality other than the optical constants) can be simply evaluated. Solution: In the method for evaluating a substrate related to a photomask blank, the surface of the substrate related to the photomask blank is photographed to obtain a surface image, the contrast of the obtained surface image is obtained from the surface image, and the substrate related to the photomask blank is evaluated using the contrast of the obtained surface image.

Description

Technical Field

[0001] The present invention relates to a method for evaluating a photomask blank, an intermediate product of a photomask blank, or a glass substrate for a photomask (hereinafter also referred to as a photomask blank-related substrate) used in the manufacture of semiconductor devices (semiconductor devices) and the like. Background Art

[0002] Semiconductor devices are manufactured by using a lithography technique in which an exposure beam is irradiated onto a pattern transfer mask 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. As the circuit patterns of semiconductor devices become more refined, the wavelength of the mainstream exposure beam is 193 nm using an argon fluoride (ArF) excimer laser. By adopting a process such as multiple combination exposure processes and multi-patterning of processing processes, patterns having a size sufficiently smaller than the exposure wavelength can be formed.

[0003] A pattern transfer mask is fabricated by forming a circuit pattern on a photomask blank, where the photomask blank has an optical film formed on a light-transmissive substrate (glass substrate for a photomask). Such an optical film is generally a film containing chromium, a film containing molybdenum, and functions as a light-shielding film, a phase shift film, etc. (see Patent Document 1). Thus, it can become a photomask blank. Further, a hard mask and an etch stop film are formed for the purpose of processing the optical film with high precision, and it can also become a photomask blank.

[0004] For further refinement, smoother surfaces of the photomask blank and the glass substrate for a photomask are required.

[0005] In addition, before forming a film on the glass substrate for a photomask to become a photomask blank, it is necessary to perform a process of laminating each optical film as described above, and it is also required that the intermediate product (intermediate product of a photomask blank) is smooth.

[0006] Prior Art Documents

[0007] Patent Documents

[0008] Patent Document 1: Japanese Patent Laid-Open No. 2002-196475 Summary of the Invention

[0009] (I) Technical Problem to be Solved

[0010] In the manufacturing process of a photomask blank, for example, the sputtering method is used in film formation. However, even if the film thickness, optical constants, etc. of the optical film are the same, the film quality may sometimes be different (even if the same film type is produced and the optical characteristics and film thickness of the film are specified values, the state of the film may sometimes change due to a malfunction in the manufacturing process). A method for simply managing the film quality in addition to the film thickness and optical constants is required.

[0011] If the film quality is different (film quality change), the processability changes, and it may not be possible to form the desired pattern shape.

[0012] As a method for managing the film quality, for example, surface roughness is considered. Here, the smoothing of the photomask blank has advanced to an Ra (arithmetic mean roughness) of 0.5 nm or less. Therefore, generally, AFM (atomic force microscope) is used for measurement. However, the measurement with AFM is a destructive inspection and cannot measure the photomask blank-related substrate itself used for manufacturing the photomask.

[0013] In addition, as miniaturization progresses, the photomask blank-related substrate needs to detect finer foreign matters, pinholes, and other defects, and the sensitivity of the detector needs to be improved. However, the problem is that in order to detect fine defects, parts that are not defects are identified as defects in the inspection, or the detector is occupied for a long time in order to detect multiple suspected defects.

[0014] Being identified as a suspected defect is, for example, because it is difficult to distinguish its height from the height of the defect due to the rough surface roughness.

[0015] The present invention has been completed in view of the above technical problems, and an object thereof is to provide an evaluation method for a photomask blank-related substrate, which can simply evaluate its surface state (film quality other than the transmittance and optical constants of an optical film formed on a transparent substrate) in the photomask blank-related substrate.

[0016] (2) Technical solution

[0017] To achieve the above object, the present invention provides an evaluation method for a photomask blank-related substrate, characterized in that a surface image of the photomask blank-related substrate is taken to obtain a surface image, the contrast of the obtained surface image is obtained from the obtained surface image, and the photomask blank-related substrate is evaluated using the contrast of the obtained surface image.

[0018] In addition, the contrast of the so-called surface image herein refers to the difference in light intensity between the brightest part and the darkest part of the image obtained within a specified range of the substrate associated with the photomask blank when light is irradiated onto the surface of the substrate associated with the photomask blank and the image is obtained through its reflection. That is, when the intensity of the reflected light of the brightest part of the image is set as Imax and the weakest part is set as Imin, the contrast Δ is defined by Δ = (Imax - Imin) / (Imax + Imin).

[0019] The inventors of the present invention conducted intensive research and found that the contrast Δ is related to the surface roughness shape of the substrate associated with the photomask blank. By measuring the contrast Δ, it can be used as an index reflecting the surface state (in the case where a film is formed on the surface, it is the state of the film surface, hereinafter also referred to as film quality) such as surface roughness and undulation of the mask blank. Moreover, the present invention is a method for evaluating the substrate associated with the photomask blank using such a new index, and can evaluate the film quality other than transmittance and optical constants without damage and simply.

[0020] In addition, by performing this evaluation method, for example, before defect inspection, it is possible to pre-remove the substrate associated with the photomask blank with multiple suspected defects. Thus, it is possible to prevent the defect detector from being occupied for a long time due to multiple suspected defects as in the past. Therefore, the efficiency of defect inspection can be improved.

[0021] Moreover, through the evaluation method of the present invention, as a result, it is possible to exclude products with abnormal film quality, for example, and stably provide high-quality substrates associated with photomask blanks.

[0022] At this time, it can be that when evaluating the substrate associated with the photomask blank, the following steps are performed: a standard contrast acquisition step of preparing a substrate associated with a standard photomask blank in advance and obtaining the contrast of the surface image of the standard substrate associated with the photomask blank as the standard contrast; an evaluation object contrast acquisition step of preparing a substrate associated with a photomask blank to be evaluated different from the standard substrate associated with the photomask blank and obtaining the contrast of the surface image of the substrate associated with the photomask blank to be evaluated as the evaluation object contrast using the same optical system as in the standard contrast acquisition step; and a contrast comparison step of evaluating the substrate associated with the photomask blank to be evaluated by comparing the evaluation object contrast with the standard contrast.

[0023] By preparing a substrate associated with a photomask blank as a standard and comparing it as a standard sample in this way, the film quality can be evaluated more accurately.

[0024] In addition, it can be that in the contrast comparison step, when the evaluation object contrast is within the specified value % of the standard contrast, the substrate associated with the photomask blank to be evaluated is regarded as a qualified product.

[0025] Specifically, it can be that in the contrast comparison process, when the contrast of the evaluation object is within ±10% of the standard contrast, the substrate associated with the evaluation object photomask blank is regarded as a qualified product.

[0026] Through these processes, it is possible to more accurately distinguish between products with normal film quality and abnormal products, and to determine qualified products from the evaluation objects. Therefore, it is possible to provide a substrate associated with a photomask blank with stable quality.

[0027] In addition, the present invention provides a method for evaluating a substrate associated with a photomask blank, characterized in that a surface image of the substrate associated with the photomask blank is taken to obtain a surface image, the contrast of the obtained surface image is obtained from the obtained surface image, a contrast magnification for making the contrast of the obtained surface image a specified value is calculated, and the substrate associated with the photomask blank is evaluated using the calculated contrast magnification.

[0028] Furthermore, the magnification (γ) of the contrast of the so-called surface image here is the magnification (ratio) when the contrast becomes a specified size. That is, when a specified contrast is set as α, the contrast magnification γ is defined by γ = α / Δ.

[0029] Using the evaluation method of the present invention in this way, it is possible to simply evaluate the film quality other than the transmittance and optical constants without damage.

[0030] In addition, by implementing it before defect inspection, etc., it is possible to pre-exclude substrates associated with photomask blanks having multiple suspected defects. In addition, it is possible to exclude products with abnormal surface states, which helps to manufacture high-quality substrates associated with photomask blanks.

[0031] At this time, it can be that when evaluating the substrate associated with the photomask blank, the following are performed: a standard contrast magnification calculation process, a substrate associated with a standard photomask blank is prepared in advance, and the contrast magnification of the contrast of the surface image of the standard substrate associated with the photomask blank is calculated as the standard contrast magnification; an evaluation object contrast magnification calculation process, a substrate associated with a photomask blank different from the standard substrate associated with the photomask blank and serving as an evaluation object is prepared, and the contrast magnification of the contrast of the surface image of the substrate associated with the evaluation object photomask blank is calculated as the evaluation object contrast magnification using the same optical system as in the standard contrast magnification calculation process; and a contrast magnification comparison process, the substrate associated with the evaluation object photomask blank is evaluated by comparing the evaluation object contrast magnification with the standard contrast magnification.

[0032] By preparing a photomask blank-related substrate as a standard in this way and comparing it as a standard sample, it is possible to more accurately evaluate the film quality.

[0033] It may be that in the contrast magnification ratio comparison step, when the evaluation object contrast magnification ratio is within a specified percentage of the standard contrast magnification ratio, the evaluation object photomask blank-related substrate is regarded as a qualified product.

[0034] In particular, it may be that in the contrast magnification ratio comparison step, when the evaluation object contrast magnification ratio is within ±10% of the standard contrast magnification ratio, the evaluation object photomask blank-related substrate is regarded as a qualified product.

[0035] According to these steps, it is possible to more reliably distinguish between normal products and abnormal products of the film quality and the glass substrate for photomasks, and it is possible to make a judgment of qualified products from the evaluation objects. Therefore, it is possible to provide a photomask blank-related substrate with stable quality.

[0036] In addition, it may be that when photographing the surface of the photomask blank-related substrate to obtain a surface image, the photographing is performed under a confocal optical system and in a bright field.

[0037] By using a confocal optical system as the optical system, it is possible to more greatly show the change in contrast with respect to the change in the height direction, so it is preferable. Especially in a confocal optical system using a laser, the height shift is easily shown as a difference in reflection intensity.

[0038] In addition, by setting it to a bright field, it is possible to more reliably obtain the contrast even without many surface irregularities.

[0039] (III) Beneficial effects

[0040] As described above, according to the present invention, in a photomask blank-related substrate, it is possible to evaluate the surface state, which is a characteristic other than the transmittance and optical constants, without damage and simply. Moreover, it is possible to prevent the long-term occupation of the defect detector due to the presence of suspected defects, which helps to stably manufacture high-quality products with good surface states. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is an example showing an evaluation process of the present invention using contrast in the manufacture of a photomask blank-related substrate.

[0042] Figure 2 It is an explanatory diagram showing an example of the correlation between the surface state of the film of a photomask blank and the contrast. Among them, (a) is the contrast Δa of the defect-free part, and (b) is the contrast Δb when the surface roughness is larger than normal.

[0043] Figure 3 It is a graph showing the AFM results of the standard substrate STD and LOT(E) in Example 1. Among them, (a) is Ra, and (b) is Rq.

[0044] Figure 4 It is a graph in Example 1, where (a) is a graph comparing the Δ of the standard substrate STD and LOT(E) with respect to Ra AVE and (b) is a graph comparing the Δ of the standard substrate STD and LOT(E) with respect to Rq AVE of the graph.

[0045] Figure 5 It is an explanatory diagram showing an example of the correlation between the surface state of the film of the photomask blank and the contrast magnification. Among them, (a) is the contrast magnification γ a of the defect-free part, and (b) is the contrast magnification γ b when the surface roughness is greater than normal.

[0046] Figure 6 It is a graph in Example 2, where (a) is a graph comparing the γ of the standard substrate STD and LOT(E) with respect to Ra AVE and (b) is a graph comparing the γ of the standard substrate STD and LOT(E) with respect to Rq AVE of the graph. Detailed implementation mode

[0047] The 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.

[0048] (First embodiment)

[0049] First, the case of using contrast as an index for evaluating the surface state of the substrate related to the photomask blank will be described.

[0050] In the evaluation method of the present invention, the process only needs to include the following content, that is, photograph the surface of the substrate related to the photomask blank to obtain a surface image, obtain the contrast of the surface image from the obtained surface image, and evaluate the substrate related to the photomask blank using the contrast of the obtained surface image. The aforementioned formula is used when obtaining the contrast.

[0051] In addition, the above-described process may be performed only on the substrate associated with the photomask blank of the evaluation object. However, as described below, in addition to the substrate associated with the photomask blank of the evaluation object, the above-described process may be performed on both the substrate associated with the standard photomask blank as a standard, and the obtained contrasts may be compared for evaluation. By preparing a substrate associated with a standard photomask blank as a standard sample for comparison, the surface state such as film quality can be evaluated more accurately.

[0052] A more specific process flow will be described below.

[0053] <Standard contrast acquisition process>

[0054] First, prepare a substrate associated with a standard photomask blank. In the case of a transparent substrate (glass substrate for photomask), an intermediate product of a photomask blank, or a photomask blank, a material having the same material of the optical film formed thereon, etc. as the substrate associated with the photomask blank of the evaluation object can be prepared.

[0055] In addition, as the substrate associated with the photomask blank to be evaluated, a transparent substrate (glass substrate for photomask) is applicable, and an intermediate product of a photomask blank when laminating a photomask blank having a Cr-containing film, a MoSi-containing film, etc. generally used for photomasks and each optical film is also applicable. In the case of a photomask blank or an intermediate product of a photomask blank, there are no particular restrictions on the film structure, film thickness, etc. It may be a structure in which a halftone film containing MoSi is formed as the film structure of the photomask blank, a structure in which a Cr-containing film as a light-shielding film is formed thereon, further a structure in which a hard mask containing Si is formed thereon, a structure in which a Cr-containing film, a MoSi light-shielding film, and a C-containing film are sequentially formed on the halftone film containing MoSi, or it may be a structure in which a Cr-containing film is formed, a Si-containing film is formed thereon, and further a Cr-containing film is formed thereon. The film formation method is not limited either, for example, a sputtering method is applicable.

[0056] Next, photograph the surface of the prepared substrate associated with the standard photomask blank to obtain a surface image. Any device capable of photographing in such a way that the contrast can be obtained from the obtained surface image may be used. For example, a defect inspection device capable of obtaining a surface image can be used.

[0057] At this time, by using a confocal optical system, the change in contrast with respect to the change in the height direction can be expressed to a greater extent. In addition, by setting it to bright field, even if there are not many irregularities on the photographed surface, the contrast can be obtained more reliably, so it is preferable. In particular, it is preferably photographed in bright field using a confocal optical system..

[0058] In addition, as the imaging range, a portion free of defects such as foreign matter, depressions, and pinholes on the surface can be cited.

[0059] Preferably, the wavelength used during imaging is, for example, 600 nm or less. There is no particular limitation on the lower limit, as long as it is, for example, 150 nm or more. A shorter wavelength can reflect the sensitivity to defects and fine unevenness, so it is preferred. In particular, in generations with a half pitch of 10 nm or less, it is preferably 400 nm or less.

[0060] Then, the contrast of the surface image is obtained from the acquired surface image. And this is used as the standard contrast.

[0061] In addition, regarding the surface image, an image in which the surface state is further emphasized using an image processing algorithm such as differential processing can also be used.

[0062] <Evaluation object contrast acquisition process>

[0063] Next, prepare another actual evaluation object photomask blank associated substrate different from the standard photomask blank associated substrate. Then, obtain the surface image in the same manner using the same optical system as in the standard contrast acquisition process, and obtain the contrast of this surface image. And this is used as the evaluation object contrast.

[0064] <Contrast comparison process>

[0065] Next, the evaluation object photomask blank associated substrate is evaluated by comparing the acquired evaluation object contrast with the standard contrast.

[0066] The criterion for the comparison evaluation here is not particularly limited. For example, a criterion within ±10% of the standard contrast can be set. That is, when the evaluation object contrast is within ±10% of the standard contrast, the evaluation object photomask blank associated substrate can be treated as a qualified product. With such a criterion, products with abnormal film quality and photomask glass substrates can be more reliably discriminated from normal products, and the qualified products of the evaluation object can be determined with high precision. Quality stabilization can be achieved.

[0067] In addition, it is not limited to within ±10%, and it can be set to within a specified value % of the standard contrast according to the desired evaluation criterion.

[0068] According to the evaluation method of the present invention as described above, different from the conventional destructive inspection using, for example, AFM, the surface state of the photomask blank associated substrate can be evaluated non-destructively and simply. Moreover, by implementing it before defect inspection, etc., it is possible to prevent the lengthening of defect inspection caused by suspected defects and achieve high efficiency. In addition, since products with abnormal surface states can be excluded, high-quality photomask blank associated substrates can be provided.

[0069] As for the present invention, in addition to evaluating / checking products, it can be used to detect errors and abnormalities in processes. For example, it can also be used for process monitoring in a film-forming process. In addition, it can be used for monitoring changes in surface roughness and undulations of a glass substrate for a photomask caused by changes in grinding conditions.

[0070] In addition, in the case where the evaluation method of the present invention is performed before defect inspection as described above, when the contrast of the evaluation object is equal to or greater than a specified value, in defect inspection, there is a high possibility of identifying a defect that actually does not exist as an existing defect. Therefore, it is only necessary to make the inspection result NG or interrupt the inspection.

[0071] For example, in the case of controlling the defect inspection process in the next process, the present invention can be implemented through the following process.

[0072] Figure 1 An example of a process showing the evaluation process of the present invention using contrast in the manufacture of a substrate related to a photomask blank is shown.

[0073] The evaluation device can use a defect inspection device capable of acquiring a surface image.

[0074] First, a program is constructed in such a way that a series of processes of surface image acquisition, contrast acquisition, and pass / fail determination (contrast comparison) are automatically executed.

[0075] Next, a standard substrate (standard substrate related to a photomask blank) is produced, a surface image is acquired, and a standard contrast Δ STD is calculated. Here, Δ STD is calculated based on, for example, the average value of a total of five points including four points at the corners and the center.

[0076] Finally, a threshold value is set in the evaluation device such that Δ STD within ±10% is regarded as a normal product.

[0077] After the above settings are completed, an inspection of the substrate related to the photomask blank to be evaluated (evaluation object substrate related to the photomask blank) is performed. In the image acquisition process, a surface image of a pre-specified coordinate is acquired. In the contrast acquisition process, the contrast is automatically measured from the acquired image. In the pass / fail determination process, the contrast of the inspected product is compared with a pre-set reference value, and only when it is judged to be within ±10%, the next process is entered. Here, for the substrate related to the photomask blank judged to be abnormal, the inspection is aborted and an alarm is issued.

[0078] According to this inspection process, it is possible to quickly detect abnormalities on the film surface that were difficult to determine pass / fail in the past, and quickly implement process improvement.

[0079] (Second Embodiment)

[0080] Next, the case where the contrast magnification is used as an index for evaluating the surface state of the substrate related to the photomask blank will be described.

[0081] In the evaluation method of the present invention, the process only needs to include the following content, that is, photograph the surface of the substrate related to the photomask blank to obtain a surface image, obtain the contrast of the surface image from the obtained surface image, calculate the contrast magnification for making the contrast of the obtained surface image a specified value, and evaluate the substrate related to the photomask blank using the calculated contrast magnification. The aforementioned formula is used when calculating the contrast magnification.

[0082] That is, compared with the first embodiment, the method is to calculate the contrast magnification after obtaining the contrast, and use the contrast magnification instead of the contrast for evaluation.

[0083] More specifically, for example, first, a standard contrast magnification calculation process is performed, that is, a standard substrate related to the photomask blank is prepared in advance, and the contrast magnification of the contrast of the surface image is calculated as the standard contrast magnification.

[0084] Next, an evaluation object contrast magnification calculation process is performed, that is, an evaluation object substrate related to the photomask blank is prepared, and the contrast magnification of the contrast of the surface image of the evaluation object substrate related to the photomask blank is calculated as the evaluation object contrast magnification using the same optical system as in the standard contrast magnification calculation process.

[0085] Then, a contrast magnification comparison process is performed, that is, the evaluation object substrate related to the photomask blank is evaluated by comparing the standard contrast magnification with the evaluation object contrast magnification.

[0086] In this way, it is also possible to evaluate the substrate related to the photomask blank without damage and simply, and the various effects described above can be achieved as in the first embodiment.

[0087] In addition, regarding other elements (for example, conditions such as a confocal optical system and bright field, the criterion in the contrast magnification comparison process: within a specified value % of the standard contrast magnification (especially within ±10%)), they can be the same as in the first embodiment.

[0088] Examples

[0089] Hereinafter, examples and comparative examples will be shown to more specifically illustrate the present invention, but the present invention is not limited thereto.

[0090] (Example 1)

[0091] The evaluation method using the contrast with respect to the phase shift film in the evaluation method of the present invention was performed.

[0092] First, on a square quartz glass substrate with one side being 6 inches (about 15 cm), a phase shift film composed of molybdenum, silicon, oxygen, and nitrogen was formed by a sputtering method using a molybdenum-silicon target and a silicon target as targets and argon, nitrogen, and oxygen as sputtering gases, and two standard substrates were fabricated. For one standard substrate, a spectrophotometer was used to measure the transmittance and reflectance, and the surface roughness was measured using AFM. The other standard substrate was made into a standard substrate STD (standard photomask blank) that serves as a contrast reference for the phase shift film.

[0093] Next, using the M6640S manufactured by LASERTEC Corporation, surface images of the defect-free portions of the corners S1 (-65 mm, -65 mm), S2 (-65 mm, 65 mm), S3 (65 mm, -65 mm), S4 (65 mm, 65 mm), and the center portion S5 (0 mm, 0 mm) of the standard substrate STD where no concave or convex defects were observed were obtained. Hereinafter, the portion where no concave or convex defects were observed in a specified detector is defined as a defect-free portion, and this surface image is defined as a defect-free image.

[0094] The contrasts Δ S1 ~Δ S5 (standard contrast) were obtained from the defect-free images of S1 to S5.

[0095] Here, first, the correlation between the surface state and the contrast will be described as an example. Figure 2 Represents the correlation between the surface state of the film of the photomask blank and the contrast. Figure 2 (a) of represents the contrast Δ a of the defect-free portion. In the case of a defect-free image, it represents the contrast value CON of the contrast depending on the surface state of the film. Figure 2 (b) of represents the case where the surface roughness of the film is larger than normal. When the surface roughness of the film is larger than Figure 2 (a) of, even in the defect-free portion, since the contrast CON is emphasized, the contrast Δ b of the defect-free portion is also larger than Δ a . In addition to this example, in the case of surface states different from normal such as large surface undulations and film quality abnormalities, it is also considered that the contrast Δ b is a larger value than Δ a .

[0096] The contrasts Δ S1 ~Δ S5 of the standard substrate are shown in Table 1 below.

[0097] Based on this result, the average contrast Δ is calculated. AVE = 11. In addition, the more images are obtained, the more the deviation of the contrast can be balanced. Considering the balance of the production efficiency of the photomask blank, it is preferably within five sheets. Additionally, when also considering the in-plane uniformity of the photomask blank, it is preferable to obtain images of the corner and center portions of the substrate.

[0098] (Table 1)

[0099] Contrast <![CDATA[Δ S1 > <![CDATA[Δ S2 > <![CDATA[Δ S3 > <![CDATA[Δ S4 > <![CDATA[Δ S5 > <![CDATA[Δ AVE > STD 11 12 11 12 11 11

[0100] Next, LOTs (A) to (D) that were formed under the same film-forming conditions as the above standard substrate, and LOT (E) (the evaluated photomask blank) that was manufactured with the same transmittance, reflectance, and film thickness as LOTs (A) to (D) by varying the film-forming gas pressure and adjusting the flow rates of nitrogen gas and oxygen were prepared as evaluation objects. Images (defect-free images) of the non-defective portions of the corners S1 to S4 and the center portion S5 were obtained in M6640S, and the contrast Δ S1 ~Δ S5 (evaluated contrast) was obtained from the images.

[0101] The contrast Δ S1 ~Δ S5 and the average contrast Δ AVE are shown in Table 2 below.

[0102] The deviation of the transmittance, reflectance, and film thickness of LOTs (A) to (E) is within 5%.

[0103] However, regarding Δ AVE of LOTs (A) to (D), compared with the standard substrate, the deviation converges within ±10%, and Δ AVE of LOT (E) is a value more than 20% larger than the standard substrate STD.

[0104] (Table 2)

[0105] Contrast <![CDATA[Δ S1 > <![CDATA[Δ S2 > <![CDATA[Δ S3 > <![CDATA[Δ S4 > <![CDATA[Δ S5 > <![CDATA[Δ AVE > LOT(A) 11 10 11 11 11 11 LOT(B) 11 12 11 12 12 12 LOT(C) 10 10 11 11 11 11 LOT(D) 11 12 11 11 12 11 LOT(E) 16 14 13 15 16 15

[0106] As the acceptance criteria, by making the evaluated contrast within ±10% of the standard contrast, the result was obtained that only LOTs (A) to (D) were judged as acceptable, while LOT (E) did not meet the requirements.

[0107] Figure 3 The AFM results of the standard substrate STD and LOT (E) are shown. As an index of surface roughness, the arithmetic mean roughness Ra and the root mean square height Rq were measured. In Figure 3 (a) shows the result of Ra, and inFigure 3 The result representing Rq in (b) of

[0108] A significant difference of about 0.1 nm was found in any index.

[0109] In addition, in Figure 4 (a) and (b) of AVE the results of comparing Δ

[0110] According to Figure 3 , 4 it was found that, compared with the standard substrate STD with a standard contrast Δ AVE of 11, where Ra and Rq are less than 0.3 nm and less than 0.4 nm respectively, for the evaluation object contrast Δ AVE of 15 (i.e., within the range of ±10% when the evaluation object contrast exceeds that of the standard substrate STD), LOT(E) is greater than 0.3 nm and greater than 0.4 nm respectively.

[0111] Moreover, the same measurements were also carried out for other LOT(A) to (D) (all within ±10% of the standard substrate STD in terms of the evaluation object contrast), and like the standard substrate STD, Ra and Rq are less than 0.3 nm and less than 0.4 nm respectively.

[0112] Regarding LOT(E), there is a possibility of being judged as a suspected defect in, for example, the defect inspection process.

[0113] According to Figure 4 the results of the standard substrate STD and LOT(E), and the results of the above-mentioned LOT(A) to (D), it can be seen that by setting the management threshold of the contrast within ±10%, it is possible to distinguish between normal and abnormal photomask blanks manufactured. LOT(A) to (D) having Ra etc. of the same level as the standard substrate STD can be judged as qualified products, and LOT(E) with increased Ra etc. can be excluded.

[0114] (Example 2)

[0115] The evaluation method using the contrast magnification rate in the evaluation method of the present invention was carried out.

[0116] First, using M6640S, defect-free images of the corner parts S1(-65 mm, -65 mm), S2(-65 mm, 65 mm), S3(65 mm, -65 mm), S4(65 mm, 65 mm), and the center part S5(0 mm, 0 mm) of the same standard substrate STD and LOT(A) to (E) as in Example 1 were obtained, and the contrast of each was obtained from the surface image, and then the contrast magnification rate γ was extractedS1 to γ S5 (Standard contrast magnification, contrast magnification of the object to be evaluated).

[0117] Here, first, the correlation between the surface state and the contrast magnification will be described as an example. Figure 5 Represents the correlation between the surface state of the film of the photomask blank and the contrast magnification. The contrast magnification is the magnification factor for magnifying the contrast of the surface image to a specific gray level. Figure 5 (a) of represents the contrast magnification γ of the defect-free part a . In the case of a defect-free image, it represents the magnification factor of the contrast CON that reflects the surface state of the film. Figure 5 (b) of represents the case where the surface roughness of the film is larger than normal. When the surface roughness of the film is Figure 5 larger than (a) of, even for the defect-free part, since the contrast CON is emphasized, the contrast magnification γ of the defect-free part b is also smaller than γ a .

[0118] The contrast magnification γ of the standard substrate is shown in Table 3 below S1 to γ S5 .

[0119] Based on this result, the average contrast magnification γ AVE = 22.4 is calculated.

[0120] (Table 3)

[0121] Contrast magnification <![CDATA[γ S1 > <![CDATA[γ S2 > <![CDATA[γ S3 > <![CDATA[γ S4 > <![CDATA[γ S5 > <![CDATA[γ AVE > STD 23.2 21.3 23.2 21.3 23.2 22.4

[0122] The contrast magnification γ in LOTs (A) to (E) is shown in Table 4 below S1 to γ S5 , and the average contrast magnification γ AVE .

[0123] Regarding γ of LOTs (A) to (D), compared with the standard substrate, the deviation converges within ±10%, and γ of LOT (E) AVE is a value more than 20% smaller than the standard substrate STD. AVE

[0124] (Table 4)

[0125] Contrast magnification <![CDATA[r S1 > <![CDATA[γ S2 > <![CDATA[γ S3 > <![CDATA[γ S4 > <![CDATA[γ S5 > <![CDATA[γ AVE > LOT(A) 23.2 25.5 23.2 24.3 23.2 23.9 LOT(B) 23.2 21.3 23.2 21.3 21.3 22.0 LOT(C) 25.6 26.5 23.2 23.2 23.2 24.1 LOT(D) 23.2 21.3 23.2 24.3 21.3 22.6 LOT(E) 15.9 18.2 19.6 17.0 15.9 17.3

[0126] As the acceptance criterion, by making the contrast magnification of the object to be evaluated within ±10% of the standard contrast magnification, the result is that only LOTs (A) to (D) are judged as acceptable, while LOT (E) does not meet the requirement. ​

[0127] In Figure 6 Figs. (a) and (b), the γ of the standard substrates STD and LOT(E) with respect to the arithmetic mean roughness Ra and the root mean square height Rq measured in the AFM are shown AVE The results of comparison are shown. Also, the other LOTs (A) to (D) were measured in the same manner

[0128] As a result, as in Example 1, the Ra and Rq of LOTs (A) to (D) in which the evaluation object contrast magnification is within ±10% of the standard contrast magnification are the same as those of the standard substrate STD, and are less than 0.3 nm and less than 0.4 nm, respectively. On the other hand, for LOT(E) outside the range of ±10%, they are greater than 0.3 nm and greater than 0.4 nm, respectively

[0129] Thus, it is understood that by setting the management threshold of the contrast magnification within 10%, it is possible to discriminate between normal and abnormal photomask blanks manufactured

[0130] In addition, the present invention is not limited to the above-described embodiments. The above-described embodiments are merely illustrative, and technical solutions having substantially the same structure as the technical idea described in the claims of the present invention and achieving the same effects are all included in the technical scope of the present invention

Claims

1. An evaluation method for the surface state of a reticle blank-related substrate, which is implemented before defect inspection, characterized in that: Taking an image of the surface of the reticle blank-related substrate to obtain a surface image; Obtaining the contrast of the surface image from the obtained surface image; Evaluating the reticle blank-related substrate by using the contrast of the obtained surface image to pre-exclude reticle blank-related substrates with suspected defects; When evaluating the reticle blank-related substrate, the following steps are carried out: A standard contrast obtaining process, preparing a reticle blank-related substrate as a standard in advance, and obtaining the contrast of the surface image of the standard reticle blank-related substrate as the standard contrast; An evaluation object contrast obtaining process, preparing a reticle blank-related substrate of an evaluation object different from the standard reticle blank-related substrate, and using the same optical system as the standard contrast obtaining process to obtain the contrast of the surface image of the evaluation object reticle blank-related substrate as the evaluation object contrast; And A contrast comparison process, evaluating the evaluation object reticle blank-related substrate by comparing the evaluation object contrast with the standard contrast.

2. The evaluation method for the surface state of a reticle blank-related substrate according to claim 1, characterized in that: In the contrast comparison process, When the evaluation object contrast is within a specified percentage of the standard contrast, the evaluation object reticle blank-related substrate is regarded as a qualified product.

3. The evaluation method for the surface state of a reticle blank-related substrate according to claim 2, characterized in that: In the contrast comparison process, When the evaluation object contrast is within ±10% of the standard contrast, the evaluation object reticle blank-related substrate is regarded as a qualified product.

4. An evaluation method for the surface state of a reticle blank-related substrate, which is implemented before defect inspection, characterized in that: Taking an image of the surface of the reticle blank-related substrate to obtain a surface image; Obtaining the contrast of the surface image from the obtained surface image; Calculating a contrast magnification factor for making the contrast of the obtained surface image reach a specified value; Evaluating the reticle blank-related substrate by using the calculated contrast magnification factor to pre-exclude reticle blank-related substrates with suspected defects; When evaluating the reticle blank-related substrate, the following steps are carried out: A standard contrast magnification factor calculating process, preparing a reticle blank-related substrate as a standard in advance, and calculating the contrast magnification factor of the contrast of the surface image of the standard reticle blank-related substrate as the standard contrast magnification factor; An evaluation object contrast magnification factor calculating process, preparing a reticle blank-related substrate of an evaluation object different from the standard reticle blank-related substrate, and using the same optical system as the standard contrast magnification factor calculating process to calculate the contrast magnification factor of the contrast of the surface image of the evaluation object reticle blank-related substrate as the evaluation object contrast magnification factor; And Contrast magnification ratio comparison step, for evaluating the photomask blank-related substrate of the object to be evaluated by comparing the contrast magnification ratio of the object to be evaluated with the standard contrast magnification ratio.

5. The method for evaluating the surface state of a photomask blank-related substrate according to claim 4, wherein: In the contrast magnification ratio comparison step, When the contrast magnification ratio of the object to be evaluated is within a specified percentage of the standard contrast magnification ratio, the photomask blank-related substrate of the object to be evaluated is regarded as a qualified product.

6. The method for evaluating the surface state of a photomask blank-related substrate according to claim 5, wherein: In the contrast magnification ratio comparison step, When the contrast magnification ratio of the object to be evaluated is within ±10% of the standard contrast magnification ratio, the photomask blank-related substrate of the object to be evaluated is regarded as a qualified product.

7. The method for evaluating the surface state of a photomask blank-related substrate according to any one of claims 1 to 6, wherein: When acquiring a surface image by photographing the surface of the photomask blank-related substrate, the photographing is performed in a confocal optical system and in a bright field.

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