Method for Identifying Substrate for EUV Lithography

Abstract

To provide a technique capable of improving identification property of quartz glass substrates.SOLUTION: An EUV lithography substrate includes a quartz glass substrate including TiO2. By processing with a Gaussian filter, an irregularity profile of a surface of the quartz glass substrate, an extraction surface where a component with a wavelength of 5.0 mm or less is extracted from the surface is created; the extraction surface is approximated by a least square method, for creating a plane obtained by the least square method as a reference plane; then an evaluation plane indicating a height distribution of the extraction plane where the reference plane is a reference is created; and at the time, a curve in a cross section of the evaluation plane is configured so that, an average pitch between salients and recesses is 2.0 mm to 8.0 mm.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present disclosure relates to 、E a method for identifying a substrate for UV lithography In the law .

Background Art

[0002] In recent years, with the miniaturization of semiconductor devices, extreme ultraviolet (EUV) lithography (EUVL) has been developed. EUV lithography is a technique for transferring a mask pattern onto a substrate using light having a wavelength of about 0.2 nm to 100 nm, typically about 13.5 nm.

[0003] Patent Document 1 describes using a quartz glass substrate as a substrate for EUV lithography. The quartz glass substrate contains TiO2 in order to reduce its coefficient of thermal expansion. Due to periodic fluctuations in the TiO2 content, striped veins occur. Since the polishing rate varies according to the TiO2 content, a striped uneven pattern is formed on the glass surface after polishing.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] One aspect of the present disclosure provides a technique for improving the distinguishability of a quartz glass substrate.

Means for Solving the Problems

[0006] The substrate for EUV lithography according to one aspect of the present disclosure includes a quartz glass substrate containing TiO₂. By processing the uneven profile of the surface of the quartz glass substrate with a Gaussian filter, an extraction surface is created that extracts components with a wavelength of 5.0 mm or less on the surface. A reference surface is created based on a plane approximated by the least squares method for the extraction surface, and an evaluation surface is created that shows the height distribution of the extraction surface with respect to the reference surface. The cross-sectional curve of the evaluation surface has an average pitch of convex and concave portions of 2.0 mm to 8.0 mm.

Effect of the Invention

[0007] According to one aspect of the present disclosure, since the average pitch of the convex and concave portions of the cross-sectional curve of the evaluation surface is 2.0 mm to 8.0 mm, it is easy to extract the characteristics of the evaluation surface, and the discriminability of the quartz glass substrate can be improved.

Brief Description of the Drawings

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Embodiments for Carrying Out the Invention

[0009] Hereinafter, embodiments for carrying out the present disclosure will be described with reference to the drawings. In each drawing, the same or corresponding components are denoted by the same reference numerals, and the description thereof may be omitted. In the specification, "~" indicating a numerical range means including the numerical values described before and after it as the lower limit value and the upper limit value.

[0010] With reference to FIGS. 1 to 3, a method for manufacturing a substrate for EUV lithography according to an embodiment will be described. The manufacturing method includes, for example, steps S101 to S104 shown in FIG. 1. In these steps S101 to S104, for example, the quartz glass substrate 2 shown in FIGS. 2 and 3 is used. The quartz glass substrate 2 includes a first main surface 21 and a second main surface 22 opposite to the first main surface 21.

[0011] The first major surface 21 is rectangular. In this specification, the rectangular shape includes a shape with chamfers at the corners. Also, the rectangle includes a square. The second major surface 22 is also rectangular, similar to the first major surface 21. The size of the first major surface 21 and the second major surface 22 is, for example, 152 mm in length and 152 mm in width. The longitudinal dimension and the transverse dimension may be 152 mm or more.

[0012] The quartz glass substrate 2 includes four end faces 23, four first chamfered faces 24, and four second chamfered faces 25. The end faces 23 are perpendicular to the first major surface 21 and the second major surface 22. The first chamfered faces 24 are formed at the boundaries between the first major surface 21 and the end faces 23. The second chamfered faces 25 are formed at the boundaries between the second major surface 22 and the end faces 23. In this embodiment, the first chamfered faces 24 and the second chamfered faces 25 are so-called C chamfered faces, but they may be R chamfered faces.

[0013] The quartz glass substrate 2 contains TiO2 in order to reduce its coefficient of linear expansion. The quartz glass substrate 2 contains, for example, 80% to 95% by mass of SiO2 and 4% to 17% by mass of TiO2. When the TiO2 content is 4% to 17% by mass, the coefficient of linear expansion near room temperature is substantially zero, and almost no dimensional change occurs near room temperature. The quartz glass may contain a third component or impurities other than SiO2 and TiO2.

[0014] Step S101 in FIG. 1 includes polishing the first major surface 21 and the second major surface 22 of the quartz glass substrate 2. In this embodiment, the first major surface 21 and the second major surface 22 are polished simultaneously by a double-sided polishing machine (not shown), but they may be polished sequentially by a single-sided polishing machine (not shown). Step S101 includes polishing the quartz glass substrate 2 while supplying a polishing slurry between the polishing pad and the quartz glass substrate 2.

[0015] As the polishing pad, for example, a urethane-based polishing pad, a non-woven fabric-based polishing pad, or a suede-based polishing pad is used. The polishing slurry contains an abrasive and a dispersion medium. The abrasive is, for example, cerium oxide particles. The dispersion medium is, for example, water or an organic solvent. The first main surface 21 and the second main surface 22 may be polished a plurality of times with abrasives of different materials or particle sizes.

[0016] Step S102 includes obtaining the uneven profile (three-dimensional surface shape) of the first main surface 21 and the second main surface 22 of the quartz glass substrate 2. For obtaining the uneven profile, for example, a non-contact measuring instrument such as a laser interferometer is used so that the glass surface is not damaged. The measuring instrument is, for example, an interferometric step gauge.

[0017] Step S103 refers to the uneven profile obtained in Step S102 and locally processes the first main surface 21 and the second main surface 22 of the quartz glass substrate 2 to improve flatness. The first main surface 21 and the second main surface 22 are locally processed in order. The order may be either first and there is no particular limitation.

[0018] For local processing, for example, at least one selected from the GCIB (Gas Cluster Ion Beam) method, the PCVM (Plasma Chemical Vaporization Machining) method, the polishing method using a magnetic fluid, and the polishing using a rotary polishing tool is used.

[0019] Step S104 includes finish-polishing the first main surface 21 and the second main surface 22 of the quartz glass substrate 2. In this embodiment, the first main surface 21 and the second main surface 22 are polished simultaneously by a double-sided polishing machine (not shown), but may be polished in order by a single-sided polishing machine (not shown). In Step S104, the quartz glass substrate 2 is polished while supplying a polishing slurry between the polishing pad and the quartz glass substrate 2. The polishing slurry contains an abrasive. The abrasive is, for example, colloidal silica particles.

[0020] By the above steps S101 to S104, a substrate for EUV lithography is obtained. As described above, the first main surface 21 and the second main surface 22 of the quartz glass substrate 2 are processed many times to improve flatness. During these processes, there is a risk of misidentifying the quartz glass substrate 2. Since the surface of the quartz glass substrate 2 is processed as a whole, it is difficult to identify it by engraving symbols or the like. Conventionally, when a misidentification occurs, the quartz glass substrate 2 has been discarded, resulting in waste of raw materials and energy.

[0021] Incidentally, as described above, the quartz glass substrate 2 contains TiO2 in order to reduce its coefficient of thermal expansion. Striped veins are generated due to periodic variations in the TiO2 content. Since the polishing rate varies according to the TiO2 content, a striped uneven pattern is formed on the polished glass surface. This uneven pattern is generated by chemically polishing the glass surface using cerium oxide particles as an abrasive, that is, it occurs in step S101.

[0022] In this embodiment, after step S101, the quartz glass substrate 2 is identified using the striped uneven pattern generated in step S101. Hereinafter, with reference to FIGS. 4 to 7, a method for identifying a substrate for EUV lithography according to an embodiment will be described. The identification method has, for example, steps S201 to S204 shown in FIG. 4. The processing after step S201 is performed, for example, in step S102. When a misidentification occurs after step S103, the processing after S201 is performed again after the misidentification to identify the quartz glass substrate 2. The processing after step S201 is performed by a human or a computer.

[0023] Step S201 includes obtaining the uneven profile (three-dimensional surface shape) of the surface 31 (see FIG. 5) of the quartz glass substrate 2. The surface 31 is at least one of the first main surface 21 and the second main surface 22. For obtaining the uneven profile, for example, a non-contact measuring machine is used. The measuring machine is, for example, an interference type step gauge.

[0024] Step S202 includes creating an extraction surface 32 (see FIG. 5) that extracts components with a wavelength of 5.0 mm or less from the surface 31 by processing the uneven profile obtained in step S201 with a Gaussian filter. Specifically, based on JIS B 0634:2017, the profile obtained by convolving and integrating a normal distribution curve with a cut-off wavelength (λc) of 5.0 mm and the uneven profile is subtracted from the original uneven profile to obtain a profile after a high-pass filter that removes low-frequency components (i.e., long-wavelength components). The amplitude transmission rate of such a high-pass filter by such processing is as shown in FIG. 6, and the gain becomes 0.5 at the point of the cut-off wavelength (λc) of 5.0 mm. Note that the truncation constant is 0.7 during the convolution and integration. By removing the long-wavelength components in this way, the striped uneven pattern caused by the periodic variation in the TiO2 concentration can be made apparent.

[0025] The extraction surface 32 is, for example, the central region of the surface 31 excluding the rectangular frame-shaped peripheral region of the surface 31, as shown in FIG. 5. The surface 31 is, for example, a square with a length of 152 mm and a width of 152 mm. In contrast, the extraction surface 32 is, for example, a square with a length of 97 mm and a width of 97 mm. Note that the size of the surface 31 and the size of the extraction surface 32 are not particularly limited.

[0026] Step S203 includes creating a reference plane based on the plane approximated by the least squares method for the extraction surface 32 extracted in step S202. In FIG. 7 and the like, the plane with a height of zero is the reference plane. By creating the reference plane, the overall inclination of the extraction surface 32 can be removed.

[0027] Step S204 includes creating an evaluation surface showing the height distribution of the extraction surface 32 with reference to the reference plane created in step S203. The evaluation surface is obtained by removing the overall inclination of the extraction surface 32 from the extraction surface 32 and has the same size as the extraction surface 32.

[0028] Step S205 includes extracting the features of the evaluation surface created in step S204. The features of the evaluation surface include the features of the striped concavo-convex pattern caused by the periodic variation of the TiO2 concentration. The striped concavo-convex pattern is a unique pattern for each quartz glass substrate 2. Therefore, by extracting the features of the striped concavo-convex pattern, even when a mistake occurs, the quartz glass substrate 2 can be identified by comparing the features before and after the mistake. Thus, the amount of waste of the quartz glass substrate 2 can be reduced, and the waste of raw materials and energy can be reduced.

[0029] Extracting the features of the evaluation surface may include determining the position of the intersection point (the point indicated by the black circle in Fig. 7, hereinafter also referred to as the first intersection point) between the first cross-sectional curve of the evaluation surface and the reference surface. The first cross-sectional curve is, for example, the intersection line between the evaluation surface and the first cross-section 41 (see Fig. 5). The first cross-section 41 is a cross-section perpendicular to the reference surface, parallel to one side of the reference surface, and passing through the center of the reference surface. In Fig. 7 and the like, the numerical values on the horizontal axis indicate the numbers of the measurement points. The larger the number of the measurement point, the farther the distance from one side of the reference surface.

[0030] The position of the first intersection point will be described in detail in the column of the embodiments. However, it hardly varies due to the processing after step S101 (for example, the local processing in step 103 and the finish polishing in step S104). Therefore, if the position of the first intersection point is measured after step S101, even if a mistake of the quartz glass substrate 2 occurs during the subsequent processing, the quartz glass substrate 2 can be identified by measuring the position of the first intersection point again later.

[0031] To improve the identification accuracy, the intersection points between adjacent convex and concave portions with a height difference of 0.5 nm or less may be excluded from the first intersection points for identification. For example, in Fig. 7, the height difference between the convex portion P1 and the concave portion V1 is 0.5 nm or less, so the intersection point between the convex portion P1 and the concave portion V1 is excluded from the first intersection points for identification. On the other hand, in Fig. 7, the height difference between the convex portion P2 and the concave portion V2 exceeds 0.5 nm, so the intersection point between the convex portion P2 and the concave portion V2 is used as the first intersection point for identification.

[0032] Extracting the features of the evaluation surface may include determining the position of the intersection point (hereinafter also referred to as the second intersection point) between the second cross-sectional curve of the evaluation surface and the reference surface. The second cross-sectional curve is, for example, the intersection line between the evaluation surface and the second cross-section 42 (see FIG. 5). The second cross-section 42 is a cross-section perpendicular to the reference surface, parallel to another side of the reference surface, and passing through the center of the reference surface. The first cross-section 41 and the second cross-section 42 are perpendicular to each other.

[0033] The position of the second intersection point will be described in detail in the Examples section, but it hardly varies due to processing after step S101 (for example, local processing in step 103 and finish polishing in step S104). Therefore, if the position of the second intersection point is measured after step S101, even if a mistake occurs in taking the quartz glass substrate 2 during subsequent processing, the quartz glass substrate 2 can be identified by measuring the position of the second intersection point again. To improve the identification accuracy, the intersection points between adjacent convex and concave portions with a height difference of 0.5 nm or less may be excluded from the second intersection points for identification.

[0034] Extracting the features of the evaluation surface may include determining the average pitch Px between the concave and convex portions in the first cross-sectional curve of the evaluation surface. The average pitch Px is obtained by dividing the length of the intersection line between the reference surface and the first cross-section (for example, 97 mm) by the number of first intersection points. The average pitch Px is a unique value for each quartz glass substrate 2. Therefore, if the average pitch Px is calculated, the quartz glass substrate 2 can be identified even when a mistake occurs.

[0035] The average pitch Px is, for example, 2.0 mm to 8.0 mm. If the average pitch Px is 2.0 mm or more, the number of first intersection points is moderately small, and the correspondence between the positions of the first intersection points before and after the mistake is easy to understand. If the average pitch Px is 8.0 mm or less, the number of first intersection points is moderately large, and the number of distinguishable quartz glass substrates 2 is large. The average pitch Px is preferably 2.0 mm to 5.0 mm.

[0036] As shown in Fig. 7, for the first cross-sectional curve, the difference ΔHx between the average value H1 of the heights of the first to fifth protrusions (e.g., the five white circles shown in Fig. 7) from the higher side of the height of the protrusions and the average value H2 of the depths of the first to fifth recesses (e.g., the five squares shown in Fig. 7) from the deeper side of the depth of the recesses is, for example, 1.1 nm to 3.0 nm. If ΔHx is 1.1 nm or more, the height difference between the protrusions and the recesses is large, and the stripe pattern of the uneven pattern is clear. If ΔHx is 3.0 nm or less, the flatness of the surface 31 is high, and the quality of various functional films formed on the surface 31 is good. ΔHx is preferably 1.2 nm to 2.0 nm.

[0037] Similarly, extracting the characteristics of the evaluation surface may include obtaining the average pitch Py of the recesses and protrusions in the second cross-sectional curve of the evaluation surface. The average pitch Py is obtained by dividing the length of the intersection line between the reference plane and the second cross-section (e.g., 97 mm) by the number of second intersection points. The average pitch Py is a unique value for each quartz glass substrate 2. Therefore, by calculating the average pitch Py, the quartz glass substrate 2 can be identified even when a mistake occurs.

[0038] The average pitch Py is, for example, 2.0 mm to 8.0 mm. If the average pitch Py is 2.0 mm or more, the number of second intersection points is moderately small, and the correspondence between the position of the second intersection point before the mistake and the position of the second intersection point after the mistake is easy to understand. If the average pitch Py is 8.0 mm or less, the number of second intersection points is moderately large, and the number of distinguishable quartz glass substrates 2 is large. The average pitch Py is preferably 2.0 mm to 5.0 mm.

[0039] For the second cross-sectional curve, the difference ΔHy between the average value of the heights of the first to fifth protrusions from the higher side of the height of the protrusions and the average value of the depths of the first to fifth recesses from the deeper side of the depth of the recesses is, for example, 1.1 nm to 3.0 nm. If ΔHy is 1.1 nm or more, the height difference between the protrusions and the recesses is large, and the stripe pattern of the uneven pattern is clear. If ΔHy is 3.0 nm or less, the flatness of the surface 31 is high, and the quality of various functional films formed on the surface 31 is good. ΔHy is preferably 1.2 nm to 2.0 nm.

[0040] Extracting the features of the evaluation surface may include obtaining the average value Pxy of the average pitch Px and the average pitch Py. The average pitch Pxy is, for example, 2.0 mm to 8.0 mm, preferably 2.0 mm to 5.0 mm. Note that the average value ΔHxy of ΔHx and ΔHy is, for example, 1.0 nm to 3.0 nm, preferably 1.2 nm to 2.0 nm.

[0041] At least one of Px, Py, and Pxy is 2.0 mm to 8.0 mm, preferably 2.0 mm to 5.0 mm.

[0042] At least a part of the evaluation surface may have concentric or spiral stripes (see FIGS. 8(B), 10(B), 13(B), and 15(B)). Compared with the case where there are no concentric or spiral stripes, the discriminability based on the positions of the first intersection point, the second intersection point, and the average pitches Px, Py, Pxy, etc. is good. It is particularly effective when discriminating a plurality of quartz glass substrates 2 obtained by slicing a transparent glass body described later.

[0043] The values of Px, Py, and Pxy can be adjusted, for example, by the method of controlling the rotation speed of the seed rod described in Patent Document 1, and a substrate with good discriminability can be obtained by adjusting the pitch of the grain pattern during substrate fabrication.

[0044] Extracting the features of the evaluation surface may include obtaining at least one of the position and the number of the centers of the concentric or spiral stripes. The position and the number of the centers of the concentric circles or vortices are unique values for each quartz glass substrate 2. Therefore, if at least one of the position and the number of the centers of the concentric circles or vortices is obtained, the quartz glass substrate 2 can be discriminated even when a mistake occurs.

[0045] Extracting the features of the evaluation surface may include creating an image (see FIGS. 8(B), 10(B), 13(B), and 15(B)) in which the evaluation surface is binarized by height. For example, a reference surface is used as the height criterion for binarization. By binarization, the striped concavo-convex pattern resulting from the periodic variation in TiO2 concentration can be clarified. The striped concavo-convex pattern becomes a unique pattern for each quartz glass substrate 2. Therefore, the quartz glass substrate 2 can be identified even when a mistake occurs. General pattern matching is used for identification.

[0046] In addition, in this embodiment, an evaluation surface is created and the features of the evaluation surface are extracted to extract the features of the extraction surface, but the features of the extraction surface may be extracted without creating an evaluation surface. For example, at least one of the position and number of the centers of the concentric or spiral stripes on the extraction surface may be obtained. Also, an image in which the extraction surface is binarized by height may be created. A distribution different from the gain distribution in FIG. 6 may be used.

[0047] Next, a method for manufacturing the quartz glass substrate 2 according to an embodiment will be described. As a method for manufacturing the quartz glass substrate 2, for example, the VAD method (vapor axial deposition method) is used. In the VAD method, glass fine particles obtained by flame hydrolysis of an Si precursor and a Ti precursor are deposited and grown on the lower end of a seed rod rotating at a set rotation speed to form a porous glass body. The seed rod is, for example, a rod made of quartz. As the glass Si precursor, a silicon halide compound or an alkoxysilane is used. As the Ti precursor, a titanium halide compound or an alkoxytitanium is used.

[0048] Next, the porous glass body is heated to the transparent vitrification temperature to be transparently vitrified, and a transparent glass body is obtained. Transparent vitrification refers to a state in which the porous glass body is densified until voids cannot be confirmed by an optical microscope. The transparent vitrification temperature refers to the temperature at which the porous glass body can be densified until voids cannot be confirmed by an optical microscope. The transparent vitrification temperature is, for example, 1400°C to 1700°C, preferably 1450°C to 1650°C.

[0049] Next, a formed glass body is obtained by heating a transparent glass body to a temperature equal to or higher than the softening point and shaping it into a desired shape. The shaping process may include pressing. The temperature of the shaping process is, for example, 1500°C to 1800°C. Thereafter, the formed glass body is heat-treated at a predetermined temperature of 600°C to 1200°C for 5 hours or more, and then cooled to a temperature of 500°C or lower at a cooling rate of 10°C / hr or less. After cooling to a temperature of 500°C or lower, it may be allowed to cool naturally. Thereafter, a plurality of quartz glass substrates 2 are obtained by slicing the transparent glass body.

[0050] The average pitches Px, Py, Pxy, etc. of the quartz glass substrate 2 can be adjusted by changing the manufacturing conditions of the quartz glass substrate 2. Any of the manufacturing conditions of the porous glass body, the manufacturing conditions of the transparent glass body, and the manufacturing conditions of the formed glass body may be changed. Examples of the manufacturing conditions of the porous glass body include the set rotation speed of the seed rod and the size (e.g., diameter) of the porous glass body. An example of the manufacturing condition of the formed glass body is the pressing pressure.

[0051] The manufacturing method of the porous glass body is not limited to the VAD method, and may be, for example, the direct method or the like.

Examples

[0052] [Example 1-1] In Example 1-1, a quartz glass substrate containing TiO2 was produced using a porous glass body weighing 25 kg to 30 kg produced by the VAD method. Thereafter, before and after finish polishing, the uneven profile of the substrate surface was acquired, an extraction surface was created using a Gaussian filter, a plane approximated by the least squares method of the extraction surface was used as a reference surface, and an evaluation surface showing the height distribution of the extraction surface with respect to the reference surface was created. Thereafter, Px, Py, Pxy, ΔHx, ΔHy, ΔHxy, etc. were measured.

[0053] As is clear from comparing FIGS. 8(A) and 8(B), by extracting components with a wavelength of 5.0 mm or less using a Gaussian filter, the striped uneven pattern due to the periodic variation in TiO2 concentration could be made apparent. This is also clear from comparing FIGS. 10(A) and 10(B). In FIGS. 8 and 10, the closer the color is to white from black, the higher the height.

[0054] As is clear from comparing the solid line and the broken line in FIG. 12(A), before and after finish polishing, the position of the first intersection was almost the same, and the average pitch Px was also almost the same. Similarly, as is clear from comparing the solid line and the broken line in FIG. 12(B), before and after finish polishing, the position of the second intersection was almost the same, and the average pitch Py was also almost the same.

[0055] [Example 1-2] In Example 1-2, in the same manner as in Example 1-1, a quartz glass substrate containing TiO2 was fabricated using a porous glass body weighing 25 kg to 30 kg fabricated by the VAD method. Then, before and after finish polishing, the uneven profile of the substrate surface was acquired, an extraction surface was created using a Gaussian filter, a plane approximated by the least squares method for the extraction surface was used as a reference plane, and an evaluation surface showing the height distribution of the extraction surface with respect to the reference plane was created. Then, Px, Py, Pxy, ΔHx, ΔHy, ΔHxy, etc. were measured.

[0056] As is clear from comparing FIGS. 13(A) and 13(B), by extracting components with a wavelength of 5.0 mm or less using a Gaussian filter, the striped uneven pattern due to the periodic variation in TiO2 concentration could be made apparent. This is also clear from comparing FIGS. 15(A) and 15(B). In FIGS. 13 and 15, the closer the color is to white from black, the higher the height.

[0057] As is clear from comparing the solid line and the broken line in Fig. 17(A), before and after finish polishing, the position of the first intersection point was almost the same, and the average pitch Px was also almost the same. Similarly, as is clear from comparing the solid line and the broken line in Fig. 17(B), before and after finish polishing, the position of the second intersection point was almost the same, and the average pitch Py was also almost the same.

[0058] [Example 2] In Example 2, different from Example 1-1 and Example 1-2, a quartz glass substrate containing TiO2 was fabricated using a 1000 kg porous glass body fabricated by the direct method. Then, before and after finish polishing respectively, the uneven profile of the substrate surface was acquired, an extraction surface was created using a Gaussian filter, a plane approximated by the least squares method for the extraction surface was created as a reference plane, and an evaluation surface showing the height distribution of the extraction surface with respect to the reference plane was created. Then, Px, Py, Pxy, ΔHx, ΔHy, ΔHxy, etc. were measured.

[0059] [Example 3] In Example 3, a pure quartz glass substrate not containing TiO2 was fabricated using a 25 kg to 30 kg porous glass body fabricated by the VAD method. Then, before and after finish polishing respectively, the uneven profile of the substrate surface was acquired, an extraction surface was created using a Gaussian filter, a plane approximated by the least squares method for the extraction surface was created as a reference plane, and an evaluation surface showing the height distribution of the extraction surface with respect to the reference plane was created. Then, Px, Py, Pxy, ΔHx, ΔHy, ΔHxy, etc. were measured.

[0060] As is clear from Fig. 18(A) and Fig. 18(B), since the TiO2 content was zero, the uneven pattern was unclear regardless of the use of the Gaussian filter. This is also clear from Fig. 20(A) and Fig. 20(B). In Figs. 18 and 20, the closer the color is to white from black, the higher the height is represented.

[0061] As is clear from comparing the solid line and the broken line in Fig. 22(A), the position of the first intersection point shifted and the average pitch Px was different before and after the finish polishing. Similarly, as is clear from comparing the solid line and the broken line in Fig. 22(B), the position of the second intersection point shifted and the average pitch Py was different before and after the finish polishing.

[0062] [Evaluation Results] Table 1 shows the evaluation results of Example 1-1, Example 1-2, Example 2, Example 3, etc. In Table 1, Px, Py, Pxy, ΔHx, ΔHy, ΔHxy, etc. are the values after the finish polishing.

[0063]

Table 1

[0064] As is clear from Table 1, according to Example 1-1, Example 1-2, and Example 2, the average pitches Px, Py, and Pxy were 2.0 mm to 8.0 mm, and 50 substrates could be discriminated. On the other hand, according to Example 3, the average pitches Px, Py, and Pxy exceeded 8.0 mm, and 20 substrates could not be discriminated.

[0065] As described above, the substrate for EUV lithography, the method for identifying the substrate for EUV lithography, and the method for manufacturing the substrate for EUV lithography according to the present disclosure have been described. However, the present disclosure is not limited to the above-described embodiments. Within the scope described in the claims, various changes, modifications, substitutions, additions, deletions, and combinations are possible. Naturally, they also belong to the technical scope of the present disclosure.

Explanation of Reference Numerals

[0066] 2 Quartz glass substrate 21 First main surface (surface) 22 Second main surface (surface)

Claims

1. TiO ２ A method for identifying a substrate for EUV lithography, comprising identifying a quartz glass substrate containing creating an extraction surface by extracting an uneven pattern derived from the grain pattern from the uneven profile of the surface of the quartz glass substrate; extracting the features of the extraction surface; A method for identifying a substrate for EUV lithography, comprising:

2. The step of extracting the extraction surface includes creating an extraction surface by processing the uneven profile of the surface of the quartz glass substrate with a Gaussian filter to extract components having a wavelength of 5.0 mm or less from the surface. The step of extracting the features of the extraction surface includes creating a plane approximated by the least squares method as a reference plane, creating an evaluation surface showing the height distribution of the extraction surface with respect to the reference plane, and extracting the features of the evaluation surface. The method for identifying a substrate for EUV lithography according to claim 1, comprising:

3. The step of extracting the features includes obtaining the position of the intersection of the cross-sectional curve of the evaluation surface and the reference plane. The method for identifying a substrate for EUV lithography according to claim 2, comprising:

4. The step of extracting the features includes obtaining the average pitch between the concave and convex portions in the cross-sectional curve of the evaluation surface. The method for identifying a substrate for EUV lithography according to claim 2 or 3, comprising:

5. At least a part of the extraction surface has concentric or spiral stripes. The step of extracting the features includes obtaining at least one of the position and the number of the centers of the concentric or spiral stripes. The method for identifying a substrate for EUV lithography according to any one of claims 1 to 4, comprising:

6. The step of extracting the features includes creating an image binarized by height using the extraction surface. The method for identifying a substrate for EUV lithography according to any one of claims 1 to 5, comprising:

Images