Glass substrate for EUV lithography and mask blank for EUV lithography

Abstract

Provided is a glass substrate for EUV lithography having high correction accuracy of a mask pattern.　This glass substrate for EUV lithography has a first main surface and a second main surface on the reverse side from the first main surface, and satisfies requirement 1 in a retardation observation sample with a thickness of 1.0 mm obtained by cutting, along a first cut surface and a second cut surface, and polishing the glass substrate.　Requirement 1: Regions obtained by equally dividing the first cut surface of the retardation observation sample into fifths in a direction parallel to the first main surface of the retardation observation sample and parallel to the first cut surface are virtually set and referred to as a first region, a second region, a third region, a fourth region, and a fifth region, respectively, from one end of the retardation observation sample, and when a retardation map formed by an aggregate of measurement pixels in each of the regions is obtained, predetermined requirement A and requirement B are satisfied in the second region, the third region, and the fourth region.

Description

Glass substrate for EUV lithography and mask blank for EUV lithography

[0001] The present invention relates to a glass substrate for EUV (Extreme Ultra Violet) lithography, and also to a mask blank for EUV lithography having the glass substrate for EUV lithography.

[0002] In recent years, EUV lithography, which uses EUV light with a central wavelength of around 13.5 nm as a light source, has been considered in order to further miniaturize semiconductor devices. Due to the characteristics of EUV light, EUV lithography uses a reflective optical system and a reflective mask. The reflective mask used in EUV lithography has a mask pattern formed on a glass substrate, in which regions that reflect EUV light and regions that suppress reflection of EUV light are patterned. The mask pattern is transferred as a resist pattern onto a wafer through an exposure tool, and subsequent processing is carried out.

[0003] In the above-described reflective mask, undesirable defects may be included, and the mask pattern may need to be corrected. A known technique for correcting a mask pattern is described, for example, in Patent Document 1. More specifically, Patent Document 1 discloses an invention relating to a technique for correcting a mask pattern by irradiating a glass substrate of a reflective mask with laser light to generate stress in the glass substrate.

[0004] Special Publication No. 2021-531502

[0005] Due to demands for further miniaturization of semiconductor devices and improved yields, there has been a demand for improved correction accuracy in the technology for correcting the mask pattern. The present inventors have studied conventional reflective masks and found that there is room for improvement in correction accuracy when correcting a mask pattern by irradiating it with laser light as described in Patent Document 1 and the like.

[0006] The present invention has been made in view of the above-mentioned problems, and has an object of providing a glass substrate for EUV lithography that allows high accuracy in mask pattern correction. Another object of the present invention is to provide a mask blank for EUV lithography.

[0007] As a result of intensive research into the above-mentioned problems, the inventors have found that the desired effect can be obtained by adjusting the retardation distribution in the cross section of a glass substrate for EUV lithography, and have arrived at the present invention.

[0008] That is, the inventors have found that the above-mentioned problems can be solved by the following configuration: [1] A glass substrate for EUV lithography having a first main surface and a second main surface opposite to the first main surface, and having a first side and a second side adjacent to each other when viewed in a normal direction of the first main surface, wherein the glass substrate for EUV lithography is cut along a first cut surface that is parallel to the first side, passes through a midpoint of the second side, and is perpendicular to the first main surface, and a second cut surface that is parallel to the first cut surface and is spaced 1.5 mm from the first cut surface, and the cut surface is obtained by polishing the cut surface to obtain a retardation observation sample having a plate thickness of 1.0 mm, and the glass substrate for EUV lithography satisfies the following requirement 1: Requirement 1: Imaginary regions are set by equally dividing the first cut surface of the retardation observation sample into five regions parallel to the first main surface of the retardation observation sample and in a direction parallel to the first cut surface, and these regions are designated as a first region, a second region, a third region, a fourth region, and a fifth region from one end of the retardation observation sample, respectively, and when a retardation map is obtained by collecting measurement pixels in each region, the second region, the third region, and the fourth region satisfy the following requirements A and B. Requirement A: In the retardation map, the average retardation Re1 of the measurement pixels whose fast axis directions are 40 to 75° with respect to the first main surface is 2.00 nm / cm or less. Requirement B: In the retardation map, the average value Re2 of the retardations of the measurement pixels whose fast axis directions are 105 to 140° with respect to the first main surface is 2.00 nm / cm or less. [2] A glass substrate for EUV lithography according to [1], which satisfies the following Requirement 2. Requirement 2: With respect to the first region, the second region, the third region, the fourth region, and the fifth region in Requirement 1, Requirement A and Requirement B are satisfied. [3] A glass substrate for EUV lithography according to [1] or [2], which satisfies the following Requirement C and Requirement D with respect to the second region, the third region, and the fourth region in Requirement 1.Requirement C: When a cumulative distribution of retardation values ​​of the measurement pixels whose fast axis directions are at an angle of 40 to 75° with respect to the first principal surface is created in the retardation map, the retardation value Re3 of 95% of the measurement pixels is 4.00 nm / cm or less. Requirement D: When a cumulative distribution of retardation values ​​of the measurement pixels whose fast axis directions are at an angle of 105 to 140° with respect to the first principal surface is created in the retardation map, the retardation value Re4 of 95% of the measurement pixels is 4.00 nm / cm or less. [4] The glass substrate for EUV lithography according to [3], further satisfying Requirements C and D in the first region and the fifth region in Requirement 1. [5] The glass substrate for EUV lithography according to any one of [1] to [4], wherein the second region, the third region, and the fourth region in Requirement 1 satisfy the following Requirement E. Requirement E: In the retardation map, the average retardation Re5 of the measurement pixels whose fast axis directions are equal to or greater than 0° and less than 180° with respect to the first principal surface is 2.40 nm / cm or less. [6] The glass substrate for EUV lithography according to [5], wherein the first region and the fifth region in Requirement 1 further satisfy Requirement E. [7] A glass substrate for EUV lithography having a first main surface and a second main surface opposite to the first main surface, and having a first side and a second side adjacent to each other when viewed in a normal direction of the first main surface, wherein the glass substrate for EUV lithography is cut along a first cut surface that is parallel to the first side, passes through a midpoint of the second side, and is perpendicular to the first main surface, and a second cut surface that is parallel to the first cut surface and is spaced 1.5 mm from the first cut surface, and the cut surface is obtained by polishing the cut surface to obtain a retardation observation sample having a plate thickness of 1.0 mm, and the glass substrate for EUV lithography satisfies the following requirement 3.Requirement 3: When five imaginary regions are set by equally dividing the first cross section of the retardation observation sample into five regions parallel to the first main surface of the retardation observation sample and in a direction parallel to the first cross section, and the regions are designated as a first region, a second region, a third region, a fourth region, and a fifth region from one end of the retardation observation sample, and a retardation map is obtained by collecting measurement pixels in each region, the second region, the third region, and the fourth region satisfy the following requirements C and D. Requirement C: When a cumulative distribution of retardation values ​​of measurement pixels whose fast axis directions are 40 to 75 degrees with respect to the first main surface in the retardation map is created, the retardation value Re3 of cumulative 95% of the measurement pixels is 4.00 nm / cm or less. Requirement D: When a cumulative distribution of retardation values ​​of the measurement pixels in the retardation map, whose fast axis directions are 105 to 140° with respect to the first principal surface, is created, the retardation value Re4 of cumulative 95% of the measurement pixels is 4.00 nm / cm or less. [8] A glass substrate for EUV lithography according to [7], further satisfying requirements C and D in the first region and the fifth region in requirement 3. [9] A glass substrate for EUV lithography according to [7] or [8], wherein the second region, the third region, and the fourth region in requirement 3 satisfy the following requirement E. Requirement E: In the retardation map, the average retardation Re5 of the measurement pixels in the fast axis directions of 0° or more and less than 180° with respect to the first principal surface is 2.40 nm / cm or less.

[10] The glass substrate for EUV lithography according to [9], wherein the first and fifth regions in Requirement 3 further satisfy Requirement E.

[11] A mask blank for EUV lithography, comprising the glass substrate for EUV lithography according to any one of [1] to

[10] .

[12] The mask blank for EUV lithography according to

[11] , wherein an EUV lithography mask formed using the mask blank for EUV lithography is used in a technique for correcting the pattern shape of an EUV lithography mask by irradiating it with laser light.

[13] The mask blank for EUV lithography according to

[12] , having a conductive film on one of the first main surface side and the second main surface side, and having a transmittance of 1.0% or more at the wavelength of the laser light.

[14] The mask blank for EUV lithography according to

[12] or

[13] , wherein the wavelength of the laser light is 632 nm.

[0009] According to the present invention, it is possible to provide a glass substrate for EUV lithography that allows high accuracy in correcting a mask pattern, and also to provide a mask blank for EUV lithography.

[0010] FIG. 1 is a perspective view showing one embodiment of a glass substrate for EUV lithography of the present invention; FIG. 2 is a plan view of a glass substrate for EUV lithography of the present invention; FIG. 3 is a perspective view of a sample for observation before polishing; FIG. 4 is a perspective view of a sample for retardation observation; FIG. 5 is a front view of a sample for observation before polishing, as seen from the normal direction of a first cut surface; ２ -TiO ２ 1 is a cross-sectional view showing the deposition of glass particles, and FIG. 2 is a contour diagram showing an index of mask pattern repair accuracy for each fast axis direction and retardation value.

[0011] The present invention will be described in detail below. The following description of the components may be based on representative embodiments of the present invention, but the present invention is not limited to such embodiments.

[0012] The following describes the meaning of each description in this specification. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits.

[0013] The glass substrate for EUV lithography of the present invention (hereinafter also simply referred to as "the glass substrate") includes a first embodiment and a second embodiment described below. The first and second embodiments of the glass substrate of the present invention will be described below. Note that when there is no need to distinguish between the first and second embodiments, they will also be simply referred to as "the glass substrate of the present invention."

[0014] <First Embodiment of Glass Substrate for EUV Lithography> A first embodiment of the glass substrate for EUV lithography (the present glass substrate) of the present invention is a glass substrate for EUV lithography having a first main surface and a second main surface opposite to the first main surface, and having a first side and a second side that are adjacent to each other when viewed from a normal direction of the first main surface. Here, the first embodiment of the glass substrate is a glass substrate for EUV lithography, wherein a retardation observation sample having a thickness of 1.0 mm obtained by cutting the glass substrate for EUV lithography along a first cut surface that is parallel to the first side, passes through a midpoint of the second side, and is orthogonal to the first main surface, and a second cut surface that is parallel to the first cut surface and is spaced 1.5 mm from the first cut surface, and polishing the cut surface satisfies the following Requirement 1. Requirement 1: Imaginary regions are set by equally dividing the first cut surface of the retardation observation sample into five regions parallel to the first main surface of the retardation observation sample and in a direction parallel to the first cut surface, and these regions are designated as a first region, a second region, a third region, a fourth region, and a fifth region from one end of the retardation observation sample, respectively, and when a retardation map is obtained by collecting measurement pixels in each region, the second region, the third region, and the fourth region satisfy the following requirements A and B. Requirement A: In the retardation map, the average retardation Re1 of the measurement pixels whose fast axis directions are 40 to 75° with respect to the first main surface is 2.00 nm / cm or less. Requirement B: In the retardation map, the average value Re2 of retardation of the measurement pixels whose fast axis directions are 105 to 140° with respect to the first principal surface is 2.00 nm / cm or less.

[0015] In the first embodiment of the glass substrate, the accuracy of correction of a mask pattern formed on the glass substrate is increased. This is believed to be due to the following reasons. When the above requirement 1 (requirement A and requirement B) is satisfied, the retardation in the region having the fast axis direction at approximately 45° or approximately 135° relative to the first main surface in the cross-sectional direction of the first embodiment of the glass substrate is small. That is, in the first embodiment of the glass substrate, even if retardation is present in a direction tilted from the first main surface in the cross-sectional direction, the retardation value can be said to be small. Here, generally, when a region having retardation exists in a glass material, it is believed that the maximum principal stress acts in a direction perpendicular to the fast axis direction of the retardation. That is, when retardation is present in a direction tilted from the first main surface, it is believed that internal stress acts in a direction tilted from the first main surface. Furthermore, the retardation value is believed to correspond to the magnitude of the acting internal stress.

[0016] When a mask pattern is modified by irradiating laser light, it is understood that the laser light locally expands the glass substrate, generating local stress, which locally deforms the glass substrate and moves the mask pattern in the planar direction of the glass substrate. Therefore, in order to modify the desired pattern, it is considered necessary for the local stress generated by the laser light irradiation to act as designed. Here, if internal stress acts on the glass substrate, it can be said that the local stress generated by the laser light irradiation is affected by the internal stress. When the above-mentioned requirement 1 (requirements A and B) is satisfied, as in the first embodiment of the present glass substrate, even if internal stress acts in a direction inclined from the first main surface, the value of the internal stress is small, so even if the local stress generated by the irradiation is affected by the internal stress, the change in the acting direction of the main stress is small, and the stress is likely to act as designed. As a result, it is considered that the first embodiment of the present glass substrate can improve the accuracy of mask pattern modification.

[0017] In addition, when the retardation has a fast axis direction parallel to or perpendicular to the first principal surface, that is, when the maximum principal stress acts in a direction perpendicular to or parallel to the first principal surface, it is considered that the stress acts easily as designed. This is because the stress acting in the above direction is unlikely to affect the stress fluctuation in the planar direction of the glass substrate (the direction parallel to the first principal surface) caused by irradiation with laser light. The above mechanism will be described in detail later. ａｄｄ See also the calculation of the value of |.

[0018] Requirement 1 and other requirements that the glass substrate for EUV lithography (first embodiment of the present glass substrate) satisfies will be described in detail below.

[0019] [Requirement 1] A first embodiment of the glass substrate and a sample for retardation observation will be described with reference to the drawings. For convenience, the drawings in this specification may be drawn at a scale different from the actual scale. FIG. 1 is a perspective view showing one aspect of the first embodiment of the glass substrate. The glass substrate 10 shown in FIG. 1 has a first main surface 12 and a second main surface 14 opposite the first main surface 12. The distance between the first main surface 12 and the second main surface 14 (the thickness of the glass substrate 10) is 0.25 inches (6.3 mm). FIG. 2 is a plan view of the glass substrate 10 shown in FIG. 1 as viewed from the normal direction of the first main surface 12. When viewed from the normal direction of the first main surface 12, the glass substrate 10 has a square shape. The first main surface 12 has a first side S1 and a second side S2 adjacent to the first side S1. The length of the first side S1 and the second side S2 is 6 inches (152.4 mm).

[0020] Next, a method for preparing a sample for retardation observation will be described with reference to FIGS. 1 and 2. To obtain a sample for retardation observation, the glass substrate 10 is first cut at a first cut surface C1 and a second cut surface C2 (see FIG. 1). The positions of the first cut surface C1 and the second cut surface C2 on the glass substrate 10 will be described with reference to FIG. 2. The first cut surface C1 is parallel to the first side S1 and passes through the midpoint of the second side S2. Furthermore, the first cut surface C1 is perpendicular to the first main surface 12. That is, the first cut surface C1 is parallel to the thickness direction of the glass substrate 10, perpendicular to the second side S2, and passes through the midpoint of the second side S2. The second cut surface C2 is parallel to the first cut surface C1 and is spaced 1.5 mm from the first cut surface C1. That is, the distance ts between the first cut surface C1 and the second cut surface C2 in FIG. 2 is 1.5 mm.

[0021] When the glass substrate 10 is cut at the first cut surface C1 and the second cut surface C2, a pre-polishing observation sample having a thickness of 1.5 mm is obtained (see FIG. 3). The pre-polishing observation sample 20 shown in FIG. 3 has the first cut surface C1 and a cut surface C2 opposite to the first cut surface C1. The distance between the first cut surface C1 and the second cut surface C2 (the thickness of the pre-polishing observation sample 20) is 1.5 mm.

[0022] Next, the pre-polishing observation sample 20 is divided into five pieces in the longitudinal direction of the pre-polishing observation sample 20 (the direction parallel to the first side S1) to obtain five divided pre-polishing observation samples. Next, the first cut surface C1 and the second cut surface C2 of each of the five divided pre-polishing observation samples are polished. Specifically, first, the pre-polishing observation sample is processed to a thickness of 1.3 mm from the first cut surface C1 side using a grinder. Next, the pre-polishing observation sample is processed to a thickness of 1.2 mm from the second cut surface C2 side using a grinder. Next, the entire circumference of the pre-polishing observation sample is C-chamfered to a dimension of 0.2 mm each using a #800 metal bond. The first cut surface C1 side and the second cut surface C2 side of each chamfered pre-polishing observation sample are polished with a ceria abrasive using a double-sided polisher to obtain retardation observation samples with a plate thickness of 1.0 mm. That is, by the above polishing, five samples for retardation observation having a thickness of 1.0 mm and having a first polished surface C1p and a second polished surface C2p are obtained.

[0023] Through the above procedure, retardation observation samples 201 to 205 are obtained. The retardation observation sample 201, representatively shown in FIG. 4, has a first polished surface C1p and a second polished surface C2p, which is the surface opposite to the first polished surface C1p. The distance between the first polished surface C1p and the second polished surface C2p (plate thickness of the retardation observation sample 201) is 1.00±0.05 mm. A micrometer with a minimum resolution of 0.001 mm is used to measure the plate thickness. The plate thicknesses of the retardation observation samples 201 to 205 are measured before obtaining the retardation maps described below.

[0024] Measurements using the retardation observation samples (retardation observation samples 201 to 205) will now be described. That is, a measurement method for requirement 1 will be described. Hereinafter, the measurement method for requirement 1 will be described with reference to FIG. 5 . FIG. 5 is a front view of the pre-polishing observation sample 20 as seen from the normal direction of the first cut surface C1. Note that the left-right direction of FIG. 5 is parallel to the first main surface 12 of the glass substrate 10 in FIG. 1 and parallel to the first cut surface C1 (first polished surface C1p). First, the first cut surface C1 (first polished surface C1p) of the pre-polishing observation sample 20 is divided into five equal regions in the left-right direction of the paper in FIG. 5 . As shown in FIG. 5 , the regions are, from one end (the left end in FIG. 5 ), a first region A1, a second region A2, a third region A3, a fourth region A4, and a fifth region A5. The retardation observation samples 201 to 205 correspond to the retardation observation samples in the first region A1, second region A2, third region A3, fourth region A4 and fifth region A5, respectively.

[0025] Next, a retardation map is obtained for each of the above regions (first region A1 to fifth region A5, i.e., retardation observation samples 201 to 205). A retardation map is a map formed by a collection of measurement pixels, which are the smallest units, and the retardation map is formed by a two-dimensional arrangement of the measurement pixels. The measurement pixels hold the direction of the fast axis and the magnitude of retardation (phase difference). A retardation map is obtained for a portion of each of the above regions. Specifically, a first measurement region AM1, a second measurement region AM2, a third measurement region AM3, a fourth measurement region AM4, and a fifth measurement region AM5 are set in each of the first region A1, second region A2, third region A3, fourth region A4, and fifth region A5 shown in FIG. 5, respectively, and a retardation map is obtained for each measurement region. Specifically, the first measurement region AM1 is positioned so that the center position of the first region A1 in the height direction (vertical direction on the paper) coincides with the center position of the first measurement region AM1 in the height direction. The distance between the left edge of the first measurement region AM1 and the left edge of the first region A1 in the width direction (horizontal direction on the paper) is 6 mm. The retardation map is obtained using the following procedure.

[0026] A birefringence microscope (Photonic Lattice, PA-110-S) was used to obtain the retardation map. The birefringence microscope had a resolution of 8 μm in the planar direction, and the reproducibility (standard deviation of retardation) during repeated measurements was less than 1 nm, with a retardation measurement range of 0 to 130 nm. The measurement wavelength was 520 nm. The retardation map was obtained by setting the center position of each measurement area (first measurement area AM1 to fifth measurement area AM5) at the center of the field of view of the birefringence microscope, and then performing the measurement. The measurement range was 4.3 mm vertically and 7 mm horizontally, and the range was divided into 538 × 875 measurement pixels. In other words, retardation measurements were performed at 470,750 locations (470,750 pixels) within the measurement range. By the above measurement, the direction of the fast axis and the magnitude of retardation (unit: nm) are retained for each measurement pixel in the measurement range, and a retardation map is obtained that visualizes the retardation distribution in the measurement range. Note that the measurement range may be appropriately adjusted depending on the thickness of the glass substrate to be measured. For example, the vertical length of the measurement range may be set to a length that is 1.0 mm less than the thickness of the glass substrate to be measured.

[0027] Here, requirement 1 satisfies requirements A and B in the second region A2, the third region A3, and the fourth region A4. Requirement A is as described above. Requirement A is analyzed using the following procedure. First, in the retardation map of each region obtained by the above procedure, measurement pixels whose fast axis direction is 40 to 75 degrees relative to the first principal surface 12 of the glass substrate 10 (the horizontal direction in FIG. 5 ) are extracted. Note that the angle of the fast axis direction is expressed as a positive value when the direction rotates counterclockwise relative to the first principal surface 12 of the glass substrate 10 (the horizontal direction in FIG. 5 ), and the angle of the fast axis direction takes a value greater than or equal to 0 degrees and less than 180 degrees. Next, the retardation values ​​of each extracted measurement pixel are arithmetically averaged, and this value is divided by the thickness (unit: cm) of the retardation observation samples 201 to 205, which was previously measured, to obtain an average value Re1. Requirement A requires that the average value Re1 be 2.00 nm / cm or less.

[0028] For requirement B, the average value Re2 is obtained by extracting and analyzing measurement pixels whose fast axis direction is 105 to 140° with respect to the first main surface 12 of the glass substrate 10 (the left-right direction on the paper surface of FIG. 5) in the same manner as requirement A. Requirement B requires that the average value Re2 be 2.00 nm / cm or less.

[0029] In requirement A, the value of the average value Re1 is preferably 1.90 nm / cm or less, and more preferably 1.80 nm / cm or less. There is no particular lower limit for the average value Re1, but it is often 0.50 nm / cm or more. In requirement B, the value of the average value Re2 is preferably 1.90 nm / cm or less, and more preferably 1.80 nm / cm or less. There is no particular lower limit for the average value Re2, but it is often 0.50 nm / cm or more. When the values ​​of the average values ​​Re1 and Re2 are within the above preferred ranges, |Δσ| / |σ, which will be described in detail later, can be obtained. ａｄｄ This is preferable because it means that the value of | approaches 1 and the accuracy of mask pattern correction is likely to be high.

[0030] [Requirement 2] In the first embodiment of the present glass substrate, the above-mentioned Requirement 1 is satisfied, but it is also preferable that the following Requirement 2 is satisfied. Requirement 2: The first, second, third, fourth, and fifth regions in Requirement 1 satisfy the above-mentioned Requirement A and Requirement B. That is, it is preferable that the first region A1 to the fifth region A5 described in FIG. 5 satisfy the above-mentioned Requirement A and Requirement B. Furthermore, in Requirement 2, it is also preferable that the first, second, third, fourth, and fifth regions in Requirement 1 satisfy the preferred ranges of Requirement A and Requirement B.

[0031] [Requirements C and D] In addition, it is also preferable that the first embodiment of the glass substrate satisfy the following requirements C and D for the second, third, and fourth regions of requirement 1. Requirement C: When a cumulative distribution of retardation values ​​of measurement pixels whose fast axis directions are 40 to 75° with respect to the first principal surface is created in the retardation map, the retardation value Re3 of cumulative 95% of the measurement pixels is 4.00 nm / cm or less. Requirement D: When a cumulative distribution of retardation values ​​of measurement pixels whose fast axis directions are 105 to 140° with respect to the first principal surface is created in the retardation map, the retardation value Re4 of cumulative 95% of the measurement pixels is 4.00 nm / cm or less. Note that the cumulative distribution in requirement C refers to a cumulative distribution obtained from a frequency distribution obtained for the retardation values ​​of measurement pixels whose fast axis directions are 40 to 75° with respect to the first principal surface. The cumulative distribution in the above requirement D refers to a cumulative distribution obtained from a frequency distribution obtained for retardation values ​​of measurement pixels whose fast axis directions are 105 to 140° with respect to the first principal surface.

[0032] Requirement C is analyzed using the following procedure. First, a retardation map is obtained in the same manner as requirement A, and measurement pixels whose fast axis directions are at 40 to 75° with respect to the first main surface 12 of the glass substrate 10 (the left-right direction in the plane of FIG. 5 ) are extracted. Next, a cumulative distribution of the retardation values ​​of the extracted measurement pixels is created. That is, the extracted measurement pixels are sorted in ascending order of retardation value. Next, the retardation values ​​of the cumulative 95% of the measurement pixels in the obtained cumulative distribution are obtained. That is, the extracted measurement pixels are sorted in descending order of retardation value, and when the number of extracted measurement pixels is 100%, the retardation values ​​of the measurement pixels corresponding to the smallest 95% are obtained. The retardation value is divided by the plate thickness (unit: cm) of the retardation observation samples 201 to 205 to obtain a value (value Re3). Requirement C requires that the value Re3 be 4.00 nm / cm or less. If there is no value that is exactly 95% of the cumulative value, the retardation value of the measurement pixel that is closest to 95% of the cumulative value is used as the retardation value of the measurement pixel that is 95% of the cumulative value.

[0033] For requirement D, measurement pixels whose fast axis direction is 105 to 140° with respect to the first main surface 12 of the glass substrate 10 (the left-right direction on the paper in FIG. 5 ) are extracted and analyzed to obtain the value Re4 in the same manner as requirement C. Requirement D requires that the value Re4 be 4.00 nm / cm or less.

[0034] In requirement C, the value Re3 is preferably 3.90 nm / cm or less, and more preferably 3.80 nm / cm or less. The lower limit of the value Re3 is not particularly limited, but is often, for example, 1.00 nm / cm or more. In requirement D, the value Re4 is preferably 3.90 nm / cm or less, and more preferably 3.80 nm / cm or less. The lower limit of the value Re4 is not particularly limited, but is often, for example, 1.00 nm / cm or more. When the values ​​Re3 and Re4 are in the above-mentioned preferred ranges, |Δσ| / |σ, which will be described in detail later, will be used. ａｄｄ This is preferable because it means that the value of | approaches 1 and the accuracy of mask pattern correction is likely to be high.

[0035] Furthermore, it is also preferable that the first and fifth regions of requirement 1 satisfy requirements C and D. That is, it is also preferable that the first to fifth regions of requirement 1 satisfy requirements C and D. It is also preferable that the first, second, third, fourth, and fifth regions of requirement 1 satisfy the preferred ranges of requirements C and D.

[0036] [Requirement E] In addition, it is also preferable that the first embodiment of the present glass substrate satisfies the following requirement E for the second region, the third region, and the fourth region in requirement 1. Requirement E: In the retardation map, the average value Re5 of the retardation of measurement pixels whose fast axis directions are at least 0° and less than 180° with respect to the first principal surface is 2.40 nm / cm or less.

[0037] Requirement E is analyzed using the following procedure. First, a retardation map is obtained in the same manner as requirement A. Next, the retardation values ​​of each measurement pixel in the retardation map are arithmetically averaged, and this value is divided by the plate thickness (unit: cm) of the retardation observation samples 201 to 205 to obtain the average value Re5. Requirement E requires that the average value Re5 be 2.40 nm / cm or less. The average value Re5 is preferably 2.30 nm / cm or less, and more preferably 2.20 nm / cm or less. There is no particular lower limit for the average value Re5, but it can be 0.50 nm / cm or more, and 1.00 nm / cm or more is preferred.

[0038] Furthermore, it is also preferable that the first and fifth regions of the requirement 1 satisfy the requirement E. In other words, it is also preferable that the first to fifth regions of the requirement 1 satisfy the requirement E.

[0039] [Requirement F] Furthermore, in the first embodiment of the glass substrate, it is also preferable that the first region and the fifth region in Requirement 1 satisfy the following Requirement F. Requirement F: In the retardation map, the main fast axis direction of the first region and the main fast axis direction of the fifth region satisfy any one of the following Requirements F1 to F4. Requirement F1: The main fast axis direction in the first region is at an angle of more than 0° and not more than 45° with respect to the first main surface, and the main fast axis direction in the fifth region is at an angle of 135° or more and less than 180° with respect to the first main surface. Requirement F2: The main fast axis direction in the first region is at an angle of 135° or more and less than 180° with respect to the first main surface, and the main fast axis direction in the fifth region is at an angle of more than 0° and not more than 45° with respect to the first main surface. Requirement F3: The angle of the main fast axis in the first region is greater than 0° and less than 45° relative to the first principal surface, and the angle of the main fast axis in the fifth region is greater than 0° and less than 45° relative to the first principal surface. Requirement F4: The angle of the main fast axis in the first region is greater than 135° and less than 180° relative to the first principal surface, and the angle of the main fast axis in the fifth region is greater than 135° and less than 180° relative to the first principal surface.

[0040] In the above requirement F, the main direction of the fast axis is defined as follows. First, the retardation value of each measurement pixel in the obtained retardation map is plotted against the angle in the fast axis direction. Here, a cumulative distribution is created for each retardation value within the range of 0° to 1°, the range of 1° to 2°, ..., the range of 178° to 179°, and the range of 179° to 180°, in 1° increments, for each angle range. Next, the retardation value at 90% of the cumulative distribution created within each of the above angle ranges is obtained and plotted as a representative value for each of the above angle ranges. Note that when plotting the representative value, half the value of each of the above angle ranges (specifically, 0.5°, 1.5°, ..., 178.5°, 179.5°) is plotted. In the plot of the representative values ​​obtained as described above, the angle having the maximum value in the range of 0° to 45° or 135° to 180° is determined to be the main direction of the fast axis.

[0041] In requirement F1, it is preferable that the main direction of the fast axis in the first region is greater than 0° and less than 30°, and that the main direction of the fast axis in the fifth region is greater than 150° and less than 180°. Furthermore, in requirement F1, it is more preferable that the main direction of the fast axis in the first region is greater than 0° and less than 15°, and that the main direction of the fast axis in the fifth region is greater than 165° and less than 180°. In requirement F2, it is preferable that the main direction of the fast axis in the first region is greater than 150° and less than 180°, and that the main direction of the fast axis in the fifth region is greater than 0° and less than 30°. Furthermore, in requirement F2, it is more preferable that the main direction of the fast axis in the first region is greater than 165° and less than 180°, and that the main direction of the fast axis in the fifth region is greater than 0° and less than 15°. In requirement F3, it is preferable that the main direction of the fast axis in the first region is greater than 0° and less than 30°, and that the main direction of the fast axis in the fifth region is greater than 0° and less than 30°. Furthermore, in requirement F3, it is more preferable that the main direction of the fast axis in the first region is greater than 0° and less than 15°, and that the main direction of the fast axis in the fifth region is greater than 0° and less than 15°. In requirement F4, it is preferable that the main direction of the fast axis in the first region is greater than 150° and less than 180°, and that the main direction of the fast axis in the fifth region is greater than 150° and less than 180°. Furthermore, in requirement F3, it is more preferable that the main direction of the fast axis in the first region is greater than 165° and less than 180°, and that the main direction of the fast axis in the fifth region is greater than 165° and less than 180°.

[0042] Regarding requirement F, requirement F1 may be satisfied, requirement F2 may be satisfied, requirement F3 may be satisfied, or requirement F4 may be satisfied, but it is preferable to satisfy requirement F1 or requirement F2.

[0043] [Requirement G] In the first embodiment of the glass substrate, it is also preferable that each of the first to fifth regions in Requirement 1 satisfy the following Requirement G. Requirement G: Any one or more of the principal directions of the fast axes in each of the first, second, third, fourth, and fifth regions in Requirement 1 is at an angle greater than 0° and less than 45° with respect to the first main surface, and any one or more of the principal directions of the fast axes in each of the first, second, third, fourth, and fifth regions in Requirement 1 is at an angle greater than 135° and less than 180° with respect to the first main surface. The principal directions of the fast axes in each region in Requirement G are determined in the same manner as in Requirement F.

[0044] In requirement G, it is preferable that any one or more of the principal directions of the fast axes in each of the first, second, third, fourth, and fifth regions be inclined more than 0° and less than 30° with respect to the first principal surface, and that any one or more of the principal directions of the fast axes in each of the first, second, third, fourth, and fifth regions be inclined more than 150° and less than 180° with respect to the first principal surface. Also, in requirement G, it is preferable that any one or more of the principal directions of the fast axes in each of the first, second, third, fourth, and fifth regions be inclined more than 0° and less than 15° with respect to the first principal surface, and that any one or more of the principal directions of the fast axes in each of the first, second, third, fourth, and fifth regions be inclined more than 165° and less than 180° with respect to the first principal surface.

[0045] [Requirement H] In the first embodiment of the present glass substrate, it is also preferable that each of the second to fourth regions in Requirement 1 satisfy the following Requirement H. Requirement H: The principal direction of the fast axis in each of the second, third, and fourth regions in Requirement 1 is greater than 0° and less than 30°, or greater than 150° and less than 180°, relative to the first principal surface. The principal direction of the fast axis in each region in Requirement H is determined in the same manner as in Requirement F.

[0046] In requirement H, it is preferable that the principal direction of the fast axis in each of the second, third, and fourth regions be greater than 0° and less than 15°, or greater than 165° and less than 180°, with respect to the first principal surface. Furthermore, in requirement H, it is more preferable that the principal direction of the fast axis in each of the second, third, and fourth regions be greater than 0° and less than 10°, or greater than 170° and less than 180°, with respect to the first principal surface. Furthermore, in requirement H, it is even more preferable that the principal direction of the fast axis in each of the second, third, and fourth regions be greater than 0° and less than 5°, or greater than 175° and less than 180°, with respect to the first principal surface.

[0047] The first embodiment of the present glass substrate may satisfy requirement H as well as either or both of requirement F and requirement G.

[0048] [Requirement I] In the first embodiment of the glass substrate, it is also preferable that each of the first to fifth regions in Requirement 1 satisfies the following Requirement I. Requirement I: The principal direction of the fast axis in each of the first, second, third, fourth, and fifth regions in Requirement 1 is greater than 0° and less than 30°, or greater than 150° and less than 180°, relative to the first principal surface. The principal direction of the fast axis in each region in Requirement I is determined in the same manner as in Requirement F.

[0049] In requirement I, it is preferable that the principal direction of the fast axis in each of the first, second, third, fourth, and fifth regions be more than 0° and less than 15°, or 165° or more and less than 180°, with respect to the first principal surface. Furthermore, in requirement I, it is more preferable that the principal direction of the fast axis in each of the first, second, third, fourth, and fifth regions be more than 0° and less than 10°, or 170° or more and less than 180°, with respect to the first principal surface.

[0050] The first embodiment of the glass substrate may satisfy requirement I and also either or both of requirement F and requirement G. Furthermore, the first embodiment of the glass substrate may satisfy requirement I and also requirement H.

[0051] [Other Requirements] The first embodiment of the present glass substrate may satisfy other requirements than those described above. Hereinafter, the requirements that the first embodiment of the present glass substrate may satisfy will be described.

[0052] In the first embodiment of the glass substrate, for the retardation maps measured in the second, third, and fourth regions of requirement 1, the standard deviation of the retardation values ​​of each measured pixel is preferably 2.00 nm / cm or less, more preferably 1.50 nm / cm or less, and even more preferably 1.30 nm / cm or less. The standard deviation of the retardation values ​​of each measured pixel is often 0.10 nm / cm or more, and preferably 0.50 nm / cm or more. Furthermore, in the first embodiment of the glass substrate, for the retardation maps measured in the first and fifth regions of requirement 1, the standard deviation of the retardation values ​​of each measured pixel is preferably within the above-mentioned range.

[0053] In the first embodiment of the glass substrate, for the retardation maps measured in the second, third, and fourth regions of requirement 1, the root mean square (RMS) of the retardation values ​​of each measured pixel is preferably 3.30 nm / cm or less, more preferably 3.00 nm / cm or less, and even more preferably 2.70 nm / cm or less. Furthermore, the RMS of the retardation values ​​of each measured pixel is often 0.50 nm / cm or more, and preferably 1.00 nm / cm or more. Furthermore, in the first embodiment of the glass substrate, for the retardation maps measured in the first and fifth regions of requirement 1, it is also preferable that the RMS of the retardation values ​​of each measured pixel be within the above-mentioned range.

[0054] [Shape] The shape of the first embodiment of the glass substrate is not limited to the embodiment (glass substrate 10) described in FIGS. 1 and 2 and can be modified in various ways. In the first embodiment of the glass substrate, the length of the first side S1 and the length of the second side S2 in FIG. 2 may be different from those described in FIGS. 1 and 2 . For example, the length of the first side S1 and the length of the second side S2 may each be 3 inches (76.2 mm) to 18 inches (457.2 mm). Furthermore, the shape of the first embodiment of the glass substrate may be rectangular when viewed from the normal direction of the first main surface 12 shown in FIG. 1 . The thickness of the first embodiment of the glass substrate is also not limited to the embodiment described in FIGS. 1 and 2 and can be modified as appropriate. For example, the thickness of the first embodiment of the glass substrate may be 0.2 inches (5.08 mm) to 0.5 inches (12.7 mm). Furthermore, each side of the first embodiment of the glass substrate may be chamfered.

[0055] [Composition] The material constituting the first embodiment of the present glass substrate is silicon dioxide (SiO ２ The material constituting the first embodiment of the present glass substrate preferably contains SiO ２ In addition to the above, it is preferable to contain other components, such as titanium dioxide (TiO ２ That is, the material constituting the first embodiment of the present glass substrate preferably contains SiO ２ -TiO ２ It is preferable that the material constituting the first embodiment of the glass substrate is SiO ２ -TiO ２ In the case of a SiO ２ and TiO ２ It may contain trace components other than SiO. ２ -TiO ２ When producing a glass containing fluorine-containing compounds, the above-mentioned requirement 1 is often not satisfied. However, the production method described below makes it easy to produce a glass that satisfies the above-mentioned requirement 1.

[0056] Furthermore, it is also preferable that the materials constituting the first embodiment of the present glass substrate contain a small amount of water. The amount of water contained in the first embodiment of the present glass substrate can be measured using a known method. For example, measurement is performed using an infrared spectrophotometer, and the water content can be determined from the absorption peak at a wavelength of 2.7 μm (see J.P. Williams et al., American Ceramic Society Bulletin, 55(5), 524, 1976). The detection limit by this method is 0.1 ppm. The water content in the materials constituting the first embodiment of the present glass substrate is preferably 1,000 mass ppm or less, more preferably 600 mass ppm or less, relative to the total mass of the materials constituting the glass substrate. The lower limit of the water content is not particularly limited, but is preferably 50 mass ppm or more, more preferably 100 mass ppm or more.

[0057] The Young's modulus of the obtained glass substrate of the first embodiment is preferably 65 GPa or more.

[0058] [Manufacturing Method] The first embodiment of the glass substrate is preferably manufactured by a soot method. ２ -TiO ２ A method for manufacturing the first embodiment of the present glass substrate, which is a SiO based glass, will be described. ２ -TiO ２ The method for producing the SiO-based glass is as follows: first, a Si precursor and a Ti precursor are decomposed to obtain SiO ２ -TiO ２ The SiO-based glass particles are deposited on the substrate and grown. ２ -TiO ２ A porous SiO2-based glass body is obtained. ２ -TiO ２ The porous glass body is heated to form a transparent SiO ２ -TiO ２ After that, transparent SiO ２ -TiO ２ The SiO-based glass is heated and shaped, and then heat-treated to form the SiO ２ -TiO ２ The resulting SiO2-based glass block is ２ -TiO２ A plate-shaped piece was cut out from the glass block, and SiO ２ -TiO ２ The glass substrate is made of a glass of the present invention. Details and preferable conditions are explained below.

[0059] SiO obtained by decomposing Si precursor and Ti precursor ２ -TiO ２ As a method for depositing SiO-based glass particles on a substrate, for example, a method in which a Si precursor and a Ti precursor are introduced into a flame and subjected to flame hydrolysis is mentioned. As a substrate, for example, a seed rod made of quartz glass is mentioned. ２ -TiO ２ The Si precursor used to obtain the porous glass body is preferably a gasifiable raw material, for example, SiCl ４ , SiHCl ３ , SiH ２ Cl ２ , SiH ３ Chlorides such as Cl, SiF ４ , SiHF ３ , SiH ２ F ２ Fluorides such as SiBr ４ , SiHBr ３ bromides such as SiI ４ silicon halide compounds such as iodides, ｎ Si(OR) ４－ｎ (wherein R is an alkyl group having 1 to 4 carbon atoms, and n is an integer of 0 to 3). The Ti precursor is preferably a gasifiable raw material, for example, TiCl ４ , TiBr ４ titanium halide compounds such as R ｎ Ti(OR) ４－ｎ (wherein R is an alkyl group having 1 to 4 carbon atoms, and n is an integer of 0 to 3). Furthermore, as the Si precursor and Ti precursor, compounds of Si and Ti, such as silicon titanium double alkoxide, can also be used.

[0060] SiO ２ -TiO ２The method for depositing the silicon-based glass particles on the substrate involves introducing the gasified silicon precursor and titanium precursor into the flame of a burner, and subjecting the silicon precursor and titanium precursor to flame hydrolysis to form SiO. ２ -TiO ２ In one example, a multi-tube burner is used as a burner, hydrogen gas and oxygen gas are supplied to the multi-tube burner to generate an oxyhydrogen flame, and the Si precursor and Ti precursor are supplied into the generated oxyhydrogen flame. ２ -TiO ２ When depositing the glass particles, it is preferable to deposit them while rotating the substrate (for example, the seed rod).

[0061] While rotating the substrate, SiO ２ -TiO ２ When depositing the SiO-based glass particles, ２ -TiO ２ The SiO2-based glass particles are supplied along the direction of the flame of the burner. ２ -TiO ２ 6 is a cross-sectional view showing the positional relationship when depositing SiO-based glass particles. ２ -TiO ２ The SiO-based glass particles are deposited on the surface of the substrate 30. ２ -TiO ２ The glass particles are generated by the flame FL of the burner 32 and are supplied toward the substrate 30 along the flame radiation axis BA. ２ -TiO ２Consider an imaginary plane VS that is in contact with the surface (the surface on which the SiO 2 -based glass particles are deposited) and is perpendicular to the rotation center axis SA of the substrate 30. The imaginary plane VS has a point P1 that is an intersection with the rotation center axis SA of the substrate 30. Furthermore, consider a point P2 that is an intersection with the imaginary plane VS and the flame emission axis BA of the burner 32. Here, the distance d1 between points P1 and P2 on the imaginary plane VS is preferably 5 mm or more, and more preferably 8 mm or more, in order to more easily obtain the first embodiment of the present glass substrate. Furthermore, the distance d1 is determined by the SiO 2 -based glass particles deposited on the surface of the substrate 30. ２ -TiO ２ In order to make it more difficult for cavities to form in the porous glass body, the length is preferably 20 mm or less, and more preferably 15 mm or less. The angle θ between the flame radiation axis BA and the rotation center axis SA is preferably 3 to 15°. The distance d2 from the tip of the burner 32 to the point P2 is preferably 150 to 250 mm. The diameter of the burner 32 is preferably φ50 to 100 mm.

[0062] SiO obtained by the above method ２ -TiO ２ The porous glass body is heated to a densification temperature under reduced pressure or in a helium atmosphere, and SiO ２ -TiO ２ The densification temperature is usually 1,250 to 1,550°C, preferably 1,300 to 1,500°C. In this specification, the densification temperature is the temperature at which SiO is dissolved until voids can no longer be confirmed with an optical microscope. ２ -TiO ２ The temperature at which the SiO2-based porous glass body can be densified is referred to as the temperature at which the SiO2-based porous glass body obtained by the above method can be densified. ２ -TiO ２ The dense body is further heated to form transparent SiO ２ -TiO ２ That is, by heating, SiO ２ -TiO ２ The dense body is made transparent. ２ -TiO ２ Making the dense body transparent means making it into a transparent glass state where crystals cannot be seen under an optical microscope. ２ -TiO ２The temperature at which the dense body becomes transparent is preferably 1,500 to 1,750°C, more preferably 1,550 to 1,700°C. ２ -TiO ２ The atmosphere in which the glass porous body is heated is preferably an atmosphere of 100% inert gas such as helium gas, or an atmosphere containing an inert gas such as helium as the main component. The atmospheric pressure is preferably reduced pressure or atmospheric pressure. In particular, when the atmospheric pressure is atmospheric pressure, helium gas is preferably used. Furthermore, when the atmospheric pressure is reduced pressure, an absolute pressure of 13,000 Pa or less is preferred.

[0063] Next, the transparent SiO obtained by the above method ２ -TiO ２ The SiO-based glass is heated and shaped, and then heat-treated to form the SiO ２ -TiO ２ The heating temperature during molding is SiO ２ -TiO ２ The heating temperature is preferably equal to or higher than the softening point of the glass-based glass. Specifically, the heating temperature during molding is preferably 1,500 to 1,800°C. When carrying out the heating, the rate of temperature rise from 1,100 to 1,500°C is preferably 0.5°C / min or higher, more preferably 1°C / min or higher, and even more preferably 2°C / min or higher, in order to more easily obtain the first embodiment of the present glass substrate. Furthermore, when carrying out the heating, it is preferable to carry out heating at 1,600°C or higher, and more preferably to carry out heating at 1,650°C or higher. When heating from 1,500°C to the above temperature (for example, 1,650°C), the rate of temperature rise is preferably less than 15°C / min, in order to more easily obtain the first embodiment of the present glass substrate. Transparent SiO ２ -TiO ２ When the glass is heated and molded, a transparent SiO ２ -TiO ２ The molding process is preferably carried out by placing a glass frame made of, for example, carbon.

[0064] Transparent SiO ２ -TiO ２After the glass is heated and shaped, it is preferably subjected to a slow cooling treatment. The slow cooling treatment is preferably performed by maintaining the temperature in the range of 600 to 1,200°C for 5 hours or more, and then lowering the temperature to 500°C or less at a rate of 10°C / hour or less. The slow cooling treatment is preferably performed in an atmosphere containing 100% inert gas such as helium gas, argon gas, or nitrogen gas, or in an atmosphere containing these inert gases as the main component. The atmospheric pressure is preferably reduced or normal pressure. When the atmospheric pressure is reduced, an absolute pressure of 13,000 Pa or less is preferred.

[0065] By the above-described process, SiO ２ -TiO ２ The resulting molded body is then ground to remove SiO ２ -TiO ２ Furthermore, the obtained SiO ２ -TiO ２ A glass plate of a desired shape is cut out from the SiO-based glass block to obtain the first embodiment of the present glass substrate. ２ -TiO ２ The size of the SiO-based glass molded body is preferably adjusted according to the size of the glass substrate to be cut out. ２ -TiO ２ The SiO-based glass molded body is preferably at least 20 mm larger than the size of the present glass substrate to be cut out, and may be at least 35 mm larger. More specifically, when the size of the present glass substrate to be cut out is 153 mm in length and 153 mm in width, ２ -TiO ２ The size of the SiO-based glass molded body is preferably 173 mm or more in length and 173 mm or more in width. ２ -TiO ２ The size of the SiO-based glass molded body may be 185 mm or more in length and 185 mm or more in width. ２ -TiO ２ The size of the SiO-based glass molding can be adjusted by changing the size of the mold used during molding. ２ -TiO ２ The glass block is made of one SiO ２ -TiO２ Alternatively, the SiO-based glass molded body may be divided and each divided molded body may be ground to obtain the SiO-based glass. ２ -TiO ２ from a molded body of SiO ２ -TiO ２ When obtaining a SiO-based glass block, the first embodiment of the present glass substrate is more easily obtained. ２ -TiO ２ It is preferable to obtain the SiO2 from the center of the SiO2-based glass block. ２ -TiO ２ When cutting a glass plate from a glass block, ２ -TiO ２ It is preferable to cut out the porous glass body so that a plane parallel to the virtual plane (a plane perpendicular to the rotation center of the substrate) of the porous glass body becomes the first main surface of the first embodiment of the present glass substrate.

[0066] The above-described method makes it possible to obtain the first embodiment of the present glass substrate that satisfies Requirement 1. Furthermore, the above-described method makes it easy to obtain the first embodiment of the present glass substrate that satisfies Requirement F or Requirement G.

[0067] The cut glass substrate of the first embodiment may be processed as appropriate. For example, the first main surface may be polished to have a predetermined flatness and surface roughness.

[0068] <Second Embodiment of Glass Substrate for EUV Lithography> A second embodiment of the glass substrate for EUV lithography (the present glass substrate) of the present invention is a glass substrate for EUV lithography having a first main surface and a second main surface opposite to the first main surface, and having a first side and a second side that are adjacent to each other when viewed from the normal direction of the first main surface. Here, the second embodiment of the glass substrate is such that a retardation observation sample having a plate thickness of 1.0 mm obtained by cutting the glass substrate for EUV lithography along a first cut surface that is parallel to the first side, passes through a midpoint of the second side, and is orthogonal to the first main surface, and a second cut surface that is parallel to the first cut surface and is spaced 1.5 mm from the first cut surface, and polishing the cut surface satisfies the following requirement 3. Requirement 3: When five imaginary regions are set by equally dividing the first cross section of the retardation observation sample into five regions parallel to the first main surface of the retardation observation sample and in a direction parallel to the first cross section, and the regions are designated as a first region, a second region, a third region, a fourth region, and a fifth region from one end of the retardation observation sample, and a retardation map is obtained by collecting measurement pixels in each region, the second region, the third region, and the fourth region satisfy the following requirements C and D. Requirement C: When a cumulative distribution of retardation values ​​of measurement pixels whose fast axis directions are 40 to 75 degrees with respect to the first main surface in the retardation map is created, the retardation value Re3 of cumulative 95% of the measurement pixels is 4.00 nm / cm or less. Requirement D: When a cumulative distribution of retardation values ​​of measurement pixels whose fast axis directions are 105 to 140° with respect to the first principal surface is created in the retardation map, the retardation value Re4 of cumulative 95% of the measurement pixels is 4.00 nm / cm or less. Note that the cumulative distribution in requirement C refers to a cumulative distribution obtained from a frequency distribution obtained for retardation values ​​of measurement pixels whose fast axis directions are 40 to 75° with respect to the first principal surface. Furthermore, the cumulative distribution in requirement D refers to a cumulative distribution obtained from a frequency distribution obtained for retardation values ​​of measurement pixels whose fast axis directions are 105 to 140° with respect to the first principal surface.

[0069] In the second embodiment of the glass substrate, the accuracy of correction of a mask pattern formed on the glass substrate is increased. This is believed to be due to the following reason. When the above requirement 3 (requirements C and D) is satisfied, the maximum value of retardation in a region having a fast axis direction at approximately 45° or approximately 135° relative to the first main surface in the cross-sectional direction of the first embodiment of the glass substrate is small. That is, in the second embodiment of the glass substrate, even if retardation is present in a direction tilted from the first main surface in the cross-sectional direction, the retardation value can be said to be small. Therefore, for the same reason as in the first embodiment of the glass substrate, the accuracy of correction of a mask pattern is believed to be increased in the second embodiment of the glass substrate.

[0070] The method for measuring requirements C and D, which are satisfied by requirement 3 in the second embodiment of the glass substrate, is the same as the method for measuring requirements C and D in the first embodiment of the glass substrate, and therefore a description thereof will be omitted. Note that it is also preferable that requirements C and D are further satisfied in the first and fifth regions of requirement 3.

[0071] Furthermore, it is also preferable that the second embodiment of the glass substrate of the present invention satisfies one or more requirements selected from the group consisting of Requirement 1, Requirement 2, Requirement E, Requirement F, Requirement G, Requirement H, Requirement I, and other requirements of the first embodiment of the glass substrate of the present invention. As for other aspects of the second embodiment of the glass substrate of the present invention, such as specific aspects, preferred aspects, shape, composition, and manufacturing method, they are the same as those of the first embodiment of the glass substrate of the present invention, and therefore description thereof will be omitted.

[0072] <Mask Blank for EUV Lithography> The mask blank for EUV lithography of the present invention includes the glass substrate for EUV lithography of the present invention (the present glass substrate) described above. The configuration of the mask blank for EUV lithography of the present invention (hereinafter also referred to as the "present mask blank") may, for example, include the present glass substrate and, on the first main surface side of the present glass substrate, a multilayer reflective film, a protective film, and an absorber film, in this order from the first main surface side, and further include a conductive film on the second main surface side of the present glass substrate. The present mask blank may also be configured to include, on the second main surface side, a multilayer reflective film, a protective film, and an absorber film, in this order from the second main surface side, and further include a conductive film on the first main surface side of the present glass substrate. The configuration of the present mask blank will be described below.

[0073] [Multilayer Reflective Film] One embodiment of the mask blank has a multilayer reflective film. The multilayer reflective film is not particularly limited as long as it has the desired properties as a reflective film for an EUV mask blank. The multilayer reflective film preferably has a high reflectivity for EUV light. Specifically, when EUV light is incident on the surface of the multilayer reflective film at an incident angle of 6°, the maximum reflectivity for EUV light with a wavelength of around 13.5 nm is preferably 60% or more, more preferably 65% ​​or more. Similarly, even when a protective film is laminated on the multilayer reflective film, the maximum reflectivity for EUV light with a wavelength of around 13.5 nm is preferably 60% or more, more preferably 65% ​​or more.

[0074] Since multilayer reflective films can achieve high reflectivity for EUV light, they are typically formed by alternately stacking multiple high-refractive index layers, which exhibit a high refractive index for EUV light, and multiple low-refractive index layers, which exhibit a low refractive index for EUV light. The multilayer reflective film may be formed by stacking multiple cycles of a stack structure in which high-refractive index layers and low-refractive index layers are stacked in this order from the substrate side, or multiple cycles of a stack structure in which low-refractive index layers and high-refractive index layers are stacked in this order. The high-refractive index layer may be a layer containing Si. Examples of materials containing Si include elemental Si and Si compounds containing one or more elements selected from the group consisting of B, C, N, and O. The use of a high-refractive index layer containing Si results in a reflective mask with excellent reflectivity for EUV light. The low-refractive index layer may be a layer containing a metal selected from the group consisting of Mo, Ru, Rh, and Pt, or an alloy thereof. Si is commonly used for the high-refractive index layer, and Mo is commonly used for the low-refractive index layer. That is, Mo / Si multilayer reflective films are most common, but the multilayer reflective films are not limited to this, and Ru / Si multilayer reflective films, Mo / Be multilayer reflective films, Mo compound / Si compound multilayer reflective films, Si / Mo / Ru multilayer reflective films, Si / Mo / Ru / Mo multilayer reflective films, Si / Ru / Mo multilayer reflective films, and Si / Ru / Mo / Ru multilayer reflective films can also be used.

[0075] The thickness of each layer constituting the multilayer reflective film and the number of repeating units of the layer can be appropriately selected depending on the film material used and the reflectivity of the reflective layer required for EUV light. Taking a Mo / Si multilayer reflective film as an example, to obtain a multilayer reflective film with a maximum reflectivity of 60% or more for EUV light, it is sufficient to laminate a Mo film with a thickness of 2.3±0.1 nm and a Si film with a thickness of 4.5±0.1 nm so that the number of repeating units is 30 to 60.

[0076] Each layer constituting the multilayer reflective film can be deposited to a desired thickness using a known deposition method, such as magnetron sputtering or ion beam sputtering. For example, when fabricating a multilayer reflective film using ion beam sputtering, ion particles are supplied from an ion source to a target of a high refractive index material and a target of a low refractive index material. When the multilayer reflective film is a Mo / Si multilayer reflective film, for example, a Si target is used to first deposit a Si layer of a predetermined thickness on the glass substrate by ion beam sputtering. Then, a Mo layer of a predetermined thickness is deposited using a Mo target. This Si layer and Mo layer constitute one cycle, and 30 to 60 cycles are stacked to form the Mo / Si multilayer reflective film.

[0077] [Protective Film] One embodiment of the mask blank may have a protective film between the reflective multilayer film and the absorber film. The protective film is provided for the purpose of protecting the reflective multilayer film from damage during etching (usually a dry etching process) when a pattern is formed on the absorber film by the etching process. Examples of materials that can achieve the above purpose include materials containing at least one element selected from the group consisting of Ru and Rh. That is, the protective film preferably contains at least one element selected from the group consisting of Ru and Rh. The protective film may further contain one or more elements selected from the group consisting of Si, Ti, Nb, Ru, Ta, and Zr. Examples of materials that can achieve the above purpose include Al and nitrides containing these metals and nitrogen, and Al. ２ O ３ Other examples include:

[0078] The thickness of the protective film is not particularly limited as long as it can function as a protective film. In order to maintain the reflectivity of EUV light reflected by the multilayer reflective film, the thickness of the protective film is preferably 1 to 10 nm, more preferably 1.5 to 6 nm, and even more preferably 2 to 5 nm.

[0079] The protective film may be a film consisting of a single layer, or a multilayer film consisting of multiple layers. When the protective film is a multilayer film, each layer constituting the multilayer film is preferably made of the above-mentioned preferred material. Furthermore, when the protective film is a multilayer film, it is also preferable that the total thickness of the multilayer film is within the above-mentioned preferred range.

[0080] The protective film can be formed by a known film formation method such as magnetron sputtering, ion beam sputtering, etc. When forming a Ru film by magnetron sputtering, it is preferable to use a Ru target as the target and Ar gas as the sputtering gas.

[0081] [Absorber Film] The absorber film of one embodiment of the mask blank of the present invention is required to have a high contrast between the EUV light reflected by the multilayer reflective film and the EUV light at the absorber film when the absorber film is patterned. The patterned absorber film (absorber film pattern) may function as a binary mask by absorbing EUV light, or may function as a phase shift mask that reflects EUV light and interferes with the EUV light from the multilayer reflective film to generate contrast.

[0082] When the absorber film pattern is used as a binary mask, the absorber film must absorb EUV light and have low reflectance for EUV light. Specifically, when EUV light is irradiated onto the surface of the absorber film, the maximum reflectance of EUV light at a wavelength of approximately 13.5 nm is preferably 2% or less. The absorber film may contain one or more metals selected from the group consisting of Ta, Ti, Sn, and Cr, as well as one or more components selected from the group consisting of O, N, B, Hf, and H. Among these, the absorber film preferably contains Ta and N or B. The crystalline state of the absorber film is preferably amorphous. This improves the smoothness and flatness of the absorber film. Furthermore, improving the smoothness and flatness of the absorber film reduces the edge roughness of the absorber film pattern, thereby improving the dimensional accuracy of the absorber film pattern. When the absorber film pattern is used as a binary mask, the film thickness of the absorber film is preferably 40 to 70 nm, more preferably 50 to 65 nm.

[0083] When the absorber film pattern is used as a phase shift mask, the absorber film preferably has a reflectance of 2% or more for EUV light. To obtain a sufficient phase shift effect, the absorber film preferably has a reflectance of 9 to 15%. Using the absorber film as a phase shift mask improves the contrast of the optical image on the wafer and increases the exposure margin. Examples of materials for forming the phase shift mask include materials containing Ru and materials containing Ta, and the above materials may contain one or more elements selected from the group consisting of B, N, and O. When the absorber film pattern is used as a phase shift mask, the absorber film preferably has a thickness of 30 to 60 nm, more preferably 35 to 55 nm.

[0084] The absorber film may be a single layer film or a multilayer film made up of multiple films. When the absorber film is a single layer film, the number of steps in manufacturing the mask blank can be reduced, thereby improving production efficiency. When the absorber film is a multilayer film, the layer disposed on the side opposite to the protective film side of the absorber film may be an anti-reflection film used when inspecting the absorber film pattern using inspection light (e.g., wavelength 193 to 248 nm). Examples of materials that form the anti-reflection film include materials containing Ta and O.

[0085] The absorber film can be formed by a known film formation method such as magnetron sputtering, ion beam sputtering, etc. For example, when a Ta nitride film is formed as the absorber film by magnetron sputtering, the absorber film can be formed by sputtering using a Ta target and supplying a gas containing Ar gas and nitrogen gas.

[0086] [Hard Mask Film] The mask blank may have a hard mask film. The hard mask film is preferably disposed on the side opposite to the glass substrate side of the absorber film. As the hard mask film, a material having high resistance to dry etching, such as a Cr-based film or a Si-based film, is preferably used. Examples of Cr-based films include Cr, and materials containing Cr and one or more elements selected from the group consisting of O, N, C, and H. Specific examples include CrO and CrN. Examples of Si-based films include Si, and materials containing Si and one or more elements selected from the group consisting of O, N, C, and H. Specific examples include SiO ２ , SiON, SiN, SiO, Si, SiC, SiCO, SiCN, and SiCON. When a hard mask film is formed on the absorber film, dry etching can be performed even if the minimum line width of the absorber film pattern is small. Therefore, it is effective for miniaturizing the absorber film pattern.

[0087] [Conductive Film] One embodiment of the mask blank has a conductive film. By providing the conductive film, the reflective mask blank can be handled using an electrostatic chuck. The conductive film of one embodiment of the mask blank preferably has a transmittance of 1.0% or more at a predetermined wavelength of laser light. The upper limit of the transmittance is not particularly limited, but may be, for example, 30.0% or less, or may be 10.0% or less. An example of the predetermined wavelength is 632 nm.

[0088] The conductive film preferably contains one or more elements selected from the group consisting of Ta and Cr. The conductive film preferably further contains at least one element selected from the group consisting of B, N, and O. The conductive film preferably has a sheet resistance of 250 Ω / sq. or less. The conductive film preferably has a surface hardness of 10.0 GPa or more.

[0089] When the conductive film has the above transmittance at the predetermined wavelength, the mask blank is preferably applicable to a technique in which an EUV lithography mask formed using the mask blank is irradiated with laser light to correct the pattern shape of the EUV lithography mask. More specifically, laser light is irradiated from the conductive film side of the EUV lithography mask formed using the mask blank, causing local expansion inside the glass substrate, generating local stress, locally deforming the glass substrate, and moving the mask pattern in the planar direction. It is believed that the mask blank having the glass substrate is more likely to be subjected to stress as designed due to the mechanism described above, thereby increasing the accuracy of mask pattern correction.

[0090] The method for patterning the absorber film of the present mask blank to form a mask pattern is not particularly limited, and known methods can be applied. For example, a method of forming a resist pattern on the absorber film of the present mask blank and dry-etching the absorber film using the resist pattern as a mask can be used. Furthermore, when the present mask blank has a hard mask film on the side opposite to the multilayer reflective film side of the absorber film, a resist pattern is first formed on the hard mask film, and the hard mask film is etched and patterned using the resist pattern as a mask. Next, a method of etching the absorber film using the patterned hard mask film as a mask can be used.

[0091] The present invention will be described in more detail below based on examples. The materials, amounts used, ratios, treatment details, treatment procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the examples shown below. Note that Examples 1 to 4 described below are examples, and Examples 5 to 8 are comparative examples.

[0092] Example 1 [Preparation of Glass Substrate] A procedure for obtaining the glass substrate of Example 1 will be described. ２ -TiO ２ It is made of glass and SiO ２ -TiO ２The glass was obtained by the soot method. First, TiCl, a Ti precursor, was ４ and SiCl, a Si precursor ４ Next, an oxyhydrogen flame was generated from the tip of a multi-tube burner, and TiCl was poured into the oxyhydrogen flame. ４ and SiCl ４ The gasified TiCl introduced into the oxyhydrogen flame was ４ and SiCl ４ is heated and hydrolyzed to produce SiO ２ -TiO ２ Glass particles were generated. ２ -TiO ２ The glass particles were deposited on the tip of a quartz glass seed rod rotating at 25 rpm, and SiO ２ -TiO ２ A porous glass body was obtained. ２ -TiO ２ When obtaining a glass porous body, the distance between the center of the rotation axis of the seed rod and the center of the flame (the distance d1) was 10 mm. The diameter of the multi-tube burner was 90 mm, and the distance from the tip of the multi-tube burner to the surface of the seed rod was 190 mm.

[0093] The obtained SiO ２ -TiO ２ The glass porous body was maintained at 1,200°C in the air for 6 hours while still deposited on the seed rod, and then removed from the seed rod. ２ -TiO ２ The glass porous body was placed in an electric furnace capable of controlling the atmosphere, and after reducing the pressure to 10 Pa or less at room temperature, the temperature was raised to 1,360°C while maintaining the reduced pressure, and the temperature was maintained for 2 hours to form SiO ２ -TiO ２ A dense body was obtained. ２ -TiO ２ The dense body was cut off by about 50 mm from both ends in the longitudinal direction (direction of the rotation axis of the seed rod), and the outer periphery was further ground off by about 1 mm. ２ -TiO ２ The dense body was heated to 1,700°C in an argon atmosphere using a carbon furnace, and transparent SiO ２ -TiO２ A glass body was obtained.

[0094] The transparent SiO obtained by the above procedure ２ -TiO ２ The glass was placed in a carbon container and heat-treated in an argon atmosphere at 1,680°C for 280 hours. The temperature was increased at a rate of 5°C / min in the range of 1,100 to 1,500°C. The temperature was increased at a rate of 0.5°C / min in the range of 1,500 to 1,680°C. The inner bottom surface of the carbon container had a square shape with sides of 190 mm, and the height of the carbon container was approximately 1,000 mm. After the heat treatment, a SiO ２ -TiO ２ A glass molding was obtained.

[0095] The SiO ２ -TiO ２ The glass molded body was uniformly ground from the outer periphery with a surface grinding machine to obtain a SiO ２ -TiO ２ A glass block was obtained. ２ -TiO ２ The glass block was cut in a direction perpendicular to the height direction, and the cut surface was polished to obtain a glass substrate having a thickness of 0.25 inches (6.3 mm). The obtained glass substrate was subjected to a slow cooling treatment. Specifically, the glass substrate was held at 950°C for 100 hours, then cooled to 500°C at a rate of 5°C / hour, and then allowed to cool to room temperature to obtain the glass substrate of Example 1.

[0096] [Measurement] For the obtained glass substrate of Example 1, a sample for retardation observation was prepared by the above-mentioned procedure, and a retardation map was obtained for each of the first to fifth measurement regions of the first to fifth regions. The results of analyzing the obtained retardation maps are shown in Table 1 below.

[0097] <Examples 2 to 8> The glass substrates of Examples 2 to 8 were obtained in the same manner as Example 1, except that the conditions were changed as shown in Table 1 below. Differences from Example 1 when obtaining the glass substrates of each Example will be explained below. In Example 2, the heat treatment time at 1,680°C was 420 hours. In Example 3, the carbon container used had an inner bottom surface that was a square with sides of 350 mm and a height of 1,000 mm. The heat treatment time at 1,680°C was 140 hours. The obtained SiO ２ -TiO ２ The glass molded body had a length of 350 mm, a width of 350 mm, and a height of 65 mm. Grinding was performed uniformly from the outer periphery, and a SiO ２ -TiO ２ In Example 4, a glass block was obtained by the same procedure as in Example 3, except that the heat treatment time at 1680°C was changed to 420 hours. ２ -TiO ２ A glass molded body was obtained. ２ -TiO ２ The glass molded body was cut into four pieces using a band saw cutter, and SiO ２ -TiO ２ The glass was molded into a molded body. ２ -TiO ２ The glass molded body was similarly ground to obtain a SiO ２ -TiO ２ A glass block was obtained. Example 5 was the same as Example 4 except that the heat treatment time at 1680°C was 280 hours. In Example 6, the distance between the center of the rotation axis of the seed rod and the center of the flame was 0 mm. In Example 7, the temperature increase rate in the range of 1500 to 1680°C was 10°C / min. In Example 8, the temperature increase rate in the range of 1100 to 1500°C was 0.5°C / min.

[0098] <Prediction of Misalignment in Repair> A mask pattern was formed using each glass substrate as a glass substrate for EUV lithography, and the repair accuracy when repairing the mask pattern by irradiating it with laser light was evaluated in the following manner. Specifically, the amount of misalignment during pattern repair predicted from the stress field (magnitude and direction of retardation) was calculated in the following manner.

[0099] The retardation Re is the refractive index n α and the refractive index n in the slow axis direction γ The maximum principal stress σ in the plane perpendicular to the observation direction of the retardation (in the plane of the first cross section C1) is expressed as the difference between the １ and the minimum principal stress σ ２ It is known that the relationship between Re and n is expressed by the following formula (1): γ -n α = K (σ １ -σ ２ In the above formula (1), K is the photoelastic coefficient, and SiO ２ -TiO ２ In glass, the photoelastic coefficient K is estimated to be about 40 nm / cm·MPa. ２ The direction in which the retardation Re acts is usually the same as the direction of the fast axis. ２ If the value of is assumed, the maximum principal stress σ １ The value of the fast axis direction, i.e., the minimum principal stress σ ２ If the direction of action is determined, the maximum principal stress σ １ For example, in the above formula (1), σ ２ Assuming that the value of is constant at 0.052 MPa, with the tensile stress being positive, the maximum principal stress σ １ and the maximum principal stress σ １ The direction in which the force acts (principal stress direction) can be determined.

[0100] By the above method, σ １ and σ ２ and the value of σ １and σ ２ The magnitude of the stress component acting in the in-plane direction of the glass substrate is calculated as σ ｘ , and the magnitude of the stress component acting in the thickness direction of the glass substrate σ ｙ Here, a part of the glass substrate expands due to irradiation with laser light, and the stress (σ ａｄｄ ) is -0.025 MPa, then σ ａｄｄ is the above σ ｘ and σ ｙ Therefore, when a part of the glass substrate is expanded by irradiating it with laser light, the above σ ｘ , σ ｙ and σ ａｄｄ A combined stress acts on the

[0101] Based on the above combined stress, the maximum principal stress σ １ａ and the minimum principal stress σ ２ａ The magnitude and direction of the maximum principal stress σ before the laser beam irradiation can be calculated by the above procedure. １ and the minimum principal stress σ ２ The principal stress ellipse obtained from the above and the maximum principal stress σ after laser light irradiation １ａ and the minimum principal stress σ ２ａ The principal stress ellipse obtained from the above equation is obtained. It can be said that the stress acting by the irradiation of the laser light is equal to the difference between the above two principal stress ellipses. Here, it can be said that the mask pattern is corrected by moving the mask pattern in the in-plane direction of the glass substrate. In other words, the mask pattern is corrected by the stress in the in-plane direction. In this case, it can be said that, of the difference between the above two principal stress ellipses, the difference in the stress component in the in-plane direction of the glass substrate effectively acts to move the mask pattern.

[0102] The theoretical stress value that is thought to be generated by irradiation with laser light is defined as σ ａｄｄ and, among the differences between the two principal stress ellipses of the glass substrate, the difference in the stress component in the in-plane direction of the glass substrate is Δσ, then σ ａｄｄ The ratio of the absolute value of Δσ to the absolute value of (|Δσ| / |σａｄｄ |) can be calculated. The ratio of the absolute values ​​can be said to be an index showing the degree to which the stress generated by the irradiation of laser light acts in the in-plane direction of the glass substrate. As the ratio of the absolute values ​​approaches 1, the stress generated by the irradiation of laser light acts as designed, and the accuracy of mask pattern correction can be said to be improved. On the other hand, when the ratio of the absolute values ​​is farther from 1, the stress generated by the irradiation of laser light does not act as designed, and the accuracy of mask pattern correction is difficult to improve. Figure 7 shows the ratio of the absolute values ​​(|Δσ| / |σ ａｄｄ 7 is a contour diagram in which the values ​​of |Δσ| / |σ) are plotted in gray scale with the fast axis direction as the horizontal axis and the magnitude of retardation Re as the vertical axis. ａｄｄ 7 is a plot of the values ​​of |Δσ| / |σ calculated at predetermined intervals. As can be seen from FIG. 7, when the magnitude of retardation Re is small in the fast axis direction ranges of 40 to 75° and 105 to 140°, the ratio of the absolute values ​​(|Δσ| / |σ ａｄｄ |) tends to be large, and the accuracy of mask pattern correction tends to improve.

[0103] The ratio of the absolute values ​​(|Δσ| / |σ ａｄｄ |) can be calculated from the fast axis direction and the magnitude of retardation Re, as described above. Therefore, by preparing a sample for retardation observation according to the above-described procedure, obtaining retardation maps for the first to fifth regions, and performing analysis of the above-described requirements E and F to calculate the average value Re5, which is the average value of retardation, and the main direction of the fast axis, the ratio of the absolute values ​​(|Δσ| / |σ ａｄｄ Therefore, the degree of correction accuracy of the mask pattern in the first to fifth regions can be calculated.

[0104] The above calculation was performed for the first to fifth regions of the glass substrate of each example. The ratio of the absolute values ​​(|Δσ| / |σ ａｄｄThe calculation results of the value of |) are shown in Table 1 below. In Table 1 below, the column "corrected deviation amount prediction" shows the ratio of absolute values ​​(|Δσ| / |σ) calculated by the above method. ａｄｄ Specifically, the value calculated from the value of 100×|1−|Δσ| / |σ is entered. ａｄｄ Enter the value calculated using || (unit: %).

[0105] <Results> Table 1 summarizes the manufacturing conditions and measurement results of the glass substrates of Examples 1 to 8. The measurement methods for each parameter of Requirements A to F in Table 1 are as described above. In Table 1, the column "Standard Deviation" indicates the standard deviation of the retardation value of each measured pixel in the retardation map. In Table 1, the column "RMS" indicates the root mean square (RMS) of the retardation value of each measured pixel in the retardation map.

[0106]

[0107] As shown in Table 1, the glass substrates of Examples 1 to 4 have average values ​​Re1 and Re2 of 2.00 nm / cm or less in the second, third, and fourth regions, respectively, and thus satisfy both Requirement A and Requirement B. That is, the glass plates of Examples 1 to 4 satisfy Requirement 1 described above. It is believed that glass substrates that satisfy Requirement 1 have higher accuracy in correcting a mask pattern formed on the glass substrate due to the mechanism described above. This can also be understood from the small values ​​listed in the "Estimated Correction Misalignment Amount" column. On the other hand, as shown in Table 1, the glass substrates of Examples 5 to 8 have at least one of the average values ​​Re1 and Re2 exceeding 2.00 nm / cm in at least one of the second, third, and fourth regions, and thus do not satisfy at least one of Requirement A and Requirement B. That is, the glass plates of Examples 5 to 8 do not satisfy Requirement 1 described above. It is believed that glass substrates that do not satisfy Requirement 1 do not have higher accuracy in correcting a mask pattern formed on the glass substrate than glass substrates that satisfy Requirement 1. This can also be understood from the fact that the values ​​shown in the "Estimated Corrected Misalignment Amount" column are larger than the values ​​for the glass substrates of Examples 1 to 4.

[0108] Furthermore, as shown in Table 1, the glass substrates of Examples 1 to 4 have retardation values ​​Re3 and Re4 of 4.00 nm / cm or less in the second, third, and fourth regions, respectively, and satisfy requirements C and D. That is, the glass plates of Examples 1 to 4 satisfy the above-mentioned requirement 3. It is believed that glass substrates that satisfy requirement 3 have high correction accuracy for mask patterns formed on the glass substrate due to the mechanism described above. This can also be understood from the small values ​​listed in the "Estimated Correction Misalignment Amount" column. On the other hand, as shown in Table 1, the glass substrates of Examples 5 to 8 have at least one of the retardation values ​​Re3 and Re4 exceeding 4.00 nm / cm in at least one of the second, third, and fourth regions, and therefore do not satisfy at least one of requirements C and D. That is, the glass plates of Examples 5 to 8 do not satisfy the above-mentioned requirement 3. It is believed that a glass substrate that does not satisfy Requirement 3 will not be able to improve the accuracy of correction of a mask pattern formed on the glass substrate compared to a glass substrate that satisfies Requirement 3. This can also be understood from the fact that the values ​​shown in the "Estimated correction deviation amount" column are larger than the values ​​for the glass substrates of Examples 1 to 4.

[0109] The entire contents of the specification, claims, drawings and abstract of Japanese Patent Application No. 2024-077171 filed on May 10, 2024 are hereby incorporated by reference as the disclosure of the present invention.

[0110] 10 Glass substrate 12 First main surface 14 Second main surface 20 Sample for observation before polishing 201 to 205 Sample for retardation observation 30 Base material 32 Burner A1 to A5 First region to fifth region AM1 to AM5 First measurement region to fifth measurement region C1 First cut surface C2 Second cut surface C1p First polished surface C2p Second polished surface FL Flame S1 First side S2 Second side

Claims

1. A glass substrate for EUV lithography having a first main surface and a second main surface opposite to the first main surface, and having a first side and a second side adjacent to each other when viewed in the normal direction of the first main surface, wherein the glass substrate for EUV lithography is cut and polished to obtain a 1.0 mm thick retardation observation sample, which satisfies Requirement 1 below. Requirement 1: The first cut surface of the retardation observation sample is equally divided into five regions, which are set in a direction parallel to the first principal surface of the retardation observation sample and parallel to the first cut surface. These regions are designated as a first region, a second region, a third region, a fourth region, and a fifth region, respectively, from one end of the retardation observation sample. When a retardation map is obtained by collecting measurement pixels in each region, the second region, the third region, and the fourth region satisfy the following requirements A and B. Requirement A: In the retardation map, the average retardation value Re1 of the measurement pixels whose fast axis direction is 40 to 75° with respect to the first principal surface is 2.00 nm / cm or less. Requirement B: In the retardation map, the average retardation value Re2 of the measurement pixels whose fast axis direction is 105 to 140° with respect to the first principal surface is 2.00 nm / cm or less.

2. The glass substrate for EUV lithography according to claim 1, which satisfies the following requirement 2: Requirement 2: The first region, the second region, the third region, the fourth region, and the fifth region in requirement 1 satisfy requirements A and B.

3. The glass substrate for EUV lithography according to claim 1 or 2, wherein the second region, the third region, and the fourth region in requirement 1 satisfy the following requirements C and D. Requirement C: When a cumulative distribution of retardation values ​​of the measurement pixels whose fast axis directions are 40 to 75 degrees with respect to the first principal surface is created in the retardation map, the retardation value Re3 of 95% of the measurement pixels is 4.00 nm / cm or less. Requirement D: When a cumulative distribution of retardation values ​​of the measurement pixels whose fast axis directions are 105 to 140 degrees with respect to the first principal surface is created in the retardation map, the retardation value Re4 of 95% of the measurement pixels is 4.00 nm / cm or less.

4. A glass substrate for EUV lithography according to claim 3, wherein the first region and the fifth region in requirement 1 further satisfy requirement C and requirement D.

5. The glass substrate for EUV lithography according to claim 1 or 2, wherein the second region, the third region, and the fourth region in requirement 1 satisfy the following requirement E: Requirement E: In the retardation map, the average value Re5 of retardation of the measurement pixels whose fast axis directions are equal to or greater than 0° and less than 180° with respect to the first principal surface is 2.40 nm / cm or less.

6. A glass substrate for EUV lithography according to claim 5, wherein the first and fifth regions of requirement 1 further satisfy requirement E.

7. A glass substrate for EUV lithography having a first main surface and a second main surface opposite to the first main surface, and having a first side and a second side adjacent to each other when viewed in the normal direction of the first main surface, wherein the glass substrate for EUV lithography is cut along a first cut surface that is parallel to the first side, passes through the midpoint of the second side, and is perpendicular to the first main surface, and a second cut surface that is parallel to the first cut surface and is 1.5 mm away from the first cut surface, and polished to obtain a retardation observation sample with a plate thickness of 1.0 mm, wherein the glass substrate for EUV lithography satisfies the following requirement 3. Requirement 3: When five imaginary regions are set by equally dividing the first cut surface of the retardation observation sample into five regions parallel to the first main surface of the retardation observation sample and in a direction parallel to the first cut surface, and the regions are designated as a first region, a second region, a third region, a fourth region, and a fifth region from one end of the retardation observation sample, and a retardation map is obtained by collecting measurement pixels in each region, the second region, the third region, and the fourth region satisfy the following requirements C and D. Requirement C: When a cumulative distribution of retardation values ​​of measurement pixels whose fast axis directions are 40 to 75 degrees with respect to the first main surface in the retardation map is created, the retardation value Re3 of cumulative 95% of the measurement pixels is 4.00 nm / cm or less. Requirement D: When a cumulative distribution of the retardation values ​​of the measurement pixels whose fast axis directions are 105 to 140° with respect to the first principal surface is created in the retardation map, the retardation value Re4 of the cumulative 95% of the measurement pixels is 4.00 nm / cm or less.

8. A glass substrate for EUV lithography according to claim 7, wherein the first region and the fifth region in requirement 3 further satisfy requirement C and requirement D.

9. The glass substrate for EUV lithography according to claim 7 or 8, wherein the second region, the third region, and the fourth region in requirement 3 satisfy the following requirement E: Requirement E: In the retardation map, the average value Re5 of retardation of the measurement pixels whose fast axis directions are equal to or greater than 0° and less than 180° with respect to the first principal surface is 2.40 nm / cm or less.

10. A glass substrate for EUV lithography according to claim 9, wherein the first and fifth regions of requirement 3 further satisfy requirement E.

11. A mask blank for EUV lithography, comprising the glass substrate for EUV lithography according to any one of claims 1, 2, 7 and 8.

12. A mask blank for EUV lithography according to claim 11, wherein an EUV lithography mask formed using the mask blank for EUV lithography is used in a technique for correcting the pattern shape of an EUV lithography mask by irradiating it with laser light.

13. A mask blank for EUV lithography according to claim 12, having a conductive film on one of the first main surface side and the second main surface side, and having a transmittance of 1.0% or more at the wavelength of the laser light.

14. A mask blank for EUV lithography according to claim 13, wherein the wavelength of the laser light is 632 nm.

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