JP2017103309A - Glass plate for imprint mold, and manufacturing method of glass plate for imprint mold - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a glass plate of an imprint mold, which is suitable for rectifying an uneven pattern.SOLUTION: A glass plate for an imprint mold, includes a non-penetration hole in a center part of one principal surface, divides the principal surface with two linear lines (X-axis and Y-axis) as a symmetric axis of the principal surface in a measurement region of an inner side of 5 mm or more from an outer peripheral edge of the principal surface and an outer side of 5 mm or more from an opening edge of the non-penetration hole into four blocks (first block to forth block), measures an angle formed by the linear line connecting a phase advance axis of double-refraction measured by vertically irradiating a light to the principal surface, a measurement point in the total blocks of the phase advance axis (±x, ±y: x and y are an optional number), and a center point of the principal surface at the measurement point in each block, and calculates a standard division σ from the angle obtained four points. An average standard deviation σcalculated by the plurality of standard divisions σ obtained by the measurement region is equal to 15° or less.SELECTED DRAWING: Figure 14

Description

  The present invention relates to a glass plate for imprint mold and a method for producing the glass plate for imprint mold.

  As an alternative technique to the photolithography method, an imprint method has attracted attention (see, for example, Patent Documents 1 and 2). The imprint method is a technique in which a transfer material is sandwiched between a mold and a substrate, and an uneven pattern of the mold is transferred to the transfer material. In the photolithography method, the resolution is limited by the wavelength of light used for exposure, but in the imprint method, a pattern can be formed according to the pattern carved in the mold, and a very fine pattern can be formed. In addition, an expensive optical system apparatus is unnecessary as compared with the photolithography method, and it can be expected to perform ultrahigh resolution lithography with a low-cost apparatus. The imprint method can be applied to the manufacture of various products such as antireflection sheets, biochips, magnetic recording media as well as semiconductor elements.

  The imprint method is expected to be developed especially for semiconductor integrated circuits. 2. Description of the Related Art In recent years, semiconductor integrated circuits have been miniaturized and integrated, and photolithography apparatuses have been improved in accuracy as a pattern transfer technique for realizing the fine processing. However, there has been a problem that the price of the apparatus becomes very high because the apparatus must be increased in size as the pattern becomes finer, and it is necessary to control the apparatus with high precision.

  On the other hand, there is an imprint method for performing a fine pattern at a low cost, and it is said that a pattern of about 10 nanometers can be transferred. The imprint method has been studied for its application to mass recording medium recording bit formation, semiconductor integrated circuit pattern formation, and the like, and is being studied for mass production.

  Here, high throughput is one of the problems in applying imprint technology to mass production. Even if the price of the imprint apparatus is low, if the throughput is low, the product cost becomes high, and a cost merit cannot be obtained as compared with a product manufactured by a conventional photolithography method.

  In the pattern transfer process, air bubbles are easily caught between the mold and the substrate. The entrained bubbles are gradually absorbed by the transfer material, and the bubbles disappear. In the transfer process, it is necessary to wait until the transfer material completely fills the space surrounded by the uneven pattern and the substrate. This is because when the transfer material is solidified with bubbles that cannot be absorbed, pattern defects are caused.

  Furthermore, as a technique for reducing the amount of entrained bubbles, a technique has been developed in which a mold having a non-through hole is transferred while being curved on the surface opposite to the pattern. In this state, the mold center and the transfer material are first contacted, and in this state, the contact area with the transfer material is gradually expanded from the mold center to the outer periphery of the mold. Can be made.

Special table 2009-536591 JP 2010-080714 A

  A glass plate is generally used for the production of an imprint mold. The glass plate has a first main surface and a second main surface. A concavo-convex pattern is formed in the central portion of the first main surface, and a non-through hole is formed in the central portion of the second main surface.

  For example, the glass plate is held by the upper chuck in a state where the first main surface faces downward and the second main surface faces upward. At this time, the second main surface is deformed following the holding surface of the chuck, and as a result, the uneven pattern on the first main surface is distorted. The distortion of the uneven pattern is corrected by clamping the outer peripheral surface of the post-chuck glass plate. Therefore, when molding a glass plate, the flatness of the glass base plate before processing has been regarded as important.

  However, even if a glass plate having a concavo-convex pattern and a non-through hole is made using a glass base plate with good flatness, the flatness of the second main surface deteriorates, and a non-uniform undulation shape appears. It was. In the glass plate in which the uneven wave shape is generated, the uneven pattern is displaced when the second main surface is chucked. The correction of the concavo-convex pattern resulting from this uneven undulation shape requires adjustment for each glass substrate and becomes complicated. On the other hand, since there is a possibility that an uncorrectable misalignment may occur, flatness as a glass plate is regarded as more important than a glass base plate.

  This invention is made | formed in view of the said subject, Comprising: It aims at provision of the glass plate for imprint molds suitable for correction of the distortion of an uneven | corrugated pattern.

In order to solve the above problems, according to one aspect of the present invention,
It has a non-through hole in the center of one main surface,
In the measurement region 5 mm or more inside from the outer peripheral edge of the main surface and 5 mm or more outside from the opening edge of the non-through hole, the two straight lines (X axis and Y axis) serving as the symmetry axes of the main surface are used. The main surface is divided into four sections (first section to fourth section), and the fast axis of birefringence measured by irradiating light perpendicular to the main surface, and the measurement points of all sections of the fast axis (± x, ± y: x and y are arbitrary numbers) and the angle formed by the straight line connecting the center point of the main surface are measured at the measurement points in the respective sections, and the obtained four angles The standard deviation σ is calculated from the standard deviation σ _ave calculated from a plurality of standard deviations σ obtained from the measurement region, and an imprint mold glass plate is provided.

  According to one aspect of the present invention, there is provided an imprint mold glass plate suitable for correcting distortion of an uneven pattern.

It is a top view of the mold produced using the glass plate by one Embodiment. It is sectional drawing of the mold along the II-II line of FIG. It is sectional drawing of the deformation | transformation state of the mold shown in FIG. It is sectional drawing of the deformation | transformation cancellation | release state of the mold shown in FIG. It is a flowchart of the manufacturing method of the glass plate by one Embodiment. It is a flowchart of the non-through-hole formation process of FIG. It is sectional drawing of the glass plate after completion of the non-through-hole formation process of FIG. It is sectional drawing of the glass plate after completion of the protrusion surface formation process of FIG. It is sectional drawing which shows the state before non-through-hole formation of the glass plate by one Embodiment. It is a top view which shows the state of the glass plate of FIG. It is sectional drawing which shows the natural state after non-through-hole formation of the glass plate by one Embodiment. It is sectional drawing which shows the restraint state by the chuck | zipper after non-through-hole formation of the glass plate by one Embodiment. It is a figure which shows an example of the relationship between the stress which acts on the measurement site | part of the birefringence of the glass plate by one Embodiment, and a fast axis. It is a figure which shows an example of the relationship between the measurement point of the birefringence of the glass plate by one Embodiment, and a fast axis. It is a figure which shows the thermal expansion coefficient distribution of the glass plate by one Embodiment. It is a diagram illustrating a TiO ₂ concentration distribution of the glass plate according to an exemplary embodiment.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. In the drawings, the same or corresponding components are denoted by the same or corresponding reference numerals, and description thereof is omitted. In this specification, the imprint mold is also simply referred to as a mold. Further, in the present specification, the plan view means that it is viewed from a direction perpendicular to the main surface.

  FIG. 1 is a plan view of a mold manufactured using a glass plate according to an embodiment. FIG. 2 is a cross-sectional view of the mold along the line II-II in FIG. FIG. 3 is a cross-sectional view of the mold shown in FIG. 2 in a deformed state. 4 is a cross-sectional view of the mold shown in FIG.

  As shown in FIG. 4, the mold 10 sandwiches the transfer material 17 between the substrate 15 and transfers the uneven pattern of the mold 10 to the transfer material 17. The concavo-convex pattern of the transfer material 17 is a inverting pattern of the mold 10.

The mold 10 is made of, for example, glass. The glass is preferably quartz glass containing 90% by mass or more of SiO ₂ . The upper limit of the SiO ₂ content in the quartz glass is 100% by mass.

  Quartz glass has higher ultraviolet transmittance than general soda lime glass. Quartz glass has a smaller coefficient of thermal expansion than ordinary soda lime glass, and its dimensional change due to temperature changes is small.

Quartz glass may contain TiO ₂ in addition to SiO ₂ . The greater the TiO ₂ content, the greater the density of OH groups on the glass surface, and the higher the affinity between the glass surface and the transfer material 17. Therefore, the disappearance time of bubbles entrained between the mold 10 and the substrate 15 can be shortened.

Quartz glass may contain 90 to 95% by mass of SiO ₂ and 5 to 10% by mass of TiO ₂ . When the TiO ₂ content is 5 to 10% by mass, the coefficient of thermal expansion near room temperature is substantially zero, and the dimensional change near room temperature hardly occurs.

Quartz glass may contain trace components other than SiO ₂ and TiO ₂ , but preferably does not contain trace components.

  As shown in FIG. 2, the mold 10 has a first main surface 11 and a second main surface 12. In a natural state where no external force is applied, the first main surface 11 and the second main surface 12 are substantially parallel.

  At the central portion of the first main surface 11, a projecting surface 13 called a mesa that is surrounded by a step and projects from the periphery is formed. In plan view, the shape of the projecting surface 13 is, for example, a rectangle as shown in FIG. An uneven pattern to be transferred to the transfer material 17 is formed on the protruding surface 13. In the plan view, the shape of the protruding surface 13 may be a circle, an ellipse, a pentagon or more polygon.

  On the other hand, a non-through hole 14 is formed at the center of the second main surface 12. The shape of the non-through hole 14 is, for example, a cylinder as shown in FIGS. The shape of the non-through hole 14 may be a truncated cone, a prism, a truncated pyramid, or the like.

  As shown in FIG. 1, the protruding surface 13 is disposed inside the opening edge 14 a of the non-through hole 14 in plan view. Further, in the plan view, the center of the protruding surface 13 and the center of the non-through hole 14 coincide with the center of the mold 10.

  As shown in FIG. 2, the portion of the mold 10 where the non-through hole 14 is formed is thinner than the peripheral portion thereof, and thus is easily bent and deformed by an external force. Therefore, as shown in FIG. 3, the projecting surface 13 can be bent and deformed convexly toward the substrate 15 around the center line of the non-through hole 14. This bending deformation is performed by, for example, pressing the outer peripheral surface of the mold 10 or the inner bottom surface of the non-through hole 14. The inner bottom surface of the non-through hole 14 may be pressed by the pressure of the gas chamber formed in the non-through hole 14.

  Next, with reference to FIGS. 3 to 4 again, an imprint method using the mold 10 having the above-described configuration will be described.

  As shown in FIG. 3, in a state where the protruding surface 13 of the mold 10 is bent and deformed convexly toward the substrate 15, the mold 10 and the substrate 15 are brought close to each other, and the liquid transfer material 17 previously applied to the substrate 15 is applied. The protruding surface 13 of the mold 10 is brought into contact with the mold 10.

  Thereafter, before the transfer material 17 is solidified, the projecting surface 13 is returned from the deformed state shown in FIG. 3 to the deformed release state shown in FIG. Thereby, the protruding surface 13 gradually comes into contact with the transfer material 17 from the central portion toward the outer peripheral portion. The gas between the mold 10 and the substrate 15 can easily escape and gas confinement can be suppressed.

  After the transfer material 17 is solidified, the transfer material 17 and the mold 10 are separated. A product constituted by the uneven layer formed by solidifying the transfer material 17 and the substrate 15 is obtained. The concavo-convex pattern of the product is a concavo-convex pattern of the mold 10 that is substantially inverted.

  FIG. 5 is a flowchart of a method of manufacturing an imprint mold glass plate according to an embodiment. FIG. 6 is a flowchart of the non-through hole forming step of FIG. FIG. 7 is a cross-sectional view of the glass plate after the non-through hole forming step of FIG. 5 is completed. FIG. 8 is a cross-sectional view of the glass plate after completion of the protruding surface forming step of FIG. In FIG. 8, an alternate long and two short dashes line shows the state of the glass plate before the start of the protruding surface forming step.

  The manufacturing method of the glass plate for imprint molds has non-through-hole formation process S11 and protrusion surface formation process S12, as shown in FIG. In FIG. 5, the protruding surface forming step S12 is performed after the non-through hole forming step S11. However, the order may be reversed, and the non-through hole forming step S11 may be performed after the protruding surface forming step S12. . Further, the protruding surface forming step S12 may be performed in the middle of the non-through hole forming step S11.

  In the non-through hole forming step S <b> 11, the non-through hole 24 is formed in the center portion of the second main surface 22 of the glass plate 20 as shown in FIG. 7. As shown in FIG. 6, the non-through hole forming step S11 includes a grinding step S13, an inner side surface polishing step S14, and an inner bottom surface polishing step S15. In FIG. 6, the inner bottom surface polishing step S15 is performed after the inner side surface polishing step S14, but the order may be reversed, and the inner side surface polishing step S14 may be performed after the inner bottom surface polishing step S15. Further, the inner surface polishing step S14 and the inner bottom surface polishing step S15 may be performed simultaneously.

  In the grinding step S13, the second main surface 22 is ground. In the inner surface polishing step S14, the inner surface of the non-through hole 24 obtained by the grinding step S13 is polished. The inner bottom surface polishing step S15 polishes the inner bottom surface of the non-through hole 24 obtained by the grinding step S13.

  In the protruding surface forming step S12, the outer periphery of the first main surface 21 of the glass plate 20 is dug down as shown in FIG. 8, and the periphery of the first main surface 21 is surrounded by a step and protrudes from the periphery. A protruding surface 23 called a mesa is formed. Etching or the like is used as a method for digging up the outer peripheral portion of the first main surface 21. Etching may be either dry etching or wet etching.

  After the projecting surface forming step S <b> 12, the first main surface 21 includes a projecting surface 23 and a peripheral surface having a step between the projecting surface 23. The peripheral surface is parallel to the protruding surface 23.

  The glass plate 20 obtained by the above manufacturing method is used as the mold 10 by forming an uneven pattern on the protruding surface 23. As a method of forming the concave / convex pattern on the protruding surface 23, for example, an etching method or the like is used. The mask pattern for etching may be produced by either an imprint method or a photolithography method.

  In the present embodiment, a step is formed on the first main surface 21 and the protruding surface 23 is formed. However, a step may not be formed on the first main surface 21. An uneven pattern may be formed at the center of the first main surface 21 without a step.

  FIG. 9 is a cross-sectional view showing a state of the glass plate before forming a non-through hole according to one embodiment. In FIG. 9, the arrow indicates the direction of the stress remaining on the glass plate. In FIG. 9, hatching is omitted for convenience. FIG. 10 is a plan view showing a state when the glass plate of FIG. 9 is viewed from the first main surface side or the second main surface side. FIG. 11 is a cross-sectional view showing a natural state after forming a non-through hole in a glass plate according to an embodiment. FIG. 12 is a cross-sectional view showing a restrained state by the chuck after the non-through hole is formed in the glass plate according to the embodiment. In FIG. 11, the bending of the glass plate is exaggerated.

  In the present embodiment, as shown in FIGS. 9A and 9B, a glass plate having a residual stress having symmetry about the center line CL in a direction orthogonal to the center line CL of the glass plate 20. 20 is used. FIG. 9A shows a state in which a tensile stress targeting the center line CL remains in a direction orthogonal to the center line CL of the glass plate 20. FIG. 9B shows a state in which compressive stress for the center line CL remains in a direction orthogonal to the center line CL of the glass plate 20. The center line CL is parallel to the thickness direction of the glass plate 20. A glass plate 20 shown in FIG. 9 has a flat first main surface 21 and a flat second main surface 22. Further, as shown in FIG. 10, the glass plate has a rotationally symmetric residual stress with the center of the first main surface 21 or the second main surface 22 as an axis.

  As shown in FIG. 11A, when the non-through hole 24 is formed at the center of the second main surface 22 having a tensile stress inside, the second main surface 22 is in a natural state without external force. 1 is convex on the side opposite to the main surface 21 (upward in FIG. 11A). On the other hand, as shown in FIG. 11B, when the non-through hole 24 is formed in the central portion of the second main surface 22 having compressive stress therein, the first main surface 21 is in a natural state without external force. Is convex on the side opposite to the second main surface 22 (convex downward in FIG. 11B). This is because the glass at the center of the second main surface 22 that restricts the outward displacement of the outer peripheral portion of the second main surface 22 disappears due to the formation of the non-through holes 24.

  Although not shown, when the shape is as shown in FIG. 11A, the second main surface 22 has a convex curved surface shape with the center point CP of the second main surface 22 at the opposite side to the first main surface 21. Become. On the other hand, if it becomes a shape like FIG.11 (b), the 1st main surface 21 will become a convex curved surface shape which makes the center point CP of the 1st main surface 21 the vertex on the opposite side to the 2nd main surface 22. FIG.

  As shown in FIG. 12A, glass is placed on the upper chuck 30 with the first main surface 21 of the glass substrate 20 shown in FIG. 11A facing down and the second main surface 22 facing up. When the plate 20 is held, the second main surface 22 is deformed following the holding surface 31 of the chuck 30. As a result, the first main surface 21 is deformed into a convex shape (convex downward in FIG. 11A) opposite to the second main surface 22, and is stretched in a direction perpendicular to the center line CL. In this state, the first main surface 21 undergoes rotationally symmetrical tensile deformation about the center point CP. On the other hand, when the glass substrate 20 shown in FIG. 11A is held by the chuck 30, it is deformed as shown in FIG. As a result, the first main surface 21 is deformed to be convex toward the second main surface 22 (convex upward in FIG. 11B) and compressed in a direction orthogonal to the center line CL. In this state, the first main surface 21 undergoes rotationally symmetrical compression deformation about the center point CP.

  The concavo-convex pattern of the projecting surface 23 that is rotationally symmetric and deformed about the center point CP can be reduced relatively easily by narrowing the outer peripheral surface of the glass plate 20. Therefore, the distortion of the uneven pattern can be corrected, and the glass plate 20 suitable for correcting the uneven pattern distortion can be obtained.

  If the second main surface 22 is a completely flat surface, it is not necessary to correct the distortion of the uneven pattern, but it is difficult to produce a completely flat surface.

  For the production of the 20 glass plates, the stress distribution of the glass plate 20 and the formation of the non-through holes 24 are used. Therefore, the processing accuracy can be reduced as compared with the case of using the rotationally symmetric curved surface processing for the production of the glass plate 20.

  By the way, the stress distribution of the glass plate 20 shows the same tendency before and after the formation of the non-through holes 24. Therefore, by examining the stress distribution of the glass plate 20 after the formation of the non-through holes 24, the tendency of the stress distribution of the glass plate 20 before the formation of the non-through holes 24 can be understood.

  The stress distribution of the glass plate 20 can be confirmed with a commercially available birefringence measuring apparatus. This is because birefringence occurs due to the stress remaining on the glass plate 20. Birefringence is caused by stress anisotropy.

  The birefringence measuring device irradiates light perpendicularly to the main surface of the glass plate 20 and detects the phase difference between two orthogonal linearly polarized waves, thereby measuring the fast axis and the retardation. The wavelength of light used for measurement is, for example, 633 nm. For example, a He—Ne laser is used as the light source, and an optical heterodyne interferometry is used as the measurement method.

  The fast axis is the axis at which light travels the fastest and has the smallest refractive index. On the other hand, the slow axis is the axis with the slowest light traveling speed and the axis with the highest refractive index. Usually, the fast axis and the slow axis are orthogonal. Retardation is the optical path difference (nm) between the fast axis and the slow axis. By dividing the retardation (nm) by the thickness (cm) of the glass plate 20, the retardation per 1 cm can be calculated.

  FIG. 13 is a diagram illustrating an example of the relationship between the stress acting on the birefringence measurement site of the glass plate and the fast axis according to one embodiment. As shown in FIG. 13, tensile stress may act in the longitudinal direction and compressive stress act in the lateral direction on the birefringence measurement site 20 </ b> S of the glass plate 20. In this case, the fast axis FA is parallel to the compressive stress and is perpendicular to the tensile stress. The anisotropy of stress is expressed by retardation. The greater the anisotropy of stress, the greater the retardation.

  FIG. 14 is a diagram illustrating an example of a relationship between a measurement point of birefringence of a glass plate and a fast axis according to an embodiment. In FIG. 14, an acute angle portion formed by the fast axis FA at the birefringence measurement point SP and the straight line SL connecting the measurement point SP and the center point CP of the second main surface 22 is defined as “θ”. The angle θ is 0 ° when the fast axis FA is parallel to the straight line SL, and 90 ° when the fast axis FA is perpendicular to the straight line SL. The angle θ formed represents the amount of rotation of the fast axis FA with respect to the straight line SL centered on the measurement point SP, and does not represent the direction of rotation. Therefore, the minimum value of the angle θ formed is 0 °, and the maximum value of the angle θ is 90 °. The measured value of the angle θ does not substantially depend on the wavelength of light used for measurement.

  In FIG. 14, the second main surface is divided into all four sections from the first section to the fourth section by X-axis and Y-axis straight lines (two straight lines serving as symmetry axes) orthogonal to each other at the center point CP. When the angle θ formed by the fast axis FA at the birefringence measurement point SP in all sections and the straight line SL connecting the measurement point SP and the center point CP of the second main surface 22 is larger than 45 °, the measurement is performed. At the point SP, it can be estimated that tensile stress remains in the direction orthogonal to the center line CL of the glass plate 20 as shown in FIG.

  Conversely, when the angle θ formed by the fast axis FA at the birefringence measurement point SP and the straight line SL connecting the measurement point SP and the center point CP of the second main surface 22 is smaller than 45 °, the measurement point SP. 9B, it can be estimated that the compressive stress remains in the direction orthogonal to the center line CL of the glass plate 20 as shown in FIG.

  For example, in the first section, the fast axis FA1 at the birefringence measurement point SP1 (coordinates: (x, y) x and y are arbitrary numbers), the measurement point SP1, and the center point CP of the second main surface 22 An angle θ1 formed by the straight line SL1 connecting the two is obtained.

  Similarly, θ2 at the birefringence measurement point SP2 (coordinates: (−x, y)) of the second section, and θ3 at the birefringence measurement point SP3 (coordinates: (−x, −y)) of the third section. And θ4 at the birefringence measurement point SP4 (coordinates: (x, -y)) of the fourth section. If the standard deviation of retardation of θ1 to θ4 is small, it can be estimated that the rotational symmetry of internal stress is good. In other words, it can be said that θ has rotational symmetry.

  The angle θ after the formation of the non-through hole 24 is measured 5 mm or more inside the outer peripheral edge 22 a of the second main surface 22 forming the non-through hole 24 and 5 mm or more outside the opening edge 24 a of the non-through hole 24. This is performed in the area (hereinafter referred to as measurement area SA). The non-through hole 24 and the vicinity thereof are easily affected by processing distortion, and are thus excluded from the measurement area SA. Further, the vicinity of the outer peripheral edge 22a of the second main surface 22 is similarly affected by the processing strain, and thus is excluded from the measurement area SA.

  The measurement point SP replaces the points obtained by dividing the measurement area SA in the X-axis direction and the Y-axis direction at intervals of 1 mm to 20 mm with coordinates. In the case of 1 mm intervals, a maximum of 143 coordinate points are formed in the X-axis direction and a maximum of 143 points in the Y-axis direction, and in the case of 20 mm intervals, a maximum of 7 points in the X-axis direction are formed. Thus, a maximum of seven coordinate points are formed. Preferably, the interval is 3 mm to 7 mm.

  The interval may be set with the center point CP as a reference, or may be set with the outer edge of the glass plate 20 as a reference, but the same number of measurement points in both the X-axis direction and the Y-axis direction across the center point CP. To be. That is, at an interval of 1 mm, the X coordinate is −72 to 72, and the Y coordinate is −72 to 72. At an interval of 20 mm, the X coordinate is −3 to 3 and the Y coordinate is −3 to 3.

In the measurement area SA of the glass plate 20, the four standard deviations σ of the angles θ1 to θ4 are obtained for each coordinate obtained by dividing the predetermined interval as described above. Then, an average value σ _ave of flatness within the measurement area SA (hereinafter, average standard deviation σ _ave ) is calculated from the obtained standard deviation σ for each coordinate. The average standard deviation σ _ave is a value obtained by dividing the average value obtained by dividing the sum of the squares of the standard deviation σ in the measurement area SA by the number of standard deviations to a power of 1/2.

In the measurement area SA of the glass plate 20, the average standard deviation σ _ave obtained from the four standard deviations of the angles θ1 to θ4 is 15 ° or less. The average standard deviation σ _ave is adopted because there are a large number of measurement points having the four standard deviations σ less than 15 ° even if there are a few measurement points having the four standard deviations σ larger than 15 °. This is because the effects described later can be obtained if it exists.

After the formation of the non-through hole 24, if the average standard deviation σ _ave of rotational symmetry is 15 ° or less in the measurement area SA, the rotational symmetry about the center point CP of the second main surface 22 in the natural state with no external force. A surface having a surface can be formed. Therefore, the glass plate 20 suitable for correcting the distortion of the uneven pattern can be obtained. After the formation of the non-through holes 24, the average standard deviation σ _ave is preferably 10 ° or less, more preferably 7 ° or less in the measurement area SA.

Similarly, before the non-through hole 24 is formed, the average standard deviation σ _ave in the measurement area SA is, for example, 15 ° or less. Prior to the formation of the non-through holes 24, the average standard deviation σ _ave in the measurement region SA is preferably 10 ° or less, more preferably 7 ° or less.

After the formation of the non-through hole 24, the maximum value Re _max of retardation Re per cm in the measurement region SA is, for example, 2 nm or more. In this case, the stress remaining on the glass plate 20 is sufficiently large. After the formation of the non-through hole 24, the maximum value Re _max of retardation Re per cm in the measurement region SA is preferably 3 nm or more, more preferably 5 nm or more. Further, after the formation of the non-through hole 24, the maximum value Re _max of retardation Re per cm in the measurement region SA is preferably 15 nm or less.

Similarly, before the formation of the non-through hole 24, the maximum value Re _max of the retardation Re per cm in the measurement region SA is, for example, 2 nm or more, preferably 3 nm or more, more preferably 5 nm or more. In addition, before the non-through hole 24 is formed, the maximum value Re _max of the retardation Re per cm in the measurement region SA is preferably 15 nm or less.

  The stress distribution shown in FIG. 9 can be realized by the thermal expansion coefficient distribution shown in FIG. 15, for example. FIG. 15 is a diagram illustrating a thermal expansion coefficient distribution of a glass plate according to an embodiment. In FIG. 15, the vertical axis represents the coefficient of thermal expansion, and the horizontal axis represents the distance from the center line CL (see FIG. 9 and the like). In FIG. 15, the closer the distance from the center line CL of the glass plate 20 is, the larger the coefficient of thermal expansion is.

  Since the glass plate 20 is molded at a temperature higher than the strain point of the glass, no stress is generated during the molding. After molding, the stress distribution shown in FIG. 9 occurs in the cooling process to room temperature. This is because the closer the distance from the center line CL of the glass plate 20 is, the greater the coefficient of thermal expansion and the greater the cooling shrinkage.

  The stress distribution shown in FIG. 9A can be realized by the thermal expansion coefficient distribution shown in FIG. FIG. 15A is a diagram showing a thermal expansion coefficient distribution of the glass plate 20 according to one embodiment. In FIG. 15A, the vertical axis represents the coefficient of thermal expansion, and the horizontal axis represents the distance from the center line CL (see FIG. 9A, etc.). In FIG. 15 (a), the closer the distance from the center line CL of the glass plate 20, the greater the coefficient of thermal expansion. Moreover, the stress distribution shown in FIG. 9B can be realized by, for example, the thermal expansion distribution shown in FIG. In FIG.15 (b), a coefficient of thermal expansion is so small that the distance from the centerline CL of the glass plate 20 is near.

  Since the glass plate 20 is molded at a temperature higher than the strain point of the glass, no stress is generated during the molding. After molding, the stress distribution shown in FIGS. 9A and 9B occurs in the cooling process to room temperature. In FIG. 9A, the closer the distance from the center line CL of the glass plate 20 is, the larger the coefficient of thermal expansion and the larger the cooling shrinkage. In FIG. 9B, the closer the distance from the center line CL of the glass plate 20, the smaller the coefficient of thermal expansion and the smaller the cooling shrinkage.

  Therefore, similarly to the angle θ, the thermal expansion coefficient is also rotationally symmetric with respect to the perpendicular to the second main surface at the center point CP in plan view (hereinafter referred to as rotational symmetry about the center point CP). It may have a coefficient of thermal expansion. In the case of the glass plate 20 subjected to the slow cooling treatment, the coefficient of thermal expansion can be converted from the glass composition, and therefore the glass composition may be measured instead of the coefficient of thermal expansion. Naturally, the coefficient of thermal expansion does not change before and after the formation of the non-through hole 24.

If the thermal expansion coefficient has rotational symmetry about the center point CP of the glass plate 20, the non-through hole 24 is formed on the second main surface of the glass plate 20 having the stress distribution shown in FIG. The first main surface can be formed into a concave shape with the center point CP as an axis in a natural state without external force. Further, when the non-through hole 24 is formed on the second main surface of the glass plate 20 having the stress distribution shown in FIG. 9B, the first main surface is convex with the center point CP as an axis in a natural state without external force. Can be formed into a shape. Therefore, the glass plate 20 suitable for correcting the distortion of the uneven pattern can be obtained. The four standard deviations σ of the thermal expansion coefficients of SP1 to SP4 are obtained for each coordinate used when measuring the angle θ. The average value σ _ave of the coefficient of thermal expansion in the measurement area SA is preferably 7 ppb / ° C. or less, more preferably 5 ppb / ° C. or less, based on the obtained standard deviation σ for each coordinate.

The thermal expansion coefficient distribution shown in FIG. 15A can be realized by the TiO ₂ concentration distribution shown in FIG. FIG. 16A is a diagram showing a TiO ₂ concentration distribution of a glass plate according to an embodiment. In FIG. 16A, the vertical axis represents the TiO ₂ concentration, and the horizontal axis represents the distance from the center line CL (see FIG. 9A, etc.). Moreover, the thermal expansion coefficient distribution shown in FIG. 15B can be realized by the TiO ₂ concentration distribution shown in FIG. 16B, for example.

Quartz glass containing TiO ₂ is produced, for example, by a VAD (Vapor-phase Axial Deposition) method. In the VAD method, silicon chloride or titanium chloride is blown together with oxygen gas or hydrogen gas from below the rotating quartz rod, and a hydrolytic reaction is caused by the flame of the gas burner. This is a method of forming a reform. The porous preform is pulled up together with the quartz rod, and is formed into a transparent mold in a baking furnace, and then molded with a mold. In the VAD method, the TiO ₂ concentration distribution can be controlled by controlling the concentration of silicon chloride and the concentration of titanium chloride. Incidentally, preparation of silica glass containing TiO ₂ is not limited to the VAD method, for example direct method may be a plasma process.

In FIG. 16A, the closer the distance from the center line CL of the glass plate 20, the lower the TiO ₂ concentration, and the higher the SiO ₂ concentration. In the case of the TiO ₂ concentration distribution shown in FIG. 16A, the thermal expansion coefficient distribution shown in FIG. 15A is obtained, and as a result, the stress distribution shown in FIG. 9A is obtained. Conversely, in FIG. 16B, the closer the distance from the center line CL of the glass plate 20, the higher the TiO ₂ concentration and the lower the SiO ₂ concentration, so the stress distribution shown in FIG. 9B. Is obtained.

Similarly to the angle θ, if the TiO ₂ concentration distribution has a rotational symmetry about the center point CP of the glass plate 20, the TiO ₂ concentration also has a rotational symmetry distribution. As a result, FIG. The stress distribution shown in a) and FIG. 10B is obtained.

If the TiO ₂ concentration distribution has rotational symmetry about the center point CP of the glass plate 20, a non-through hole 24 is formed on the second main surface of the glass plate 20 having the stress distribution shown in FIG. Then, in a natural state with no external force, the first main surface can be formed in a concave shape with the center point CP as an axis. Further, when the non-through hole 24 is formed on the second main surface of the glass plate 20 shown in FIG. 9B, the first main surface can be formed into a convex shape with the center point CP as an axis in a natural state without external force. . The four standard deviations σ of the TiO ₂ concentrations of SP1 to SP4 are obtained for each coordinate used in the measurement of the angle θ. The average value σ _ave of the TiO ₂ concentration in the measurement area SA is preferably 0.07% by mass or less, more preferably 0.04% by mass or less, from the obtained standard deviation σ for each coordinate. .

  The ratio of the rotational symmetry about the center point CP of the flatness of the second main surface is, for example, the root mean square of the flatness of the rotational symmetry component in the square value of the root mean square (RMS) of the flatness. It can be shown by the ratio of the square value of (RMS). When the ratio of rotational symmetry about the center point CP of the second main surface is high, when the first main surface is held down and the second main surface is held up by the upper chuck In addition, the uneven pattern on the first main surface can be prevented from being distorted unevenly. Therefore, the distortion of the concavo-convex pattern can be easily corrected. The proportion of rotational symmetry is preferably 60% or more, and more preferably 80% or more.

TiO ₂ —SiO ₂ glass fine particles obtained by introducing silicon tetrachloride (silica precursor) and titanium tetrachloride (titania precursor) into an oxyhydrogen flame are rotated around a shaft at a certain speed. A seed glass made of quartz glass was used as a base material, and was deposited and grown on the base material to form a porous TiO ₂ —SiO ₂ glass body. By adjusting the flow rate ratio of silicon tetrachloride and titanium tetrachloride when growing the silica / titania glass, the composition of the obtained silica / titania glass was 94 mass% for silica and 6 mass% for titania.

The obtained porous TiO ₂ —SiO ₂ glass body was heated to a temperature of about 1500 ° C. in a helium atmosphere to obtain a TiO ₂ —SiO ₂ glass ingot. Both ends in the major axis direction of the TiO ₂ —SiO ₂ glass ingot were cut by about 50 mm each, and the outer periphery was removed to a depth of about 2 to 3 mm, and unused portions were removed by grinding.

The TiO ₂ —SiO ₂ glass ingot obtained by removing the unused portion as described above was put into a carbon container having a shape of an inner bottom surface of a square having a side length of 190 mm and a height of about 1000 mm, and was placed under an argon atmosphere. And heated to a temperature of about 1750 ° C. to obtain a TiO ₂ —SiO ₂ glass molded body. This TiO ₂ —SiO ₂ glass molded body was 190 × 190 × 220 mm and weighed about 17 kg.

The obtained TiO ₂ —SiO ₂ glass molded body was heated in air to a temperature of 1100 ° C. or higher, and then annealed to lower the temperature to 700 ° C. or lower at an average temperature drop rate of 100 ° C./hr or lower. .

After removing the upper and lower surfaces and the side surfaces of the obtained molded body by about 20 mm each by grinding, slice each piece from the upper surface and the lower surface in parallel with the upper and lower surfaces to a thickness of 1.5 mm, and concentration of _two TiO ₂ A glass substrate for measurement (hereinafter referred to as a measurement substrate) was collected. The measurement substrate was mirror-polished to a thickness of 1 mm. Then, a measuring substrate central point CP2 of taken from the center point CP1 and the lower surface of the measurement substrate taken from the top surface, to measure the concentration of TiO ₂ of the respective measurement substrate, determine the concentration of TiO ₂ as a reference. A straight line connecting the center point CP1 and the center point CP2 of the measurement substrate taken from the upper surface and the lower surface is taken as the axis of the TiO ₂ —SiO ₂ glass molded body. Grinding is performed so that the axis of the molded body is a center point CP of 152 mm square, and the slice is sliced to a thickness of 7 mm.

Here, how to determine the center points CP1 and CP2 will be described. First, the point at which the diagonal lines of the measurement substrate intersect is the temporary center, the straight line on the measurement substrate passing through the temporary center is the X axis, and the TiO ₂ concentration is measured at intervals of 20 mm in the X axis direction. Then, the measurement value is plotted on a graph with the measurement position on the horizontal axis and the TiO ₂ concentration on the vertical axis, and the smooth line obtained from the measurement value is approximated by a sixth order polynomial. Next, in this approximate curve, the local maximum value or local minimum value near the temporary center is set as the center of the X axis.

Next, a straight line perpendicular to the X axis passing through the center of the X axis is taken as the Y axis, and the TiO ₂ concentration is measured at intervals of 20 mm in the Y axis direction. Then, the measurement value is plotted on a graph with the measurement position on the horizontal axis and the TiO ₂ concentration on the vertical axis, and the smooth line obtained from the measurement value is approximated by a sixth order polynomial. Next, in this approximate curve, the local maximum value or local minimum value near the temporary center is set as the center of the Y axis. The centers of the Y axes are the center points CP1 and CP2.

  After flatly polishing both the first main surface and the second main surface of the glass plate 20 formed to a thickness of 7 mm, a cylindrical non-through hole is formed in the center of the second main surface, and then the external force The shape of the second main surface in a natural state was confirmed. The quartz glass plate had a length of 152 mm, a width of 152 mm, and a thickness of 6.35 mm, and the non-through hole had a diameter of 64 mm and a depth of 5.25 mm. For the sake of convenience, no protruding surface or uneven pattern was formed at the center of the first main surface of the glass plate. The tendency of the result does not change depending on the presence or absence of the protruding surface or the uneven pattern.

In Examples 1 to 3, it is a glass plate in which the axis center of the TiO ₂ concentration distribution is aligned with the center of the glass plate. Comparative Example 1 is a glass plate manufactured by grinding the outer periphery to a uniform thickness without measuring the TiO ₂ concentration distribution.

The angle θ formed by the straight line SL and the fast axis FA in the measurement area SA and the retardation Re per cm in the measurement area SA were measured by a birefringence measuring apparatus (trade name ABR10A) manufactured by Uniopt. These measurements were performed at 5 mm pitches in the vertical and horizontal directions. Based on these measurement results, the standard deviation σ of the angle θ formed by the fast axis FA and the straight line SL at the measurement points SP1 to SP4 in all four sections in the measurement area SA was calculated at 137 points. The average standard deviation σ _ave was calculated from 137 standard deviations σ. That is, the average value of the square of the standard deviation σ was calculated by raising to the 1/2 power.

  After the formation of the non-through hole, the shape of the second main surface in a natural state with no external force was measured using FM200 manufactured by Corning Tropel.

  Of the flat component of the second main surface, the ratio of the rotationally symmetric component about the center point CP is the root mean square (RMS) of the flatness of the second main surface in the area of radius 35 mm to radius 70 mm of the second main surface. ) In the square value of the rotationally symmetric component in the square value of the root mean square (RMS). The root mean square (RMS) of the flatness of the rotationally symmetric component was calculated by performing polynomial approximation function surface fitting using the least square method.

  The test results are shown in Table 1.

  As is clear from Table 1, in Examples 1 to 3, the average standard deviation σ of the fast axes SP1 to SP4 in all four sections is 15 ° or less, so that the rotationally symmetric component about the center point CP in the natural state Was obtained, and a glass plate suitable for correcting the uneven pattern formed on the first main surface was obtained. On the other hand, in Comparative Example 1, since the average standard deviation σ of the angle θ formed by the fast axis FA and the straight line SL at the measurement points SP1 to SP4 in all four sections is larger than 15 °, the second main surface is in a natural state. The ratio of the rotationally symmetric component about the center point CP has become a low value.

  As mentioned above, although embodiment of the glass plate for imprint molds, etc. was described, the present invention is not limited to the above-mentioned embodiment etc., and within the scope of the gist of the present invention described in the claims, various modifications, Improvements are possible.

DESCRIPTION OF SYMBOLS 10 Mold 11 1st main surface 12 2nd main surface 13 Projection surface 14 Non-through-hole 15 Substrate 17 Transfer material 20 Glass plate 21 First main surface 22 Second main surface 23 Projection surface 24 Non-through-hole 24a Opening edge SA Measurement area SP Measuring point FA Phase angle θ

Claims (4)

It has a non-through hole in the center of one main surface,
In the measurement region 5 mm or more inside from the outer peripheral edge of the main surface and 5 mm or more outside from the opening edge of the non-through hole, the two straight lines (X axis and Y axis) serving as the symmetry axes of the main surface are used. The main surface is divided into four sections (first section to fourth section), and the fast axis of birefringence measured by irradiating light perpendicular to the main surface, and the measurement points of all sections of the fast axis (± x, ± y: x and y are arbitrary numbers) and the angle formed by the straight line connecting the center point of the main surface are measured at the measurement points in the respective sections, and the obtained four angles A glass sheet for imprint molds, in which a standard deviation σ is calculated from the standard deviation σ _ave calculated from a plurality of standard deviations σ obtained from the measurement region.   The glass plate for imprint molds according to claim 1, wherein a maximum value of retardation per cm measured by irradiating light having a wavelength of 633 nm perpendicular to the main surface in the measurement region is 2 nm / cm or more. . Formed of quartz glass containing TiO ₂ ;
The average value of the TiO ₂ concentration in the portion inside the opening edge of the non-through hole in plan view is smaller than the average value of the TiO ₂ concentration in the portion outside the opening edge of the non-through hole in plan view. The glass plate for imprint molds according to claim 1 or 2.   The glass plate for imprint molds of any one of Claims 1-3 which has an uneven | corrugated pattern in the center part of the main surface on the opposite side to the said main surface.

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