JP2014008555A - Polishing method of glass substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polishing method for a glass substrate, which is configured to, when polishing the glass substrate by using a double-sided polishing device, suppress adsorption of the glass substrate to an abrasive pad mounted on an upper surface plate and prevent occurrence of undulation onto a substrate surface.SOLUTION: An abrasive pad 24 mounted on upper and lower surface plates of a double-sided polishing device 10 has a degree of hardness (Shore A hardness) of 70 or less and a surface roughness (Ra) of 50 μm or less. At least one is selected out of an average opening diameter, numerical aperture per unit area, numerical aperture, opening ratio, and surface roughness for a polishing surface of a lower side abrasive pad and an upper side abrasive pad, in such a manner that a relationship shown in the following formula is satisfied by adsorption power F(N) of the polishing surface of the abrasive pad mounted on the lower surface plate 14 and a main surface of the glass substrate, and by adsorption power Fof the abrasive pad mounted on the upper surface plate 12. F>F-w×g (w is a mass (g) of the glass substrate, and g is gravity acceleration (m/s)).

Description

The present invention relates to a method for polishing a glass substrate. More specifically, the present invention relates to a method for polishing a glass substrate for use in which a PV value in a wavelength range of 100 μm to 100 mm on the polished glass substrate surface is required to be 30 nm or less.
The glass substrate polishing method of the present invention includes a reflective mask and a reflective mirror substrate used in lithography (hereinafter abbreviated as “EUVL”) using EUV (Extreme Ultra Violet) light. It is suitable for polishing a glass substrate used as a glass substrate (hereinafter abbreviated as “a glass substrate for EUVL optical base material”).
The glass substrate polishing method of the present invention includes a transparent mask base material using a KrF excimer laser (wavelength 248 nm), an ArF excimer laser (wavelength 193 nm), and an F ₂ excimer laser (wavelength 157 nm) as a light source. It can also be used for polishing.

  Conventionally, in a semiconductor manufacturing process, an exposure apparatus for manufacturing an integrated circuit by transferring a fine circuit pattern onto a wafer has been widely used. In recent years, along with the higher integration and higher functionality of semiconductor integrated circuits, the miniaturization of integrated circuits has progressed, and an optical substrate used in a photomask of an exposure apparatus to accurately form a circuit pattern on a wafer surface. The glass substrate for materials is required to have high flatness and smoothness.

  Further, in such a technical trend, a lithography technique using EUV light as a next generation exposure light source (ie, EUVL technique) is considered to be applicable over a plurality of generations of 45 nm and after, and has attracted attention. EUV light refers to light in the wavelength band of the soft X-ray region or the vacuum ultraviolet region, specifically, light having a wavelength of about 0.2 to 100 nm. At present, the use of 13.5 nm wavelength light as a lithography light source is being studied. The EUVL exposure principle is the same as that of conventional lithography in that a mask pattern is transferred using a projection optical system, but a refractive optical system is used because there is no material that transmits light in the EUV light energy region. Therefore, a reflective optical system is used, and a reflective mask or a reflective mirror is used (see Patent Document 1).

A reflective mask used for EUVL basically includes (1) a base material, (2) a reflective multilayer film formed on the base material, and (3) an absorber layer formed on the reflective multilayer film. . In the case of a reflective mirror, it is basically composed of (1) a base material and (2) a reflective multilayer film formed on the base material.
As a base material (EUVL optical base material) used for manufacturing a reflective mask or a reflective mirror, a material having a low thermal expansion coefficient is required so that distortion does not occur even under EUV light irradiation. A glass substrate (a glass substrate for EUVL optical base material) made of glass or crystallized glass has been studied. The glass substrate for EUVL optical base material is manufactured by polishing and washing these glass and crystallized glass materials with high accuracy.

  In general, a method for polishing a magnetic recording medium substrate, a semiconductor substrate, or the like to a highly smooth surface is known. For example, Patent Document 2 discloses a polishing method for finishing polishing of a memory hard disk and polishing of a substrate for a semiconductor element, etc., in which the surface roughness of the polished object is small and fine protrusions (convex defects) are reduced. And polishing with a polishing composition comprising water, an abrasive and an acid compound, having an acidic pH and an abrasive concentration of less than 10% by weight, and a polishing pad. Yes. Examples of the abrasive include aluminum oxide, silica, cerium oxide, and zirconium oxide, and examples of acids for making the pH acidic include nitric acid, sulfuric acid, hydrochloric acid, and organic acids.

The glass substrate for EUVL optical substrate is also mechanically polished with a specific polishing slurry and a polishing pad to reduce convex defects and concave defects on the substrate surface and improve the surface smoothness of the glass substrate. The method of making it is described in Patent Document 3.
It is required to reduce convex defects and concave defects on the surface of a glass substrate. When a reflective multilayer film is formed on a glass substrate surface where convex defects and concave defects exist, the periodic structure of the reflective multilayer film is disturbed, and the phase This is because defects are produced.

When mechanically polishing a glass substrate for EUVL optical base material (hereinafter sometimes simply referred to as “glass substrate”), the time required for polishing can be shortened, and the flatness of the substrate on the front and back surfaces can be secured at the same time. Double-side polishing is usually used because the deviation (TTV) can be reduced, and because non-polished surfaces need to be chucked in single-side polishing, and particle adhesion occurs on the non-polished substrate surface. A device is used (Patent Document 3).
When polishing a glass substrate using a double-side polishing apparatus, as shown in Patent Document 3, the glass substrate held by the carrier is sandwiched between an upper surface plate and a lower surface plate each having a polishing pad attached thereto, While supplying polishing liquid (polishing slurry) between the polishing pad of the upper and lower surface plates and the glass substrate, both main surfaces of the glass substrate are simultaneously polished while revolving and rotating the carrier holding the glass substrate.

When a glass substrate is polished using a double-side polishing apparatus, the glass substrate may be adsorbed to a polishing pad attached to one of the upper and lower surface plates at the end of polishing.
In general, the lower surface of the glass substrate tends to be adsorbed to the polishing pad attached to the lower surface plate by its own weight, but the upper surface of the glass substrate may be adsorbed to the polishing pad attached to the upper surface plate. In this case, the glass substrate adsorbed on the polishing pad attached to the upper surface plate may fall and be damaged.

  When performing double-sided polishing, methods of preventing the object to be adhered (adsorption) to the polishing pad attached to the upper surface plate include providing a grid-like groove on the polishing surface or rotating the polishing pad at the center of rotation. It is known to provide a plurality of grooves extending radially from (see Patent Document 4).

Japanese translation of PCT publication No. 2003-505891 JP 2003-211351 A JP 2005-59184 A JP 2009-88027 A

  However, it has been found that when a polishing pad having a groove on the polishing surface is used, waviness occurs on the surface to be polished of the glass substrate. Such waviness is problematic because it causes convex defects on the substrate surface.

  In order to solve the problems of the prior art described above, the present invention suppresses the adsorption of the glass substrate to the polishing pad attached to the upper surface plate when polishing the glass substrate using a double-side polishing apparatus, and An object of the present invention is to provide a glass substrate polishing method capable of preventing the occurrence of undulation on the substrate surface.

The present invention provides a polishing surface of a polishing pad attached to an upper and lower surface plate of a double-side polishing apparatus, sandwiching a glass substrate held by a carrier, and is provided on at least one of both polishing surfaces of the upper and lower surface plates. Or both main surfaces of the glass substrate by relatively moving the upper and lower platen and the glass substrate held by the carrier while supplying a fluid containing abrasive particles from one or a plurality of supply holes A method of polishing a glass substrate for polishing
The polishing pad attached to the upper and lower surface plates has a hardness (Shore A hardness) of 70 or less and a surface roughness (Ra) of 50 μm or less.
Adsorption force F ₁ (N) between the polishing surface of the polishing pad (a) attached to the lower surface plate and the main surface of the glass substrate, and the polishing surface of the polishing pad (b) attached to the upper surface plate and the glass substrate So that the adsorbing force F ₂ with the main surface satisfies the relationship represented by the following formula (1), the average opening diameter per unit area on the polishing surface of the polishing pad (a) and the polishing pad (b) Provided is a glass substrate polishing method (1), wherein at least one of a numerical aperture, an aperture ratio, and a surface roughness (Ra) is adjusted.
F ₁ > F ₂ −w × g (1)
(Wherein, w is the mass (g) of the glass substrate, and g is the gravitational acceleration (m / s ² ).)

Further, the present invention provides a polishing surface of a polishing pad attached to an upper and lower surface plate of a double-side polishing apparatus, sandwiching a glass substrate held by a carrier, and is provided on at least one of both polishing surfaces of the upper and lower surface plates. While the fluid containing abrasive particles is supplied from one or a plurality of supply holes, the upper and lower platen and the glass substrate held by the carrier are relatively moved to move both of the glass substrates. A method for polishing a glass substrate for polishing a main surface,
The polishing pad attached to the upper and lower surface plates has a hardness (Shore A hardness) of 70 or less and a surface roughness (Ra) of 50 μm or less.
Adsorption force F ₁ (N) between the polishing surface of the polishing pad (a) attached to the lower surface plate and the main surface of the glass substrate, and the polishing surface of the polishing pad (b) attached to the upper surface plate and the glass substrate So that the adsorbing force F ₂ with the main surface satisfies the relationship represented by the following formula (1), the average opening diameter per unit area on the polishing surface of the polishing pad (a) and the polishing pad (b) Provided is a glass substrate polishing method (2), wherein at least one of a numerical aperture, an aperture ratio, and a surface roughness (Ra) is different from each other.
F ₁ > F ₂ −w × g (1)
(Wherein, w is the mass (g) of the glass substrate, and g is the gravitational acceleration (m / s ² ).)

In the glass substrate polishing method (1), (2) of the present invention, the average opening diameter on the polishing surface of the polishing pad attached to the upper and lower surface plates is in the range of 1 to 100 μm,
The ratio of the average opening diameter on the polishing surface of the polishing pad (a) attached to the lower surface plate to the average opening diameter on the polishing surface of the polishing pad (b) attached to the upper surface plate is preferably 0.95 or less.

  In the polishing methods (1) and (2) of the glass substrate of the present invention, the polishing pad (a) attached to the lower surface plate with respect to the numerical aperture per unit area on the polishing surface of the polishing pad (b) attached to the upper surface plate The ratio of the numerical aperture per unit area on the polished surface is preferably 0.95 or less.

  In the polishing methods (1) and (2) of the glass substrate of the present invention, the polishing rate of the polishing pad (a) attached to the lower surface plate relative to the aperture ratio of the polishing surface of the polishing pad (b) attached to the upper surface plate The ratio of the aperture ratio is preferably 0.95 or less.

  In the polishing methods (1) and (2) of the glass substrate of the present invention, the polishing pad (a) attached to the lower surface plate with respect to the surface roughness (Ra) on the polishing surface of the polishing pad (b) attached to the upper surface plate It is preferable that the ratio of the surface roughness (Ra) on the polished surface is 0.95 or less.

  In the glass substrate polishing methods (1) and (2) of the present invention, it is preferable that the polishing load by the polishing surfaces of the upper and lower surface plates is 0.1 to 12 kPa.

  In the glass substrate polishing methods (1) and (2) of the present invention, the abrasive particles are preferably colloidal silica or cerium oxide.

ADVANTAGE OF THE INVENTION According to this invention, when grind | polishing a glass substrate using a double-side polish apparatus, it can suppress that a glass substrate adsorb | sucks to the polishing pad attached to the upper surface plate.
Moreover, according to this invention, it can prevent that a wave | undulation generate | occur | produces on the glass substrate surface after grinding | polishing. For this reason, the glass substrate surface after grinding | polishing is excellent in smoothness, and PV value in the wavelength range of 100 micrometers-100 mm will be 30 nm or less.

FIG. 1 is a side sectional view showing an example of the configuration of a double-side polishing apparatus used in the glass substrate polishing method of the present invention. FIG. 2 is a diagram showing a configuration example of the arrangement of the glass substrates 22 in the double-side polishing apparatus 10 shown in FIG. FIG. 3 is a view showing one configuration of the upper surface plate 12 in the double-side polishing apparatus 10 shown in FIG. FIG. 4 is a schematic view showing an example of a polishing pad used in the glass substrate polishing method of the present invention, and shows a state before the polishing surface side is ground to open micropores. FIG. 5 is a view similar to FIG. 4 and shows a state after the polishing surface side of the polishing pad is ground to open the micropores.

The glass substrate polishing method of the present invention will be described below with reference to the drawings.
In the glass substrate polishing method of the present invention, both main surfaces of the glass substrate are polished using a double-side polishing apparatus. Here, the main surface of a glass substrate refers to the surface which functions as a substrate at the time of use, specifically the front and back surfaces excluding the end surfaces. Hereinafter, in this specification, in the case of double-side polishing of a glass substrate, it refers to polishing both main surfaces of the glass substrate, that is, the front and back surfaces of the glass substrate.
There are various configurations of the double-side polishing apparatus, but the glass substrate held by the carrier is sandwiched between the polishing surfaces of the upper and lower surface plates, and a fluid containing abrasive particles (hereinafter, referred to as a supply hole provided in the upper surface plate). In this specification, it is common in that both surfaces of the glass substrate are polished by relatively moving the upper and lower surface plates and the glass substrate held by the carrier while supplying “polishing slurry”). It is.
Hereinafter, a double-side polishing apparatus will be described with reference to the drawings, but the double-side polishing apparatus used in the substrate polishing method of the present invention only needs to satisfy the above requirements. The arrangement of the glass substrate is not limited to this.

FIG. 1 is a side sectional view showing an example of the configuration of a double-side polishing apparatus used in the glass substrate polishing method of the present invention.
A double-side polishing apparatus 10 shown in FIG. 1 is a planetary gear type polishing apparatus that polishes both surfaces of a glass substrate 22. A double-side polishing apparatus 10 shown in FIG. 1 includes an upper surface plate 12, a lower surface plate 14, a sun gear 16, and an internal gear 18. As will be described in detail later, the sun gear 16 and the internal gear 18 are means for relatively moving the upper and lower surface plates (upper surface plate 12, lower surface plate 14) and the glass substrate 22 held by the carrier 20. It is. The shape of the sun gear 16 and the internal gear 18 is generally a gear shape, but a configuration in which a plurality of pins stand in place of the gear can be substituted. By moving the carrier 20 by pinching the gear of the carrier 20 to the pins, the upper and lower surface plates (upper surface plate 12, lower surface plate 14) and the glass substrate 22 held by the carrier 20 are relatively moved. be able to. (Hereinafter, in the present specification, the gear shape and the pin shape are not distinguished and are referred to as “gear”.)
Both the upper and lower surface plates (upper surface plate 12, lower surface plate 14) have a donut shape having cavities 12a and 14a at the center.

FIG. 2 is a diagram showing a configuration example of the arrangement of the glass substrate 22 in the double-side polishing apparatus 10 shown in FIG. 1, and shows a state in which the carrier 20 holding the glass substrate 22 is arranged on the lower surface plate 14. Yes. In FIG. 2, a plurality of carriers 20 are arranged on the lower surface plate 14 (in practice, between the upper and lower surface plates (the upper surface plate 12 and the lower surface plate 14)). For example, in a donut-shaped region between the sun gear 16 and the internal gear 18 in FIG. 1, the plurality of carriers 20 are arranged in the circumferential direction of the lower surface plate 14 (actually, the upper surface plate 12 and the lower surface plate 14). Arranged side by side.
The carrier 20 is a disk-like body having a square hole-shaped through-hole that accommodates the glass substrate 22 in the center, and a gear is provided on the outer periphery. The sun gear 16 and the internal gear 18 are provided on the outer periphery. Mesh with. Each carrier 20 holds one glass substrate 22. In FIG. 2, each carrier 20 holds one glass substrate 22, but each carrier may hold a plurality of glass substrates.

The upper surface plate 12 and the lower surface plate 14 are upper and lower surface plates of the glass substrate 22. The upper surface plate 12 and the lower surface plate 14 are donut-shaped bodies, and the glass substrate 22 held by the carrier 20 is polished on its polishing surface (centered on the surface plate center axis 102 which is the central axis of these donut-shaped bodies). The glass held by the upper and lower surface plates and the carrier by rotating one or both of the upper and lower surface plates while sandwiching between the upper and lower surface plates (polishing surfaces of the upper surface plate 12 and the lower surface plate 14)) The substrate is moved relatively.
The upper surface plate 12 and the lower surface plate 14 have a polishing pad 24 attached to the surface facing the substrate 22. In this specification, when the polishing surfaces of the upper and lower surface plates (upper surface plate 12, lower surface plate 14) are referred to, the pads of the polishing pad 24 attached to the upper and lower surface plates (upper surface plate 12, lower surface plate 14). Refers to the surface.

FIG. 3 is a diagram showing a configuration example of the upper surface plate 12 in the double-side polishing apparatus 10 shown in FIG. As shown in FIG. 3, a polishing slurry supply hole 30 is provided in the upper surface plate 12. Thus, the double-side polishing apparatus 10 supplies the polishing slurry between the polishing pad 24 provided on the polishing surfaces of the upper surface plate 12 and the lower surface plate 14 and the substrate 22. In FIG. 3, the upper surface plate 12 is provided with a plurality of supply holes 30. 3 shows the supply holes 30 in the upper surface plate 12, the same supply holes as in FIG. 3 also exist in the polishing pad provided on the polishing surface of the upper surface plate 12.
The plurality of supply holes 30 are arranged at regular intervals in a spiral manner from the rotation axis side of the upper surface plate 12 to the outside and toward the traveling side in the rotation direction of the upper surface plate 12. However, FIG. 3 shows a configuration example of the arrangement of the polishing slurry supply holes 30 in the upper surface plate 12, and the arrangement of the polishing slurry supply holes 30 in the upper surface plate 12 is not limited to this.
In FIG. 3, a plurality of supply holes 30 are provided in the upper surface plate 12, but the number of supply holes provided in the upper surface plate may be one.
Further, not the upper surface plate but the lower surface plate may be provided with polishing slurry supply holes, and both the upper surface plate and lower surface plate may be provided with polishing slurry supply holes.

  The sun gear 16 and the internal gear 18 are gears that mesh with the outer peripheral surface of the carrier 20. The sun gear 16 is an externally toothed gear that comes into contact with the carrier 20 from the center side of the upper surface plate 12 and the lower surface plate 14, and is formed in the cavities 12 a and 14 a at the center of the upper and lower surface plates (upper surface plate 12 and lower surface plate 14). It is provided and rotates about a rotation axis concentric with the center axis 102 of the surface plate which is the rotation axis of the upper and lower surface plates (upper surface plate 12 and lower surface plate 14). The internal gear 18 is an internal gear that contacts the carrier 20 from the outer peripheral side of the upper surface plate 12 and the lower surface plate 14. The internal gear 18 is a ring-shaped gear having a gear inside, and is provided on the outer periphery of both upper and lower surface plates (upper surface plate 12 and lower surface plate 14), and a surface plate central axis 102 that is a rotation axis of the surface plate. Rotate on a concentric rotation axis.

  The sun gear 16 and the internal gear 18 are engaged with the gear of the carrier 20 to rotate the carrier 20. Moreover, by this, the sun gear 16 and the internal gear 18 revolve and rotate the carrier 20 holding the glass substrate 22 between the upper surface plate 12 and the lower surface plate 14, so that both surfaces of the glass substrate 20 are rotated. Grind.

As described above, when both surfaces of the glass substrate 20 are polished using the double-side polishing apparatus 10, the polishing pad 24 attached to one of the upper and lower surface plates (upper surface plate 12 and lower surface plate 14) is attached at the end of the polishing. The glass substrate may be adsorbed.
In general, the lower surface of the glass substrate 20 is easily adsorbed to the polishing pad 24 attached to the lower surface plate 14 by its own weight, but the upper surface of the glass substrate 20 may be adsorbed to the polishing pad 24 attached to the upper surface plate 12 in some cases. In this case, the glass substrate 20 adsorbed on the polishing pad 24 attached to the upper surface plate 12 may fall and be damaged.
Therefore, at the end of polishing, in order to prevent the upper surface of the glass substrate 20 from adsorbing to the polishing pad 24 attached to the upper surface plate 12, the lower surface of the glass substrate 20 is attached to the lower surface plate 14. It is desirable to adsorb to.

In the glass substrate polishing method of the present invention, the adsorption force F ₁ (N) between the polishing surface of the polishing pad 24 attached to the lower surface plate 14 and the main surface of the glass substrate 20, and the polishing pad attached to the upper surface plate 12. The average opening diameter and the number of numerical apertures per unit area on the polishing surface of the polishing pad 24 so that the adsorption force F ₂ between the polishing surface 24 and the main surface of the glass substrate 20 satisfies the relationship represented by the following formula (1). , At least one of the aperture ratio and the surface roughness (Ra) is adjusted.
F ₁ > F ₂ −w × g (1)
In said formula (1), w is the mass (g) of the glass substrate 20, and g is a gravitational acceleration (m / s < ² >).
In addition, the average opening diameter, the numerical aperture per unit area, the numerical aperture, and the surface roughness (Ra) on the polishing surface of the polishing pad 24 so that the above F ₁ and F ₂ satisfy the relationship represented by the formula (1). ) Will be described later as a specific means for adjusting at least one. As a polishing pad attached to the upper and lower surface plates, there is a means that uses a polishing pad in which at least one of the average opening diameter, the numerical aperture per unit area, the opening ratio, and the surface roughness (Ra) is different from each other.

In the above formula (1), the adsorption forces F ₁ and F ₂ between the polishing surface of the polishing pad and the main surface of the glass substrate are similar to those between the polishing surface of the polishing pad and the main surface of the glass substrate as in the end of polishing. The minimum force required to peel off the glass substrate having the main surface adsorbed on the polishing surface of the polishing pad in the direction perpendicular to the polishing surface in the presence of the polishing slurry.
Note that the upper and lower surface plates (upper surface plate 12, lower surface plate 14) are not attracted to the polishing surface of the polishing pad 24 and the main surface (upper surface, lower surface) of the glass substrate 20. The adsorbing force between the polishing surface of the polishing pad 24 attached to the board (upper surface plate 12 and lower surface plate 14) and the main surface of the glass substrate 20 is the upper and lower sides in order to eliminate the influence of the weight of the glass substrate. The polishing pad 24 before being attached to the surface plate (upper surface plate 12, lower surface plate 14) is in a state in which the orientation of the glass substrate 20 that adsorbs the main surface is the same (for example, the lower surface of the glass substrate 20 with respect to the polishing pad 24). This is because the adsorbing force is evaluated in a state in which the adsorbing agent is adsorbed.

The attraction forces F ₁ and F ₂ between the polishing surface of the polishing pad 24 attached to the upper and lower surface plates (upper surface plate 12 and lower surface plate 14) and the main surface of the glass substrate 20 are represented by the relationship expressed by the above formula (1). If the above condition is satisfied, at the end of polishing, the lower surface of the glass substrate 20 tends to be adsorbed to the polishing pad 24 attached to the lower surface plate 14, and the upper surface of the glass substrate 20 is polished to the upper surface plate 12. Adsorption to the pad 24 is suppressed.

Various factors influence the adsorption force between the polishing surface of the polishing pad and the main surface of the glass substrate. By adjusting such factors with the polishing pad attached to the upper and lower surface plates, the relationship represented by the above formula (1) can be satisfied. However, it should be noted that this affects the surface properties of the glass substrate at the end of polishing.
Regarding the average opening diameter, the number of openings per unit area, the opening ratio, and the surface roughness on the polishing surface of the polishing pad, the glass substrate polishing method of the present invention achieves the surface properties of the glass substrate after polishing is completed. As long as the polishing pad is within the range to be filled, even if a difference is made between the polishing pads attached to the upper and lower surface plates, the influence on the surface properties of the glass substrate at the end of polishing is negligible and can be ignored.

  The characteristics to be satisfied by the polishing pad used in the glass substrate polishing method of the present invention are shown below.

When the hardness of the polishing pad used for polishing the glass substrate is too high, the surface of the glass substrate to be polished may be scratched due to the pressing of the polishing slurry particles. For this reason, in the glass substrate polishing method of the present invention, a polishing pad having a hardness (Shore A hardness) of 70 or less is used.
The hardness (Shore A hardness) of the polishing pad is preferably 60 or less, and more preferably 50 or less.
The lower limit of the hardness of the polishing pad used for polishing the glass substrate is not particularly limited. However, if the hardness of the polishing pad is too low, the polishing efficiency may decrease and a sufficient polishing rate may not be obtained. In addition, the controllability of the flatness of the glass substrate to be polished may be deteriorated.
Therefore, the hardness (Shore A hardness) of the polishing pad is preferably 5 or more, and more preferably 10 or more.

If the surface roughness of the polishing pad used for polishing the glass substrate is too large, there will be a distribution of polishing load and unevenness of the polishing slurry particles, which may cause concave defects on the surface of the glass substrate being polished. Polishing is difficult to achieve. For this reason, in the glass substrate polishing method of the present invention, a polishing pad having a surface roughness (Ra) of 50 μm or less is used.
The surface roughness (Ra) of the polishing pad is preferably 20 μm or less, more preferably 15 μm or less, and even more preferably 10 μm or less.

Here, when the relationship between the surface roughness (Ra) of the polishing surface of the polishing pad and the adsorption force with the main surface of the glass substrate is considered, the adsorption force increases as the surface roughness of the polishing surface increases. The smaller the roughness, the smaller the adsorption force.
In the glass substrate polishing method of the present invention, when the relationship shown in the above formula (1) is satisfied by making a difference in the surface roughness (Ra) of the polishing pad attached to the upper and lower surface plates, the polishing attached to the upper surface plate The ratio of the surface roughness (Ra) on the polishing surface of the polishing pad attached to the lower surface plate to the surface roughness (Ra) on the polishing surface of the pad is preferably 0.95 or less, and is 0.9 or less. Is more preferable, and it is further more preferable that it is 0.85 or less. There is no particular lower limit, but the ratio between the two is preferably 0.01 or more.

If the average opening diameter of the polishing pad used for polishing the glass substrate is too large, a distribution of polishing load is generated, and it may be difficult to maintain a predetermined polishing quality. For this reason, in the glass substrate grinding | polishing method of this invention, it is preferable to use the polishing pad whose average opening diameter is 100 micrometers or less. The average opening diameter of the polishing pad is more preferably 40 μm or less, further preferably 30 μm or less, and further preferably 25 μm or less.
On the other hand, if the average opening diameter of the polishing pad used for polishing the glass substrate is too small, there is a possibility that the polishing slurry cannot be held and polished without unevenness. For this reason, in the glass substrate grinding | polishing method of this invention, it is preferable to use the polishing pad whose average opening diameter is 1 micrometer or more.
The average opening diameter on the polished surface can be obtained by observing the polished surface using a CCD camera.

Here, when the relationship between the opening diameter on the polishing surface of the polishing pad and the adsorption force with the main surface of the glass substrate is considered, the adsorption force increases as the opening diameter decreases, and the adsorption force decreases as the opening diameter increases. .
In the glass substrate polishing method of the present invention, when the relationship shown in the above formula (1) is satisfied by making a difference in the average opening diameter of the polishing pad attached to the upper and lower surface plates, the polishing of the polishing pad attached to the upper surface plate is performed. The ratio of the average opening diameter at the polishing surface of the polishing pad attached to the lower surface plate to the average opening diameter at the surface is preferably 0.95 or less, more preferably 0.9 or less, and 0.85 or less. More preferably. There is no particular lower limit, but the ratio between the two is preferably 0.01 or more.

Here, when looking at the relationship between the numerical aperture per unit area on the polishing surface of the polishing pad and the adsorption force with the main surface of the glass substrate, the smaller the numerical aperture per unit area, the greater the adsorption force. The larger the number, the smaller the adsorption power.
In the glass substrate polishing method of the present invention, when the relationship shown in the above formula (1) is satisfied by making a difference in the numerical aperture per unit area of the polishing pad attached to the upper and lower surface plates, the polishing attached to the upper surface plate The ratio of the numerical aperture per unit area on the polishing surface of the polishing pad attached to the lower surface plate to the numerical aperture per unit area on the polishing surface of the pad is preferably 0.95 or less, and preferably 0.9 or less. Is more preferable, and it is further more preferable that it is 0.85 or less. There is no particular lower limit, but the ratio between the two is preferably 0.01 or more.
The numerical aperture on the polished surface can be obtained by observing the polished surface using a CCD camera.

Here, when looking at the relationship between the aperture ratio on the polishing surface of the polishing pad and the adsorption force with the main surface of the glass substrate, the lower the aperture ratio, the greater the adsorption force, and the higher the aperture ratio, the smaller the adsorption force. Become.
In the glass substrate polishing method of the present invention, when the relationship expressed by the above formula (1) is satisfied by making a difference in the aperture ratio of the polishing pad attached to the upper and lower surface plates, the polishing surface of the polishing pad attached to the upper surface plate The ratio of the aperture ratio at the polishing surface of the polishing pad attached to the lower surface plate to the aperture ratio at is preferably 0.95 or less, more preferably 0.9 or less, and 0.85 or less. Is more preferable. There is no particular lower limit, but the ratio between the two is preferably 0.01 or more.
Note that the aperture ratio in the polished surface refers to the ratio of the area of the opening to a certain unit area of the polished surface. The aperture ratio on the polished surface can be obtained by observing the polished surface using a CCD camera.

In the glass substrate polishing method of the present invention, as a polishing pad attached to the upper and lower surface plates, at least one of the average opening diameter, the numerical aperture per unit area, the opening ratio, and the surface roughness (Ra) is different from each other. Use a pad.
A configuration example of a polishing pad suitable for producing polishing pads having different average opening diameters is shown below.
FIG. 4 is a schematic view showing a configuration example of a polishing pad suitable for producing polishing pads having different average opening diameters. However, the polishing pad 1 in FIG. 4 shows only the portion of the surface layer 2 including the polishing surface P. In the polishing pad 1 shown in FIG. 4, micropores 4 are formed in the surface layer 2 including the polishing surface P. When the polishing pad 1 is used, the microporous 4 is opened 5 as shown in FIG. 5 by grinding the polishing surface P side of the surface layer 2.
Since the cross-sectional shape of the microporous 4 is a rounded substantially triangular shape, the diameter thereof changes in the thickness direction of the surface layer 2. Therefore, by changing the grinding amount of the surface layer 2, the opening diameter of the polishing pad 1 can be changed, and polishing pads having different average opening diameters can be produced.

  The polishing pad used in the glass substrate polishing method of the present invention is required to have a hardness (Shore A hardness) of 70 or less, and the surface layer 2 is microporous as in the polishing pad 1 shown in FIG. 4 is preferably formed, at least the constituent material of the surface layer 2 is preferably a polyurethane resin.

  The preferable aspect in the glass substrate grinding | polishing method of this invention is shown below.

[Glass substrate]
The glass substrate polished using the glass substrate polishing method of the present invention is a glass substrate for applications in which a PV value in a wavelength range of 100 μm to 100 mm on the polished glass substrate surface is required to be 30 nm or less. A typical example of such a use is a glass substrate for EUVL optical base material.
The glass constituting the glass substrate for an EUVL optical substrate is preferably a glass having a small coefficient of thermal expansion and small variations. Specifically, a low expansion glass having a thermal expansion coefficient at 20 ° C. of 0 ± 30 ppb / ° C. is preferable, an ultra low expansion glass having a thermal expansion coefficient at 20 ° C. of 0 ± 10 ppb / ° C. is more preferable, and a thermal expansion coefficient at 20 ° C. Is more preferably an ultra low expansion glass having a 0 ± 5 ppb / ° C.
As the low expansion glass and ultra low expansion glass, glass mainly composed of SiO ₂ , typically quartz glass can be used. Synthetic quartz glass in particular containing 1 to 12 wt% of TiO ₂ as a main component, for example, SiO _2, ULE (registered trademark Corning Code 7972) can be mentioned. The glass substrate is usually polished with a rectangular plate-like body, but the shape is not limited thereto.

The glass substrate polishing method of the present invention is used as a base material for a transmission mask using a KrF excimer laser (wavelength 248 nm), an ArF excimer laser (wavelength 193 nm), or an F ₂ excimer laser (wavelength 157 nm) as a light source. It can also be used for polishing glass substrates.

[Polishing slurry]
As described above, the polishing slurry in the present invention is a fluid containing abrasive particles.
As the abrasive particles, colloidal silica or cerium oxide is preferable. When colloidal silica is used, it becomes possible to polish a glass substrate more precisely, and as a result, a glass substrate in which concave defects are reduced or removed can be obtained with better accuracy. Therefore, it is particularly preferable.

When using colloidal silica, the average primary particle size is preferably 1 nm or more and 100 nm or less. More preferably, it is 10 nm or more and 50 nm or less. Here, when the average primary particle diameter of colloidal silica is 1 nm or more, it becomes possible to improve the polishing efficiency of a glass substrate. On the other hand, when the average primary particle diameter of colloidal silica is 100 nm or less, it becomes possible to reduce the surface roughness of the substrate polished with the polishing slurry.
On the other hand, when cerium oxide is used, the average primary particle size is preferably 10 to 5000 nm, more preferably 100 to 3000 nm, and even more preferably 500 to 2000 nm.

The content of colloidal silica in the polishing slurry is preferably 1% by mass or more and 40% by mass or less. More preferably, it is 10 mass% or more and 30 mass% or less. When the content of colloidal silica in the polishing slurry is 1% by mass or more, the polishing efficiency of the glass substrate can be improved. On the other hand, when the content of the colloidal silica in the polishing slurry is 40% by mass or less, it is possible to improve the cleaning efficiency of the polished glass substrate.
On the other hand, the content of cerium oxide in the polishing slurry is preferably 1 to 50% by mass, more preferably 5 to 40% by mass, and still more preferably 10 to 30% by mass.

  The fluid in the polishing slurry is a dispersion medium of abrasive particles. Examples of the dispersion medium include water and organic solvents.

[Polishing load]
When carrying out the glass substrate polishing method of the present invention, the polishing load by the polishing surfaces of the upper and lower surface plates is set to 0.1 to 12 kPa because the glass substrate can be polished to a surface with few concave defects and excellent surface smoothness. preferable. When the polishing load is less than 0.1 kPa, it is difficult to control the load of the polishing pad and the polishing effect may not be substantially obtained. Further, when the polishing load is larger than 12 kPa, it becomes difficult to suppress the generation of concave defects and improve the surface roughness.
Further, the polishing load at the time of carrying out the glass substrate polishing method of the present invention may be constant or may be changed gradually or stepwise. For example, the load may be a large load at the start of polishing, the polishing load may be reduced gradually or stepwise, and the load may be reduced at the end of polishing. Conversely, the load may be small at the start of polishing, the polishing load may be increased gradually or stepwise, and the load may be increased at the end of polishing.
For example, polishing is started at a polishing load of 5 to 12 kPa, preferably 5 to 10 kPa, the polishing load is lowered gradually or stepwise, and the load at the end of polishing is 0.5 to 5 kPa, more preferably 0. .5 to 2 kPa. Conversely, at the start of polishing, the load is 0.5 to 5 kPa, more preferably 0.5 to 2 kPa, and the polishing load is increased gradually or stepwise, and the load is 5 to 12 kPa, preferably 5 to 5 kPa. Polishing may be terminated at 10 kPa.
Further, for example, polishing can be performed with a constant load of 5 to 12 kPa, preferably 5 to 10 kPa.

  According to the glass substrate polishing method of the present invention, the main surface of the glass substrate can be polished extremely smoothly. Specifically, the PV value in the wavelength region of 100 μm to 100 mm on the polished glass substrate surface is 30 nm or less. In addition, in this specification, in the case of the PV value in the wavelength range of 100 μm to 100 mm, in addition to the PV value in the entire wavelength range of 100 μm to 100 mm, the PV value in a part of the wavelength range of 100 μm to 100 mm Is included. For example, in Examples described later, PV values in a wavelength range of 5 mm to 20 mm were evaluated.

  The glass substrate polishing method of the present invention is particularly suitable, for example, as final polishing performed at the end when a glass substrate is polished in a plurality of polishing steps having different degrees of polishing, and polishing immediately before that. In the initial stage of the polishing process, in order to prevent the glass substrate from adsorbing to the polishing pad, for example, a polishing pad provided with a groove on the polishing surface is used. As a result, the surface to be polished of the glass substrate is wavy. However, it can be corrected in the subsequent polishing step.

  For example, in the glass substrate polishing step, preliminary polishing is performed a plurality of times, and then final polishing is performed. In this preliminary polishing, the glass substrate is roughly polished to a predetermined thickness, end face polishing and chamfering are performed, and both the main surfaces are preliminary polished so that the surface roughness and flatness are not more than a certain level. deep. This preliminary polishing may be performed a plurality of times, for example, two to three times. The preliminary polishing method is not limited and can be performed by a known method. For example, a plurality of double-sided lapping machines are installed in succession, and the two main surfaces of the glass substrate are preliminarily maintained at a predetermined surface roughness and flatness by sequentially polishing with the polishing machine while changing the polishing material and polishing conditions. Can be polished.

  When the glass substrate polishing method of the present invention is used as final polishing, the surface roughness (Rms) after preliminary polishing is preferably 1 nm or less, and more preferably 0.5 nm or less.

Hereinafter, the present invention will be described in detail with reference to examples. However, the present invention is not limited to this.
Example 1
A polishing pad 1 having a surface layer structure shown in FIG. 4 was prepared. As the polishing pad 1, a commercially available polishing pad made of polyurethane foam (K7512 manufactured by Kanebo, Shore A hardness 30) was used.
The surface layer 2 of the polishing pad 1 is formed with a substantially triangular microporous 4 having a rounded cross-sectional shape. The surface layer 2 of the polishing pad 1 was ground (buffed) with sandpaper to open the micropores 4 as shown in FIG.
The polishing pad A attached to the upper surface plate of the double-side polishing apparatus was buffed by 200 μm using # 320 sandpaper. The polishing pad B attached to the lower surface plate of the double-side polishing apparatus was buffed by 50 μm using # 320 sandpaper.
The polishing surfaces of the polishing pads A and B were observed using a CCD camera, and the average aperture diameter, the numerical aperture per unit area, and the aperture ratio on the polishing surface were determined. The results are as follows.
Polishing pad A
Average opening diameter: 46 μm
Numerical aperture per unit area (per 1.2 mm ² ): 175
Opening ratio: 27%
Polishing pad B
Average opening diameter: 23 μm
Numerical aperture per unit area (per 1.2 mm ² ): 390
Opening ratio: 15%
The surface roughness Ra of each of the polishing pads A and B was 4.6 μm.
For the polishing pads A and B, the adsorption force between the polishing surface of the polishing pad and the main surface of the glass substrate was determined by the following procedure.
A glass substrate was placed on a polishing pad in which polishing slurry was dispersed on the polishing surface. A suction cup was affixed to the upper surface of the glass substrate, and the glass substrate was pulled upward through only the spring. The adsorption force between the polishing surface of the polishing pad and the main surface of the glass substrate was determined by subtracting the weight of the substrate from the reading of only the spring when the glass substrate was peeled off from the polishing pad. In addition, what was mentioned later was used for the polishing slurry and the glass substrate.
The suction force of the polishing pad A was 67N, and the suction force of the polishing pad B was 91N.

Next, ten glass substrates (made of synthetic quartz glass (containing 7% by mass of TiO ₂ ), 152 mm square (thickness 6.35 mm)) were prepared, and the glass substrate was set on a carrier of a double-side polishing apparatus. Then, both main surfaces of the glass substrate were polished.
Polishing conditions <br/> Number of rotations of upper and lower surface plates: 35 rpm
Polishing time: 60 minutes Polishing load: 4.9 kPa
Polishing slurry: Use of colloidal silica having an average primary particle diameter of less than 50 nm contained in 20% by mass of pure water (0.1 μm or more foreign matter filtration).
Slurry flow rate: 10 liters / min
The above procedure was performed 10 times, and a total of 100 glass substrates were polished. After polishing, the ratio of the glass substrate adsorbed to the polishing pad A attached to the upper surface plate was 1% (only one of the 100 glass substrates adsorbed to the polishing pad A).
Moreover, after washing | cleaning the glass substrate taken out from the carrier of a double-side polish apparatus, the wave | undulation did not exist in both main surfaces of a glass substrate. When the PV value in the wavelength range of 5 mm to 20 mm was measured using a Fizeau laser interference flatness measuring machine, the PV value was 10 nm.

(Example 2)
In this embodiment, the polishing pad C attached to the upper surface plate of the double-side polishing apparatus is buffed with 200 μm using # 100 sandpaper, and the polishing pad D attached to the lower surface plate is used with # 320 sandpaper. 200 μm buffed.
When the surface roughness Ra of the polishing surfaces of the polishing pads C and D was measured using a stylus type surface roughness meter, the surface roughness Ra of the polishing pad C was 5.2 μm, and the surface roughness of the polishing pad D was Ra was 4.6 μm.
When the polishing surfaces of the polishing pads C and D were observed using a CCD camera and the average opening diameter, the numerical aperture per unit area, and the opening ratio were determined, the average opening diameter was 46 μm. The numerical aperture per unit area (per 1.2 mm ² ) was 175, and the aperture ratio was 27%.
When the adsorption force between the polishing surface of the polishing pad and the main surface of the glass substrate was determined in the same procedure as in Example 1, the adsorption force of the polishing pad C was 59 N, and the adsorption force of the polishing pad D was 67 N. It was.
In the same procedure as in Example 1, both main surfaces of the glass substrate were polished using a double-side polishing apparatus.
After the polishing, the ratio of the glass substrate adsorbed to the polishing pad C attached to the upper surface plate was 3% (3 out of 100 glass substrates adsorbed to the polishing pad C).
Moreover, after washing | cleaning the glass substrate taken out from the carrier of a double-side polish apparatus, the wave | undulation did not exist in both main surfaces of a glass substrate. When the PV value in the wavelength range of 5 mm to 20 mm was measured using a Fizeau laser interference flatness measuring machine, the PV value was 10 nm.

(Comparative Example 1)
In Comparative Example 1, both polishing pads E and F attached to the upper and lower surface plates were buffed by 200 μm using # 320 sandpaper. However, lattice-like grooves having a width of 30 mm and a width of 5 mm are formed on the polishing surface of the polishing pad E attached to the upper surface plate.
When the polishing surfaces of the polishing pads E and F were observed using a CCD camera and the average opening diameter, the numerical aperture per unit area, and the opening ratio were obtained, the average opening diameter was 46 μm. The numerical aperture per unit area (per 1.2 mm ² ) was 175, and the aperture ratio was 27%.
When the surface roughness Ra of the polishing surfaces of the polishing pads E and F was measured using a stylus type surface roughness meter, the surface roughness Ra of the polishing pad E was 4.6 μm, and the surface roughness of the polishing pad F was Ra was 4.6 μm.
When the adsorption force between the polishing surface of the polishing pad and the main surface of the glass substrate was determined in the same procedure as in Example 1, the adsorption force of the polishing pad E was 50 N, and the adsorption force of the polishing pad F was 67 N. It was.
In the same procedure as in Example 1, both main surfaces of the glass substrate were polished using a double-side polishing apparatus.
After polishing, the ratio of the glass substrate adsorbed on the polishing pad E attached to the upper surface plate was 2% (2 out of 100 glass substrates adsorbed on the polishing pad E).
Further, when the glass substrate taken out from the carrier of the double-side polishing apparatus was washed and both main surfaces of the glass substrate were observed, undulations with a period of 30 mm were present on the surface of the glass substrate polished with the polishing pad E. When the PV value in the wavelength range of 5 mm to 20 mm was measured for both the main surfaces using a Fizeau laser interference flatness measuring machine, the PV value of the glass substrate surface polished with the polishing pad E was 35 nm. The PV value of the glass substrate surface polished with the polishing pad F was 10 nm.

(Comparative Example 2)
In Comparative Example 2, the polishing pad G attached to the upper surface plate of the double-sided polishing apparatus is buffed by 50 μm using # 320 sandpaper, and the polishing pad H attached to the lower surface plate is # 320 sandpaper. 200 μm buffed.
The polishing surfaces of the polishing pads G and H were observed using a CCD camera, and the average aperture diameter, the numerical aperture per unit area, and the aperture ratio on the polishing surface were determined. The results are as follows.
Polishing pad G
Average opening diameter: 23 μm
Numerical aperture per unit area (per 1.2 mm ² ): 390
Opening ratio: 15%
Polishing pad H
Average opening diameter: 46 μm
Numerical aperture per unit area (per 1.2 mm ² ): 175
Opening ratio: 27%
The surface roughness Ra of each of the polishing pads G and H was 4.6 μm.
When the adsorption force between the polishing surface of the polishing pad and the main surface of the glass substrate was determined in the same procedure as in Example 1, the adsorption force of the polishing pad G was 91 N, and the adsorption force of the polishing pad H was 67 N. It was.
In the same procedure as in Example 1, both main surfaces of the glass substrate were polished using a double-side polishing apparatus.
After polishing, the ratio of the glass substrate adsorbed to the polishing pad G attached to the upper surface plate was 66% (out of 100 glass substrates, 66 adsorbed to the polishing pad G).
Moreover, after washing | cleaning the glass substrate taken out from the carrier of a double-side polish apparatus, the wave | undulation did not exist in both main surfaces of a glass substrate. When the PV value in the wavelength range of 5 mm to 20 mm was measured using a Fizeau laser interference flatness measuring machine, the PV value was 10 nm.

(Comparative Example 3)
In Comparative Example 3, the polishing pads I and J attached to the upper and lower surface plates were buffed by 50 μm using # 320 sandpaper.
When the polishing surfaces of the polishing pads I and J were observed using a CCD camera and the average opening diameter, the numerical aperture per unit area, and the opening ratio were determined, the average opening diameter was 23 μm. The numerical aperture per unit area (per 1.2 mm ² ) was 390, and the aperture ratio was 15%. The surface roughness Ra of each of the polishing pads I and J was 4.6 μm.
When the adsorption force between the polishing surface of the polishing pad and the main surface of the glass substrate was determined in the same procedure as in Example 1, the adsorption force of the polishing pad I was 91 N, and the adsorption force of the polishing pad J was 91 N. It was.
In the same procedure as in Example 1, both main surfaces of the glass substrate were polished using a double-side polishing apparatus.
After polishing, the ratio of the glass substrate adsorbed on the polishing pad I attached to the upper surface plate was 38% (38 out of 100 glass substrates adsorbed on the polishing pad I).
Moreover, after washing | cleaning the glass substrate taken out from the carrier of a double-side polish apparatus, the wave | undulation did not exist in both main surfaces of a glass substrate. When the PV value in the wavelength range of 5 mm to 20 mm was measured using a Fizeau laser interference flatness measuring machine, the PV value was 10 nm.

1: Polishing pad 2: Surface layer 4: Microporous 5: Opening 10: Double-side polishing apparatus 12: Upper surface plate 12a: Cavity 14: Lower surface plate 14a: Cavity 16: Sun gear 18: Internal gear 20: Carrier 22: Glass substrate 24: Polishing pad 30: Polishing slurry supply hole 102: Surface plate central axis 104: Carrier rotation axis

Claims (8)

The polishing surface of the polishing pad attached to the upper and lower surface plates of the double-side polishing apparatus sandwiches the glass substrate held by the carrier, and one provided on at least one of both polishing surfaces of the upper and lower surface plates, or Glass that polishes both main surfaces of the glass substrate by relatively moving the upper and lower surface plates and the glass substrate held by the carrier while supplying a fluid containing abrasive particles from a plurality of supply holes. A method for polishing a substrate,
The polishing pad attached to the upper and lower surface plates has a hardness (Shore A hardness) of 70 or less and a surface roughness (Ra) of 50 μm or less.
Adsorption force F ₁ (N) between the polishing surface of the polishing pad (a) attached to the lower surface plate and the main surface of the glass substrate, and the polishing surface of the polishing pad (b) attached to the upper surface plate and the glass substrate So that the adsorbing force F ₂ with the main surface satisfies the relationship represented by the following formula (1), the average opening diameter per unit area on the polishing surface of the polishing pad (a) and the polishing pad (b) A method for polishing a glass substrate, comprising adjusting at least one of a numerical aperture, an aperture ratio, and a surface roughness (Ra).
F ₁ > F ₂ −w × g (1)
(Wherein, w is the mass (g) of the glass substrate, and g is the gravitational acceleration (m / s ² ).) The polishing surface of the polishing pad attached to the upper and lower surface plates of the double-side polishing apparatus sandwiches the glass substrate held by the carrier, and one provided on at least one of both polishing surfaces of the upper and lower surface plates, or Glass that polishes both main surfaces of the glass substrate by relatively moving the upper and lower surface plates and the glass substrate held by the carrier while supplying a fluid containing abrasive particles from a plurality of supply holes. A method for polishing a substrate,
The polishing pad attached to the upper and lower surface plates has a hardness (Shore A hardness) of 70 or less and a surface roughness (Ra) of 50 μm or less.
Adsorption force F ₁ (N) between the polishing surface of the polishing pad (a) attached to the lower surface plate and the main surface of the glass substrate, and the polishing surface of the polishing pad (b) attached to the upper surface plate and the glass substrate So that the adsorbing force F ₂ with the main surface satisfies the relationship represented by the following formula (1), the average opening diameter per unit area on the polishing surface of the polishing pad (a) and the polishing pad (b) A method for polishing a glass substrate, wherein at least one of a numerical aperture, an aperture ratio, and a surface roughness (Ra) is different from each other.
F ₁ > F ₂ −w × g (1)
(Wherein, w is the mass (g) of the glass substrate, and g is the gravitational acceleration (m / s ² ).) The average opening diameter on the polishing surface of the polishing pad attached to the upper and lower surface plates is in the range of 1 to 100 μm,
The ratio of the average opening diameter at the polishing surface of the polishing pad (a) attached to the lower surface plate to the average opening diameter at the polishing surface of the polishing pad (b) attached to the upper surface plate is 0.95 or less. Or the grinding | polishing method of the glass substrate of 2.   The ratio of the numerical aperture per unit area on the polishing surface of the polishing pad (a) attached to the lower surface plate to the numerical aperture per unit area on the polishing surface of the polishing pad (b) attached to the upper surface plate is 0.95 or less The method for polishing a glass substrate according to claim 1, wherein   The ratio of the opening ratio of the polishing surface of the polishing pad (a) attached to the lower surface plate to the opening ratio of the polishing pad (b) attached to the upper surface plate is 0.95 or less. The glass substrate polishing method according to any one of the above.   The ratio of the surface roughness (Ra) of the polishing surface of the polishing pad (a) attached to the lower surface plate to the surface roughness (Ra) of the polishing pad (b) attached to the upper surface plate is 0.95 or less. The method for polishing a glass substrate according to claim 1, wherein   The polishing method of the glass substrate in any one of Claims 1-6 whose polishing load by the polishing surface of the said upper and lower surface plates is 0.1-12 kPa.   The method for polishing a glass substrate according to claim 1, wherein the abrasive particles are colloidal silica or cerium oxide.

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