JP4616061B2 - Square substrate polishing guide ring, polishing head, and method for polishing a rectangular substrate - Google Patents

Description

  The present invention relates to a guide ring used for preventing excessive polishing of a peripheral portion of a substrate when a square substrate such as a photomask substrate or a liquid crystal substrate is polished.

  In recent years, with the high integration of integrated circuits such as DRAM, the demand for miniaturization of pattern rules for circuit design has been increasing year by year. Along with this, the wavelength used for the light source used in the photolithography process has shifted to the direction of using i-line, KrF excimer laser, ArF excimer laser, and shorter wavelengths.

  While shortening the exposure wavelength improves the critical resolution, the depth of focus becomes shallower, so it has become an important issue to remove other factors that make the depth of focus shallower. If the flatness of the substrate in the photomask used in the lithography process is low, the distance between the mask pattern and the lens varies depending on the position of the mask pattern, resulting in a shallow depth of focus. Therefore, higher flatness has been required for a photomask substrate as a photomask material. For example, in a 152 mm × 152 mm photomask, the flatness is 0.5 μm or less, and further 0.3 μm. The following are becoming desirable:

As the photomask substrate, a synthetic quartz glass substrate is mainly used. When manufacturing such a photomask substrate, normally, after forming a glass ingot as a raw material, it is melted by heat and formed into a square shape, which is sliced into a substrate shape. A flat photomask substrate can be obtained by performing polishing several times in order to increase the accuracy from rough polishing to precise polishing.
When polishing a substrate in manufacturing such a photomask substrate, there is a method of polishing a plurality of substrates with a double-side polishing apparatus. Polishing both surfaces of a plurality of substrates simultaneously is advantageous in terms of mass production. In addition, the transmissive mask mainly used is required to be free from defects such as scratches on both sides of the photomask substrate in order to sufficiently transmit the exposure light, and double-side polishing is also effective as a countermeasure against scratches. .

A general double-side polishing apparatus is designed so that the mask substrate is polished while revolving while rotating on the polishing surface plate in order to prevent the symmetry of the mask substrate from being lost. However, since the relative speed of the substrate with respect to the surface plate is fastest at the corner of the substrate farthest from the center of rotation and slowest at the center, excessive polishing tends to occur at the corner of the substrate. Therefore, it is necessary to devise polishing conditions in order to maintain the symmetry of the mask substrate and to make the degree of polishing uniform at the center and corners of the substrate.
For example, a method of finishing a substrate with high flatness by mixing abrasives having different particle sizes and performing polishing has been proposed (see Patent Document 1). Also, after making a concave substrate under the condition that the central part of the substrate is polished quickly by the double-side polishing apparatus, the flatness is high by polishing under the condition that the peripheral part is polished faster by the single-side polishing apparatus. A method for obtaining a substrate has been proposed (see Patent Document 2).

Since the single-side polishing apparatus can more uniformly control the pressure acting between the polishing cloth and the substrate, it is generally used particularly in finishing polishing. FIG. 7 schematically shows a configuration of a general single-side polishing apparatus 21. The photomask substrate 27 is sucked and held by the polishing head 26, and the surface plate 24 and the polishing head 26 to which the polishing cloth 25 is attached are rotated in predetermined directions. Polishing is performed by supplying the polishing agent 22 from the polishing agent supply nozzle 23 to the polishing cloth 25 and pressing the substrate 27.
However, when higher flatness is required for the photomask substrate, it is extremely difficult to obtain a substrate having high flatness over the entire surface even if polishing is performed using a single-side polishing apparatus. The problem of overpolishing is likely to occur.

  Therefore, when the photomask substrate is polished using the single-side polishing apparatus 21 as described above, there is a method of polishing using an annular jig called a guide ring 30 as shown in FIG. The photomask substrate 27 is held in a guide ring 30 provided in the polishing head and pressed against the polishing cloth with a predetermined pressure. By pressing the polishing cloth around the substrate 27 by the guide ring 30, an effect of suppressing excessive polishing of the peripheral portion of the substrate 27 can be obtained.

However, even when the photomask substrate 27 is polished using the guide ring 30, the corner portion of the substrate 27 is farthest from the center of rotation, so that the relative speed with the polishing cloth is high and the polishing is more fresh. Since the agent is easily supplied, over-polishing is likely to occur at the corners.
In addition, when trying to obtain a substrate having good flatness from a photomask substrate having a distorted target, the effect of correcting the flatness can be obtained even by using a general guide ring 30 as shown in FIG. There is a problem that can not be.

  On the other hand, a method of dividing the guide ring into several parts and independently controlling the pressing of each part has been proposed (see Patent Documents 3 and 4). For example, in the guide ring 40 divided into eight as shown in FIG. 9, the step pieces 41, 43, 45, 47 corresponding to the corners of the substrate have step pieces 42, 44, 46 corresponding to the side portions of the substrate. , 48 is set to a pressure stronger than that for polishing. In this way, it is possible to reduce the difference in polishing rate between the side portion and the corner portion of the substrate by performing the polishing by individually controlling the pressing of the step pieces 41 to 48 of the guide ring 40. Yes.

In addition, as a means for finishing a mask substrate having high flatness, a method has been proposed in which pressure control is independently performed on a substrate by a plurality of pressure bodies (see Patent Document 5).
However, control by these methods is technically very difficult, and high flatness may not always be achieved even when the substrate is polished by these methods.

JP 2004-314294 A JP 2005-43838 A JP 2003-48148 A JP 2003-51472 A Japanese Patent Laid-Open No. 2004-29735

  In view of the above problems, the present invention mainly provides a guide ring that can be easily and reliably finished into a square substrate having high flatness when polishing a square substrate such as a photomask substrate. And

In order to achieve the above object, according to the present invention, when polishing while pressing a square substrate against a polishing cloth, the polishing cloth is pressed around the substrate so that the peripheral portion of the substrate is excessive. A guide ring for preventing polishing, having a housing portion for housing the substrate, at least on the surface in contact with the polishing cloth, increasing the polishing rate of the peripheral portion of the square substrate of the housing portion , A square shape characterized in that a portion having a clearance larger than that of the other portion is formed at a position corresponding to a portion where polishing is desired to be accelerated so as to penetrate in the thickness direction of the substrate. A guide ring for polishing a substrate is provided (claim 1).

  With such a square substrate polishing guide ring, in a portion where a large clearance is formed, the sinking of the polishing cloth is smaller than in other portions where the clearance is small, and the elastic force of the polishing cloth is relatively high. Polishing efficiency is increased. Therefore, when this guide ring is used, selective polishing is possible even without a complicated pressing mechanism, and the corners and sides of the substrate are polished to the same extent, or the symmetry of the substrate is lost. The flatness can be corrected, and a square substrate having high flatness and symmetry can be easily and surely finished.

The housing portion may house a square prismatic substrate (claim 2).
Since a photomask substrate requiring high flatness is generally rectangular, the guide ring as described above can be preferably used.

Further, at a position corresponding to at least one side of the square substrate accommodated in the accommodating portion (Claim 3), preferably at a position corresponding to each side than a position corresponding to the corner portion of the substrate. It can be set as the guide ring for square substrates in which the part where a clearance becomes large is formed (Claim 4).
A square substrate is more easily polished at the corner than at the side, but if a guide ring having a large clearance formed at a position corresponding to the side of the substrate is used, Polishing is promoted, and the corner and side portions can be polished at substantially the same polishing rate.

  Further, in the present invention, a polishing head for holding a square substrate and pressing the substrate against a polishing cloth for polishing, comprising at least a substrate holding means for sucking and holding the substrate, and the substrate A square substrate polishing head comprising a substrate pressing means for pressing against a polishing cloth and the guide ring according to the present invention is provided.

  In the polishing head having the guide ring according to the present invention, during polishing, the sinking of the polishing cloth is reduced at a portion where a large clearance is formed between the guide ring and the substrate, and the peripheral portion of the corresponding substrate. It is possible to promote polishing of the substrate. Therefore, if this polishing head is used, position-selective polishing can be performed even without a complicated pressing mechanism, and a square substrate having high flatness and symmetry can be easily and surely finished.

In this case, a clearance part abrasive supply mechanism for supplying the abrasive to a part where the clearance between the guide ring accommodating part and the substrate is increased can be further provided.
If a mechanism for supplying an abrasive to a portion where the clearance is increased is further provided, polishing in a corresponding portion of the substrate is further promoted, and a square substrate having higher flatness and symmetry can be more efficiently finished. it can.

  Furthermore, according to the present invention, the guide ring according to the present invention is used in a method of holding a square substrate, supplying an abrasive to the polishing cloth, and polishing while pressing the substrate against the polishing cloth. A polishing method for a rectangular substrate is provided in which the rectangular substrate is accommodated in the accommodating portion of the guide ring to perform polishing (Claim 7).

  That is, when the square substrate is polished using the guide ring according to the present invention, the sinking of the polishing cloth is reduced at the portion of the large clearance formed between the substrate and the guide ring, and the polishing is promoted. Will be. Therefore, according to this method, a square substrate having high flatness and symmetry can be easily and reliably finished without using a complicated pressing mechanism.

The abrasive may be supplied to a portion where the clearance between the guide ring housing and the substrate is increased.
If polishing is performed while supplying an abrasive to a portion where the clearance is increased, polishing at a corresponding portion of the substrate is further promoted, and a square substrate having high flatness and symmetry can be obtained more efficiently.

In this case, a photomask substrate can be polished as the square substrate.
Since the photomask substrate is a square substrate that requires particularly high flatness, the polishing method using the guide ring according to the present invention is particularly effective.

The guide ring according to the present invention has a relatively large clearance with the square substrate in a part of the periphery of the accommodating portion, so that the sinking of the polishing cloth is reduced and the elastic force by the polishing cloth is strongly received. It will be.
When a square substrate such as a photomask substrate is polished using such a guide ring, the corner and side portions of the substrate are polished at the same polishing rate, or the flatness of the substrate whose symmetry has been lost. Can be finished to a square substrate with high flatness.

The present invention will be described in detail below.
The inventors of the present invention have made extensive studies on polishing of a square substrate such as a photomask substrate, and as a result, a guide having a relatively large clearance with the substrate is formed in a part of the periphery of the housing portion that houses the substrate. It has been found that if a ring is used, polishing of the peripheral portion of the substrate can be promoted in a portion where a large clearance is formed. In the peripheral part of the square substrate, the clearance with the substrate is relatively increased in the part where the polishing rate is to be increased, and the clearance with the substrate is decreased in the part where the polishing rate is to be suppressed, so that the peripheral part of the substrate is substantially uniform. It has been found that the flatness of the substrate that has been polished or broken in symmetry can be corrected, and that the substrate can be finished with a high flatness as a whole, and the present invention has been completed.

Hereinafter, a more specific description will be given with reference to the accompanying drawings.
FIG. 1 schematically shows an example of a guide ring for a square substrate according to the present invention. The guide ring 1 has an accommodating portion 2 for accommodating a rectangular photomask substrate 6. The accommodating portion 2 is formed in a substantially circular shape inside the guide ring 1, and a position corresponding to the corner portion 6 b of the substrate 6 for positioning and supporting the substrate 6 on the surface 3 on the side in contact with the polishing pad. A support portion 5 is formed on the surface. With the guide ring 1 having such a shape, when the substrate 6 is accommodated in the accommodating portion 2, the position corresponding to each side 6a of the substrate 6 is more than the position corresponding to the corner portion 6b of the substrate 6. A portion 4a where the clearance is increased is formed.

  The material of the guide ring 1 is not particularly limited, but synthetic resin such as vinyl chloride resin, PPS, and PEEK can be used, for example, from the viewpoint of moldability and durability, and prevention of scratches and contamination on the substrate. Further, quartz which is the same material as the photomask substrate can be used.

  2A and 2B schematically show a cross section of the polishing head 10 provided with the guide ring 1 shown in FIG. 1, and FIG. 2A shows the AA ′ line in FIG. FIG. 2B shows a cross section taken along line BB ′. The polishing head 10 has a disk-shaped top ring 9 as means for holding the substrate 6 and pressing it against the polishing cloth 13, and the guide ring 1 is provided so as to surround the top ring 9.

  Inside the top ring 9 is formed a ventilation path 8 for vacuum suction of the substrate 6. Further, a rubber ring (rubber packing) 7 is attached to the lower surface of the top ring 9 so as to be in contact with the peripheral portion on the back surface side of the substrate 6. The rubber ring 7 is for sealing the space between the top ring 9 and the substrate 6 and holding the substrate 6 by vacuum suction, and is made of silicone rubber, nitrile rubber, styrene butadiene rubber, fluorine rubber, or the like. Can do. Alternatively, a ring made of a synthetic resin such as a polyacetal resin or a fluorine resin can be used. By using such a ring 7 made of rubber or synthetic resin, the substrate 6 can be adsorbed and held without being scratched. However, in order to more reliably prevent the contamination of the substrate 6 and the influence of the scratch on the exposure of the photomask, the rubber ring 7 has a peripheral portion on the back surface that does not affect the exposure of the photomask, for example, the outermost peripheral portion (edge) Part) is preferably provided so as to be in contact with an area of 1 to 3 mm.

  When polishing by holding the photomask substrate 6 with such a polishing head 10, first, the substrate 6 is accommodated in the accommodating portion 2 of the guide ring 1. The four corners 6b of the substrate 6 are positioned by being supported by the support portions 5 of the guide ring 1. The substrate 6 is sucked and held via the rubber ring 7 by vacuum suction through the ventilation path 8.

  The surface plate to which the polishing cloth 13 is attached and the polishing head 10 are each rotated in a predetermined direction to supply an abrasive to the polishing cloth 13 and the substrate 6 held by the polishing head 10 is attached to the polishing cloth 13. Press. At this time, since a load is applied to the peripheral portion of the substrate 6 via the rubber ring 7, the peripheral portion is easily polished. Therefore, if the substrate 6 is brought into contact with the polishing cloth 13 and then air or nitrogen is supplied through the air passage 8 to pressurize the back side of the substrate 6, the polishing load of the entire substrate can be made substantially uniform. The suction of the substrate 6 is released by supplying air or the like from the air passage 8 and pressurizing it. However, since the corner 6b of the substrate 6 is supported in the accommodating portion 2 of the guide ring 1, the substrate 6 6 is not displaced in the guide ring 1 or detached from the guide ring 1.

The top ring 9 and the guide ring 1 may be controlled to be pressed by the same pressing mechanism, or a pressing mechanism for the guide ring 1 may be provided separately from the pressing mechanism of the top ring 9.
The abrasive can be supplied from the outside of the polishing head as in the polishing apparatus of FIG. 7, but a mechanism for supplying the abrasive to the inside of the polishing head may be provided.
Further, instead of the rubber ring 7, the substrate 6 may be held via a rubber backing pad 11 as shown in FIG. By using the backing pad 11 having a large number of ventilation holes formed on the entire surface, the substrate 6 can be vacuum-sucked through the ventilation path 8 of the top ring 9, and the entire surface of the substrate 6 is pressed uniformly through the backing pad 11. be able to.

When the substrate 6 and the polishing pad 13 are slidably brought into contact with each other using the guide ring of the present invention as described above, the periphery of the accommodating portion 2 of the guide ring 1 and the substrate as shown in FIG. 6 is polished in a state in which a large clearance 4a is formed between the positions corresponding to the respective sides 6a. Since the sinking of the polishing pad 13 is reduced in the portion where the large clearance 4a is formed, the central portion of the side 6a of the substrate 6 is particularly strongly subjected to the elastic force by the polishing pad 13 and the polishing is promoted.
On the other hand, at the position corresponding to the corner 6b of the substrate 6, the clearance 4b between the accommodating portion 2 of the guide ring 1 and the substrate 6 is small as seen in FIG. In other words, the polishing cloth 13 sinks largely by the guide ring 1 around the corner portion 6b of the substrate 6, and the polishing by the elastic force of the polishing cloth 13 is suppressed compared to the central portion of the side 6a of the substrate 6. .

Therefore, if polishing is performed while holding the photomask substrate 6 with the polishing head 10 having such a guide ring 1, the polishing efficiency is relatively high at the central portion of the side 6a of the substrate 6 where the polishing rate is generally reduced. The polishing efficiency becomes relatively small around the corner 6b where the polishing rate tends to increase and the polishing rate tends to increase. As a result, a photomask substrate having high flatness over the entire periphery of the substrate 6 can be finished.
Further, the polishing head 10 provided with such a guide ring 1 has the advantage that it is not necessary to provide a complicated pressing mechanism, the pressing control is easy, and the cost is low.

In the present invention, the shapes of the top ring, the guide ring, and the like are not limited to those shown in FIGS. 2A and 2B, and other shapes can also be employed.
4A and 4B show a polishing head 14 provided with a rectangular top ring 15 similar to the photomask substrate 6. The photomask substrate 6 is sucked and held via a rubber ring 7, and a clearance 4a is formed between the guide ring 16 and the side 6a of the substrate 6 so as to penetrate in the thickness direction. Also in this case, the surface on the side in contact with the polishing pad 13 is in the same state as in FIG. 1, and the corners 6 b of the four corners of the substrate 6 are supported by the support portions 16 a of the guide ring 16. A large clearance 4a is formed.

  5A and 5B show a polishing head 17 having a disk-like top ring 18 having a diameter larger than that of the top ring 9 shown in FIG. The lower portion of the guide ring 19 is thick at a position corresponding to the central portion of the side 6a of the photomask substrate 6, and a support portion 19a is formed at a position corresponding to the corner portion 6b. Also in this case, the surface on the side in contact with the polishing pad 13 is in the same state as in FIG. 1, and the corners 6 b at the four corners of the substrate 6 are supported by the support portions 19 a of the guide ring 19. A clearance 4a is formed.

  FIG. 6 shows another example of the guide ring according to the present invention. The guide ring 20 is formed with a relatively large clearance 4 a between the guide ring 20 and the substrate 6 at a position corresponding to one side 6 a of the photomask substrate 6. Such a guide ring 20 can be suitably used when correcting the flatness of a substrate whose symmetry has been lost. For example, in the initial polishing, when the double-side polishing apparatus is used to polish the left and right sides of the substrate in a form in which the symmetry has been lost, the substrate 6 is formed so that a larger clearance 4a is formed on the side to be scraped to increase the flatness. Is accommodated in the accommodating portion 2. Since the central portion of the side 6a of the substrate 6 corresponding to the large clearance 4a is strongly subjected to the elastic force by the polishing cloth, the polishing is promoted and the flatness is greatly improved. That is, when such a guide ring 20 is used, position-selective polishing can be performed without providing a complicated pressing mechanism, and the flatness of the substrate whose symmetry is broken can be corrected.

In the guide rings 1 and 20 shown in FIG. 1 and FIG. 6 respectively, a large arc-shaped clearance 4a is formed, but the shape of the clearance is not limited to the arc shape, and may be, for example, a triangle or another square. Further, the portion where the clearance is relatively large may be formed at a position corresponding to two or three sides of the photomask substrate, if necessary.
Alternatively, when it is desired to further promote polishing at the corners of the square substrate, a guide ring may be used in which a relatively large clearance is formed at a position corresponding to the corners.

  As described above, when polishing is performed by holding the photomask substrate with the polishing head equipped with the guide ring according to the present invention, for example, a flat area of 0.3 μm or less in the region excluding the innermost 5 mm from the outermost peripheral portion of the substrate. Degree can be achieved. When a photomask is manufactured using the polished photomask substrate, a photomask capable of stably transferring a high-density integrated circuit such as LSI or VLSI onto a semiconductor wafer can be obtained.

Examples of the present invention and comparative examples will be described below.
(Example)
Polishing was performed while holding a 152 mm × 152 mm × 6.35 mm synthetic quartz glass substrate using a polishing head as shown in FIGS. 1 and 2 in a single-side polishing apparatus. The pressing load of the substrate was 20 kPa, colloidal silica was used as an abrasive, and a suede cloth was used. Polishing was started from the concave substrate, and the time point when the central portion of the side of the substrate was almost the same height as the central portion of the substrate was used as an indication of completion of polishing.
When the flatness was measured in an inner region of 142 mm × 142 mm, it was 0.318 μm before polishing, but a flatness of 0.169 μm was achieved after polishing for 10 minutes.

(Comparative example)
As shown in FIG. 8, the synthetic quartz glass substrate was polished in the same manner as in the example using a general guide ring in which the clearance between the accommodating portion and the substrate was uniformly formed.
When the flatness was measured in the inner region of 142 mm × 142 mm, it was 0.322 μm before polishing, but it deteriorated to 0.376 μm after polishing, and in particular, the over-polishing at the corners of the four corners was marked compared to the side. It was.

  The present invention is not limited to the above embodiment. The above embodiment is merely an example, and the present invention has the same configuration as that of the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

  For example, in the above embodiment, the case of polishing a substantially square photomask substrate has been described. However, the rectangular substrate to be polished according to the present invention is not limited to this, and high flatness such as a liquid crystal substrate or a disk substrate is required. It can also be applied to polishing a square substrate, and the shape of the substrate may be a rectangular substrate or a polygonal substrate.

  Further, since the guide ring according to the present invention can improve the polishing efficiency in a portion having a large clearance, position selective polishing can be performed without providing a complicated pressing mechanism for the guide ring. In order to further increase the weight of the guide ring, a plurality of pressing mechanisms may be provided to partially increase the weight of the guide ring, or the guide ring may be divided into a plurality of parts.

  Furthermore, as shown in FIG. 10, a clearance part abrasive supply mechanism 50 for supplying an abrasive to a part where the clearance between the accommodating part of the guide ring 16 and the substrate 6 is increased may be provided. For example, if the abrasive is positively supplied to the portion 4a where the clearance between the guide ring 16 and the side portion of the substrate 6 is increased, the polishing in the corresponding portion of the substrate 6 is further promoted, and high flatness and It becomes possible to obtain a square substrate having symmetry more efficiently.

It is a schematic plan view which shows an example of the guide ring which concerns on this invention. It is a schematic sectional drawing which shows an example of the grinding | polishing head provided with the guide ring of FIG. (A) AA 'line cross section (B) BB' line cross section It is a schematic sectional drawing which shows the state which hold | maintained the board | substrate via the backing pad. It is a schematic sectional drawing which shows the other example of the grinding | polishing head which concerns on this invention. (A) AA 'line cross section (B) BB' line cross section It is a schematic sectional drawing which shows the further another example of the grinding | polishing head which concerns on this invention. (A) AA 'line cross section (B) BB' line cross section It is a schematic plan view which shows the other example of the guide ring which concerns on this invention. It is the schematic which shows an example of a structure of a single-side polish apparatus. It is a schematic plan view which shows an example of the general guide ring for square substrates. It is a schematic plan view which shows an example of the divided | segmented guide ring. It is the schematic which shows an example of a clearance part abrasive | polishing agent supply mechanism.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Guide ring, 2 ... Storage part, 3 ... Surface on the side which contacts polishing cloth, 4a, 4b ... Clearance, 5 ... Supporting part, 6 ... Photomask substrate, 6a ... Side part, 6b ... Corner part, 7 DESCRIPTION OF SYMBOLS ... Rubber ring (rubber packing), 8 ... Air passage, 9 ... Top ring, 10 ... Polishing head, 11 ... Backing pad, 13 ... Polishing cloth, 50 ... Clearance part abrasive | polishing agent supply mechanism.

Claims (9)

A guide ring for preventing excessive polishing of a peripheral portion of a substrate by pressing the polishing cloth around the substrate when the square substrate is polished against the polishing cloth. The substrate is placed at a position corresponding to a portion where the polishing speed of the peripheral portion of the square substrate of the housing portion is increased and polishing is promoted at least on the surface in contact with the polishing cloth. A square substrate polishing guide ring, wherein a portion having a clearance larger than that of the other portion is formed so as to penetrate the substrate in the thickness direction.   The square substrate polishing guide ring according to claim 1, wherein the accommodating portion accommodates a rectangular prismatic substrate.   2. A portion having a clearance larger than a position corresponding to a corner portion of the substrate is formed at a position corresponding to at least one side of the square substrate accommodated in the accommodating portion. Alternatively, a guide ring for polishing a square substrate according to claim 2.   The part where clearance becomes larger than the position corresponding to each corner of the substrate is formed at a position corresponding to each side of the rectangular substrate accommodated in the accommodating portion. Guide ring for polishing square substrates.   A polishing head for holding a square substrate and pressing the substrate against a polishing cloth for polishing, at least a substrate holding means for adsorbing and holding the substrate, and pressing the substrate against the polishing cloth A polishing head for a square substrate, comprising: the substrate pressing means; and the guide ring according to any one of claims 1 to 4.   6. The polishing for a square substrate according to claim 5, further comprising a clearance portion abrasive supply mechanism for supplying an abrasive to a portion where the clearance between the accommodation portion of the guide ring and the substrate is increased. head.   5. The method according to claim 1, wherein the substrate is held while the polishing agent is supplied to the polishing cloth and the substrate is pressed against the polishing cloth while the substrate is pressed. A method for polishing a square substrate, comprising: using a guide ring; and storing the square substrate in a receiving portion of the guide ring to perform polishing.   8. The method for polishing a square substrate according to claim 7, wherein polishing is performed while supplying an abrasive to a portion where the clearance between the housing portion of the guide ring and the substrate is increased.   The method for polishing a square substrate according to claim 7 or 8, wherein a photomask substrate is polished as the square substrate.

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