JP3880976B2 - Mask blank substrate manufacturing method - Google Patents

Description

  The present invention relates to a method for manufacturing a mask blank substrate that polishes and finishes a mask blank substrate with high flatness.

Conventionally, it has been required to improve the flatness of a substrate for an electronic device. For example, in the case of a mask blank substrate, the demand for high flatness of a substrate is increasing with the recent increase in the density and accuracy of a VLSI device. Has become more severe year by year. Under such circumstances, a substrate having a flatness of 0.5 μm or less is required as a next-generation mask blank substrate.

As a method for precise polishing of mask blank substrates, etc., the glass surface is polished with a polishing agent mainly composed of cerium oxide by a double-side polishing method using a double-side polishing machine, and then finished with colloidal silica. There is a method of polishing (Patent Document 1).

According to the precision polishing method disclosed in Patent Document 1, in a so-called batch type polishing method in which a plurality of substrates are simultaneously polished, high-speed polishing is performed using an abrasive mainly composed of cerium oxide having a large particle size. In addition, the work-affected layer generated by this polishing is finish-polished using colloidal silica having a small particle diameter.

JP-A 64-40267

By the way, the polishing agent used in the precision polishing method is generally the type of crystallite (polishing agent type) contained in the polishing agent and the average particle size of the polishing agent in consideration of the surface roughness of the substrate to be finally obtained. The diameter is selected. However, even if the type of abrasive and the average particle size of the abrasive are selected in this way, the substrate obtained through a plurality of stages of polishing steps varies in flatness from substrate to substrate, and has a high flatness. Could not be produced stably.
In view of the above problems, an object of the present invention is to provide a method for manufacturing a mask blank substrate that can stably obtain a mask blank substrate having high flatness.

The present inventor conducted numerous experiments using a large number of abrasives having different abrasive types and average particle sizes of the abrasives in order to find the cause of the variation in the flatness of the substrates from substrate to substrate. However, the typical ones are as follows.
The first is that when the type of abrasive is different, the surface shape (unevenness) of the substrate and its degree change. That is, when polishing is performed using an abrasive containing a certain type of crystallite, the surface shape of the substrate becomes concave, and when polishing is performed using an abrasive containing another type of crystallite, the surface shape of the substrate is It became convex. In other words, it has been found that there are a convex abrasive that makes the surface shape of the substrate convex by polishing and a concave abrasive that makes it concave.
The second is that even if the abrasive type is the same (for example, cerium oxide), if the average particle size is different, the surface shape after polishing may be concave or convex. .

Third, even when polishing is performed using an abrasive containing the same abrasive species (for example, cerium oxide), the flatness of the substrate changes over time, and the surface shape changes from convex to concave. Or change from concave to convex.
Furthermore, the fourth is that even when abrasives of the same type and the same particle diameter are used, the surface shape of the substrate becomes convex over time due to the change over time of the polishing pad.

As described above, there are characteristics for each type and average particle size of the crystallites contained in the abrasive, and that the characteristics change over time, and further, the state change due to the use of the polishing pad is caused by the surface shape. Up until now, it has never been known to produce a convex shape.
These things were the same in single-sided polishing and double-sided polishing, but the concave shape of the substrate and the deterioration of flatness during continuous polishing were significant in the case of double-sided polishing.

  The present invention has been made on the basis of the above knowledge, and by taking into account the change in the surface shape of the workpiece caused by various factors, by selecting an abrasive and polishing, a substrate having high flatness can be stabilized. It aims at providing the manufacturing method of the board | substrate for mask blanks made to obtain by doing.

In order to achieve the above object, a method for manufacturing a mask blank substrate according to the present invention includes a polishing platen having a polishing pad affixed to a surface, and a workpiece holding for holding a mask blank substrate placed on the polishing platen. And a polishing agent is supplied to the surface of the mask blank substrate on the polishing pad side held by the work holding means, and the mask blank substrate and the polishing pad are moved relative to each other, thereby mask blanks. A mask blank substrate manufacturing method for manufacturing a mask blank substrate through a polishing step for polishing a surface of the substrate, wherein the substrate can be polished at once by holding the mask blank substrate on the work holding means. The unit of the substrate is set as one batch, and after completion of polishing of this batch, the substrate different from the substrate is polished over a plurality of batches. A mask blank substrate manufacturing method for manufacturing a mask blank substrate, wherein the polishing agent has a concave abrasive having an average particle size of 0.5 to 3 μm and an average particle size of the polishing agent. A method is used in which a convex abrasive of 0.03 to 0.9 μm is used separately for each batch or a plurality of batches.
When the above-mentioned concave abrasive is used to polish a mask blank substrate surface (work surface) using the abrasive, a reference surface arbitrarily provided on the substrate surface (preferably, The initial surface shape of the substrate surface with respect to the virtual absolute plane (focal plane) calculated by the method of least squares is a polishing agent that acts in a concave shape, and convex abrasives have a convex surface shape on the substrate surface. It is an abrasive that acts on the surface. Then, polishing is performed by effectively using the characteristics of the concave abrasive whose initial surface shape acts concavely and the convex abrasive whose surface initial shape acts convexly. A mask blank substrate having a flatness of not more than a predetermined value can be obtained.

In addition, by varying the average particle size of the concave abrasive and the average particle size of the convex abrasive, and within a specific particle size, according to the surface shape of the substrate that changes during the polishing step, A more appropriate abrasive can be selected and used.
In addition, let the average particle diameter of the abrasive | polishing agent in this invention be an average particle diameter obtained by measuring with an optical diffraction method.
Preferably, a mask blank substrate having a more stable and high flatness can be obtained by using an abrasive having a specific surface area of ² to 15 m ² / g of the concave abrasive. More preferably, the specific surface area of the concave abrasive is 4 to 12 m ² / g.
The specific surface area is represented by the total surface area (unit: m ² / g) of all crystallites contained in the unit weight of the abrasive. The specific surface area in the present invention is a specific surface area obtained by measurement by the BET method.
Further, when the polishing pad is a suede type polishing pad, the action of the convex abrasive and the concave abrasive can be further enhanced, and the controllability of the flatness can be improved.
In addition, when a plurality of polishing pads are used in succession, the substrate surface shape tends to become convex due to the aging of the polishing pad. By polishing the latter batch with the concave abrasive using the agent, it is possible to obtain a mask blank substrate having a more stable and high flatness.

Moreover, it is preferable to use cerium oxide as the polishing agent, and it is preferable to use a polishing platen having a platen accuracy of 30 μm or less (not including 0) as the polishing platen.
As described above, when cerium oxide is used as the abrasive, the polishing efficiency is improved, and it is particularly effective when used in a pre-process of precision polishing using colloidal silica. Further, when a polishing platen having a platen accuracy of 30 μm or less (not including 0) is used, the substrate surface can be easily controlled by the abrasive. The surface plate accuracy is the maximum value of the surface shape relative to the reference surface calculated by the least square method when the surface shape of the surface of the polishing surface plate on the side where the polishing pad is applied is measured at a certain reference length. And the minimum value.

  The surface flatness of the mask blank substrate can be increased by polishing the multi-stage polishing using an optimum polishing agent.

In particular, it is preferable to carry out at least the polishing step before the ultra-precision polishing step in the method for manufacturing a mask blank substrate having an ultra-precision polishing step using a colloidal silica abrasive.
In the manufacturing method of a mask blank substrate that requires high flatness and high smoothness of the surface, if the above polishing method is used, the flatness and smoothness as required or close to that, for mask blanks with smoothness and smoothness. A substrate can be obtained.

  As described above, according to the present invention, a mask blank substrate having a uniform surface shape and high flatness can be obtained by using a convex abrasive and a concave abrasive separately for polishing. . In particular, a mask blank substrate having higher flatness can be stably obtained by changing from a convex abrasive to a concave abrasive in accordance with the change of the polishing pad over time.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[Overview of polishing apparatus]
First, an example of a polishing apparatus for carrying out the mask blank substrate manufacturing method of the present invention will be described with reference to FIG.

FIG. 1 is a schematic sectional view of a polishing apparatus.
As shown in FIG. 1, the polishing apparatus includes a planetary gear type polishing processing unit including a lower surface plate 10, an upper surface plate 20, a sun gear 30, an internal gear 40, a carrier 50, an abrasive supply unit 60, and the like. I have.

  The lower surface plate 10 is a disk member having an annular horizontal upper surface, and a suede type (nonwoven fabric type) polishing pad 11 is attached to the upper surface. The lower surface of the lower surface plate 10 is fixed to a lower support member 12 that can rotate around a vertical axis A (a vertical axis that passes through the center of the polishing portion). The lower support member 12 is linked to the lower surface plate rotation drive unit 13, and the lower surface plate 10 and the lower support member 12 are rotated by the drive.

The upper surface plate 20 is a disk member having an annular horizontal lower surface, and a suede type (nonwoven fabric type) polishing pad 21 is attached to the lower surface facing the lower surface plate 10. The upper surface of the upper surface plate 20 is fixed to an upper support member 22 that can rotate about a vertical axis A. The upper support member 22 is linked to the upper surface plate rotation drive unit 23, and the upper surface plate 20 and the upper support member 22 are rotated by the drive.
The upper surface plate 20 and the upper support member 22 are supported so as to be movable up and down along the vertical axis A, and are moved up and down by driving an upper surface plate lifting and lowering drive unit (not shown).

  The sun gear 30 is rotatably provided at the center position of the polishing unit, and is rotated about the vertical axis A according to the drive of the sun gear rotation drive unit 31. However, when rotating the internal gear 40, the sun gear 30 may be fixed so as not to rotate.

The internal gear 40 is a ring-shaped gear having a tooth row on the inner peripheral side, and the sun gear 30.
It is arranged concentrically on the outside. Although the internal gear 40 of the present embodiment is fixed so as not to rotate, the internal gear 40 can rotate about the vertical axis A, and rotates in accordance with the drive of an internal gear rotation drive unit (not shown). It may be.

The carrier (planetary gear) 50 is a thin plate-like disk member having a tooth row on the outer peripheral portion, and one or a plurality of workpiece holding holes 50a for holding the workpiece W (mask blank substrate) are formed.
The carrier 50 may be of a double carrier type in which a holder for a workpiece W (mask blank substrate) is loosely inserted into a hole formed in the carrier.

A plurality of carriers 50 are usually arranged in the polishing portion. These carriers 50 mesh with the sun gear 30 and the internal gear 40 and rotate while revolving around the sun gear 30 according to the rotation of the sun gear 30 and / or the internal gear 40.
That is, the workpiece W (mask blank substrate) is held by holding the workpiece W (mask blank substrate) held by the carrier 50 between the upper surface plate 20 and the lower surface plate 10 and revolving and rotating the carrier 50 in this state. The upper and lower surfaces of the are polished.

  In such a polished portion, the outer diameters of the upper surface plate 20 and the lower surface plate 10 are usually smaller than the inner diameter of the internal gear 40, and between the sun gear 30 and the internal gear 40 and above A donut-shaped region sandwiched between the surface plate 20 and the lower surface plate 10 is an actual polishing region.

The abrasive supply means 60 has a plurality of abrasive storage units 61 for storing the abrasives, and supplies a plurality of abrasives stored in the abrasive storage units 61 to the polishing region between the upper surface plate 20 and the lower surface plate 10. The tube 62 is configured.
The abrasive reservoir 61 forms an annular abrasive reservoir on a horizontal plane, and is provided above the upper support member 22 via a plurality of support members 63.

The upper support member 22, the upper surface plate 20, and the polishing pad 21 are formed with a plurality of through holes 22a, 20a, and 21a communicating with each other, and the lower ends of the tubes 62 are connected thereto. Thereby, the abrasive | polishing agent stored by the abrasive | polishing agent storage part 61 is supplied to the grinding | polishing area | region between the upper surface plate 20 and the lower surface plate 10 through the tube 62 and through-hole 22a, 20a, 21a.
Although illustration is omitted, the polishing agent supplied to the polishing region is recovered in the tank through a predetermined recovery path, and then again through the reduction path in which a pump and a filter are interposed. It is sent to the storage unit 61.

The polishing method for the workpiece W (mask blank substrate) of the present invention can also be implemented by a single-side polishing apparatus.
In the case of a single-side polishing apparatus, there is only one polishing platen, and the work holding means uses a pressure plate equipped with vacuum suction, a retainer, or the like. In the single-side polishing method, a mask blank substrate held on a pressure plate is pressed against a polishing surface plate on which a polishing pad rotating in one direction is attached, and one surface of the mask blank substrate is polished. Usually, the pressure plate rotates in the same direction as the rotation direction of the polishing surface plate and is further swung to perform polishing.

[Manufacturing method of substrate for mask blanks]
The method for manufacturing a mask blank substrate of the present invention includes a polishing step of performing a workpiece (mask blank substrate) polishing method described later. The workpiece referred to below is an object to be polished and means a mask blank substrate.
Next, an embodiment of the workpiece polishing method of the present invention will be described.
When polishing the workpiece, the upper surface plate 20 is raised while the rotation of the lower surface plate 10, the upper surface plate 20, and the sun gear 30 (internal gear 40) is stopped, and the lower surface plate 10 and the upper surface plate 20 are moved. Separate. In this state, the workpiece W is set in the workpiece holding hole 50a of the carrier 50.

The upper surface plate 20 is lowered, the work W held by the carrier 50 is sandwiched between the upper surface plate 20 and the lower surface plate 10, and the abrasive is supplied from the abrasive material supply means 60 to the polishing region. The surface plate 20 and the sun gear 30 (internal gear 40) are rotated to start polishing the workpiece W.

The carrier 50 holding the workpiece W rotates while revolving around the sun gear 30 according to the rotation operation of the sun gear 30 (internal gear 40).
The gear drive may be both the sun gear 30 and the internal gear 40 or any one of them. The upper surface plate 20 and the lower surface plate 10 are rotated as necessary.

After processing for a predetermined time (or a predetermined polishing processing amount), the rotation of the lower surface plate 10, the upper surface plate 20, and the sun gear 30 (internal gear 40) is stopped and the supply of the abrasive is stopped. The upper surface plate 20 is raised.
The polished workpiece is carried out from the workpiece holding hole 50a of the carrier 50.

As the abrasive, a fine crystallite dispersed in a liquid is generally used, and the crystallites are aggregated and formed as a lump (abrasive) and dispersed in the liquid. . The average particle size referred to in the present invention refers to the average particle size of the lump (abrasive) formed by agglomeration of these fine crystallites.
Examples of the abrasive include silicon carbide, aluminum oxide, cerium oxide, zirconium oxide, manganese oxide, and colloidal silica.
In this embodiment, when the workpiece surface is polished, a convex abrasive in which the initial surface shape of the workpiece surface is convex with respect to an arbitrarily provided reference surface of the workpiece surface, and a concave abrasive in which the workpiece is concave are 1 Use properly for each batch or multiple batches.

  Here, when the workpiece surface is polished, the convex abrasive in which the initial surface shape of the workpiece is convex and the concave abrasive in which the workpiece is concave means the following. That is, normally, when used continuously, the abrasive changes so that the surface shape of the workpiece becomes concave as the use progresses, but in the initial stage of use, the workpiece surface becomes convex and concave. There are things that become. Therefore, in the present specification, what makes the workpiece surface convex in the initial stage of use is referred to as a convex abrasive that makes the initial surface shape of the workpiece convex (sometimes simply referred to as a convex abrasive). In some cases, the surface of the workpiece that is concaved in the initial stage is referred to as a concave abrasive in which the initial shape of the workpiece is concave (sometimes simply referred to as a concave abrasive).

The change from the convex abrasive to the concave abrasive or the change from the concave abrasive to the convex abrasive can be performed at any time during the polishing process, for example, every batch or every batch.
In order to prevent mixing of the abrasive when changing the abrasive, it is preferable to wash the abrasive used in the previous batch prior to changing the abrasive.

  The proper use of the convex abrasive and the concave abrasive is determined in consideration of the relationship with the polishing pad. That is, according to the above-mentioned experiment of the present inventor, when using a plurality of batches of polishing pads continuously, the surface of the workpiece after polishing is increased as the latter batch is used, even if the same type and the same average particle size of the abrasive is used. It was found that the shape tends to be convex. Therefore, when performing polishing over multiple batches using the same polishing pad, the workpiece surface shape due to changes in the polishing pad over time is obtained by using a convex abrasive in the first half batch and using a concave abrasive in the second half batch. Can be suppressed. As a result, it is possible to finally obtain a workpiece having a desired flatness.

  Further, according to the results of the above experiment by the present inventor, whether the surface shape of the workpiece surface obtained after polishing is convex or concave depends greatly on the average particle size of the abrasive, and further, It was found that it also depends on the specific surface area. Therefore, as the abrasive used in the workpiece polishing method, a convex abrasive having a predetermined average particle diameter that makes the surface shape of the workpiece surface obtained after polishing convex, and a predetermined abrasive that has a concave surface shape on the workpiece surface. By using properly the concave abrasive having an average particle diameter, it becomes possible to stably manufacture a workpiece having high flatness. Furthermore, by suppressing the specific surface areas of the above-described convex abrasive and concave abrasive within a certain predetermined range, it is possible to manufacture a workpiece having higher flatness more stably.

Specifically, the average particle size of the abrasive particles in the abrasive having a convex and concave surface shape is selected from the following average particle size range. That is, the average particle size of the convex abrasive is 0.03 to 0.9 μm, and the average particle size of the concave abrasive is 0.5 to 3 μm.
Examples of the abrasive having an average particle size of 0.03 to 0.9 μm include cerium oxide, zirconium oxide, aluminum oxide, manganese oxide, colloidal silica, diamond, and silicon carbide. Examples of the abrasive having an average particle size of 0.5 to 3 μm include cerium oxide, zirconium oxide, manganese oxide, diamond, and silicon carbide.
Based on such knowledge, it is also possible to select the type of abrasive based on the average particle size of the abrasive.

The abrasive used properly may be the same or different. For example, in the case of different types of abrasives, a combination of cerium oxide having an average particle diameter of 0.5 to 3 μm and colloidal silica having an average particle diameter of 0.03 to 0.2 μm can be mentioned.
However, from the viewpoint of cleaning properties and prevention of scratches, it is preferable to use the same type as much as possible. As the same abrasive species from which the surface shape of the workpiece after polishing is convex or concave, there is cerium oxide.
This cerium oxide is generally used in a polishing step prior to the ultra-precision polishing step using colloidal silica when performing ultra-precision polishing using colloidal silica. The main purpose of the ultra-precision polishing process with colloidal silica is to smooth the surface of the workpiece. It is almost decided by.
Therefore, it is effective to use an abrasive seed containing cerium oxide in a polishing process for manufacturing a mask blank substrate, particularly a glass substrate.

When polishing using a convex abrasive and a concave abrasive separately, it is preferable that the surface plate accuracy of the polishing platen be 30 μm or less, particularly 0.1 to 10 μm. This is because if the surface plate accuracy of the polishing surface plate deviates from the above range, the influence of the polishing surface plate on the surface shape of the work substrate becomes too strong, and it becomes difficult to control the surface of the work substrate with the abrasive.
The level of change between the convex abrasive and the concave abrasive depends on the change in the polishing pad over time (use period), the surface plate accuracy of the polishing surface plate, the type of polishing pad, and the processing conditions (of the polishing surface plate) It is determined appropriately according to the number of revolutions). For example, when the polishing platen has a platen accuracy of 30 μm or less and is continuously polished using the same polishing pad, polishing using a convex abrasive is performed over about 1/3 of the total number of batches, Then, it is preferable to polish using a concave abrasive.

In the present specification, the shape of the workpiece surface is convex (trend) refers to a shape in which the vicinity of the center of the workpiece is raised as shown in FIG. The concave shape (trend) means a shape in which the vicinity of the center of the workpiece is depressed as shown in FIG.
Further, the flatness (flatness) is calculated from the reference surface arbitrarily provided on the surface side of the workpiece surface by the difference between the maximum height and the minimum height of the surface shape in the workpiece surface (calculated from the measurement surface by the least square method). The difference between the maximum value and the minimum value of the measurement surface relative to the virtual absolute plane (focal plane). The flatness measurement method in this case is not particularly limited. It may be a stylus-type contact-type flatness measurement method or a non-contact-type flatness measurement method using light interference, but it is a non-contact type from the viewpoint of measurement accuracy, measurement area (wide range), etc. A flatness measurement method is preferred.
Furthermore, a preferable flatness value (predetermined value) on the workpiece surface is appropriately determined depending on the use of the workpiece. For example, in the case of a mask blank substrate, in consideration of an exposure wavelength to be used, pattern position accuracy when a mask is used, and pattern transfer accuracy when pattern exposure is performed, 1 μm or less, 0.5 μm or less, and 0.25 μm or less are set. A preferable flatness value (predetermined value) on the workpiece surface is used.

Such a workpiece polishing method is suitably used as a polishing method for a mask blank substrate. Here, the material of the mask blank substrate is not particularly limited, and is appropriately selected according to each application.
For example, synthetic quartz glass, aluminosilicate glass, aluminoborosilicate glass, borosilicate glass, soda lime glass, alkali-free glass and the like are used.

In the polishing process for the mask blank substrate, a plurality of stages of polishing with different average particle diameters of the polishing agent are carried out in order to mirror the substrate surface.
In that case, an abrasive having a smaller average particle diameter is used as the polishing process proceeds. From the viewpoint of mirroring the substrate, it is preferable that the final polishing step is polished with a single abrasive. Therefore, it is preferable that the above-described polishing method is performed in a polishing step before the ultraprecision polishing step using an abrasive using colloidal silica as an abrasive species.

[Examples and Comparative Examples]
Examples of the present invention and comparative examples will be described below.
<Example 1>
As a workpiece, a mask blank substrate (size: 152.4 mm × 152.4 mm) (hereinafter simply referred to as a glass substrate) made of synthetic quartz glass that has been subjected to a grinding process is prepared, and 12 glass plates are provided in a double-side polishing apparatus. The substrate was set, and double-side polishing (precision polishing) was performed using the following double-side polishing apparatus.
Double-side polishing by the double-side polishing apparatus was performed using the polishing apparatus shown in FIG. That is, a glass substrate is put into a plurality of holding holes provided in a disk-shaped carrier, and the upper and lower surface plates are held in a state where the substrate is sandwiched between a lower surface plate and an upper surface plate to which a polishing pad in a double-side polishing apparatus is attached. This was done by rotating them counterclockwise. As a result, both sides of the glass substrate were polished simultaneously while revolving.
In addition, the polishing agent is the first to sixth batches of convex abrasive A, which has a convex surface shape on the surface of the substrate when the glass substrate is polished using the initial abrasive. The system abrasive B was selectively used from the 7th batch to the 18th batch, and 18 batches were continuously polished from the start of polishing to the end of polishing (the abrasive was circulated). Polishing was performed by replacing the abrasive with a new one every three batches. The same polishing pad was used from 1 batch to 18 batches.

The used abrasives A and B are
Abrasive A (convex abrasive) = cerium oxide (average particle size 0.7 μm)
Abrasive B (concave abrasive) = cerium oxide (average particle size 1 μm)
The polishing liquid is abrasive A + water, abrasive B + water,
The used polishing pad was a soft polisher (suede type).
The above-mentioned average particle diameter is a value measured by a light diffraction method.
Moreover, the surface plate accuracy of the polishing surface plate (upper and lower surface plates) was 5 μm or less, and the processing load during polishing was a processing load: 50 to 150 g / cm ² .
In addition, the flatness of 12 glass substrates per batch was measured, and the average value of the flatness of 12 glass substrates was defined as the flatness of the batch. The transition of the flatness of 18 batches at that time is shown in FIG. 3 (the flatness was measured with a flatness measuring machine (FM200 manufactured by Tropel) (the same applies to the following comparative examples)).
As shown in FIG. 3, the flatness of the glass substrate obtained when 18 batches are polished continuously is almost concave from about 0.5 μm to 1.5 μm, and the absolute value is 1. It could be suppressed to less than 5 μm.

Next, the glass substrate (216 sheets) obtained by the above-mentioned double-side polishing was used, and ultraprecision polishing was performed under the following conditions. As the polishing machine for ultra-precision polishing, the same double-side polishing machine as described above was used.
Polishing liquid: Colloidal silica (average particle size 70 nm) + water Polishing pad: Super soft polisher (suede type)
Processing load: 50-100 g / cm ²
Example 216 When the flatness of 216 glass substrates was measured, 72% of the glass substrates having a flatness of 0.5 μm or less were obtained, and 96% of the glass substrates having a flatness of 1 μm or less were obtained.

<Comparative Examples 1 and 2>
The abrasives A and B used in Example 1 above are not used properly, and only the abrasive A (Comparative Example 1) and the abrasive B (Comparative Example 2) are used (replaced with new ones every 3 batches). Then, a glass substrate was prepared in the same manner as in Example 1 except that 18 batches were polished continuously. FIG. 3 shows the change in flatness when 18 batches of precision polishing were performed continuously. As shown in FIG. 3, when the abrasive A was used, the flatness was about 0.4 μm to about 1.1 μm, and the absolute value was suppressed to less than 1.2 μm, which was better than that of Example 1. However, there were many cases where the surface shape of the substrate was relatively convex. On the other hand, when the abrasive B was used, the flatness was about 0.4 μm to about 1.7 μm, and the flatness varied compared to Example 1. In addition, as a surface shape of a board | substrate, there were many results with a comparatively concave shape.
Further, as in Example 1, after finishing the ultraprecision polishing, the flatness of 216 glass substrates polished in Comparative Examples 1 and 2 was measured. In the case of Comparative Example 1, the flatness was 0.5 μm. The following glass substrates accounted for 21% of the total, and glass substrates with a flatness of 1 μm or less accounted for 53%. In Comparative Example 2, the glass substrate having a flatness of 0.5 μm or less was 48%, and the glass substrate having a flatness of 1 μm or less was 82%.

  As described above, it has been found that by properly using the convex abrasive and the concave abrasive, particularly by properly using them together with the change over time of the polishing pad, it is possible to stably obtain a glass substrate having high flatness.

<Examples 2 and 3>
Next, in Example 1 described above, the specific surface area of the abrasive B was adjusted to ² to 15 m ² / g (Example 2), and the specific surface area of the abrasive B was further adjusted to the range of 4 to 12 m ² / g. Except having used the agent, after grind | polishing similarly to Example 1, the above-mentioned superprecision grinding | polishing was performed and the glass substrate was obtained.
As a result, in the case of Example 2, the glass substrate having a flatness of 0.5 μm or less is 75% of the whole, and the glass substrate having a flatness of 1 μm or less is 98%. In the case of Example 3, the flatness is 0.5 μm or less. The glass substrate was 80% of the total, and the glass substrate having a flatness of 1 μm or less was 98%. Thus, even better results were obtained than in Example 1. Thus, it was confirmed that the ratio of the glass substrate having a flatness of 0.5 μm or less is particularly increased by suppressing the specific surface area of the concave abrasive (abrasive B) to a certain range.

<Examples 4 and 5>
Next, in Example 1 described above, abrasives A and B were changed to abrasives C and D (Example 4) and abrasives E and F (Example 5) in the same manner as in Example 1. After polishing, the above-described ultraprecision polishing was performed to obtain a glass substrate.
Abrasive C (convex abrasive) = cerium oxide (average particle size 0.9 μm)
Abrasive D (concave abrasive) = cerium oxide (average particle size 3 μm)
Abrasive E (convex abrasive) = cerium oxide (average particle size 0.3 μm)
Abrasive F (concave abrasive) = cerium oxide (average particle size 0.5 μm)
As a result, in Example 4, the glass substrate having a flatness of 0.5 μm or less is 70% of the whole, and the glass substrate having a flatness of 1 μm or less is 90%. In Example 5, the glass having a flatness of 0.5 μm or less is used. The substrate was 75% of the whole, and the glass substrate having a flatness of 1 μm or less was 97% of the whole.
In the above examples, the convex abrasive has an average particle size larger than that of the abrasive used in the ultraprecision polishing step, and the effect of the present invention can be confirmed up to about 0.03 μm as the lower limit. It was.

It is sectional drawing of the grinding | polishing apparatus used when implementing this invention. The surface shape of the workpiece is schematically shown. (A) shows a convex shape, and (b) shows a concave shape. It is a graph which shows transition of the flatness of the example of the present invention, and a comparative example.

Explanation of symbols

W Work 10 Lower surface plate 20 Upper surface plate 30 Sun gear 40 Internal gear 50 Carrier 60 Abrasive supply means

Claims (6)

A polishing surface plate having a polishing pad affixed to the surface; and a work holding means for holding a mask blank substrate placed on the polishing surface plate, on the polishing pad side held by the work holding means. A mask blank for manufacturing a mask blank substrate through a polishing process in which a polishing agent is supplied to the surface of the mask blank substrate and the surface of the mask blank substrate is polished by relative movement of the mask blank substrate and the polishing pad. A method for manufacturing a substrate for an automobile, comprising:
A unit of the substrate that can be polished at a time by holding the mask blank substrate on the work holding means is one batch, and after the completion of this one batch polishing, polishing of a substrate different from the substrate is performed over a plurality of batches. A method for manufacturing a mask blanks substrate for polishing and manufacturing a plurality of mask blanks substrates,
As the abrasive, one batch or a plurality of concave abrasives with an average particle diameter of 0.5 to 3 μm and convex abrasives with an average particle diameter of 0.03 to 0.9 μm. A method for producing a mask blank substrate, which is used separately for each batch. The method for producing a mask blank substrate according to claim 1, wherein the concave abrasive has a specific surface area of ² to 15 m ² / g.   3. The method for manufacturing a mask blank substrate according to claim 1, wherein the polishing pad is a suede type polishing pad.   4. The mask according to claim 1, wherein, in polishing over a plurality of batches, the first batch is polished using the convex abrasive and the latter batch is polished using the concave abrasive. A method for manufacturing a substrate for blanks.   For the surface of the polishing platen on the side where the polishing pad is affixed, when measuring the surface shape at a certain reference length, the maximum value and the minimum value in the surface shape with respect to the reference surface calculated by the least square method The method for producing a mask blank substrate according to any one of claims 1 to 4, wherein the polishing platen represented by the difference has a platen accuracy of 30 µm or less (not including 0).   The said grinding | polishing process has a superprecision grinding | polishing process using the abrasive | polishing agent of colloidal silica, and implements it at least in the grinding | polishing process before the said superprecision grinding | polishing process. Of manufacturing a mask blank substrate.

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