JP2004054285A - Glass substrate for mask blanks, method for manufacturing glass substrate for mask blanks, mask blanks, method for manufacturing mask blanks, transfer mask, and method for manufacturing same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method for a glass substrate for an electronic device which has no surface defect such as a flaw nearby a glass substrate surface and an edge small droop of a glass substrate end surface, a manufacturing method for photomask blanks free of an under-film defect, and a manufacturing method for a photomask which is free of a pattern defect, can securely be mounted on a stepper of an exposing machine and has excellent pattern precision. <P>SOLUTION: The manufacturing method for the glass substrate for the electronic device and manufacturing methods for the photomask blanks and photomask are characterized in that in the manufacturing method of manufacturing the glass substrate by precisely polishing the glass substrate surface by using relatively small polishing abrasives after a rough polishing process using relatively large polishing abrasives, a crack which extend from the glass substrate surface along the depth and remains after the precise polishing process is made visual in a defect inspecting process carried out after the precise polishing process by etching the glass substrate surface (preferably by using an alkali solution) before the precise polishing processing. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention uses a glass substrate for a mask blank used for a transfer mask (and a mask blank that is a master plate of the transfer mask) used for manufacturing a semiconductor integrated circuit, a liquid crystal display panel, and the like, and a method for manufacturing the same, and using the substrate. The present invention relates to a method for manufacturing a mask blank and a transfer mask.

Photomask blanks and information recording media that use glass substrates for electronic devices are manufactured using functional thin films such as light-shielding films and phase shift films that cause an optical change to transfer exposure light, and recording films that record information. It is manufactured by forming one or more layers on a device glass substrate. In a process of manufacturing an electronic device such as a photomask blank or an information recording medium, a defect inspection for inspecting a defect existing on a glass substrate or a defect inspection is usually performed after an electronic device is manufactured. Defects present on the glass substrate for electronic devices are scratches, dirt, bubbles, striae, and the like. These defects are visually inspected and transmitted or scattered light from the glass substrate by irradiating the glass substrate surface with inspection light. Inspection is performed by a defect inspection apparatus that detects a defect by using the inspection.

On the other hand, the defect inspection after manufacturing the electronic device is performed to check whether there is any foreign matter or pinhole in the functional thin film or on the functional thin film, and whether there is any problem such as optical characteristics and recording characteristics.

In particular, among the defects existing in the glass substrate for electronic devices, a defect in a crack state called a crack is used in a grinding step or a polishing step (for example, cerium oxide before a final polishing step in which the grain size of abrasive grains is relatively large). It is formed in the main polishing step), cannot be detected at all in a certain direction, and is hard to detect in a certain direction because it has almost no width on the glass substrate surface.

In the above-mentioned defect inspection, visual inspection is performed, which is advantageous in that the glass substrate can be immediately inspected from all directions and the efficiency and reliability of the inspection and the discrimination of the defect type are performed. Cannot be detected, and cracks are often overlooked because the size on the glass substrate surface is very small. Despite the small cracks originally on the glass substrate surface, the glass substrate that passed the defect inspection is the first in the defect inspection process performed when forming a functional thin film on the glass substrate and manufacturing an electronic device, Detected by a defect inspection machine.

Since cracks are sub-film defects, they cannot be repaired after the electronic device is manufactured. Therefore, when an electronic device is manufactured, if a sub-film defect of a crack is detected, the electronic device must be discarded or a functional thin film must be removed and the glass substrate surface must be precisely polished again to re-create the electronic device. There is a problem that the yield is low and the manufacturing cost is high.

Hereinafter, a glass substrate for a photomask blank will be described as an example of a glass substrate for an electronic device.

At present, when a semiconductor integrated circuit or a liquid crystal display panel is manufactured, a photolithography technique is applied in a process of forming wiring and other regions.

In this photolithography process, a photomask used as an exposure master has a patterned light-shielding film formed on a transparent substrate, and the light-shielding film pattern is applied to a silicon wafer or a glass substrate through an exposure apparatus. It is transferred onto a transfer body, and a semiconductor integrated circuit and a liquid crystal display panel are manufactured. Pattern characteristics transferred onto a silicon wafer or a glass substrate are directly related to the light-shielding film pattern formed on the photomask, and it is important that the light-shielding film pattern has no pattern defects.

The causes of pattern defects include sub-film defects due to defects on the glass substrate surface for electronic devices (such as scratches and foreign particles), and defects in photomask blanks (such as foreign particles and half pinholes (the foreign particles that have adhered to the film come off). Pinholes), defects in the film, defects on the film, etc. are considered. However, in combination with the miniaturization of patterns, surface defects in glass substrates for electronic devices that are difficult or impossible to correct after manufacturing electronic devices. And the precision of the substrate shape has become more stringent.

For example, as disclosed in Patent Document 1, a glass substrate for an electronic device is polished using an abrasive mainly composed of cerium oxide, and then finish-polished (precision polishing) using colloidal silica. It is manufactured through

FIG. 6 is a diagram showing a conventional method for manufacturing a glass substrate for an electronic device.

In FIG. 6, after a rough polishing step (S601) of polishing the main surface of a glass substrate using relatively large abrasive grains having an average particle size of about 1 to 3 μm, a relatively average particle size of 1 μm or less is obtained. After performing a precision polishing step (S602) of polishing using small abrasive grains, a defect inspection step (S603) such as visual inspection is performed to manufacture a glass substrate.
JP-A-1-40267

Cracks among the defects of the glass substrate must be confirmed by a defect inspection device by irradiating inspection light from the front and back surfaces of the photomask blanks only when a photomask blank is manufactured by forming a film on the glass substrate. There are many. Further, when a photomask is formed using a photomask blank having such a sub-film defect, the pattern formed on the photomask is disconnected, resulting in a defect.

(4) With the recent miniaturization of patterns, the line width of patterns drawn on photomasks is becoming narrower, and complicated patterns are required. Due to such recent miniaturization of patterns, it takes several days to produce one photomask from one photomask blank. Therefore, a defect that can be corrected is sufficient, but in the case of a defect that cannot be corrected, the photomask blank must be recreated from scratch. Further, there is a problem that even a repairable defect requires cost and time.

Therefore, as one means for solving the above-mentioned problem, in order to surely remove the crack by the finish polishing, the polishing time of the final polishing is lengthened, and the crack is removed by securing a sufficient polishing allowance. An attempt was made to do so.

However, although the cracks certainly changed in the direction of decreasing by this method, the depth of cracks formed in the polishing process before the precision polishing varied, and cracks often remained due to insufficient polishing allowance.

Further, if the polishing time of the precision polishing is increased in order to surely remove cracks existing near the substrate surface, there is a problem that the edge of the glass substrate end face becomes large.

In recent years, the precision in mounting a photomask (reticle) on a stepper of an exposure machine has become strict due to the miniaturization of patterns, and the shape (flatness) accuracy of the end face of a glass substrate has been required. If the shape accuracy of the end face of the glass substrate (for example, edge droop of the end face of the substrate) is poor, the suction of the substrate at the time of mounting on the stepper is not reliably performed, and the positional accuracy at the time of mounting is deteriorated.

特 開 Also, as a method for sorting glass substrates, Japanese Patent Application Laid-Open No. 2002-201042 has been proposed. This is done by polishing the sliced silica glass substrate raw material, cleaning and drying, and then inspecting the silica glass substrate obtained by etching. If the defect is 0.3 μm or more in the direction parallel to the substrate surface, It is characterized by selecting a silica glass substrate that does not exist on the substrate surface.

ク Cracks (latent scratches) which cause concave defects of the glass substrate, which are problematic here, mainly occur in the grinding process (lapping process). The polishing step (coarse polishing, precision polishing) after the grinding step aims at removing defects such as cracks and scratches.

で は In this method, the glass substrate surface is etched after lapping, rough polishing, and final precision polishing, so that no consideration is given to the roughness of the glass substrate surface due to the etching. Furthermore, when this method is used, the cracks formed in the lapping step may be deformed in the depth direction by the local pressurization of the cracks by a polishing agent such as cerium oxide performed in rough polishing due to the properties of silica glass. The cracks cannot be removed without excessive final precision polishing (increase in polishing allowance = long polishing time). Therefore, there is a problem that the productivity is reduced and the edge droop amount of the end face of the glass substrate is increased.

(4) Since the amount of etching removal by chemicals after the final precision polishing is 0.2 to 0.5 μm, the surface roughness of the quartz glass substrate becomes rough even when there are no concave defects.

ガ ラ ス A glass substrate used for lithography such as a glass substrate for mask blanks is required to have high flatness and high smoothness as the exposure wavelength becomes shorter (miniaturization of the pattern). Focusing on the smoothness, when the exposure wavelength is ArF excimer laser (wavelength 193 nm) and F2 excimer laser (wavelength 157 nm), the root mean square roughness (RMS) is 0.2 nm or less, and when the exposure wavelength is EUV (wavelength 13 to 14 nm). , A root mean square roughness (RMS) of 0.15 nm or less is required. However, under the above-described etching conditions, the surface roughness of the glass substrate becomes rough, and these requirements cannot be satisfied.

Therefore, the present invention solves the above-mentioned problems of the prior art. First, the present invention has high smoothness that can be used even in a short wavelength region such as an ArF excimer laser, an F2 excimer laser, and EUV. It is an object to provide a glass substrate for a mask blank and a method for manufacturing the same.

Secondly, in addition to the above, there is provided a glass substrate for a mask blank having no surface defect on the main surface of the glass substrate, a glass substrate for a mask blank which is not affected by edge drooping of an end surface of the glass substrate, and a method of manufacturing the same. The purpose is to:

Thirdly, it is an object of the present invention to provide a mask blank having no sub-film defects and which can be securely mounted on a stepper of an exposure machine, and a method for manufacturing the same.

Fourthly, it is an object of the present invention to provide a transfer mask free from pattern defects (pattern breakage or the like) and capable of being securely mounted on a stepper of an exposure machine, and a method for manufacturing the same.

た め In order to solve the above problems, the present invention has the following configurations.

(Configuration 1)
In the glass substrate for a mask blank obtained through a post-treatment process including a precision polishing process after the etching treatment, the surface roughness of the main surface of the glass substrate is 0.2 nm or less in root mean square roughness (RMS). A glass substrate for mask blanks, comprising:

(Configuration 2)
2. The glass substrate for a mask blank according to Configuration 1, wherein the etching treatment has a function of exposing defects remaining on a main surface of the glass substrate.

(Configuration 3)
The glass substrate for a mask blank according to Configuration 1 or 2, wherein a surface defect on a main surface of the glass substrate cannot be detected by visual inspection.

(Configuration 4)
4. The glass substrate for a mask blank according to any one of Configurations 1 to 3, wherein an edge droop amount of a peripheral portion of the main surface of the glass substrate is -2 μm to 0 μm.

(Configuration 5)
5. A mask blank comprising a glass substrate for a mask blank according to any one of the constitutions 1 to 4, wherein a thin film which causes an optical change to transfer exposure light is formed on a main surface of the glass substrate.

(Configuration 6)
A transfer mask, wherein a thin film pattern that causes an optical change to transfer exposure light is formed on a main surface of the glass substrate for a mask blank according to any one of the constitutions 1 to 4.

(Configuration 7)
In the method for manufacturing a glass substrate for a mask blank having a step of exposing defects remaining on the main surface of the glass substrate, after the step of exposing the defects, a post-processing step including precision polishing is performed. A method for manufacturing a glass substrate for mask blanks.

(Configuration 8)
The glass substrate for a mask blank according to Configuration 7, wherein the post-processing step includes a precision polishing step of precision polishing the main surface and a cleaning step of cleaning the main surface after the precision polishing step. Production method.

(Configuration 9)
The glass substrate for a mask blank according to claim 8, wherein the main surface of the glass substrate after the cleaning step has a roughness of 0.2 nm or less in root mean square roughness (RMS). Production method.

(Configuration 10)
8. The method of manufacturing a glass substrate for a mask blank according to Configuration 7, wherein the step of exposing the defects is performed by etching the main surface.

(Configuration 11)
The method for manufacturing a glass substrate for a mask blank according to Configuration 8 or 9, further comprising a defect inspection step after the cleaning step.

(Configuration 12)
After a rough polishing step of polishing the glass substrate surface using polishing abrasive grains having a predetermined average particle diameter, a precision polishing step of polishing using polishing abrasive grains having an average particle diameter smaller than the predetermined average particle diameter In the method of manufacturing a glass substrate for mask blanks to produce a glass substrate by performing
Before performing the precision polishing step, by etching the surface of the glass substrate, extending in the depth direction from the surface of the glass substrate, cracks remaining after the precision polishing step, in a defect inspection step performed after the precision polishing step A method for producing a glass substrate for mask blanks, which is made to be obvious.

(Configuration 13)
13. The method of manufacturing a glass substrate for a mask blank according to Configuration 12, wherein a cleaning step of cleaning a main surface of the glass substrate is performed after the precision polishing step.

(Configuration 14)
14. The method for manufacturing a glass substrate for a mask blank according to Configuration 13, wherein a main surface of the glass substrate after the cleaning step has a roughness of 0.2 nm or less in root mean square roughness (RMS). Method.

(Configuration 15)
The method according to configuration 13 or 14, wherein the cleaning step uses a cleaning liquid having an etching effect, and performs cleaning under a condition that a removal amount of the glass substrate by etching is more than 0 μm and less than 0.01 μm. A method for manufacturing a glass substrate for mask blanks.

(Configuration 16)
13. The method of manufacturing a glass substrate for a mask blank according to configuration 11 or 12, wherein the defect inspection step is performed by visual inspection.

(Configuration 17)
The etching treatment is performed on the surface of the glass substrate on the side to be precisely polished in a range of 0.01 to 0.1 mm. 13. The method for manufacturing a glass substrate for a mask blank according to configuration 10 or 12, wherein the glass substrate is removed by 2 μm.

(Configuration 18)
A mask, characterized in that a thin film that causes an optical change to transfer exposure light is formed on a main surface of a glass substrate obtained by the method of manufacturing a glass substrate for a mask blank according to any one of the constitutions 7 to 17. Blanks manufacturing method.

(Configuration 19)
20. A method for manufacturing a transfer mask, comprising: forming a thin film pattern by patterning the thin film in the mask blank according to Configuration 18.

ADVANTAGE OF THE INVENTION According to this invention, a defect detection can be facilitated by making the latent defect in the vicinity of the surface of the glass substrate for mask blanks easy, and, specifically, the following industrially useful remarkable effects are obtained. Play.

1) It is possible to provide a glass substrate for an electronic device having high smoothness that can be used even in a short wavelength region such as an ArF excimer laser, an F2 excimer laser, and EUV, and a method for manufacturing the same.

2) In addition to the above, there is provided a glass substrate for a mask blank having no surface defect on the main surface of the glass substrate, a glass substrate for a mask blank which is not affected by edge drooping of an end surface of the glass substrate, and a method of manufacturing the same. it can.

3) It is possible to provide a mask blank which has no sub-film defects and which can be securely mounted on a stepper of an exposure machine, and a method of manufacturing the same.

4) It is possible to provide a transfer mask free from pattern defects (pattern disconnection or the like) and that can be securely mounted on a stepper of an exposure machine, and a method for manufacturing the same.

実 施 Embodiments of the present invention will be described for each of the above configurations.

The glass substrate for a mask blank in Configuration 1 is a glass substrate for a mask blank obtained through an etching process and a post-processing process including a precision polishing process, wherein a surface roughness of a main surface of the glass substrate is a root mean square. The roughness (RMS) is 0.2 nm or less. Preferably, the root mean square roughness (RMS) is 0.15 nm or less.

Since the surface roughness of the main surface of the glass substrate for mask blanks is as high as 0.2 nm or less in root mean square roughness (RMS), it can be used in short wavelength regions such as ArF excimer laser, F2 excimer laser, and EUV. A glass substrate for a possible mask blank can be provided.

{Circle around (2)} The glass substrate for mask blanks according to the second aspect is characterized in that the glass substrate for mask blanks has an action of embedding the above-mentioned etching treatment in the first aspect or the defects remaining on the main surface of the glass substrate. Since the etching treatment having a function of exposing defects remaining on the main surface of the glass substrate is performed before the precision polishing step, a glass substrate for mask blanks having high smoothness can be obtained.

欠 陥 Defects remaining on the main surface of the glass substrate referred to here are concave surface defects such as cracks.

{Circle around (3)} The glass substrate for a mask blank in Configuration 3 is characterized in that surface defects on the main surface of the glass substrate in Configuration 1 or 2 cannot be detected by visual inspection.

Since the surface defect of the main surface of the glass substrate is a glass substrate for a mask blank that cannot be detected by a visual inspection performed after precision polishing after the etching process, there is no surface defect that becomes a sub-film defect when the mask blank is formed. A highly reliable glass substrate can be provided.

{Circle around (4)} The glass substrate for a mask blank in the configuration 4 is characterized in that the edge sag amount of the peripheral portion of the main surface of the glass substrate in any of the configurations 1 to 3 is −2 μm to 0 μm. By setting the edge droop amount of the peripheral portion to −2 μm to 0 μm, it is possible to improve the positional accuracy when the substrate is mounted on the stepper of the exposure machine.

The edge droop amount of the peripheral portion (end face) of the main surface of the glass substrate is preferably -1 μm to 0 μm, more preferably −0.5 μm to 0 μm. The edge droop amount is shown in FIG. As shown, when 3 to 16 mm is defined as a virtual reference plane from the boundary between the main surface of the glass substrate and the chamfered surface and the height of the virtual reference surface is set to 0, the distance between the main surface and the chamfered surface is It is defined by the maximum height within a range of 3 mm from the boundary. Here, a maximum height of negative (-) refers to a shape in which the periphery of the main surface of the substrate is hanging (edge drooping shape), and a maximum height of positive (+) refers to a periphery of the main surface of the substrate. Refers to the shape that has risen.

{Circle around (5)} The mask blank in the configuration 5 is characterized in that a thin film that causes an optical change to transfer exposure light is formed on the main surface of the glass substrate for a mask blank in any of the configurations 1 to 4. Since the mask blank is formed using the glass substrate for the mask blank in any one of the constitutions 1 to 4, it can be used even in a short wavelength region such as an ArF excimer laser, an F2 excimer laser, and an EUV, and can be used as a transfer mask having no sub-film defects. Then, a mask blank that can be securely mounted on the stepper of the exposure machine is obtained.

{Circle around (6)} The transfer mask according to Configuration 6 is characterized in that a thin film pattern that causes an optical change to the transfer exposure light is formed on the main surface of the glass substrate for mask blanks according to any one of Configurations 1 to 4. Since the transfer mask is formed by using the mask blank glass substrate in any one of the constitutions 1 to 4, it can be used even in a short wavelength region such as an ArF excimer laser, an F2 excimer laser, or an EUV, and has no pattern defects (pattern disconnection, etc.). In addition, since the edge of the glass substrate end surface (peripheral portion of the main surface of the glass substrate) is small, a transfer mask that can be securely mounted on a stepper of an exposure machine can be obtained.

The method for producing a glass substrate for a mask blank in Configuration 7 is a method for producing a glass substrate for a mask blank having a step of exposing defects remaining on a main surface of the glass substrate, and after the step of exposing the defects, And a post-processing step including precision polishing is performed.

工程 Since the step of exposing defects remaining on the main surface of the glass substrate is performed before the post-processing step including precision polishing, a glass substrate for mask blanks having high smoothness can be obtained.

欠 陥 Defects remaining on the main surface of the glass substrate referred to here are concave surface defects such as cracks.

The method of manufacturing a glass substrate for a mask blank in Configuration 8, wherein the post-treatment process in Configuration 7 includes a precision polishing process of performing precision polishing on the main surface, and a cleaning process of cleaning the main surface after the precision polishing process. It is characterized by including.

After the precision polishing process, a cleaning process of cleaning the main surface is performed, so that the abrasive grains used in the precision polishing process and foreign substances adhered to the substrate surface can be removed. A glass substrate for mask blanks free from surface defects due to the above is obtained.

洗浄 Examples of the cleaning liquid used in the cleaning step include an acidic solution such as hydrofluoric acid, silicic hydrofluoric acid, and sulfuric acid, an alkaline solution such as sodium hydroxide and potassium hydroxide, and pure water. In order to remove the deposits on the main surface of the glass substrate, a solution having an etching action (an acidic solution or an alkaline solution) is preferable from the viewpoint of removing ability. The removal amount of the glass substrate by the etching action is performed by appropriately adjusting cleaning conditions such as the type, concentration, time, and temperature of the chemical solution. In order to prevent surface roughness due to cleaning, cleaning conditions are selected so that the removal amount is more than 0 μm and less than 0.01 μm. From the viewpoint of detergency, hydrofluoric acid or silicic hydrofluoric acid is preferable, and the concentration of hydrofluoric acid or silicic hydrofluoric acid is preferably a low concentration of 0.5% or less.

The manufacturing method of a glass substrate for a mask blank in Configuration 9 is that the main surface of the glass substrate after the cleaning step in Configuration 8 has a roughness of 0.2 nm or less in root mean square roughness (RMS). Features.

Since the surface roughness of the main surface of the glass substrate is as high as 0.2 nm or less in root mean square roughness (RMS), a mask that can be used in short wavelength regions such as ArF excimer laser, F2 excimer laser, and EUV A glass substrate for blanks can be provided. Preferably, the root mean square roughness (RMS) is 0.15 nm or less.

The method for manufacturing a glass substrate for a mask blank in the configuration 10 is characterized in that the step of revealing the defect in the configuration 9 is performed by etching the main surface of the glass substrate. This is preferable because defects remaining on the main surface can be effectively brought out and a cleaning effect can be obtained.

製造 The method for manufacturing a glass substrate for a mask blank in Configuration 11 is characterized by further including a defect inspection process after the cleaning process in Configuration 8 or 9. After the cleaning step, a defect inspection step is performed to select a glass substrate having no surface defects, so that an extremely reliable glass substrate having no surface defects affecting pattern defects can be provided.

The method for manufacturing a glass substrate for a mask blank according to the twelfth aspect, is characterized in that, after a rough polishing step of polishing the glass substrate surface using abrasive grains having a predetermined average particle size, the average particle size is smaller than the predetermined average particle size. A method of manufacturing a glass substrate for a mask blank, which performs a precision polishing step of polishing using abrasive grains having a glass substrate to produce a glass substrate, wherein the surface of the glass substrate is subjected to an etching treatment before performing the precision polishing step. Thus, cracks extending in the depth direction from the surface of the glass substrate and remaining after the precision polishing step are made apparent in a defect inspection step performed after the precision polishing step.

マ ス ク A glass substrate for mask blanks having no surface defects on the main surface of the glass substrate and having less edge droop on the end surface of the glass substrate (the peripheral portion of the main surface of the glass substrate) is obtained.

The rough polishing step in the present invention is performed for the purpose of removing scratches on the main surface of the glass substrate formed in the grinding step or the like and maintaining the flatness obtained in the grinding step, and the average grain size of the polishing abrasive grains. This is a step of polishing using relatively large abrasive grains having a diameter of about 1 to 3 μm.

材質 The material of the abrasive grains is appropriately selected according to the glass substrate material and the like, and for example, cerium oxide, zirconium oxide, or the like is used.

粗 Also, the rough polishing step may be performed once or may be performed a plurality of times. The polishing pad used in the rough polishing step may be either a hard polisher or a soft polisher.

Further, the precision polishing step in the present invention is performed for the purpose of removing the texture formed on the main surface of the substrate by the above-described rough polishing step or the like and mirroring the substrate, and the average particle diameter of the polishing abrasive grains. Is a step of polishing using relatively small abrasive grains of about 1 μm or less (for example, 30 nm to 1 μm). The material of the abrasive grains is appropriately selected according to the glass substrate material and the like as described above. Colloidal silica is preferred from the viewpoint that the average particle size is small and a smooth substrate surface can be obtained. In addition, since the main surface of the precisely polished glass substrate can be mirror-finished by using the abrasive grains as colloidal silica, cracks remaining after the fine polishing step are detected because they are present in a smooth surface state. It's easy to do. It is preferable that the average number diameter be small from the viewpoint of mirror finishing. It is preferable to use a soft or ultra-soft polisher for the polishing pad used in the precision polishing step from the viewpoint of mirror finishing. The surface roughness of the glass substrate for mask blanks finally obtained through the precision polishing process should be 0.2 nm or less in average surface roughness Ra and 0.2 nm or less in root mean square roughness (RMS). Is preferred.

In addition, the term “to be revealed in a defect inspection step performed after the precision polishing step” in the present invention means that a latent crack that cannot be visually confirmed or is difficult before etching is enlarged by etching, This means that cracks can be more significantly confirmed through a polishing process. For example, in the etching process, the glass substrate is enlarged to such a size that the presence or absence of a crack in the glass substrate can be determined in a defect inspection process performed after the precision polishing process. Specifically, it means to enlarge the width to such a degree that the presence or absence of a defect can be confirmed by the visual inspection of the structure 15, and it is preferable to enlarge the crack to a width of 0.2 μm or more on the surface of the glass substrate.

In addition, the etching process described in the above-described configurations 1, 2, 10, and 12 is performed before the precision polishing process for mirror polishing the surface of the glass substrate, before the rough polishing process, or after the rough polishing process. However, it may be performed before the precision polishing step or both after the rough polishing step and after the coarse polishing step and before the precision polishing step. For the purpose of eliminating surface defects after the precision polishing step, it is preferable to perform the etching treatment at least after the rough polishing step and before the precision polishing step.

Etching treatment may be either dry etching or wet etching.

ラ ッ ク The cracks are enlarged by this etching process. For example, when the etching is wet etching, the crack extending from the glass substrate surface toward the center is isotropically etched, and the depth of the crack in the center direction does not change much according to the etching amount on the glass substrate surface. However, the size (width) of the crack in the in-plane direction increases. In the present invention, since the etching process is performed before the precision polishing process, and then the precision polishing for mirror finishing is performed, in the defect inspection process performed after the precision polishing process, the glass substrate surface is ultra-smooth due to the precision polishing process. As a result, cracks having a certain size (width) due to the etching process are easily detected because they are present in a smooth surface state.

In addition, since the etching process is performed before the precision polishing process (particularly, after the rough polishing process and before the precision polishing process), the irregularities on the glass substrate surface become relatively smooth, and the glass substrate is mirror-finished. In this case, the load of the precision polishing step can be suppressed, and the shape of the end surface of the glass substrate becomes good (the edge droop amount of the peripheral portion of the main surface of the glass substrate becomes small).

精密 Generally, in the precision polishing process, a glass substrate is polished using a polishing pad of a soft or ultra-soft polisher, so that the shape of the end surface of the glass substrate tends to be edged as the polishing time advances. As described above, since the load of the precision polishing step can be reduced, the edge droop amount of the glass substrate end surface can be reduced.

The edge droop amount of the glass substrate end surface (the peripheral portion of the glass substrate main surface) can be set to −2 μm to 0 μm, preferably −1 μm to 0 μm, and more preferably −0.5 μm to 0 μm. .

A crack refers to a crack that extends in the depth direction from the surface of the glass substrate. Cracks are formed in a grinding step or a polishing step (for example, a polishing step using cerium oxide as a main component) before a finish polishing step in which the diameter of abrasive grains is relatively large, and the glass substrate surface has almost no width. So it is almost impossible to detect. Note that the cracks that are a problem in the present invention are, among others, cracks remaining after the precision polishing step, that is, cracks that are too deep to be removed in the precision polishing step. That is, if the cracks are shallow enough to be removed in the precision polishing process, they will disappear after the precision polishing process.

エ ッ チ ン グ Also, it is preferable to use an alkaline aqueous solution for the etching treatment. Here, the alkaline aqueous solution is preferably an aqueous solution of sodium hydroxide (NaOH) or potassium hydroxide (KOH), or a mixed aqueous solution thereof.

製造 The manufacturing method of a glass substrate for a mask blank in the configuration 13 is characterized in that, in the configuration 12, a cleaning step of cleaning a main surface of the glass substrate is performed after the precision polishing step.

After the precision polishing process, a cleaning process of cleaning the main surface is performed, so that the abrasive grains used in the precision polishing process and foreign substances adhered to the substrate surface can be removed. A glass substrate for mask blanks free from surface defects due to the above is obtained.

In the manufacturing method of a glass substrate for a mask blank in the configuration 14, the main surface of the glass substrate after the cleaning step in the configuration 13 has a roughness of 0.2 nm or less in root mean square roughness (RMS). Features.

Since the surface roughness of the main surface of the glass substrate is as high as 0.2 nm or less in root mean square roughness (RMS), a mask that can be used in short wavelength regions such as ArF excimer laser, F2 excimer laser, and EUV A glass substrate for blanks can be provided. Preferably, the root mean square roughness (RMS) is 0.15 nm or less.

In the manufacturing method of the glass substrate for a mask blank in the configuration 15, in the configuration 13 or 14, the cleaning step uses a cleaning liquid having an etching effect, and the removal amount of the glass substrate by etching is more than 0 μm and less than 0.01 μm. It is characterized by washing under conditions.

Normally, cleaning performed for the purpose of removing abrasive grains and foreign substances adhering to the substrate surface uses a detergent, an acid, an alkali, or the like, but a cleaning liquid (acid, alkali) having an etching action on the glass substrate is used. When used, the conditions are such that the surface of the glass substrate is removed more than 0 μm and less than 0.01 μm. This is because if the amount of etching removal in the cleaning step is 0.01 μm or more, unevenness due to the etching residue is formed, which is not preferable.

The method of manufacturing a glass substrate for a mask blank in Configuration 16 is characterized in that, in Configuration 11 or 12, the defect inspection step is performed by visual inspection.

Defect inspection methods include, but are not particularly limited to, visual inspection and inspection using a defect inspection apparatus that performs defect inspection by irradiating inspection light onto a glass substrate and detecting light scattered or leaking from the glass substrate. It is preferable to use a visual inspection, which is advantageous in improving the efficiency, reliability, and discrimination of defect types.

The method for manufacturing a glass substrate for a mask blank in the configuration 17 is the method according to the configuration 10 or 12, wherein the etching treatment removes the surface of the glass substrate on the side to be precisely polished by 0.01 to 0.2 μm. .

If it is less than 0.01 μm, it is not preferable because it becomes difficult to determine the presence or absence of cracks in a defect inspection step performed after the precision polishing step, and if it exceeds 0.2 μm, the surface roughness due to etching of the glass substrate This is not preferable because the surface shape (flatness) deteriorates.

エ ッ チ ン グ The etching rate in the etching treatment is preferably from 0.2 nm / min to 2.0 nm / min. If the etching rate is less than 0.2 nm / min, the degree of latent defect appearance is small, which is not preferable. If the etching rate is more than 2 nm / min, the glass substrate is rapidly corroded, and the surface roughness and surface shape (flatness) are deteriorated. Is not preferred. Preferably, it is 0.3 nm / min to 0.7 nm / min.

The manufacturing method of a mask blank in the constitution 18 is a method of manufacturing a mask blank glass substrate according to any one of the constitutions 7 to 17, wherein a thin film that causes an optical change to transfer exposure light is formed on the main surface of the glass substrate obtained by the method. It is characterized by forming. Since the mask blanks are manufactured using the glass substrate having no surface defects obtained by excluding the glass substrate having the cracks obtained in the configurations 7 to 17, the mask blanks having no sub-film defects can be obtained.

転 写 The method of manufacturing a transfer mask in Configuration 19 is characterized in that a thin film pattern is formed by patterning the thin film of the mask blank in Configuration 18. Since the transfer mask is manufactured using the mask blank having no sub-film defect obtained in the configuration 17, a transfer mask having no pattern defect (pattern break) and which can be securely mounted on a stepper of an exposure machine can be obtained.

Incidentally, the mask blanks in the present invention, in a broad sense, a photomask blanks in which only a light-shielding film having a function of shielding transfer exposure light on the main surface of a glass substrate, or transfer exposure light It includes a phase shift mask blank in which a phase shift film having a phase shift function for causing a phase difference change is formed, and a reflective mask blank in which a reflective film that reflects transfer exposure light and an absorber film that absorbs the transfer exposure light are formed.

マ ス ク Furthermore, the form of the mask blanks includes those in which a resist film is formed on the light-shielding film, the phase shift film, the reflection film, or the like.

材料 Further, the material of the glass substrate in the present invention is not particularly limited. Examples of the material for the glass substrate include quartz glass, non-alkali glass, soda lime glass, and aluminoborosilicate glass. Above all, quartz glass is a hard and brittle material compared to other glass materials, and therefore, cracks are likely to occur on the glass substrate surface in the grinding step and the rough polishing step. Therefore, the above-mentioned glass substrate for mask blanks and the method for manufacturing the same are particularly effective when the glass substrate material is quartz glass.

Hereinafter, the method for producing a glass substrate for mask blanks of the present invention will be described. In the following description, the mask blank glass substrate is referred to as an electronic device glass substrate.

製造 A method of manufacturing a glass substrate for an electronic device according to the present invention will be described with reference to FIG.

The method for manufacturing the glass substrate for an electronic device of FIG.
A rough polishing step (S101) of polishing both main surfaces of a glass substrate for an electronic device using relatively large abrasive grains after finishing both the main surface of the substrate with a lapping machine and the like; ,
An etching process (S102) for revealing latent cracks extending in the depth direction from the surface of the glass substrate by etching;
A precision polishing step (S103) of polishing using relatively small abrasive grains;
And a defect inspection step (S104) for inspecting the glass substrate for defects.

(1) The defect inspection step (S104) in FIG. 1 is performed for the purpose of removing a glass substrate having a defect that is still present even after performing a precision polishing step and mirror-polishing the main surface of the glass substrate as a defective product.

{Circle around (2)} The processing conditions of the above-mentioned etching step (S102) are determined as follows.

(4) In the defect inspection step of the above-described step (S104), cracks extending in the depth direction from the surface of the glass substrate are enlarged to such an extent that the cracks can be reliably detected and confirmed, and various conditions for realizing the cracks are set. In other words, cracks remaining after the precision polishing process are enlarged by the etching process performed before the precision polishing process, and the amount of etching that can be accurately detected and confirmed in the defect inspection process after the precision polishing process, specifically, Is defined as an etching condition of removing 0.01 to 0.2 μm. By doing so, the crack can be expanded to a width of 0.2 μm or more on the surface of the glass substrate, so that defects existing on the surface of the glass substrate can be reliably detected and confirmed.

More preferably, after finishing the precision polishing step for the purpose of mirror-finishing the glass substrate, the flatness of the glass substrate and the amount of edge droop of the glass substrate end surface are within a desired range (specifically, using a glass substrate. When a transfer mask (for example, a photomask) is used, the process (S102) is performed so that the photomask enters into a stepper of an exposure machine to have a predetermined degree of pattern position accuracy when the photomask is mounted on a stepper. ), The surface of the glass substrate becomes relatively smooth, and the stock removal amount in the precision polishing process can be reduced (the load of the precision polishing process for mirror finishing is reduced). It is preferable to set various conditions that can reduce the amount of change of the substrate end surface in the above.

For that purpose, it is preferable that the etching rate of the etching process is relatively slow, specifically, 0.2 nm / min to 2 nm / min. It is preferable to use an alkaline aqueous solution having a weak etching effect on the glass substrate.

In the manufacturing method of FIG. 1 described above, the polishing method in the rough polishing step and the precision polishing step may be any of a single-side polishing method and a double-side polishing method. Further, either a single wafer type or a batch type may be used.

Further, in the manufacturing method of FIG. 1 described above, after the rough polishing step or after the precision polishing step, removal of the polishing abrasive grains so that the polishing abrasive grains used in each polishing step are not carried over to the next step; A cleaning step is provided as necessary for the purpose of removing foreign substances adhering to the substrate surface. Cleaning methods include chemical (acid or alkali) cleaning, detergent, cleaning with pure water or ultrapure water, wet cleaning with functional water such as hydrogen water, and dry cleaning with UV (ultraviolet) irradiation or ozone treatment. From among these, one or a plurality of cleaning methods are selected and performed depending on the object to be removed.

When the cleaning is performed using a chemical solution having an etching effect on the glass substrate, the etching removal amount is more than 0 μm and less than 0.01 μm, preferably more than 0 μm and less than 0.005 μm so that unevenness due to the etching residue is not formed. It is desirable to do.

FIGS. 3 to 5 are cross-sectional views of the vicinity of the surface of the glass substrate before and after a crack due to etching treatment using an alkaline aqueous solution is made obvious. In addition, in order to make the description easy to understand, the description will be made assuming that the stock removal in the precision polishing step is 1 μm.

FIG. 3 is a cross-sectional view of the vicinity of the surface of the glass substrate after the rough polishing step and before the etching process.

表面 The surface of the glass substrate 1 after the rough polishing step is not yet completely mirror-finished, and irregularities such as texture are formed on the entire substrate surface. There are crack-like cracks 2 formed from the surface of the glass substrate 1 toward the center in places where irregularities like this texture are formed. This crack is formed during the grinding step or the rough polishing step in which the grain size of the abrasive grains is relatively large, and the depth thereof is various, such as cracks 21 and 22 having a diameter of more than 1 μm and cracks 23 having a diameter of less than 1 μm.

In the case of the shallow crack 23, it is removed in the subsequent precision polishing step, but in the case of the cracks 21 and 22 having a depth of 1 μm or more, which is deeper than the polishing allowance in the precision polishing step, it cannot be removed in the subsequent precision polishing step.

In the state of FIG. 3, cracks existing on the surface of the glass substrate cannot be visually confirmed.

FIG. 4 is a cross-sectional view of the vicinity of the surface of the glass substrate after the etching process.

In FIG. 4, the dotted line indicates the glass substrate surface before the etching process, and the solid line indicates the substrate surface after the etching process.

(4) Since the surface of the glass substrate is isotropically etched in the plane and in the depth direction by the etching process, the crack 2 is enlarged. However, in this state, the surface of the glass substrate is still almost the same as the state shown in FIG. 3, so that even if the crack is enlarged, it is difficult to visually check it because it is hidden by unevenness of the texture, and it may be overlooked.

FIG. 5 is a cross-sectional view near the surface of the glass substrate after the precision polishing step.

表面 The surface of the glass substrate 1 after the precision polishing step is in a mirror state with an average surface roughness Ra of 0.2 nm or less.

As shown in FIG. 5, a crack existing at a position deeper than the polishing allowance in the precision polishing step such that the depth from the glass substrate surface exceeds 1 μm is enlarged by etching as shown in the drawing. Since the cracks 31 and 32 formed in the mirror state of the surface of the glass substrate 1 can be reliably and easily detected in the defect inspection step (visual inspection) after the precision polishing step.

<Example 1> (Method of manufacturing glass substrate for electronic device in FIG. 1)
(1) Rough polishing step The end face of a synthetic quartz glass substrate (6 inches x 6 inches (1 inch = 25.4 mm)) is shaped and the glass substrate that has been ground by a double-sided lapping machine is batch-type double-side polished. Twelve sheets were set in the apparatus, and a rough polishing step was performed under the following polishing conditions. The processing load and polishing conditions were adjusted as appropriate.

Polishing liquid: Cerium oxide (average particle size 1-2 μm) + water Polishing pad: Hard polisher (urethane pad)
After the rough polishing step, the glass substrate was immersed in an aqueous solution containing hydrofluoric acid for cleaning in order to remove abrasive grains attached to the glass substrate.

表面 The surface roughness of the main surface of the obtained glass substrate was measured by an atomic force microscope (AFM), and the average surface roughness Ra was 0.25 nm.

(2) Etching Step Next, the obtained glass substrate is immersed in a chemical solution (alkali: sodium hydroxide) to etch away the surface of the glass substrate by about 0.05 nm, thereby enlarging cracks existing near the surface of the glass substrate. Was. The chemical concentration at this time was set so that the etching rate with respect to the glass substrate was 0.8 nm / min. When the surface roughness of the main surface of the obtained glass substrate was measured with an atomic force microscope, the average surface roughness Ra was 0.23 nm, and it was confirmed that the surface shape was slightly smooth.

(3) Precision Polishing Step Twelve obtained glass substrates were set in the double-sided polishing apparatus described above, and a precision polishing step was performed under the following polishing conditions. The processing load and the polishing conditions were appropriately adjusted (the polishing time was such that the change in the shape of the substrate end face was small due to the precision polishing step, and the polishing time required for the glass substrate surface to be mirror-finished (polishing allowance was small). A polishing time of about 1 μm) was set.)

Polishing liquid: Colloidal silica (average particle size 50-80 nm) + water Polishing pad: Soft polisher (Sweed type)
After the completion of the precision polishing step, the glass substrate was immersed in a washing tank of an alkaline aqueous solution and washed in order to remove abrasive grains attached to the glass substrate. The cleaning conditions with the alkaline aqueous solution were set so that the etching removal amount from the glass substrate was about 0.005 μm.

When the surface roughness of the main surface of the obtained glass substrate was measured with an atomic force microscope, a high smoothness of 0.14 nm in average surface roughness Ra and 0.18 nm in root-mean-square roughness RMS was obtained. Had been converted.

(4) Defect Inspection Step A defect inspection was conducted on the obtained 12 glass substrates by visual inspection. As a result, it was confirmed that one of the 12 glass substrates had a surface defect which seemed to have an enlarged crack. No surface defects such as cracks were observed in the ten glass substrates.

Further, when the shape of the end face of the glass substrate (the amount of edge drooping) was measured by a stylus type roughness meter (Surf Test 501) according to the above definition, the total number was in the range of −0.5 μm to −0.25 μm. It was good. Further, when the flatness of the main surface of the glass substrate was measured by a flatness measuring instrument (FM200: manufactured by Tropel), the total number was 1 μm or less, which was good.

The obtained glass substrate can be used as a glass substrate for a mask blank for ArF excimer laser and a glass substrate for a mask blank for F2 excimer laser.

In Example 1 described above, after the completion of the precision polishing step, the glass substrate was immersed in a cleaning tank of a low-concentration aqueous solution of hydrofluoric acid (concentration: 0.15%) in order to remove the abrasive grains attached to the glass substrate, and washed. A glass substrate was manufactured in the same manner as in Example 1 except that the washing conditions with the aqueous solution of hydrofluoric acid were set so that the immersion time was set such that the etching removal amount from the glass substrate was about 0.003 μm.

The surface roughness of the main surface of the obtained glass substrate was measured with an atomic force microscope. As a result, a high smoothness of 0.09 nm in average surface roughness Ra and 0.15 nm in root-mean-square roughness RMS was obtained. Had been converted.

A defect inspection was performed by visual inspection on the obtained 12 glass substrates. As a result, one of the 12 glass substrates was found to have a surface defect that seemed to have cracks, but the other 11 glass substrates were not. No surface defects such as cracks were observed.

Further, when the shape of the end face of the glass substrate (the amount of edge drooping) was measured by a stylus type roughness meter (Surf Test 501) according to the above definition, the total number was in the range of −0.5 μm to −0.25 μm. It was good. Further, when the flatness of the main surface of the glass substrate was measured by a flatness measuring instrument (FM200: manufactured by Tropel), the total number was 1 μm or less, which was good.

The obtained glass substrate can be used as a glass substrate for mask blanks for EUV.

<Comparative Examples 1 and 2>
In the method for manufacturing a glass substrate for an electronic device of Example 1, a glass substrate for an electronic device was produced under the same conditions except that the etching treatment step (2) was not performed (Comparative Example 1).

In the method for manufacturing a glass substrate for an electronic device of Example 1, the etching process in (2) is not performed, and the polishing conditions in the precision polishing process in (3) are changed by the rough polishing process in (1). A glass substrate for an electronic device was produced under the same conditions except that a polishing time required for a polishing allowance required for completely removing the scratches (a polishing time at which the polishing allowance is 5 μm) was set ( Comparative Example 2).

When the glass substrate for an electronic device of Comparative Example 2 was inspected for defects by visual inspection, the stock removal was sufficiently performed and all of the glass substrates were good. However, the shape of the glass substrate end face (the amount of edge drooping) was 100%. Below −2.0 μm, the shape of the substrate end face was deteriorated. In addition, when the flatness of the main surface of the glass substrate was measured by a flatness measuring device (FM200: manufactured by Tropel), the total number exceeded 1 μm (some of them exceeded 2 μm), and was deteriorated.

欠 陥 Incidentally, the glass substrate for an electronic device of Comparative Example 1 was inspected for defects by visual inspection, but no surface defects were confirmed.

<Evaluation of making photomask blank and photomask>
A photo in which a chromium nitride film / a chromium carbide film / a chromium oxynitride film was laminated by sputtering (total thickness of 900 Å) on one main surface of the glass substrate obtained in Example 1 and Comparative Examples 1 and 2 described above. A mask blank and a phase shift mask blank in which a nitrided molybdenum silicide film was formed on one main surface of a glass substrate by a sputtering method (800 angstrom thick) were manufactured. After film formation, scrub cleaning was performed to produce a photomask blank and a phase shift mask blank.

When the obtained photomask blank and phase shift mask blank were checked by a surface defect inspection apparatus, the glass substrate for an electronic device of Example 1 (a glass substrate for an electronic device having no surface defect in a concave portion) and the glass substrate for an electronic device of Comparative Example 2 were used. No sub-film defects were found in the photomask blanks prepared by the method described above, but three out of 12 photomask blanks prepared using the electronic device glass substrate of Comparative Example 1 had sub-film defects. (The film formed on the glass substrate was peeled off, and the surface of the glass substrate was treated by the etching treatment of (2). It was confirmed that the crack had a shape similar to that of the surface defect of the recessed portion because the crack was enlarged by the etching process. Is considered.).

Here, considering the above results, the method for manufacturing a glass substrate for an electronic device of Example 1 performs an alkali treatment before the precision polishing step to enlarge cracks present on the glass substrate, and to perform precision polishing. In the defect inspection process after the process, a surface defect was confirmed, and a photomask blank was manufactured using a glass substrate having no surface defect to obtain a photomask blank having no sub-film defect. However, in the method for manufacturing a glass substrate for an electronic device of Comparative Example 1, a glass substrate was manufactured without expanding a crack existing in the glass substrate, and a defect inspection was performed. The glass substrate having the surface defect described above was determined to be a non-defective product, and the process of manufacturing a photomask blank was started, and a photomask blank having a sub-film defect was obtained. This resulted in a significant decrease in the manufacturing yield of photomask blanks.

{Circle around (2)} A resist film was formed on the above film by a spin coating method, and a photomask and a phase shift mask having desired patterns were produced.

As a result, a photomask blank manufactured using the glass substrate for an electronic device in which the surface defect of the concave portion was not confirmed in Example 1 and a photomask manufactured using the glass substrate for an electronic device in Comparative Example 1 Among the blanks, no pattern defects such as a photomask blank having no sub-film defect and a photomask blank produced from the photomask blank of Comparative Example 2 were found.

However, among photomask blanks produced using the glass substrate for an electronic device of Comparative Example 1, a photomask was produced using a photomask blank in which a sub-film defect was found. A flaw was found.

Next, in order to carry out a substrate deformation test, a substrate holding test machine for vacuum chucking two sides of the substrate was prepared so that the mounting of the exposure machine on the stepper could be reproduced in the same manner. The degree of flatness was measured by an optical interferometer (Zygo Mark GPI) using the optical interferometer (Zygo Mark GPI). As for the photomasks manufactured using the electronic device glass substrates of Example 1 and Comparative Example 1, the flatness changes. Although the amount was 0.1 μm and almost no change was observed, the flatness change amount of the photomask manufactured using the electronic device glass substrate of Comparative Example 2 exceeded 0.5 μm, and A mounting failure due to the cause was confirmed.

Although the above embodiments have been described with reference to the preferred embodiments of the manufacturing method of the present invention, the present invention is not limited to the contents described in the above embodiments, but is described in the section for solving the above-mentioned problem. Also includes the content that was done.

According to the present invention, a glass substrate for an electronic device having high smoothness, which can be used even in a short wavelength region such as an ArF excimer laser, an F2 excimer laser, and EUV, is obtained. Further, in the above embodiments, the glass substrate for mask blanks has been described as the most useful example, but the glass substrate for liquid crystal display, the glass substrate for information recording media (magnetic disk, magneto-optical disk, optical disk), semiconductor wafer The manufacturing method of the present invention can also be applied to the above. Further, the shape of the substrate is a square shape (for example, a square shape (square or rectangular shape)), a disk shape, a substantially circular shape, or the like. Examples of the square substrate include a photomask blank, a phase shift blank, and a reflective mask blank. Glass substrate for mask blanks, glass substrate for liquid crystal display, etc. are available. Examples of the disk-shaped substrate include a glass substrate for an information recording medium, and a circular substrate is a semiconductor wafer.

It is a figure which shows the manufacturing method of the conventional glass substrate for electronic devices. It is a figure showing the manufacturing method of the glass substrate for electronic devices of the present invention. It is a figure showing the manufacturing method of the glass substrate for electronic devices of the present invention. FIG. 4 is a cross-sectional view of the vicinity of the surface of the glass substrate before a latent defect revealing process. FIG. 4 is a cross-sectional view of the vicinity of the surface of the glass substrate after a latent defect revealing process. 3 is a flowchart illustrating a method for manufacturing a glass substrate for an electronic device according to the present invention.

Explanation of reference numerals

1: glass substrate,
2, 21, 22, 23: cracks 31, 32, 33: enlarged cracks

Claims (19)

In the glass substrate for a mask blank obtained through the post-processing step including the precision polishing step after the etching processing, the surface roughness of the main surface of the glass substrate is 0. 0 in terms of root mean square roughness (RMS). A glass substrate for mask blanks having a thickness of 2 nm or less. 2. The glass substrate for a mask blank according to claim 1, wherein the etching treatment has a function of exposing defects remaining on a main surface of the glass substrate. 3. The glass substrate for a mask blank according to claim 1, wherein a surface defect on the main surface of the glass substrate cannot be detected by visual inspection. (4) The glass substrate for a mask blank according to any one of (1) to (3), wherein an edge droop amount of a peripheral portion of the main surface of the glass substrate is -2 μm to 0 μm. (5) A mask blank, wherein a thin film that causes an optical change to transfer exposure light is formed on a main surface of the glass substrate for a mask blank according to any one of (1) to (4). (5) A transfer mask, wherein a thin film pattern that causes an optical change to transfer exposure light is formed on a main surface of the glass substrate for a mask blank according to any one of (1) to (4). In the method of manufacturing a glass substrate for a mask blank having a step of exposing defects remaining on the main surface of the glass substrate, after the step of exposing the defects, a post-processing step including precision polishing is performed. A method for manufacturing a glass substrate for mask blanks. 8. The glass for a mask blank according to claim 7, wherein the post-processing step includes a precision polishing step of precision polishing the main surface, and a cleaning step of cleaning the main surface after the precision polishing step. Substrate manufacturing method. 9. The glass substrate for a mask blank according to claim 8, wherein the main surface of the glass substrate after the cleaning step has a roughness of 0.2 nm or less in root mean square roughness (RMS). Production method. 8. The method of manufacturing a glass substrate for a mask blank according to claim 7, wherein the step of revealing the defect is performed by etching the main surface. 10. The method for manufacturing a glass substrate for a mask blank according to claim 8, further comprising a defect inspection step after the cleaning step. After a rough polishing step of polishing the surface of the glass substrate using polishing abrasive grains having a predetermined average particle diameter, a precision polishing step of polishing using polishing abrasive grains having an average particle diameter smaller than the predetermined average particle diameter In the method of manufacturing a glass substrate for mask blanks to produce a glass substrate by performing
Before performing the precision polishing step, by etching the surface of the glass substrate, extending in the depth direction from the surface of the glass substrate, cracks remaining after the precision polishing step, in a defect inspection step performed after the precision polishing step A method for producing a glass substrate for mask blanks, which is made to be obvious. 13. The method of manufacturing a glass substrate for a mask blank according to claim 12, wherein a cleaning step of cleaning a main surface of the glass substrate is performed after the precision polishing step. 14. The glass substrate for a mask blank according to claim 13, wherein the main surface of the glass substrate after the cleaning step has a roughness of 0.2 nm or less in root mean square roughness (RMS). Production method. The cleaning step according to claim 13 or 14, wherein a cleaning liquid having an etching action is used as the cleaning liquid, and the glass substrate is cleaned under a condition in which the removal amount of the glass substrate by etching is more than 0 µm and less than 0.01 µm. A method for manufacturing a glass substrate for mask blanks. 13. The method for manufacturing a glass substrate for mask blanks according to claim 11, wherein the head defect inspection step is performed by visual inspection. 13. The method of manufacturing a glass substrate for a mask blank according to claim 10, wherein the etching treatment removes a surface of the glass substrate on the side to be precisely polished by 0.01 to 0.2 [mu] m. A thin film that causes an optical change to transfer exposure light is formed on a main surface of a glass substrate obtained by the method for manufacturing a glass substrate for a mask blank according to any one of claims 7 to 17. Manufacturing method of mask blanks. A method of manufacturing a transfer mask, comprising: patterning the thin film in the mask blank according to claim 18 to form a thin film pattern.

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