JP2012111664A - Mask blank substrate, mask blank, and method for manufacturing transfer mask - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a mask blank substrate which is capable of eliminating defects such as internal cracks caused near the main surfaces of a substrate after a grinding step.SOLUTION: The method for manufacturing a mask blank substrate comprising a substrate having opposite two main surfaces includes: a step of grinding the main surfaces of the substrate; a step of bringing a flame whose combustion temperature is equal to or higher than the softening point of the substrate into contact with the ground main surfaces of the substrate; and a step of polishing the main surfaces of the substrate after the flame contact step.

Description

  The present invention relates to a method for manufacturing a mask blank substrate, and a mask blank using the mask blank substrate and a method for manufacturing a transfer mask.

  In general, in a manufacturing process of a semiconductor device, a fine pattern is formed using a photolithography method. Further, a number of substrates called transfer masks are usually used for forming this fine pattern. This transfer mask is generally a transparent mask blank substrate provided with a fine pattern made of a metal thin film or the like. When a fine pattern is provided on a metal thin film or the like of a transfer mask, a photolithography method is used. The transfer mask is usually made from a mask blank in which a light shielding film is formed on a transparent mask blank substrate. In order to obtain a transfer mask having a fine pattern, the mask blank substrate is required to have high flatness and high parallelism. In addition, if there are defects (scratches, foreign matter, etc.) on the mask blank substrate, defects will also exist in the transfer mask manufactured using them, causing defects when forming a fine pattern. End up. Therefore, the mask blank substrate is required to be free from defects.

  As a conventional mask blank substrate, for example, in Patent Document 1, in a glass substrate for mask blanks obtained through a post-treatment process including a precision polishing process after an etching process, the surface roughness of the main surface of the glass substrate. Discloses a glass substrate for mask blanks characterized in that the root mean square (RMS) is 0.2 nm or less. In addition, in Patent Document 1, as a method for manufacturing a mask blank glass substrate, in the method for manufacturing a mask blank glass substrate, which has a step of revealing defects remaining on the main surface of the glass substrate, the defects are manifested. The manufacturing method characterized by performing the post-processing process including precision grinding | polishing after the process to make is disclosed. Further, Patent Document 1 describes that the step of revealing defects remaining on the main surface of the glass substrate is performed by etching the main surface.

  Moreover, in patent document 2, as a device which grinds the surface of a glass disk, it was provided in the outer edge of the lower surface plate, the sun gear provided in the center part of this lower surface plate, and the lower surface plate. Double-side grinding apparatus having an internal gear, a disk-shaped carrier having a tooth portion meshing with the sun gear and the internal gear on the outer peripheral portion and holding a glass disk, and an upper surface plate facing the lower surface plate Is disclosed. When the double-side grinding apparatus described in Patent Document 2 is used, the carrier holds the glass disk, and the teeth of the outer periphery of the carrier are engaged with the sun gear and the internal gear. By rotating and driving at least one of these, a process of relatively sliding the surface plate and the glass disk held by the carrier can be performed, and the glass disk can be ground.

  Further, in Patent Document 3, as a polishing apparatus for a mask blank substrate, an upper surface plate and a lower surface plate that are provided facing each other in the vertical direction, a sun gear, and a concentric circle arranged outside the sun gear. A polishing apparatus is disclosed that includes an internal gear and a planetary gear-shaped carrier that holds the workpiece to be polished and meshes with the sun gear and the internal gear.

  Patent Document 4 discloses a method for correcting dimensions of a processed quartz glass product. Specifically, in Patent Document 4, a quartz glass processed product whose size is to be corrected is disposed at a predetermined distance from a quartz glass welding rod, and a combustible gas flame of a burner is disposed at the end of the quartz glass welding rod. The quartz glass welding rod is radiated to heat and sublimate the quartz to form gaseous quartz, and the gaseous quartz is blown in the direction of the burner's combustible gas flame to correct the size of the processed quartz glass product. After depositing gaseous quartz on the surface, the opaque quartz deposited layer deposited and deposited is heated and welded to form a transparent quartz glass layer, and the size of the processed quartz glass product is corrected. A method for correcting dimensions of a processed quartz glass product is described.

JP 2004-54285 A JP 2007-90452 A Japanese Patent No. 3974535 JP 2002-326828 A

  In order to finish the mask blank substrate with high flatness, high smoothness, and no defects such as scratches, grinding is usually performed after the step of cutting out from the synthetic quartz glass ingot to the shape of the mask blank substrate (cutout step). A (lapping) process and a polishing (polishing) process are performed in a plurality of stages.

  A grinding process is a process of grinding with respect to the main surface, end surface, and chamfering surface of the cut-out substrate. The grinding process is performed for the purpose of adjusting to a predetermined plate thickness and improving the flatness.

  The polishing step is a step of polishing the main surface, end surface and chamfered surface of the substrate after the grinding step. The polishing step is performed for the purpose of further improving the smoothness of the main surface of the substrate while maintaining and improving the flatness obtained by the grinding step. The main surface is generally polished on both sides simultaneously using a double-side polishing apparatus. In the polishing process, polishing is performed in a plurality of stages while gradually reducing the grain size of the abrasive grains. For example, after performing rough polishing and precision polishing with cerium oxide abrasive grains having an average particle diameter of 0.3 to 3 μm, precision polishing with abrasive grains using colloidal silica or the like having an average particle diameter of 300 nm or less is 1-2. Done in stages. As a result, a mask blank substrate is manufactured in which the two main surfaces of the front and back surfaces have a flatness and surface roughness of a predetermined value or less and have no surface defects (convex defects or concave defects) on the main surface.

  The mask blank substrate polished in the polishing process is subjected to defect inspection such as surface defects. In this defect inspection, a mask blank substrate in which a surface defect having a size larger than an allowable value is found on the main surface of the substrate is usually returned to the polishing step as a rejected product, and the main surface is polished again. Become. Surface defects are broadly divided into convex defects and concave defects. In the polishing for removing the concave defects, in order to maintain the parallelism and flatness, the main surface must be removed not locally but entirely, so that the necessary polishing allowance increases. In addition, if the mask blank substrate has been returned to the precision polishing stage many times and becomes thinner than the specified thickness, it cannot be used as a mask blank substrate and discarded. Is done.

  In recent years, due to the demand for further miniaturization of semiconductor devices, the demand for parallelism, flatness, surface roughness and surface defects of a mask blank substrate has also increased. In particular, with respect to surface defects, an allowable defect size is determined by the grade of the mask blank manufactured using the mask blank substrate, and the presence of surface defects larger than the predetermined size is not allowed. In the case of mask blank substrates used to produce state-of-the-art semiconductor devices, the size of surface defects that can be tolerated is very severe.

  In the grinding process for grinding the main surface of the substrate, the grinding surface of the upper and lower surface plates that are in contact with the main surface of the substrate is usually formed of a material having high hardness such as metal or diamond fixed abrasive grains. For this reason, compared with the polishing step, the grinding surface hits the main surface of the substrate more strongly, and defects such as internal cracks are likely to occur near the main surface of the substrate. However, since the substrate after the grinding process has a ground glass surface state, it is not easy to find an internal crack even if the substrate is inspected after the grinding process. Also, in the polishing process, if the size in the thickness direction from the main surface where the internal crack is generated is expected and polishing is performed to remove the internal crack, the polishing allowance (in the thickness direction from the main surface) It is necessary to increase the polishing dimension). In order to increase the polishing allowance, it is necessary to lengthen the polishing time. When the polishing time becomes long, there arises a problem that the amount of edge droop at the outer peripheral edge of the main surface of the substrate tends to increase. “Edge fringing” means that the substrate is rotated at the time of polishing, so that the polishing rate of the portion far from the central portion is faster than the central portion of the substrate, and the amount of polishing of the portion far from the central portion is increased. It means to end. Edge fringes are particularly problematic for rectangular substrates compared to circular substrates.

  Patent Document 1 has a characteristic of etching a substrate such as sodium hydroxide with respect to the substrate after the grinding process instead of taking a lot of polishing allowance in order to solve the problem of the occurrence of internal cracks in the substrate. Including the process of immersing the substrate in the solution to reveal internal cracks, then performing precision polishing, performing defect inspection, and preventing the substrate with internal cracks from flowing out as a pass product during defect inspection A method for manufacturing a substrate is described. According to this manufacturing method, it is possible to suppress the outflow of the substrate having the internal cracks, but there is a problem that the yield is reduced.

  Patent Document 4 describes a method for correcting a size of a processed quartz glass product using a technique of depositing and depositing gaseous quartz on a portion whose size is to be corrected. However, if a technique for depositing and depositing gaseous quartz is applied to the defective portion of the mask blank substrate, it is inevitable that quartz is deposited also around the defect and adversely affects the flatness and surface roughness. Since the size of the defect is often on the order of μm and is very small, a polishing process is required to remove the quartz deposited excessively on portions other than the defect. Defects, in the polishing process, foreign matter such as solidified abrasive grains invaded between the polishing cloth on the surface plate and the main surface of the substrate that is rotating in a processing pressure applied state, Often caused by damaging the main surface. There is a problem in that a risk of occurrence of a new surface defect is generated on the mask blank substrate by performing a polishing process for removing excess deposited quartz. Furthermore, the width of defects such as internal cracks is generally very small, and it is very difficult to deposit gaseous quartz to the bottom. Therefore, it is difficult to use the invention disclosed in Patent Document 4 in order to correct the surface defect of the mask blank substrate.

  Then, an object of this invention is to obtain the manufacturing method of the board | substrate for mask blanks which can remove defects, such as an internal crack which generate | occur | produces in the main surface vicinity of the board | substrate after a grinding process. In addition, the present invention corrects defects in the mask blank substrate easily and without adversely affecting the flatness and surface roughness of the substrate even if defects such as internal cracks occur in the mask blank substrate in the grinding process. An object of the present invention is to provide a method for manufacturing a mask blank substrate with low cost and high yield, and a method for manufacturing a mask blank and a transfer mask. Another object of the present invention is to simultaneously obtain both the effect of improving the yield of manufacturing a substrate and the effect of suppressing the outflow of a substrate having internal cracks as an acceptable product.

  Also, when making a transfer mask from a mask blank manufactured using a substrate with internal cracks, the etching gas, etchant, cleaning chemicals, etc. expand the cracks, and part of the vicinity of the main surface of the substrate falls off. The present invention aims to suppress such problems.

  In addition, when a transfer mask manufactured using a substrate having an internal crack is used, the crack is enlarged by the cleaning chemical when the transfer mask is cleaned, and a part of the transfer mask near the main surface of the substrate is dropped. However, an object of the present invention is to suppress such problems and extend the life of the transfer mask.

  The present inventor examined various methods for removing defects such as internal cracks generated in the vicinity of the main surface of the substrate after the grinding step when manufacturing the mask blank substrate. As a result, it was found that by bringing a flame having a combustion temperature equal to or higher than the softening point of the substrate into contact, defects such as internal cracks generated in the vicinity of the main surface of the substrate after the grinding step can be removed, and the present invention was completed. Is. That is, in order to solve the above problems, the present invention has the following configuration.

  The present invention has the following configurations 1 to 4, a method for manufacturing a mask blank substrate, a method for manufacturing a mask blank that is the following configuration 5, and a method for manufacturing a transfer mask that is the following configuration 6 It is.

(Configuration 1)
A mask blank substrate manufacturing method comprising a substrate having two opposing main surfaces, the step of grinding the main surface of the substrate, and the main surface of the substrate subjected to grinding, A mask blank comprising a step of contacting a flame having a combustion temperature equal to or higher than a softening point of the substrate, and a step of polishing the main surface of the substrate after performing the step of contacting the flame. It is a manufacturing method of the board | substrate.

(Configuration 2)
2. The mask blank substrate manufacturing method according to Configuration 1, wherein the substrate is made of synthetic quartz glass.

(Configuration 3)
3. The method for manufacturing a mask blank substrate according to Configuration 1 or 2, wherein the flame has a combustion temperature of 1600 ° C. or higher.

(Configuration 4)
4. The mask blank according to claim 1, wherein the step of contacting the flame softens the main surface of the substrate and removes internal cracks existing in the vicinity of the main surface of the substrate. It is a manufacturing method of the board | substrate.

(Configuration 5)
This invention has the process of forming the thin film for pattern formation on the main surface of the mask blank board | substrate manufactured with the manufacturing method of the mask blank board | substrate of any one of the structures 1-4. It is the manufacturing method of the mask blank characterized.

(Configuration 6)
The present invention is a method for manufacturing a transfer mask, comprising a step of forming a transfer pattern on a thin film for pattern formation of a mask blank manufactured by the method for manufacturing a mask blank described in Structure 5.

  Next, configurations 1 to 4 of the method for manufacturing a mask blank substrate of the present invention will be described.

  The present invention provides a mask blank substrate manufacturing method comprising a substrate having two opposing main surfaces as in Configuration 1, wherein the main surface of the substrate is ground and the grinding is performed. Polishing is performed on the main surface of the substrate after performing a step of bringing a flame having a combustion temperature equal to or higher than the softening point of the substrate and a step of bringing the flame into contact with the main surface of the broken substrate. And a process for producing a mask blank substrate.

  As in Configuration 1, in the mask blank substrate manufacturing method of the present invention, a flame having a combustion temperature equal to or higher than the softening point of the substrate is brought into contact with the main surface of the substrate that has been ground, and the grinding step Defects such as internal cracks generated near the main surface of the subsequent substrate are removed. The “substrate softening point” is the softening point of the substrate material constituting the substrate. When the viscosity of the substrate material is η (poise), the viscosity satisfying log η = 7.6 is satisfied. The temperature at which the rate is reached. Note that the viscosity (viscosity) can be measured using an intrusion method. If necessary, the viscosity can be measured using a measuring method such as a beam bending method or a ball pulling method. In addition, as illustrated in FIG. 3, the “main surface” of the substrate is a peripheral portion of the substrate (the end surface 72 and the chamfered surface 73, and the end surface 72 and the chamfered surface 73 are also referred to as “side surface”. )) Refers to the surface. That is, the “main surface” of the substrate refers to a surface shown as two “main surfaces 71” facing each other in FIG.

  When the present inventor brings a flame having a combustion temperature equal to or higher than the softening point of the substrate into contact with a portion (surface defect portion) where a defect such as an internal crack of the mask blank substrate is present, the substrate material including the portion near the defect is obtained. It has been found that the substrate material can be flowed to soften and remove defects such as internal cracks and, as a result, the defects can be removed. In the present specification, the process using a flame for removing the defect is referred to as “flame process”. In the manufacturing method of the present invention, it is not necessary to attach a substrate material such as synthetic quartz glass in order to remove defects such as internal cracks, and a flame having a predetermined combustion temperature or higher is brought into contact with the mask blank substrate. Thus, the defect can be removed by softening and slightly flowing the substrate material around the defect such as an internal crack. Even when a surface defect of a concave defect exists as a defect, the surface defect can be flattened by causing the substrate material to flow so as to fill the concave defect portion of the surface. Even when a convex defect exists as a surface defect, the surface defect can be flattened by flowing the substrate material so as to spread from the surface defect portion.

  Since defects such as internal cracks often occur in the grinding process (grinding process), this flame contact process (flame treatment process) is performed after the grinding process. The flame treatment process can be performed to such an extent that deterioration of the flatness of the substrate does not cause a problem in a later process. If the deterioration of the flatness of the substrate is not large, the deterioration of the flatness caused in the flame treatment process can be corrected by performing a polishing process (polishing process) after the flame treatment process. The polishing step after the flame treatment step can be performed with a conventional polishing time.

  It should be noted that the order of each step can be appropriately changed as necessary. For example, the flame treatment process can be performed after the grinding process and the polishing process. This is because performing a flame treatment on a flatter substrate surface may be more effective for removing defects such as internal cracks. In the case of performing the flame treatment step after the polishing step, it is preferable to perform the polishing step again after the flame treatment step because a flatter surface can be obtained.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the board | substrate for mask blanks which can remove defects, such as an internal crack which generate | occur | produces in the main surface vicinity of the board | substrate after a grinding process, can be obtained. That is, according to the present invention, defects such as internal cracks in the substrate can be removed by performing a simple process called flame treatment on the substrate. Furthermore, it is also possible to correct surface defects such as concave defects and convex defects on the substrate by flame treatment. Therefore, according to the present invention, even when a defect such as an internal crack occurs in the mask blank substrate in the grinding process, the defect of the mask blank substrate can be easily performed without adversely affecting the flatness and surface roughness of the substrate. It is possible to provide a method for manufacturing a mask blank substrate with a low cost and a high yield, and a method for manufacturing a mask blank and a transfer mask. As a result, it is possible to simultaneously obtain both the effect of improving the yield of manufacturing the substrate and the effect of suppressing the substrate having internal cracks from flowing out as an acceptable product.

  When producing a transfer mask from a mask blank manufactured using a substrate having an internal crack, an etching gas or an etching solution may enlarge the crack, and a portion near the substrate main surface may fall off. When the part from which the substrate has dropped is a transmission part that transmits the exposure light of the transfer pattern, irregular reflection of the exposure light and phase defects occur. In addition, in the case where the thin film for pattern formation is left on the upper surface of the part where the substrate is dropped (light shielding film, phase shift film, light semi-transmissive film, etc.), the thin film is dropped together with the part where the substrate is dropped. As a result, a pattern defect (white defect) occurs. If a mask blank substrate is manufactured by the manufacturing method having the flame treatment process of the present invention, defects such as internal cracks can be removed, so that these problems in manufacturing a transfer mask from the mask blank are suppressed. can do.

  If a transfer mask manufactured using a substrate with internal cracks is used, the cleaning mask may cause cracks to expand during cleaning of the transfer mask, and a portion of the transfer mask near the main surface of the substrate may fall off. is there. When a part of the substrate is dropped, exposure light irregular reflection, phase defects, and pattern defects occur for the same reason as described above. If a mask blank substrate is manufactured by the manufacturing method having the flame treatment process of the present invention, defects such as internal cracks can be removed, so that the problem that a part of the transfer mask substrate drops off is suppressed. be able to. Therefore, if a mask blank substrate is manufactured using the manufacturing method of the present invention, the life of a transfer mask manufactured using the mask blank substrate can be increased compared to the conventional one. .

  In the method for manufacturing a mask blank substrate according to the present invention as in Configuration 2, it is preferable that the substrate is made of synthetic quartz glass.

  As in Structure 2, it is preferable to use synthetic quartz glass as the substrate material. Synthetic quartz glass is chemically stable and has features such as extremely low thermal expansion coefficient compared to other industrial materials. In addition, synthetic quartz glass has high light transmittance with respect to exposure light of an ultrahigh pressure mercury lamp used in a transfer mask for FPD manufacturing. Furthermore, synthetic quartz glass has high light transmittance with respect to exposure light of a KrF excimer laser (wavelength: about 248 nm) or ArF excimer laser (wavelength: about 193 nm) used in a transfer mask for semiconductor device manufacturing applications. As can be seen from these, synthetic quartz glass can be suitably used as the material for the mask blank substrate.

  In the method for producing a mask blank substrate according to the present invention, as set forth in Configuration 3, it is preferable that the flame has a combustion temperature of 1600 ° C. or higher.

  As in Configuration 3, the flame is preferably at a combustion temperature of 1600 ° C. or higher. Although the softening point of synthetic quartz glass is generally 1600 ° C. or higher depending on the type, the synthetic quartz glass around the surface defects is slightly flowed by using a flame having a combustion temperature of 1600 ° C. Defects can be planarized. In order to ensure the flow of the synthetic quartz glass, the flame is more preferably a combustion temperature of 1700 ° C. or higher, and further preferably a combustion temperature of 1800 ° C. or higher. The upper limit of the flame combustion temperature is preferably a temperature that does not adversely affect the synthetic quartz glass, and is, for example, 2800 ° C. or lower, preferably 2500 ° C. or lower, more preferably 2300 ° C. or lower.

  In addition, as described in Structure 4, in the mask blank substrate manufacturing method of the present invention, the step of bringing the flame into contact softens the main surface of the substrate and eliminates internal cracks existing in the vicinity of the main surface of the substrate. It is preferable to be removed.

  As in Configuration 4, it is preferable that the step of bringing the flame into contact with the substrate softens the main surface of the substrate and removes internal cracks existing in the vicinity of the main surface of the substrate. When a flame with a combustion temperature higher than the softening point of the substrate comes into contact with a defect-existing part (surface defect part) of the mask blank substrate, the substrate material including the part in the vicinity of the defect is softened to cause internal cracks, etc. The substrate material can be flowed to remove the defects.

  Next, the structure 5 of the manufacturing method of the mask blank of this invention is demonstrated.

  In the present invention, as in Configuration 5, a thin film for pattern formation is formed on the main surface of the mask blank substrate manufactured by the method for manufacturing a mask blank substrate described in any one of Configurations 1 to 4. It is a manufacturing method of the mask blank characterized by having the process to form into a film.

  As described in Configuration 5, in the method for manufacturing a mask blank substrate according to any one of Configurations 1 to 4, a mask blank substrate having a low cost and a high yield can be obtained by easily correcting a surface defect by flame treatment. Obtainable. Therefore, the mask blank in which the thin film for pattern formation is formed on any one of the mask blank substrates of configurations 1 to 4 can also be manufactured at low cost and high yield. The formation of the pattern forming thin film on the mask blank substrate can be performed using a known method.

  Next, the structure 6 of the manufacturing method of the transfer mask of this invention is demonstrated.

  The present invention provides a transfer mask comprising a step of forming a transfer pattern on a thin film for pattern formation of a mask blank manufactured by the method for manufacturing a mask blank according to configuration 5, as in configuration 6. It is a manufacturing method.

  As in Configuration 6, the mask blank manufacturing method of Configuration 5 according to the present invention can achieve low cost and high yield. Therefore, the transfer mask in which the transfer pattern is formed on the thin film of the mask blank having the structure 5 can also be manufactured at low cost and high yield. The transfer pattern can be formed on the mask blank thin film using a known method.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the board | substrate for mask blanks which can remove defects, such as an internal crack which generate | occur | produces in the main surface vicinity of the board | substrate after a grinding process, can be obtained. Therefore, according to the present invention, even when a defect such as an internal crack occurs in the mask blank substrate in the grinding process, the defect of the mask blank substrate can be easily performed without adversely affecting the flatness and surface roughness of the substrate. It is possible to provide a method for manufacturing a mask blank substrate with a low cost and a high yield, and a method for manufacturing a mask blank and a transfer mask. As a result, it is possible to simultaneously obtain both the effect of improving the production yield of the substrate and the effect of suppressing the substrate having an internal crack from flowing out as an acceptable product. Conventionally, cerium oxide, zirconium oxide, or the like is often used for polishing grains in a rough polishing process or a precision polishing process, which is a polishing process for removing internal cracks. By using the present invention, the rough polishing step and the precision polishing step are not performed, or the polishing time can be shortened, and the amount of these abrasive grains used can be suppressed or not used. As a result, the amount of rare earth or rare metal used in the polishing process can be suppressed or not used.

  In addition, when a transfer mask is manufactured from a mask blank manufactured using a substrate having an internal crack, the etching gas or the etchant may enlarge the crack and part of the vicinity of the main surface of the substrate may fall off. According to the present invention, such a problem can be prevented, so that various problems caused by a part of the substrate falling off when a transfer mask is manufactured from the mask blank can be suppressed.

  In addition, when a transfer mask manufactured using a substrate having an internal crack is used, the crack is enlarged by the cleaning chemical when the transfer mask is cleaned, and a part of the transfer mask near the main surface of the substrate is dropped. However, according to the present invention, such a problem can be suppressed, so that the life of the transfer mask can be extended.

It is a cross-sectional schematic diagram which shows an example of a mode that the mask blank is flame-treating. It is a figure which shows an example of the process of the manufacturing method of the board | substrate for mask blanks of this invention. It is a schematic diagram which shows the board | substrate for mask blanks which can be used for the manufacturing method of this invention. It is a schematic block diagram of an example of the flame processing apparatus which can be used for the manufacturing method of this invention. It is a cross-sectional schematic diagram which shows an example of the process of manufacturing a transfer mask using a mask blank.

<Description of Manufacturing Method of Mask Blank Substrate 1>
A method for manufacturing the mask blank substrate 1 of the present invention will be described. Hereinafter, although the case where synthetic quartz glass is used as a material for the mask blank substrate 1 will be described as an example, the present invention is not limited thereto.

  The manufacturing method of the mask blank substrate 1 of the present invention includes the steps shown in FIG. 2, that is, the cutting step (S101), the grinding step (S102), the flame treatment step (S103), the polishing step (S104), and the defect inspection (S105). ). Moreover, the manufacturing method of the board | substrate 1 for mask blanks of this invention can have a side surface (an end surface and a chamfering surface) partial mirror polishing process, a defect manifestation process, etc. as needed.

  In addition, during each process such as between the grinding process and the polishing process, the abrasive grains attached to the substrate are removed so that the next process does not affect the abrasive grains used in the previous process. A cleaning step for the purpose can be provided as appropriate.

(1) Cutting process (S101)
First, a sheet-shaped synthetic quartz glass (sheet glass) is cut out from a synthetic quartz glass ingot. Next, a rectangular substrate 1 having a predetermined shape can be obtained by cutting out from a sheet glass made of synthetic quartz glass with a grinding wheel. The rectangular dimensions vary depending on the application. In this step, the end surface 72 of the substrate 1 is chamfered to form a chamfered surface 73, which can be shaped as shown in FIG.

(2) Grinding (lapping) step (S102)
In the grinding process (lapping process), the shape of the substrate 1 is adjusted and the main surface 71 is ground. In the grinding process, processing is performed using a double-side grinding apparatus and alumina abrasive grains, and the dimensional accuracy and shape accuracy of the substrate are set to predetermined ones. A grinding process can be performed using the apparatus according to the double-sided grinding apparatus described in patent document 2, for example. Each of the upper and lower surface plates of the double-side grinding apparatus includes, for example, a configuration in which a plurality of grooves are formed in a lattice shape on a sliding contact surface with a substrate using a material having high rigidity such as spheroidal graphite-containing cast iron. . Further, instead of forming the plurality of grooves in a lattice shape, a diamond sheet in which a large number of diamond fixed abrasive grains are arranged may be attached to the upper and lower surface plates to contact the main surface of the substrate. In this grinding process, the grinding of both main surfaces 71 on the front and back of the substrate 1 is performed under the same conditions as in the prior art using the above-described double-side grinding apparatus.

(3) Flame treatment process (S103)
Flame treatment is performed on the substrate 1 after the grinding process. In the grinding process, unlike the polishing process, the main surface 71 of the substrate 1 is ground while the robust surface plate (the lower surface plate 123 and the upper surface plate 122) and the substrate are in contact with each other (in the case of the polishing step, the upper surface plate). Since it comes into contact with the main surface of the substrate 1 via a resin polishing pad affixed to each surface of the lower surface plate, there are internal cracks in the vicinity of the main surface 71 of the substrate 1 after the grinding process. Defect 5 often occurs. Therefore, in the manufacturing method of the present invention, the main surface 71 of the substrate 1 is flame-treated to remove the defects 5 such as internal cracks generated in the vicinity of the main surface 71 of the substrate 1. Specifically, in the flame treatment process, the flame 52 is irradiated near the main surface 71 of the substrate 1 and heated so that the flame 52 is in contact with the substrate 1, thereby softening the portion of the substrate irradiated with the flame 52. Or it is made to melt | dissolve and it is made to flow so that the defects 5, such as an internal crack, may be removed, and it will restore | restore in a state without an internal crack. When the manufacturing method of the present invention includes a flame treatment process, it is possible to simultaneously obtain both the yield improvement effect of manufacturing the substrate and the effect of suppressing the substrate 1 having the internal cracks from flowing out as an acceptable product. Further, since there is no need for large-scale equipment for the flame treatment, it is possible to remove the defects 5 such as internal cracks easily and at low cost.

  FIG. 1 shows a schematic cross-sectional view of an example of a state in which a defect 5 such as an internal crack of the substrate 1 is flame-treated. The defect 5 such as an internal crack of the substrate 1 is flame-treated by being heated by the flame 52 irradiated from the flame irradiation device 50. Since it is not easy to specify the portion where the defect 5 such as an internal crack of the substrate 1 exists, it is preferable to perform the flame treatment over the entire main surface 71 of the substrate 1 in the flame treatment step. It is not easy to uniformly irradiate the large flame 52 on the entire main surface 71 of the substrate 1. Further, when the temperature reaches a temperature higher than the softening point up to the internal temperature of the substrate, the substrate shape itself may be deformed. Therefore, by using a device that generates a relatively small flame 52, the main surface 71 of the substrate 1 is scanned by scanning the entire surface of the main surface 71 of the substrate 1 while locally irradiating the flame 52, that is, performing a scanning flame treatment. By uniformly processing the entire surface, it is possible to remove the defects 5 such as internal cracks of the substrate 1. Further, by setting the flame 52 to an appropriate temperature and size during the scanning flame treatment, it is possible to remove the defects 5 such as internal cracks while suppressing the substrate 1 from being heated more than necessary.

  As the flame irradiation device 50 for performing the flame treatment, a burner or the like that generates the flame 52 by burning the flammable gas 105 can be used. The flammable gas 105 used in the flame irradiation device 50 is preferably selected from hydrocarbons such as methane, propane, butane and acetylene, hydrogen, a mixed gas of oxygen and hydrogen, and the like. Since flame treatment can be performed at a higher temperature, it is more preferable to use a flammable gas 105 which is a mixed gas of butane or hydrogen and oxygen.

  In the flame treatment used in the manufacturing method of the present invention, the temperature of the portion of the flame 52 varies depending on the softening point of the material of the substrate 1. When the material of the substrate 1 is synthetic quartz glass, the temperature of the flame 52 is preferably 1600 ° C. or higher, more preferably 1700 ° C. or higher, and further preferably 1800 ° C. or higher. By bringing the flame 52 in such a temperature range into contact with the portion of the substrate 1 where the defect 5 such as an internal crack exists, the temperature of the portion of the substrate 1 in contact with the flame 52 becomes approximately the same as the temperature of the flame 52. As a result, the portion where the defect 5 such as an internal crack is present softens and flows, and the defect 5 such as the internal crack can be removed. The portion of the substrate 1 subjected to the flame treatment tends to change the concentration distribution of OH groups compared to the other portions.

  The distance between the flame irradiation device 50 and the substrate 1 during the flame treatment does not prevent the generation of the flame 52, the flame 52 comes into contact with the main surface 71 of the substrate 1, and the defect 5 such as an internal crack is removed. It can select suitably in the range performed effectively. The distance between the flame irradiation device 50 and the main surface 71 of the substrate 1 during the flame treatment effectively removes defects 5 such as internal cracks without preventing the flame 52 from contacting the main surface 71 of the substrate 1. From the point of performing, it is preferable to set it as 1 mm-50 mm, and it is more preferable to set it as 2 mm-20 mm.

  In order to flame-treat the defects 5 such as internal cracks while suppressing the heating of the substrate 1, an apparatus that generates a relatively small flame 52 is used, and the main surface 71 of the substrate 1 is irradiated with the flame 52 locally while being irradiated locally. It is preferable to perform a flame treatment of defects 5 such as internal cracks by performing a process (scanning flame treatment) of scanning the entire surface of one main surface 71. In FIG. 4, the schematic block diagram of the flame processing apparatus 100 for performing a scanning flame process is shown. During the scanning flame treatment, the flame 52 can be irradiated while observing the main surface 71 of the substrate 1 with an optical microscope or the like. When performing the scanning flame treatment, the irradiation diameter of the flame 52 with respect to the defect 5 such as an internal crack is preferably 0.1 mm to 10 mm, more preferably 0.2 mm to 5 mm, and 0.5 mm to 4 mm. More preferably.

In the flame processing apparatus 100 shown in FIG. 4, the stage 1 is moved by using the stage controller 112 and the stage 102, and the irradiation position of the flame 52 is scanned so that the flame 52 irradiates the entire main surface 71 of the substrate 1. be able to. By using the flame treatment apparatus 100 provided with the flame control unit 104 for controlling the flame 52 by controlling the flow rate of the flammable gas 105 and the like, and the flame treatment control unit 114 connected to the stage controller 112, The irradiation position of the flame 52 during the scanning flame process can be automatically scanned.
In FIGS. 1 and 4, the substrate 1 is arranged almost horizontally and the flame 52 is applied to the main surface 71 from above, but the present invention is not limited to this. For example, the substrate 1 may be placed diagonally or vertically, and the flame 52 may be placed on the main surface 71 diagonally upward or laterally. Further, the substrate 1 may be supported substantially horizontally so that the lower main surface 71 is exposed, and the flame 52 may be applied to the lower main surface 71 from below. By adopting such a positional relationship, it is possible to reduce the temperature rise at the tip opening portion of the flame irradiation device 50 and to reduce the heat resistance specifications required for the metal material used for the tip opening portion.

(4) Defect revealing step In order to confirm that the defect 5 such as the internal crack in the substrate 1 has been removed by the flame treatment, the manufacturing method of the present invention reveals the defect 5 such as the internal crack. It is preferable to have a defect revealing step. As the defect revealing step, the defect revealing method described in Patent Document 1 can be used. When it is confirmed that the defect 5 such as the internal crack is not completely removed by the defect revealing step, the defect 5 can be completely removed by performing the flame treatment again. Further, since the revealed defect 5 is large in size, if it is determined that the defect 5 cannot be removed by flame treatment or the like, the grinding process can be performed again. If the defect 5 is a defect that cannot be repaired, the substrate 1 can be discarded. If the size of the defect 5 is a size that can be removed in the next polishing step, for example, a size smaller than about 0.05 mm in depth, its existence can be allowed.

  Specifically, the defect revealing step can be performed as follows. That is, the defects 5 such as internal cracks in the substrate 1 can be made apparent by etching the main surface 71 of the substrate 1. The etching process can effectively expose defects remaining on the main surface 71 and can have a cleaning effect.

  As an etching method used for the etching process for revealing the defect 5, both dry etching and wet etching can be used.

  By this etching process, the defects 5 such as internal cracks are enlarged. For example, when the etching is wet etching, the defects 5 such as internal cracks extending in the center direction from the surface of the substrate 1 are isotropically etched, so that the center of the defect 5 is combined with the etching amount of the surface of the substrate 1. The depth in the direction does not change greatly, but the size (width) in the in-plane direction of the defect 5 such as a crack increases. Therefore, the defect 5 can be easily found. Further, usually, after the etching process, precision polishing for mirroring the main surface 71 of the substrate 1 is performed. Therefore, during the defect inspection performed after the polishing process, the main surface 71 of the substrate 1 is brought into an ultra-smooth state by the polishing process. Therefore, the defect 5 having a certain size (width) by the etching process is particularly easy to detect in a smooth surface state after the polishing process.

  Further, if the etching process is performed before the polishing process, the unevenness of the surface of the substrate 1 becomes relatively smooth, so that the load of the polishing process for mirroring can be suppressed, and the shape of the side surface of the substrate 1 is also good. Become. In addition, since the polishing time can be shortened by suppressing the load of the polishing process, the amount of fringing of the peripheral edge portion of the main surface 71 of the substrate 1 can be reduced.

  In addition, a crack means the thing of the crack state extended in the depth direction from the surface of the board | substrate 1. FIG. Cracks are often formed by a grinding process and have almost no width on the surface of the substrate 1 and are almost impossible to detect. In addition, the crack which becomes a problem in the present invention refers to a crack remaining after the polishing process, that is, a deep crack that cannot be removed by the polishing process. This is because if the crack is shallow enough to be removed in the polishing process, it can be removed in the polishing process.

  It is preferable to use an alkaline aqueous solution for the etching treatment for revealing the defect 5 such as a crack. The alkaline aqueous solution is preferably an aqueous solution such as sodium hydroxide (NaOH) or potassium hydroxide (KOH) or a mixed aqueous solution thereof.

  The etching process for revealing the defect 5 such as a crack is preferably performed by removing the main surface 71 of the substrate 1 by 0.01 to 0.2 μm.

  When the thickness is less than 0.01 μm, it is difficult to determine the presence or absence of cracks in the defect inspection performed after the polishing process, and when it exceeds 0.2 μm, the surface roughness or surface due to etching of the substrate 1 is not preferable. Since the shape (flatness) deteriorates, it is not preferable.

  In addition, it is preferable that the etching rate in the etching process for revealing the defects 5 such as cracks is 0.2 nm / min to 2.0 nm / min. When the etching rate is less than 0.2 nm / min, the degree of revealing of potential defects is small, which is not preferable. When the etching rate exceeds 2 nm / min, the substrate 1 is corroded quickly, Since surface shape (flatness) deteriorates, it is not preferable. The etching rate is preferably 0.3 nm / min to 0.7 nm / min.

(5) Side mirror polishing process It is preferable to include the side mirror polishing process of grind | polishing and mirror-finishing the end surface 72 and the chamfering surface 73 which are the side surfaces of the board | substrate 1 after a grinding process. Polishing in the side mirror polishing step can be performed with a brush or the like using an abrasive. As the abrasive grains contained in the abrasive used in the side mirror polishing process, any abrasive grains capable of polishing the substrate 1 can be used without particular limitation. Examples of the abrasive grains include cerium oxide (CeO ₂ ) abrasive grains and colloidal silica abrasive grains. It is particularly preferable to use cerium oxide abrasive grains. The particle size of the abrasive grains can be selected as appropriate, but for example, a particle size of about 0.5 to 3 μm is preferable. Further, in the side mirror polishing step, it is preferable to add a liquid such as water (pure water) to an abrasive containing abrasive grains and use this abrasive as a slurry.

(6) Polishing step (S104)
Next, in the polishing step (S104), scratches and distortions formed during the grinding step are removed while maintaining the flatness of the substrate 1 obtained in the above-described grinding step (S102). The polishing step is further performed for the purpose of mirroring the main surface 71 of the substrate 1. Usually, in the polishing step, removal of scratches and distortion and mirror polishing are performed by separate polishing. Therefore, it is common to perform polishing several times in the polishing step.

  The polishing step can be performed by a known method. For example, the polishing step can be performed using a polishing apparatus described in Patent Document 2. As the polishing liquid, one in which fine abrasive particles are dispersed in a liquid is generally used. The abrasive particles are, for example, silicon carbide, aluminum oxide, cerium oxide, zirconium oxide, manganese oxide, colloidal silica, and the like, and are appropriately selected according to the material of the workpiece W and the surface roughness of the workpiece. These abrasive particles are dispersed in a liquid such as water, an acidic solution, or an alkaline solution to obtain a polishing liquid.

  The mask blank substrate 1 can be manufactured through the manufacturing steps up to the polishing step described above.

(7) Defect inspection (S105)
Next, the presence or absence of defects 5 such as flatness, surface roughness and internal cracks of the mask blank substrate 1 obtained by the polishing process is inspected by defect inspection (S105). Although the mask blank substrate 1 obtained by the conventional manufacturing process has high flatness and high smoothness, it is known that defects 5 such as internal cracks exist frequently. The size of the defect 5 such as an allowable internal crack varies depending on the use of the mask blank 10 manufactured from the mask blank substrate 1 and the transfer mask. However, when a mask for transfer is produced using a mask blank manufactured from the mask blank substrate 1 having internal cracks, the etching gas or the etchant expands the cracks, and a portion near the substrate main surface falls off. May end up. In addition, when a transfer mask manufactured using the mask blank substrate 1 having internal cracks is used, the crack expands due to the cleaning chemical when the transfer mask is cleaned, and the transfer mask has a portion near the main surface of the transfer mask. The part may fall off. Therefore, in order to extend the life of the transfer mask, it is preferable that no internal crack exists even if it is very small. For this reason, it is preferable that the defects 5 such as internal cracks are revealed by a defect revealing step before the defect inspection.

  Defects 5 such as internal cracks can be measured for size, shape and position by a surface inspection apparatus using an optical microscope. In addition, laser scattered light type defect inspection devices and confocal optical defect inspection devices can also be applied. For example, in the case of the mask blank substrate 1 for use in FPD manufacturing, it is often determined that the defect 5 such as a concave internal crack is not allowed to have a width larger than 1 μm. In this defect inspection, as a result of inspecting the mask blank substrate 1, the main surface 71 has a flatness and surface roughness of a predetermined level or more, and a size that is not allowed among the detected defects 5 such as internal cracks. First, an operation to select a non-defective mask blank substrate 1 is performed. For the non-defective mask blank substrate 1, a process of forming a thin film for pattern formation is performed after the cleaning.

  Next, the mask blank substrate 1 in which at least one of the flatness and the surface roughness of the main surface 71 does not satisfy a predetermined value is returned to the polishing step at a stage where it can be corrected and re-polished. On the other hand, the flame treatment process may be performed again on the mask blank substrate 1 in which both the flatness and the surface roughness satisfy the predetermined conditions, but the defect 5 such as an internal crack having an unacceptable size exists. it can. In addition, the mask blank substrate 1 that has been determined to be impossible to repair the flatness and surface roughness or to remove the defects 5 such as internal cracks by the re-polishing and the flame treatment process again is discarded.

<Description of Mask Blank Substrate 1>
It is preferable that the mask blank substrate 1 obtained by the production method of the present invention has a high flatness according to its use and further has a high parallelism. For example, the mask blank substrate 1 includes a pair of main surfaces 71 provided opposite to each other as shown in FIG. 3, two sets of end surfaces 72 orthogonal to the main surfaces, and the main surfaces 71 and 72. This is a square (square) substrate having a chamfered surface 73 sandwiched between the two. In the case of the mask blank substrate 1 for use in manufacturing semiconductor devices, the size is generally about 152 mm × about 152 mm × about 6.35 mm. In the case of this mask blank substrate 1, the flatness in a 142 mm square region with respect to the center of the main surface is required to be, for example, more than 0 μm and 0.5 μm or less, preferably 0.3 μm or less. It is desirable that Further, the surface roughness needs to be 0.25 nm or less in terms of the square root mean roughness Rq.

  In addition, in the case of the mask blank substrate 1 for FPD manufacturing, the size is various and is 330 mm × 450 mm or more, for example, a shape of 500 mm × 800 mm, a thickness of 10 mm, a shape of 800 mm × 920 mm, and a thickness of 10 mm. There are 1220 mm × 1400 mm, 13 mm thick shape, 1400 mm × 1600 mm, 15 mm thick shape, 2140 mm × 2400 mm, 15 mm thick shape, etc. In the case of this mask blank substrate 1, the flatness of the main surface 71 (preferably both main surfaces 71) (in the main surface 71 of the mask blank substrate 1, the flatness of the inner region excluding 30 mm from the end face). Therefore, the chamfered surface 73 is inevitably removed.) However, in the case of a small mask blank substrate 1 (less than 330 mm × 450 mm), it exceeds 0 μm and is 5 μm or less, and the large mask blank substrate 1 (330 mm × 450 mm or more). Then, it is a substrate having a high flatness exceeding 0 μm and 30 μm or less. Moreover, about surface roughness, it is 0.2 nm or less by average surface roughness Ra, More preferably, it is 0.15 nm or less.

<Description of Mask Blank 10 and Transfer Mask>
Next, an embodiment of a method for manufacturing the mask blank 10 and the transfer mask of the present invention will be described.

  The present invention is a method for manufacturing a mask blank 10 having a pattern forming thin film for forming a transfer pattern on the above-described mask blank substrate 1 of the present invention. In the production method of the present invention, one or more pattern forming thin films are formed on the mask blank substrate 1 of the present invention described above.

  The pattern forming thin film for forming the transfer pattern is greatly different between the case of the mask blank 10 for use in semiconductor device manufacture and the case of the mask blank 10 for use in FPD manufacture. As a method for forming the pattern forming thin film on the mask blank substrate 1, for example, a sputter film forming method is preferably exemplified, but the present invention is not necessarily limited to the sputter film forming method. A transfer mask can be obtained by forming a predetermined fine pattern on the pattern forming thin film of the mask blank 10 by a known photolithography method.

  In the case of the mask blank 10 for use in manufacturing semiconductor devices, examples of the thin film for pattern formation include a light semi-transmissive film such as a light shielding film and a halftone type phase shift film. The light shielding film is a thin film having high light shielding performance with respect to exposure light. The light-shielding film hardly transmits exposure light (generally, the transmittance is about 0.1% or less). The mask blank 10 to which this light shielding film is applied is also called a binary mask blank. The transfer mask produced from the mask blank 10 is also called a binary mask.

  A halftone phase shift film, which is one type of light semi-transmissive film, transmits light having an intensity that does not substantially contribute to exposure (for example, 1% to 20% with respect to the exposure wavelength). Phase difference (for example, 180 degrees). Light is transmitted through the phase shift section by a phase shift section obtained by patterning the halftone phase shift film and a light transmission section that does not have the phase shift section and transmits light having an intensity that substantially contributes to exposure. So that the phase of the light is substantially inverted with respect to the phase of the light transmitted through the light transmitting portion, the phase shift portion and the light transmitting portion pass through the vicinity of the boundary portion, and the other phenomenon is caused by the diffraction phenomenon. Lights that enter the area can cancel each other. As a result, the light intensity at the boundary can be made almost zero, and the contrast at the boundary, that is, the resolution can be improved.

  As a light semi-transmissive film other than the halftone phase shift film, a resist film for pattern transfer is a thin film that transmits exposure light at a predetermined transmittance that is not exposed to light. Some thin films are adjusted so as not to cause a phase difference with the exposure light that has passed through the part having no light. The mask blank 10 to which this type of translucent film is applied is often used when producing an enhancer mask. Since both the halftone phase shift film and the light semi-transmissive film have a predetermined transmittance with respect to the exposure light, when the exposure is performed on the resist film of the transfer object in the exposure apparatus, the resist is exposed. The film may be exposed. For this reason, in many cases, a film configuration is formed by laminating a light shielding film for forming a light shielding band on a halftone type phase shift film or a light semi-transmissive film.

  On the other hand, in the case of the mask blank 10 for FPD manufacturing, the transfer mask produced from the mask blank 10 is generally used in an exposure apparatus using an ultrahigh pressure mercury lamp as a light source (exposure light). The exposure light of the ultra-high pressure mercury lamp is not single-wavelength light such as ArF excimer laser, but multicolor light. The exposure light of the ultra-high pressure mercury lamp is light having particularly strong light intensity at three wavelengths of i-line (365 nm), h-line (405 nm), and g-line (436 nm). In such multicolor light, it is difficult to obtain a phase shift effect, so that the halftone phase shift film is hardly used in the mask blank 10 for FPD manufacturing. Similar to the mask blank 10 for manufacturing semiconductor devices, a mask blank 10 (binary mask blank) in which a light-shielding film is applied to a thin film for pattern formation is used.

  As a transfer mask for FPD manufacturing, there is a multi-tone mask having a configuration in which a transfer pattern is formed on each of a plurality of pattern forming thin films having different transmittances. Using this multi-tone mask, transfer exposure is performed on the resist film to be transferred, and development processing is performed. In the resist film, all the resist is dissolved, and a certain film thickness is dissolved. As a result, an almost undissolved region is formed. Therefore, a plurality of patterns are formed on the resist film. In such a resist pattern, first, the thin film under the resist film can be patterned using the first pattern composed of the remaining area where the resist is completely dissolved and the remaining area where the other resist remains as a mask. it can. Next, a process of removing the resist film by a predetermined thickness on the entire surface is performed until the resist in a region where the resist film is dissolved to some extent disappears. As a result, the region other than the region where the resist is hardly dissolved in the initial stage is a missing region where the resist is completely dissolved, and a second pattern can be formed. Using this second pattern as a mask, a pattern different from the first pattern can be formed on the thin film under the resist film. By using such a process, a single multi-tone mask can be used where two transfer masks are originally required.

  As a method of manufacturing a multi-tone mask, first, a method of completing a multi-tone mask by repeating the formation of a pattern forming thin film and the etching process of pattern formation is given. In addition, a multi-tone mask blank 10 having a structure in which a light semi-transmissive film (one or more steps) and a light-shielding film are laminated on the mask blank substrate 1 is manufactured in advance. There is a method in which an etching process is performed to complete a multi-tone mask.

  Other thin films for pattern formation include an etching mask (hard mask) film and an etching stopper film.

  As a material applicable to the thin film for pattern formation, a material mainly composed of chromium is first mentioned. In addition to chromium alone, chromium-based materials include chromium compounds in which elements such as oxygen, nitrogen, carbon, hydrogen, and boron are added to chromium.

  In addition, as a material applicable to the pattern forming thin film, a material containing transition metal and silicon as main components (a material containing transition metal silicide as a main component) is also applicable. In addition to transition metal silicide alone, transition metal silicide compounds in which elements such as oxygen, nitrogen, carbon, hydrogen, and boron are added to transition metal silicide include materials containing transition metal silicide as a main component. As the transition metal of the transition metal silicide, molybdenum, tantalum, tungsten, titanium, hafnium, nickel, vanadium, zirconium, niobium, palladium, ruthenium, rhodium, or the like can be applied.

  In addition, as a material applicable to the thin film for pattern formation, a material mainly composed of tantalum can be given. In addition to tantalum alone, tantalum-based materials include tantalum compounds in which elements such as oxygen, nitrogen, carbon, hydrogen, and boron are added to tantalum.

  In the case of a light shielding film, since it has a high light shielding property, the reflectance with respect to exposure light tends to be high. In order to suppress this, the light shielding film often has a laminated structure in which an antireflection layer for suppressing the reflectance is formed on a light shielding layer having a high content of light shielding performance or a transition metal silicide. Further, when it is necessary to suppress the reflectance of the light shielding film on the substrate side, there may be a laminated structure in which a back surface antireflection layer is further formed between the substrate and the light shielding layer. As a material for the antireflection layer and the back surface antireflection layer, a metal compound material or a transition metal silicide compound material in which oxygen or nitrogen is contained in a metal or a transition metal silicide is suitable. On the other hand, since the light shielding layer needs to have high light shielding performance, it is preferable to use a metal material, a transition metal silicide, or a metal compound or a transition metal silicide compound material with as little oxygen or nitrogen as possible.

  Examples of materials applicable to the light semi-transmissive film such as the halftone phase shift film include the chromium compounds, tantalum compounds, and transition metal silicide compounds. In particular, the compound containing oxygen or nitrogen is preferable in order to adjust transmittance and the like.

  Next, the present invention will be described more specifically with reference to examples of the present invention.

Example 1
The mask blank substrate 1 was manufactured by the following steps: (1) cutting process, (2) grinding process, (3) flame treatment process, (4) polishing process, and (5) defect inspection process. Hereinafter, each process will be described in detail.

(1) Cutting process The synthetic quartz glass cut out on the flat plate from the synthetic quartz glass ingot was prepared. Next, it cut out from the sheet glass which consists of synthetic quartz glass with the grinding stone, and the square board | substrate 1 was obtained. The size of the substrate 1 to be cut out was set in consideration of a substrate polishing allowance so that a mask blank substrate 1 having a thickness of about 152 mm × about 152 mm and a thickness of about 6.35 mm could be finally obtained.

  Next, by grinding using a grindstone, a predetermined chamfering process was performed on the side surface of the synthetic quartz glass substrate 1 to form an end surface 72 and a chamfered surface 73.

(2) Grinding process Next, the main surface 71 of the obtained synthetic quartz glass substrate 1 was ground. In the grinding process, the double-sided grinding apparatus having the planetary gear mechanism was used to perform the process using a grinding liquid containing alumina abrasive grains, and the dimensional accuracy and shape accuracy of the synthetic quartz glass substrate 1 were set to be predetermined. As the upper surface plate 2 and the lower surface plate of the planetary gear mechanism, those made of spheroidal graphite-containing cast iron were used.

  It was confirmed that the obtained synthetic quartz glass substrate 1 had a square shape with a side of about 152 mm and a thickness of 6.4 mm.

  When the surface shape of the synthetic quartz glass substrate 1 was observed, the surface roughness of the main surface 71 was about 2 μm for Rmax and about 0.3 μm for Ra.

  Next, after grinding the end surface 72 of the synthetic quartz glass substrate 1 to adjust the external dimensions, the chamfered surface 73 was also ground. When the surface roughness was observed, both the end face 72 and the chamfered face 73 were 14 μm in Rmax and 0.5 μm in Ra.

(3) Flame treatment process The synthetic quartz glass substrate 1 after the grinding process was subjected to flame treatment on the entire main surface 71 thereof. The flame treatment was performed by scanning flame treatment under the following conditions.
・ Flame temperature: 2200 ℃
-Distance between the flame irradiation device 50 and the substrate 1: 15 mm
・ Flame diameter: 3mm
・ Flame scanning speed: 0.6mm / min ・ Types of flammable gas: Mixed gas of butane and oxygen

(4) Polishing process Next, the grinding | polishing process was performed with respect to the board | substrate 1 which performed the flame processing by the flame processing process. In addition, this grinding | polishing process can consist of one time or a some grinding | polishing process. Moreover, it can have a washing | cleaning process for performing predetermined washing | cleaning after predetermined grinding | polishing. In addition, before the final polishing process for the main surface 71, a side mirror polishing process for performing mirror processing on the end surface 72 and the chamfered surface 73 is performed. Here, cerium oxide polishing abrasive grains (average particle diameter: 1 μm) were used, and the brush was brought into contact with the end face 72 and the chamfered face 73 for mirror polishing.

The polishing step was performed using the double-side polishing apparatus described in Patent Document 2. An ultra-soft polisher was used as the polisher, and the polishing was performed under the following conditions.
Polishing liquid: Colloidal silica (average particle size 100 nm) Free abrasive grains with water added to abrasive grains Polishing cloth: Super soft polisher (suede type), thickness 2 mm

  The substrate 1 that had been subjected to the polishing step was washed by sequentially immersing it in each cleaning bath of neutral detergent, pure water, pure water, IPA, and IPA (steam drying). In addition, ultrasonic waves were applied to each cleaning tank.

  The substrate 1 after the polishing process was cleaned by immersing it in alkali (NaOH) and sulfuric acid in order. In addition, ultrasonic waves were applied to each cleaning tank. Furthermore, it wash | cleaned by immersing in each washing tank of neutral detergent, a pure water, a pure water, IPA, and IPA (steam drying) one by one. The mask blank substrate 1 was obtained through the above steps.

(5) Defect inspection Next, the obtained substrate 1 was inspected for the flatness, surface roughness, presence or absence of defects 5 such as internal cracks, and their positions. Presence / absence of the defect 5 such as an internal crack was evaluated by revealing the defect 5 such as the internal crack by the method using the etching process described in Patent Document 1. Here, the flatness required for the mask blank substrate 1 was 0.5 μm or less, and the surface roughness was 0.1 μm or less in terms of arithmetic average roughness Ra.

  About the mask blank substrate 1 obtained as described above, it was confirmed that the defect 5 such as the internal crack does not exist after the etching treatment for revealing the defect 5 such as the internal crack. Further, when the flatness and the surface roughness of the main surface 71 of the substrate 1 were measured, the substrate 1 could be corrected to a level usable as a non-defective mask blank substrate 1.

(6) Production of Mask Blank 10 Next, a halftone phase shift film (thin film for pattern formation) 2 made of nitrided molybdenum and silicon was formed on the mask blank substrate 1 described above.

Specifically, using a mixed target of molybdenum (Mo) and silicon (Si) (Mo: Si = 12 at%: 88 at%), mixing argon (Ar), nitrogen (N ₂ ), and helium (He) In a gas atmosphere (gas flow ratio Ar: N ₂ : He = 8: 72: 100), a gas pressure of 0.3 Pa, a DC power source power of 3.0 kW, reactive sputtering (DC sputtering), molybdenum, silicon, and A MoSiN film made of nitrogen was formed to a thickness of 69 nm. Next, the substrate on which the MoSiN film was formed was subjected to a heat treatment as an annealing treatment. Specifically, using a heating furnace, heat treatment was performed in the atmosphere at a heating temperature of 550 ° C. and a heating time of 1 hour. This MoSiN film had an transmittance of 6.1% and a phase difference of 184 degrees in an ArF excimer laser.

Next, a light-shielding film (pattern forming thin film) 3 made of a chromium-based material was formed on the halftone phase shift film 2.
Specifically, using a chromium (Cr) target, a mixed gas atmosphere (gas flow ratio Ar: CO ₂ : N) of argon (Ar), carbon dioxide (CO ₂ ), nitrogen (N ₂ ), and helium (He). ₂ : He = 22: 39: 6: 33), the gas pressure was 0.2 Pa, the power of the DC power source was 1.7 kW, and a CrOCN film was formed to a thickness of 30 nm by reactive sputtering (DC sputtering). Subsequently, using a chromium (Cr) target, a mixed gas atmosphere of argon (Ar) and nitrogen (N ₂ ) (gas flow ratio Ar: N ₂ = 83: 17), gas pressure of 0.1 Pa, and DC power supply A CrN film having a thickness of 4 nm was formed by reactive sputtering (DC sputtering) with an electric power of 1.7 kW. Furthermore, a mixed gas atmosphere (gas flow ratio Ar: CO ₂ : N ₂ : He) of argon (Ar), carbon dioxide (CO ₂ ), nitrogen (N ₂ ), and helium (He) is used using a chromium (Cr) target. = 21: 37: 11: 31), the gas pressure was 0.2 Pa, the power of the DC power source was 1.8 kW, and the CrOCN film was formed to a thickness of 14 nm by reactive sputtering (DC sputtering). As described above, the light-shielding film 3 made of a chromium-based material having a three-layer structure of a CrOCN film, a CrN film, and a CrOCN film was formed from the substrate 1 side. Through the above steps, a halftone phase shift mask blank (mask blank) 10 was obtained.

  Next, a halftone phase shift mask 15 was produced using the phase shift mask blank 10 described above. FIG. 5 is a schematic cross-sectional view showing a process of manufacturing the phase shift mask 15 using the phase shift mask blank 10. First, a chemically amplified positive resist film for electron beam lithography (PRL009 manufactured by Fuji Film Electronics Materials) was formed as a resist film 4 on the mask blank 10 (see FIG. 1A). The resist film 4 was formed by spin coating using a spinner (rotary coating apparatus).

  Next, a phase shift pattern was drawn on the resist film 4 formed on the mask blank 10 using an electron beam drawing apparatus, and then developed with a predetermined developer to form a resist pattern 4a ( (See (b) in the figure).

Next, using the resist pattern 4a as a mask, the light shielding film 3 (Cr-based light shielding film) was etched to form a light shielding film pattern 3a (see FIG. 4C). A mixed gas of Cl ₂ and O ₂ was used as a dry etching gas.

Next, the halftone phase shift film 2 (MoSiN film) was etched using the light shielding film pattern 3a as a mask to form a phase shift pattern 2a (see FIG. 4D). A mixed gas of SF ₆ and He was used as a dry etching gas.

  Next, a chemically amplified positive resist film for electron beam drawing (PRL009 manufactured by Fuji Film Electronics Materials) is similarly formed as a resist film 4 on the mask blank 10, and a light shielding band is formed using an electron beam drawing apparatus. After pattern drawing, the resist pattern 4b was formed by developing with a predetermined developer (see FIG. 5E).

Next, using the resist pattern 4b as a mask, the light shielding film pattern 3a (Cr-based light shielding film) was etched to form a light shielding film pattern (light shielding band) 3b. A mixed gas of Cl ₂ and O ₂ was used as a dry etching gas.

  Next, the remaining resist pattern was peeled off to obtain a phase shift mask 15 (see FIG. 5F). The phase shift mask 15 could be used without any problem. Further, the transmittance and phase difference of the phase shift film were hardly changed compared to the production of the mask blank 10.

  Using this phase shift mask 15, an exposure apparatus using an ArF excimer laser as a light source performed exposure transfer of a phase shift pattern onto a resist film to be transferred. When the resist film of the transfer object is developed, the resist pattern is normally formed even if the phase shift mask 15 (transfer mask) is produced using the mask blank substrate 1 subjected to the flame treatment. It has been confirmed that.

(Comparative Example 1)
100 mask blank substrates 1 were manufactured in the same manner as in Example 1 except that the flame treatment process was not performed. In the defect inspection after the polishing step, internal cracks were found in 3 out of 100 mask blank substrates 1. Therefore, in order to obtain the mask blank substrate 1 having no internal cracks, it became clear that it is necessary to perform a flame treatment in the manufacturing process.

  When a mask for transfer is produced using a mask blank manufactured from the mask blank substrate 1 in which an internal crack exists, the etching gas or the etchant expands the crack and a part near the substrate main surface falls off. Probability is high. When the part where the substrate is dropped is a transmission part that transmits the exposure light of the transfer pattern, irregular reflection of the exposure light and phase defects occur. In particular, in the case of a phase shift mask or enhancer mask that realizes an edge enhancement effect of a transfer pattern due to the phase difference of exposure light, a fatal problem occurs in exposure transfer. Even in the case of a binary transfer mask, this is an unacceptable problem. On the other hand, in the case where a thin film for pattern formation (such as a light-shielding film, a phase shift film, and a light semi-transmissive film) is left on the upper surface of the part where the substrate has fallen, the thin film will be dropped together with the part where the substrate is dropped As a result, a pattern defect (white defect) occurs. Pattern defects are unacceptable problems for exposure transfer regardless of the type of transfer mask.

  Furthermore, when the transfer mask is cleaned, cracks may expand due to cleaning chemicals and the like, and a part of the substrate of the transfer mask may be peeled off. Therefore, it is certain that the life of the transfer mask is shortened. Therefore, it is clear that the transfer mask using the mask blank substrate 1 having the internal cracks of Comparative Example 1 is difficult to use on the production line.

1 Mask blank substrate (synthetic quartz glass substrate)
2 Halftone phase shift film (thin film for pattern formation)
2a Phase shift pattern 3 Light-shielding film (thin film for pattern formation)
3a, 3b Light-shielding film pattern 4 Resist film 4a, 4b Resist pattern 5 Defect 10 Mask blank 15 Phase shift mask 50 Flame irradiation device 52 Flame 71 Main surface 72 End face 73 Chamfering surface 100 Flame treatment device 102 Stage 104 Flame control unit 105 Inflammation Gas 112 Stage controller 114 Flame treatment controller

Claims (6)

A method of manufacturing a mask blank substrate comprising a substrate having two opposing main surfaces,
Grinding the main surface of the substrate;
A step of bringing a flame having a combustion temperature equal to or higher than the softening point of the substrate into contact with the main surface of the substrate that has been ground;
And a step of polishing the main surface of the substrate after performing the step of bringing the flame into contact with each other.   The method for manufacturing a mask blank substrate according to claim 1, wherein the substrate is made of synthetic quartz glass.   The method for manufacturing a mask blank substrate according to claim 1, wherein the flame has a combustion temperature of 1600 ° C. or higher. The mask according to any one of claims 1 to 3, wherein the step of bringing the flame into contact softens the main surface of the substrate and removes internal cracks existing in the vicinity of the main surface of the substrate. A method for manufacturing a blank substrate.   It has the process of forming the thin film for pattern formation on the main surface of the mask blank board | substrate manufactured with the manufacturing method of the mask blank board | substrate of any one of Claims 1-4. Mask blank manufacturing method.   A method for producing a transfer mask, comprising a step of forming a transfer pattern on a thin film for pattern formation of a mask blank produced by the method for producing a mask blank according to claim 5.