Method for producing photomask substrate, method for producing photomask blanks, method for producing photomask, method for reusing photomask substrate, photomask substrate, photomask blanks, photomask, and device for processing quartz glass substrate

Abstract

The purpose of the present invention is to provide a method for repeatedly reproducing photomask substrates without altering the photomask substrate thickness.　The method for producing a photomask substrate from a quartz glass substrate comprises: a concavity treatment step (1-(1)) for irradiating a concavity-including irradiation range on a first face of a quartz glass substrate using laser light having a peak wavelength of 9.2 μm to 12 μm, a pulse width of 1 ns to100 ms, and an average output density of 50 W / cm2 to 700 W / cm2; and a substrate surface processing step (1-(3)) for removing the region that includes the irradiation range from the surface of the first face that has undergone the concavity treatment step.

Description

Photomask substrate manufacturing method, photomask blank manufacturing method, photomask manufacturing method, photomask substrate recycling method, photomask substrate, photomask blank, photomask, quartz glass substrate processing device

[0001] The present invention relates to a method for manufacturing a photomask substrate, a method for manufacturing a photomask blank, a method for manufacturing a photomask, a method for recycling a photomask substrate, and a processing apparatus for a photomask substrate, a photomask blank, a photomask, and a quartz glass substrate. This invention claims priority from Japanese Patent Application No. 2024-069239, filed on April 22, 2024, and the contents of that application are incorporated by reference into this application in designated states where incorporation by reference of documents is permitted.

[0002] Patent Document 1 discloses a photomask blank having a film on a photomask substrate. When a photomask substrate having scratches or the like is regenerated by the conventional method of scraping off the scratches, the thickness of the photomask substrate is significantly reduced, and the number of times it can be regenerated is limited to approximately one. There is a need for a method for repeatedly regenerating photomask substrates without changing the thickness of the photomask substrate.

[0003] JP 2016-105158 A

[0004] One aspect of the present invention is a method for manufacturing a photomask substrate from a quartz glass substrate, in which a photomask substrate is manufactured from a quartz glass substrate, and a laser beam having a peak wavelength of 9.2 μm or more and 12 μm or less, a pulse width of 1 ns or more and 100 ms or less, and an average power density of 50 W / cm is applied to an irradiation area including a recess on a first surface of the quartz glass substrate. ２ More than 700W / cm ２ This is a method for manufacturing a substrate for a photomask, which includes a recess processing step of irradiating the substrate with the following laser light, and a substrate surface processing step of removing an area including the irradiated area from the surface of the first surface on which the recess processing step has been performed.

[0005] Another aspect of the present invention is a method for manufacturing a photomask blank, which comprises forming at least one type of film selected from a light-shielding film, a halftone film, and a phase shift film on a photomask substrate produced by the above-described method for manufacturing a photomask substrate, thereby manufacturing a photomask blank.

[0006] Another aspect of the present invention is a method for manufacturing a photomask, which comprises carrying out fine line circuit processing on a photomask blank produced by the above-described method for manufacturing a photomask blank.

[0007] Another aspect of the present invention is a method for recycling photomask substrates, in which used photomask substrates are repeatedly recycled into new photomask substrates by carrying out the above-described method for manufacturing a photomask substrate.

[0008] Another aspect of the present invention is a photomask substrate including a quartz glass substrate, the photomask substrate having one or more retardations of 5 nm or more on the quartz glass substrate and a PV value of 30 μm or less. Another aspect of the present invention is a photomask blank having at least one type of film selected from a light-shielding film, a halftone film, and a phase shift film on the photomask substrate. Another aspect of the present invention is a photomask having a pattern formed on the photomask blank. Another aspect of the present invention is a processing device for a quartz glass substrate used for a photomask substrate, the device comprising: a laser unit that irradiates the quartz glass substrate with a laser; and a moving unit that moves the irradiation position on the quartz glass substrate by the laser unit, the laser unit and the moving unit irradiating an irradiation range including a recess on the quartz glass substrate with the laser, and melting at least a portion of the irradiation range to reduce the depth of the recess.

[0009] FIG. 1 is a cross-sectional view schematically illustrating an example of a method for manufacturing a photomask substrate (laser refining method) according to the present embodiment; FIG. 2 is a cross-sectional view schematically illustrating another example of a method for manufacturing a photomask substrate (laser refining method) according to the present embodiment; FIG. 3 is a cross-sectional view schematically illustrating an example of a method for manufacturing a photomask substrate (laser refining method + CVD refining method) according to the present embodiment; FIG. 4 is a cross-sectional view schematically illustrating another example of a method for manufacturing a photomask substrate (laser refining method + CVD refining method) according to the present embodiment; FIG. 5 is a block diagram of a quartz glass substrate processing device according to the present embodiment; FIG. 6 is a bubble chart collating coordinates and depths of recesses in quartz glass substrates recovered from used photomask substrates; and FIG. 7 is a diagram illustrating an image of recesses becoming shallower by carbon dioxide laser irradiation.

[0010] An embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described below. The present embodiment is an example for explaining the present invention, and is not intended to limit the present invention to the following content. The present invention can be practiced with appropriate modifications within the scope of its gist.

[0011] Typically, a photomask for a flat panel display (FPD) refers to a substrate made of parallel flat quartz glass with a first surface and a second surface opposite the first surface polished, on which a thin line pattern of a light-shielding film such as chrome, a halftone film, or a phase shift film such as chrome or molybdenum silicide is formed. Panel manufacturers that produce a variety of liquid crystal displays and organic EL displays use projection exposure machines or proximity exposure machines to transfer and fix the thin line pattern of the photomask onto the quartz glass substrate for the display, thereby manufacturing the displays.

[0012] Similarly, a photomask for semiconductor circuits refers to a parallel plate substrate made of quartz glass with its first and second surfaces polished, on which a thin line pattern of a light-shielding film such as chrome, a half-tone film, or a phase shift film such as chrome or molybdenum silicide is formed. Manufacturers of semiconductor devices use a reduced projection exposure machine to reduce and transfer the thin line pattern of the photomask onto various substrates for semiconductor devices.

[0013] Photomask substrates that have finished being used as photomasks by panel manufacturers and semiconductor device manufacturers are sometimes collected for recycling purposes if they are in a state where there is no visible damage. To recycle collected photomask substrates, the photomask pattern formed on the substrate surface, consisting of a Cr film, MoSi film, etc., is first dissolved and removed by immersion in a solvent. After the photopattern is dissolved and removed, the substrate, with the quartz glass exposed, typically has scratches on its front and back surfaces. Therefore, the substrate cannot be used as a recycled photomask by forming a new photomask in its current state. The scratches must be removed by some means, and the first and second surfaces of the quartz glass substrate must be flat again before forming the photomask.

[0014] This embodiment will be described in detail below.

[0015] <Method of Manufacturing a Photomask Substrate> A method of manufacturing a photomask substrate according to this embodiment is a method of manufacturing a photomask substrate from a quartz glass substrate, and includes irradiating a first surface of the quartz glass substrate with a light having a peak wavelength of 9.2 μm or more and 12 μm or less, a pulse width of 1 ns or more and 100 ms or less, and an average power density of 50 W / cm with a photoirradiation area including recesses on the first surface of the quartz glass substrate. ２ More than 700W / cm ２ This is a method for manufacturing a substrate for a photomask, comprising: a recess processing step of irradiating the substrate with the following laser light; and a substrate surface processing step of removing an area including the irradiated area from the surface of the first surface on which the recess processing step has been performed.

[0016] (i) Recess processing step In the recess processing step, for example, by irradiating a laser having a wavelength of 10.6 μm, the quartz glass in and around the recess is melted and flows into the recess, making it possible to reduce the depth of the recess as shown in FIG. 7.

[0017] The depth of the recesses before being irradiated with a laser in the recess processing step is not particularly limited, but is, for example, 0.1 μm or more. The lower limit of the recess depth is preferably 15 μm, more preferably 30 μm, more preferably 50 μm, and even more preferably 80 μm. This embodiment can be used more effectively for recesses of such depths. The upper limit of the depth of the recesses before being irradiated with a laser in the recess processing step is, for example, 500 μm.

[0018] In the recess processing step, the depth of the recess is set to 30 μm or less. The upper limit of the depth of the recess after the recess processing step is preferably 20 μm, more preferably 10 μm.

[0019] In the recess processing step, the quartz glass in and around the recess melts and flows into the recess, making the depth of the recess shallower, so that the composition of the irradiated area after the laser irradiation is silicon dioxide.

[0020] In the recess processing step, the depth of the recess can be further reduced by irradiating the quartz glass substrate with a laser having a wavelength of 9.2 μm or more and 12.0 μm or less, in addition to a laser having a wavelength of 10.6 μm. The lower limit of the wavelength of the irradiated laser is preferably 9.5 μm, more preferably 9.6 μm. The upper limit of the wavelength of the irradiated laser is preferably 11.0 μm, more preferably 10.8 μm.

[0021] Silica glass is composed of Si-O chemical bonds. Heating silica glass means exciting the Si-O bonds (vibrationally exciting them). The absorption wavelength of the Si-O vibration is between 9 μm and 10 μm (1100 cm ―１ More than 1000cm ―１ ) or less. Therefore, in order to efficiently heat and melt quartz glass, it is sufficient to irradiate it with electromagnetic waves having a wavelength of 9.2 μm or more and 12.0 μm or less. A carbon dioxide laser is an example of a typical laser oscillator capable of stimulated emission of light in this wavelength range. The laser used in this embodiment is not limited to a carbon dioxide laser, as long as it is a laser oscillator capable of emitting electromagnetic waves having a wavelength of 9.2 μm or more and 12.0 μm or less.

[0022] In the recess processing step, the temperature of the irradiation range during the laser irradiation period is preferably around 2000°C, at which quartz glass melts, for example, 1800°C or higher and 2300°C or lower. The lower limit of the temperature is preferably 1900°C, more preferably 2000°C. The upper limit of the temperature is preferably 2200°C, more preferably 2100°C. If the temperature of the irradiation range during the laser irradiation period is low, the quartz glass substrate will not melt easily, and the efficiency of reducing the depth of the recess will tend to decrease, and if the temperature of the irradiation range during the laser irradiation period is too high, the evaporation of the quartz glass will tend to be significant.

[0023] The laser irradiation period can be appropriately selected depending on the laser energy fluence and the depth of the recess. The appropriate period is, for example, 3 seconds to 30 minutes. The lower limit of the appropriate period is preferably 10 seconds, more preferably 15 seconds, and even more preferably 20 seconds. The upper limit of the appropriate period is preferably 20 minutes, more preferably 10 minutes, and even more preferably 5 minutes. By locally heating the recess in this manner, the recess and its surroundings are locally melted and flow into the recess, thereby reducing the depth of the recess. Therefore, the temperature of the irradiation range during the laser irradiation period need only be a temperature at which the quartz glass can melt and flow. Even at a relatively low temperature of 1800°C to 1900°C, the depth of the recess can be reduced by relatively extending the laser irradiation time, for example, 10 minutes to 120 minutes. The laser irradiation range refers to the area on the surface of the quartz glass substrate directly irradiated with the laser, and the diameter of the irradiation range is synonymous with the laser beam diameter on the surface of the quartz glass substrate. The boundary between the area where the laser is directly irradiated and the area where it is not is 1 / e in the spatial distribution of the laser intensity, where e is the maximum intensity of the laser. ２ The temperature in the laser irradiation range refers to the average value of the temperature in the laser irradiation range.

[0024] Preferred conditions for laser irradiation (laser light irradiation) in the recess processing step will be described below.

[0025] There are two types of lasers: pulsed lasers and continuous wave lasers, but it is preferable to use a pulsed laser in this embodiment. When a pulsed laser is used, laser light is irradiated in pulses, which causes repeated heating and heat dissipation in the laser irradiation area, making it possible to maintain the quartz glass substrate at a temperature suitable for melting.

[0026] The pulse width of a laser (laser light) is 1 ns (10 －９ s) or more, and －７ s) or more, and 1 μs (10 －６ It is more preferable that the pulse width of the laser is 100 ms (10 －１ s) or less, and －２ s) or less, and more preferably 1 ms (10 －３ It is more preferable that the laser pulse width is equal to or less than 1 / 2 s. When the laser pulse width is set within this range, the quartz glass substrate can be efficiently melted, and the depth of the recesses can be reduced. Furthermore, if the laser pulse width is too large, the quartz glass substrate is excessively heated, causing significant evaporation and making it difficult to reduce the recesses. If the laser pulse width is too small, the temperature of the quartz glass substrate does not rise, and an ablation phenomenon occurs in which Si-O covalent bonds are directly broken by electronic excitation, making it difficult to reduce the recesses. The pulse width is determined by the half-width, and the irradiation range is determined by the laser light intensity being 1 / e of the peak intensity. ２ This is the range above.

[0027] The repetition rate of the laser (laser light) is 5 Hz (5 x 10 ０ Hz) or more, and 50 Hz (5 × 10 １ Hz) or more, and 500 Hz (5 × 10 ２ Hz) or more. The repetition rate of the laser is preferably 5 MHz (5×10 ６ Hz) or less, and 500 kHz (5 × 10 ５ Hz) or less, and more preferably 50 kHz (5×10 ４Hz) or less. When the laser repetition frequency is in this range, the quartz glass substrate can be moderately heated and melted by vibrational excitation. On the other hand, if the laser repetition frequency is too high, the quartz glass substrate tends to be ablated by electronic excitation, making it difficult to reduce the size of the recesses. If the laser repetition frequency is too low, the quartz glass substrate tends to be excessively heated by vibrational excitation, causing significant evaporation and making it difficult to reduce the size of the recesses.

[0028] The duty ratio of the laser (laser light) is preferably 5% or more, more preferably 10% or more, and even more preferably 20% or more. Furthermore, the duty ratio of the laser is preferably 90% or less, more preferably 80% or less, and even more preferably 70% or less. When the laser duty ratio is within this range, the quartz glass substrate is sufficiently heated while the irradiated portion of the quartz glass substrate is appropriately intermittently cooled during laser irradiation, thereby preventing the quartz glass from being excessively heated and causing significant evaporation. If the laser duty ratio is too large, intermittent cooling of the irradiated portion of the quartz glass during laser irradiation becomes impossible, the quartz glass substrate is excessively heated, causing significant evaporation, and the recess tends to be difficult to reduce. If the laser duty ratio is too small, the time during which the laser is irradiated within the irradiation time is substantially short, and the quartz glass substrate tends to be insufficiently heated and difficult to melt.

[0029] The average power density of the laser (laser light) (average laser output per unit area of ​​the laser irradiation part) is 100 W / cm ２ It is preferable that the power is 150 W / cm or more. ２ More preferably, it is 200 W / cm or more. ２ It is more preferable that the average power density is 700 W / cm or more. ２ It is preferable that the power is 600 W / cm or less. ２ More preferably, it is 500 W / cm or less. ２It is more preferable that the average power density of the laser is within this range, so that the quartz glass substrate can be heated to a temperature suitable for melting. If the average power density of the laser is too high, the quartz glass substrate tends to be excessively heated, causing significant evaporation and making it difficult to reduce the size of the recesses. If the average power density of the laser is too low, the quartz glass substrate tends to be insufficiently heated, making it difficult to melt.

[0030] When the intensity of the laser light in the center of the laser irradiation area is stronger than the intensity of the laser light in the peripheral area of ​​the irradiation area, the average power density of the laser (laser light) (average laser output per unit area of ​​the laser irradiation area, average power density) is 100 W / cm ２ It is preferable that the power is 150 W / cm or more. ２ More preferably, it is 200 W / cm or more. ２ It is more preferable that the average power density is 700 W / cm or more. ２ It is preferable that the power is 600 W / cm or less. ２ More preferably, it is 500 W / cm or less. ２ It is more preferable that the following is true: An example of a shape in which the intensity of the laser light in the center of the irradiation range is stronger than the intensity of the laser light in the peripheral part of the irradiation range is a Gaussian distribution.

[0031] When the intensity of the laser light is constant in the laser irradiation range, the average power density of the laser (laser light) (average laser output per unit area of ​​the laser irradiation part, average power density) is 50 W / cm ２ It is preferable that the power is 75 W / cm or more. ２ More preferably, it is 100 W / cm or more. ２ It is more preferable that the average power density is 350 W / cm or more. ２ It is preferable that the power is 300 W / cm or less. ２ More preferably, it is 250 W / cm or less. ２It is more preferable that the intensity of the laser beam is constant in the laser irradiation range, which can also be said to have a top hat shape.

[0032] An example of a preferable combination of conditions for laser (laser light) irradiation is a laser with a wavelength of 9.2 μm or more and 12 μm or less, a pulse width of 1 ns or more and 100 ms or less, and an average power density of 50 W / cm ２ More than 700W / cm ２ The following is the irradiation.

[0033] The peak power density of the laser (laser light) (peak laser output per unit area of ​​the laser irradiation part, Peak power density) is 200 W / cm ２ Pulse or more is preferable, 300 W / cm ２ Pulse or more is more preferable, 400 W / cm ２ It is more preferable that the peak power density is 1,400 W / cm or more. ２ Pulse or less is preferable, 1,200 W / cm ２ Pulse or less is more preferable, 1,000 W / cm ２ It is more preferable that the laser peak power density is equal to or less than 1 / 4 pulse. When the laser peak power density is within this range, the quartz glass substrate can be heated to a temperature suitable for melting. If the laser peak power density is too high, the quartz glass substrate tends to be excessively heated, causing significant evaporation and making it difficult to reduce the size of the recesses. If the laser peak power density is too low, the quartz glass substrate tends to be insufficiently heated, making it difficult to melt.

[0034] When the intensity of the laser light in the center of the laser irradiation area is stronger than the intensity of the laser light in the peripheral area of ​​the irradiation area, the peak power density of the laser (laser light) (peak laser output per unit area of ​​the laser irradiation area, Peak power density) is 200 W / cm ２ It is preferable that the power is 300 W / cm or more. ２ More preferably, it is 400 W / cm or more. ２It is more preferable that the peak power density is 1400 W / cm or more. ２ Preferably, the power is 1200 W / cm or less. ２ More preferably, it is 1000 W / cm or less. ２ It is even more preferable that:

[0035] When the intensity of the laser light is constant in the laser irradiation range, the peak power density of the laser (laser light) (peak laser output per unit area of ​​the laser irradiation part, Peak power density) is 100 W / cm ２ It is preferable that the power is 150 W / cm or more. ２ More preferably, it is 200 W / cm or more. ２ It is more preferable that the peak power density is 700 W / cm or more. ２ It is preferable that the power is 600 W / cm or less. ２ More preferably, it is 500 W / cm or less. ２ It is even more preferable that:

[0036] The diameter (beam diameter) of the laser (laser light) irradiation range on the surface of the quartz glass substrate is preferably 100 μm or more, more preferably 500 μm or more, and even more preferably 1 mm or more. The laser beam diameter is preferably 30 mm or less, more preferably 20 mm or less, and even more preferably 10 mm or less. When the laser beam diameter is within this range, the quartz glass substrate can be melted over a sufficient area relative to the recess, and the depth of the recess can be efficiently reduced. Furthermore, if the laser beam diameter is too large, it may cause birefringence deep into the quartz glass substrate. If the laser beam diameter is too small, position adjustment for irradiating the laser so that the spot overlaps the recess tends to become complicated. As mentioned above, the boundary of the laser (laser light) irradiation range is determined by the point where the laser intensity reaches 1 / e of the peak value. ２ Therefore, the diameter of the irradiation range of the laser (laser light) is the position where the laser intensity is 1 / e of the peak value. ２When the diameter of the irradiation area of ​​the laser (laser light) on the surface of the quartz glass substrate is adjusted, the adjustment method is not particularly limited, and for example, a beam expander may be used or defocusing may be used.

[0037] The integrated energy amount (total energy applied to one location) at one location on the quartz glass substrate irradiated with a laser (laser light) is preferably 4,000 J or less, more preferably 3,000 J or less, and even more preferably 2,000 J or less. By setting the integrated energy amount applied to one location within this range, the depth of the recess can be reduced while minimizing the adverse effects of laser irradiation on the quartz glass substrate. If the integrated energy amount applied to one location is too large, heat will be conducted to the periphery of the recess, which tends to cause warping of the quartz glass substrate. The integrated energy amount applied to one location can be calculated by multiplying the average power density by the irradiation time. When scanning the irradiation area, it is preferable to prevent the integrated energy amount applied to one location from becoming too large, taking into account the laser output, the area of ​​the irradiation area, the scanning speed, etc.

[0038] Additionally, when a quartz glass substrate is used as a photomask substrate, it is important that the substrate has high flatness. As mentioned above, by limiting the integrated energy at one laser irradiation point to 4,000 J or less, warping of the quartz glass substrate can be prevented, and the depth of the recess can be made shallow while maintaining high flatness. Furthermore, warping can be restored by annealing a warped quartz glass substrate using a known method.

[0039] The irradiation range of the laser (laser light) may be stationary relative to the recess to be irradiated, or may be scanned. When the irradiation range of the laser is scanned relative to the recess, the scanning speed and number of times can be set appropriately. The faster the scanning speed, the greater the number of scans required to reduce the depth of the recess. The irradiation angle of the laser relative to the quartz glass substrate is not particularly limited. For example, it can be set to an angle close to perpendicular from the viewpoint of more uniform and efficient application of energy to the quartz glass substrate, or it can be irradiated from an oblique angle when it is desired to distribute the energy applied to the quartz glass substrate according to the shape of the recess.

[0040] A quartz glass substrate may have a plurality of recesses. In this case, the other recesses may also be irradiated with a laser (laser light) under the above-described conditions. For example, a laser with a wavelength of 9.2 μm to 12 μm and a pulse width of 1 ns to 100 ms may be irradiated to an irradiation area including the other recesses at an average power density of 50 W / cm. ２ More than 700W / cm ２ The laser is irradiated in a combination of the following. The laser may be irradiated as many times as the number of recesses, or it may be irradiated selectively to recesses with a large depth. Even when irradiating multiple recesses with a laser, by keeping the integrated energy at one laser irradiation point at 4,000 J or less, it is possible to prevent warping of the quartz glass substrate and reduce the depth of the recesses while maintaining a high degree of flatness.

[0041] (ii) Substrate Surface Processing Step The substrate surface processing step is a step of reducing and flattening the substrate, and can be performed by polishing or precision polishing. The depth of the recess after the substrate surface processing step is smaller than the depth of the recess before the step.

[0042] In the polishing process, for example, cerium oxide having a particle diameter of about 100 μm is used as an abrasive. In the precision polishing process, planarization is performed using, for example, ultrafine silicon dioxide particles having a particle diameter of about several μm as an abrasive. Either the polishing process or the precision polishing process may be used, or the precision polishing process may be performed after the polishing process.

[0043] The arithmetic mean height Sa (surface roughness; ISO 25178) of the first surface after the substrate surface processing step is smaller than the arithmetic mean height Sa (surface roughness; ISO 25178) of the first surface before the step is performed. Specifically, in the substrate surface processing step, the arithmetic mean height Sa (surface roughness; ISO 25178) of the first surface is set to 20 μm or less. The upper limit of the arithmetic mean height of the first surface after the substrate surface processing step is preferably 7 μm, more preferably 5 μm, and even more preferably 3 μm. In particular, it is more preferable to set the arithmetic mean height Sa (surface roughness; ISO 25178) of the entire first surface to 20 μm or less. The upper limit of the arithmetic mean height of the entire first surface after the substrate surface processing step is preferably 7 μm, more preferably 5 μm, and even more preferably 3 μm.

[0044] The substrate surface processing step can also be considered as removing the area of ​​the surface of the first side that has been subjected to the recess processing step, including the laser irradiation range. By performing surface removal on the area including the recesses and their surroundings, whose depth has been reduced by the recess processing step, the depth of the recesses can be further reduced compared to before the substrate surface processing step. In addition to physical polishing such as grinding and precision polishing, chemical polishing may also be used. In the substrate surface processing step, removal may be performed on the entire surface of the first side, so that the arithmetic mean height Sa (surface roughness; ISO 25178) of the first side is reduced compared to before the substrate surface processing step.

[0045] (iii) Layer Forming Step The method for manufacturing a photomask substrate according to this embodiment can include a layer forming step of forming a silicon dioxide layer on the first surface.

[0046] In the layer formation step, the depressions of the recesses are filled and repaired by the deposition of a silicon dioxide layer. Note that in the layer formation step, the silicon dioxide layer may be formed to a thickness greater than or equal to that which completely fills the deepest recess among the multiple recesses present on the substrate. In this way, after the layer formation step has been performed, all recesses present on the first surface of the quartz glass substrate are completely filled with a silicon dioxide layer, and excess silicon dioxide layer is deposited over the entire area of ​​the quartz glass substrate.

[0047] The layer formation process uses at least one of plasma CVD (chemical vapor deposition), thermal CVD, laser ablation, sputtering, ion plating, and vacuum deposition. ４ Gas and O ２ Plasma CVD using a gas mixture can form a silicon dioxide layer at a rate of 1 μm / 10 min or more. Furthermore, in the CVD process, it is important to control the CVD conditions to form the silicon dioxide layer so that the difference in refractive index between the quartz glass substrate and the silicon dioxide layer is small, i.e., so that the chemical composition and density of the quartz glass substrate and the silicon dioxide layer are approximately equivalent. This is because a large difference in refractive index between the quartz glass substrate and the silicon dioxide layer adversely affects the exposure performance when used as a photomask. The refractive index difference should be controlled to 0.01 or less, preferably 0.005 or less, and more preferably 0.002 or less, at a wavelength of 365 nm. By forming a silicon dioxide layer with a small refractive index difference on a smooth quartz glass substrate, the interface between the quartz glass substrate and the silicon dioxide layer becomes almost indistinguishable. Furthermore, the surface roughness of the recesses is reduced, allowing them to be completely covered with the silicon dioxide layer without any voids remaining. Furthermore, in order to prevent the silicon dioxide layer covering the recesses from peeling off or falling off semi-permanently, it is preferable to control the CVD conditions in the CVD step to minimize the residual stress in the silicon dioxide layer in advance. In addition, two or more types of layers can be laminated in the layer formation step.

[0048] In the layer forming step, a silicon dioxide layer can be formed on the first surface before the recess processing step is performed, and in the layer forming step, a silicon dioxide layer can be formed on the first surface after the recess processing step is performed.

[0049] (iv) Layer Planarization Step The method for manufacturing a photomask substrate according to this embodiment can include a layer planarization step of polishing the silicon dioxide layer to reduce the arithmetic mean height Sa (surface roughness; ISO 25178) of the first surface on which the silicon dioxide layer is formed.

[0050] The layer planarization process is a process for reducing and flattening the silicon dioxide layer, and can use a polishing process or a precision polishing process, similar to the substrate surface processing process described above. In the polishing process, an abrasive such as cerium oxide with a particle diameter of about 100 μm is used. In the precision polishing process, planarization is performed using an abrasive such as ultrafine silicon dioxide particles with a particle diameter of about several μm. Either the polishing process or the precision polishing process can be used, or the precision polishing process can be used after the polishing process.

[0051] In the layer formation process, the interface between the silicon dioxide layer and the quartz glass substrate has already been assimilated to a state where it is almost indistinguishable. Therefore, in the layer planarization process, it is not necessary to completely remove the silicon dioxide layer from the first surface of the quartz glass substrate. As long as it is within the upper and lower tolerance limits of the substrate thickness dimension, even if the silicon dioxide layer remains, it will not affect the optical performance of the photomask. By planarizing the silicon dioxide layer, the first surface becomes flat enough to form a photomask, and by adjusting the thickness appropriately, the photomask substrate is completed. Alternatively, a photomask substrate can be manufactured by planarizing the silicon dioxide layer of the substrate until it reaches the quartz glass substrate before layer formation, and then performing a further substrate surface processing process on the partially exposed quartz glass substrate.

[0052] In the method for manufacturing a photomask substrate according to this embodiment, the quartz glass substrate before the recess processing step (i) may be a used photomask from which the photomask pattern has been removed. Furthermore, the method for manufacturing a photomask substrate according to this embodiment may optionally include steps (v) to (viii) described below.

[0053] (v) Smoothing Step If fine irregularities exist on the inner surface of the recess on the quartz glass substrate before the layer formation step (iii) is performed, the fine irregularities that constitute the surface roughness of the inner surface of the recess on the quartz glass substrate can be removed by performing the smoothing step, thereby smoothing the inner surface of the recess. In other words, the surface roughness of the inner surface of the recess (arithmetic mean height Sa (surface roughness; ISO 25178)) can be reduced. Note that "fine irregularities" refers to the uneven parts of the inner surface of the recess, and includes irregularities, cracks, etc.

[0054] In the smoothing step, the arithmetic mean height Sa (surface roughness; ISO25178) of the inner surface of the recess is set to 50 nm or less, preferably 25 nm or less, and more preferably 10 nm or less.

[0055] For the smoothing process, solvent immersion or plasma dry etching is effective. In solvent immersion, the inner surface of the recess is immersed in at least one solution selected from the group consisting of an aqueous solution of hydrofluoric acid, an aqueous solution of buffered hydrofluoric acid, and an aqueous solution of strong alkali, which dissolves and removes the minute irregularities that make up the surface roughness of the inner surface of the recess, thereby making the inner surface of the recess smooth. Examples of the aqueous solution of strong alkali include an aqueous solution of sodium hydroxide and an aqueous solution of potassium hydroxide. In plasma dry etching, the quartz glass substrate is placed in a reduced pressure plasma generating vessel, and CF ４ , C ２ F ６ Fluorocarbon gases such as NF ３ Gas or SF ６ A gas is introduced to generate low-pressure plasma by controlling the pressure inside the chamber to a range of 0.1 Pa to 10 Pa. The quartz glass substrate exposed to the active fluorine radicals and ions is etched, and the inner surfaces of recesses, which have many defects, are selectively etched, making the inner surfaces of the recesses smooth.

[0056] In the smoothing step, the inner surface of the recess can be smoothed by reactive plasma etching, reactive sputtering, or ion beam sputtering in addition to the above-mentioned solvent immersion and plasma dry etching.

[0057] Laser irradiation can also be used in the smoothing process. A laser with a wavelength of 9.2 μm to 10.8 μm is irradiated onto recesses on the front or back surface of the quartz glass substrate, and the recesses are rapidly heated locally to approximately 1500°C to 1900°C, thereby locally melting the inner surface of the recesses and smoothing the inner surface of the recesses. A carbon dioxide laser with a wavelength of 10.6 μm can be used for the laser irradiation. Rapid heating refers to heating each recess for a period of 10 seconds to 600 seconds, for example.

[0058] By carrying out the layer forming step after the smoothing step, the silicon dioxide layer can be formed in better adhesion to the quartz glass substrate in the layer forming step.

[0059] (vi) Recess position specifying step The recess position specifying step is a step performed before the recess processing step (i), and is a step of capturing an image of the quartz glass substrate to obtain position information of the recess on the first surface. In the recess processing step (i), the quartz glass substrate can be irradiated with a laser based on the position information obtained in the recess position specifying step.

[0060] (vii) Pattern Removal Step The pattern removal step is a step of removing the photomask pattern from the used photomask to obtain a quartz glass substrate.

[0061] (viii) Photomask Recovery Step The photomask recovery step is a step of recovering used photomasks.

[0062] The difference between the thickness of the photomask substrate manufactured by the photomask substrate manufacturing method according to this embodiment and the thickness of the thickest part of the quartz glass substrate before the recess processing step (i) is 0.2 mm or less. The upper limit of this thickness difference is preferably 0.15 mm, more preferably 0.1 mm.

[0063] The quartz glass substrate used in the method for manufacturing a photomask substrate according to this embodiment may be composed of only silicon and oxygen, or may be doped with a small amount of other elements to improve the performance of the photomask substrate and the photomask. A small amount is, for example, 1% or less in atomic percent. Examples of the doped elements include TiO. ２ Furthermore, being composed only of silicon and oxygen does not exclude the inclusion of unavoidable impurities.

[0064] A specific example of the method for manufacturing a photomask substrate according to this embodiment will be described below using Figures 1 to 4. The initial states 1-(1), 2-(1), 3-(1), and 4-(1) in each figure are states in which the fine line pattern formed on the substrate surface has been dissolved and removed, exposing the quartz glass surface. The flatness of the entire surface in each initial state is the same as that after the previous precision polishing. However, when viewed locally, the surface of the quartz glass substrate always has depressions, without exception.

[0065] 1-(1) in Figure 1 is an example showing a location with one recess on the first surface. 2-(1), 3-(1), and 4-(1) in Figures 2 to 4 are examples showing locations with two deep recesses in the peripheral region and three shallow recesses near the center. The deep recesses in the peripheral region in Figures 2 to 4 correspond to scratches that occur at the position where the photomask contacts the photomask support of the exposure machine when held in the exposure machine, or scratches located near the frame of a pellicle previously attached to the surface of the quartz glass substrate and that occur when the pellicle is peeled off using a tool. In other words, numerous large scratches were detected in the peripheral region of the substrate, resulting from contact with the photomask support of the exposure machine or from pellicle peeling. The peripheral region generally refers to, for example, within 50 mm from the outer periphery of the substrate. Deep recesses in Figures 2 to 4 refer to, for example, a depth of 100 μm or less, and shallow recesses refer to, for example, a depth of approximately 15 μm. Furthermore, numerous finer irregularities exist within all of the recesses shown in Figure 4.

[0066] In reality, at least about 10 recesses, and in some cases several dozen recesses, are present on the quartz glass substrate in the initial state of each figure. Furthermore, in reality, multiple recesses exist not only on the first surface but also on the opposing second surface, similar to the first surface. To reuse the quartz glass substrate as a photomask, the recesses must be removed. If a photomask is formed on a quartz glass substrate with recesses, the fine line pattern will straddle the recesses. There is a risk of the fine lines being damaged at the locations that straddle the recesses, preventing the desired fine line pattern from being transferred to the glass substrate for ICs or displays, resulting in defects in the display area of ​​the semiconductor device or display.

[0067] <Regarding Fig. 1> Fig. 1 is a diagram illustrating a laser refining method according to one embodiment of the present invention. A recess on a quartz glass substrate in State 1-(1) is irradiated with laser light having a wavelength of 9.2 μm or more and 12 μm or less, and the recess and its surrounding area are locally heated to a temperature of 1800°C or more and 2300°C or less, thereby locally melting the recess and its surrounding area and reducing the depth of the recess, resulting in State 1-(2) (recess processing step).

[0068] The quartz glass substrate in state 1-(2) is subjected to polishing or precision polishing until the shallow recesses are flattened, thereby completing a photomask substrate in state 1-(3) (substrate surface processing step).

[0069] In this way, the laser refining method repairs quartz glass substrates with recesses by melting the glass locally with laser irradiation to make the recesses shallower, rather than scraping away the substrate by the depth of the recesses as in conventional methods. In this case, the amount of reduction in substrate thickness is limited to the depth of the shallowed recesses, making it possible to significantly increase the number of times the substrate can be recycled.

[0070] <Regarding Fig. 2> Fig. 2 is a diagram illustrating a laser refining method according to another embodiment of the present invention. Two deep recesses present in the peripheral portion of a quartz glass substrate in State 2-(1) are irradiated with laser light having a wavelength of 9.2 μm or more and 12 μm or less, and the recesses are locally heated to a temperature of 1800°C or more and 2300°C or less, thereby locally melting the recesses and their surroundings and shallowing the depth of the recesses to achieve State 2-(2) (recess processing step).

[0071] The quartz glass substrate in state 2-(2) is subjected to polishing or precision polishing until the shallow recesses and the three shallow recesses present in the center are flat, thereby completing a photomask substrate in state 2-(3) (substrate surface processing step).

[0072] In this way, in the laser refining method, the laser may be selectively irradiated onto deep recesses. In this way, the amount of reduction in the thickness of the substrate is limited to the depth of the shallow recesses and the shallow recesses, making it possible to significantly increase the number of times the substrate can be regenerated. In other words, the laser may be irradiated so as to leave shallow recesses up to a depth of about 15 μm, i.e., the laser may be selectively irradiated onto recesses with a depth of 15 μm or more. As mentioned above, since deep recesses are generally present in the peripheral portion of the substrate, the laser may be selectively irradiated onto recesses in the peripheral portion.

[0073] Additionally, it is effective to combine the laser refining method with the CVD refining method. The CVD refining method can repair the recesses more efficiently than scraping off the shallow recesses by polishing, and therefore can further increase the productivity of reused substrates. The CVD refining method does not remove all of the shallow recesses within the effective area of ​​a used photomask substrate by polishing or precision polishing, but rather smooths the inner surface of the recesses and removes the recesses by CVD-SiO ２The substrate is repaired by forming a new layer, and then the entire surface is flattened by precision polishing. This method makes it possible to completely eliminate the loss of thickness of the substrate, making it semi-permanently reusable. The CVD refining method significantly reduces process time by at least partially replacing polishing and precision polishing with CVD, making mass production possible.

[0074] <Regarding Fig. 3> Fig. 3 is a diagram illustrating a combination of laser refining and CVD refining according to one embodiment of the present invention. Two deep recesses present in the peripheral portion of a quartz glass substrate in State 3-(1) are irradiated with laser light having a wavelength of 9.2 μm or more and 12 μm or less, and the recesses and their surroundings are locally heated to a temperature of 1800°C or more and 2300°C or less, thereby locally melting the recesses and their surroundings and shallowing the depth of the recesses, resulting in State 3-(2) (recess processing step).

[0075] A silicon dioxide layer is formed by CVD on the quartz glass substrate in state 3-(2) to form state 3-(3) (layer formation step). In state 3-(3), the recess that existed in the center of state 3-(2) is completely filled with the silicon dioxide layer, and excess silicon dioxide is deposited over the entire surface of the quartz glass substrate.

[0076] The silicon dioxide layer is polished or precision polished until the substrate in State 3-(3) is flat, thereby completing the photomask substrate in State 3-(4) (layer flattening step). Note that a photomask substrate can also be manufactured by flattening the silicon dioxide layer until it reaches the quartz glass substrate before layer formation, and then performing a further substrate surface processing step on the partially exposed quartz glass substrate.

[0077] <Regarding Fig. 4> Fig. 4 is a diagram illustrating a combination of laser refining and CVD refining according to another embodiment of the present invention. Two deep recesses with fine irregularities present in the peripheral portion of a quartz glass substrate in state 4-(1) are irradiated with laser light having a wavelength of 9.2 μm or more and 12 μm or less, respectively, to locally heat the interior of the recesses to 1800°C or more and 2300°C or less. By locally melting the recesses and their surroundings, the depth of the recesses is reduced, resulting in state 4-(2) (recess processing step). At this time, the inner surface of the recesses has low surface roughness and is smooth.

[0078] The inner surfaces of three shallow recesses with fine irregularities present in the center of the quartz glass substrate in state 4-(2) are subjected to treatments such as solvent immersion and plasma dry etching to reduce the surface roughness of the inner surfaces of the recesses, resulting in state 4-(3) (smoothing process).

[0079] A silicon dioxide layer is formed by CVD on the quartz glass substrate in state 4-(3) to form state 4-(4) (layer formation step). In state 4-(4), the recess that existed in the center of state 4-(3) is completely filled with the silicon dioxide layer, and excess silicon dioxide is deposited over the entire surface of the quartz glass substrate.

[0080] The silicon dioxide layer is polished or precision polished until the substrate in state 4-(4) is flat, thereby completing the photomask substrate in state 4-(5) (layer flattening step).

[0081] As described above, in the photomask substrate manufacturing method according to this embodiment, the photomask substrate can be regenerated by simply melting only the deep recesses with a laser using the laser refining method, and then reducing the shallower recesses and the other shallow recesses until they are flat. Furthermore, by combining the laser refining method with a layer formation process (e.g., a CVD method), it is possible to simultaneously repair the recesses, maintain flatness, and maintain the thickness. As long as the substrate is not accidentally hit or dropped and severely damaged, it can be regenerated multiple times to semi-permanently.

[0082] Although the processing for the first surface has been specifically described above, the same processing as for the first surface can also be performed for the second surface opposite to the first surface.

[0083] <Photomask Substrate> The photomask substrate according to this embodiment is a photomask substrate including a quartz glass substrate, and has one or more retardations of 5 nm or more on the quartz glass substrate. Retardation is the phase difference that occurs between the horizontal and vertical polarization components of incident light when a light beam passes through a portion where a refractive index difference occurs due to birefringence. In the recess processing step (i), distortion occurs inside the quartz glass substrate irradiated with a laser, and therefore the presence and degree of retardation can be used to determine whether the photomask substrate was manufactured according to this embodiment.

[0084] The retardation can be calculated by multiplying the phase difference when light is emitted from the sample by the measured wavelength λ. For example, if the wavenumbers in the sample are fast axis: 6.3 × λ / 2 and slow axis: 8 × λ / 2, the difference between the two is 1.7 × λ / 2. If the measured wavelength λ is 523 nm, the retardation is 1.7 × 523 nm / 2 = 444.6 nm.

[0085] If the quartz glass substrate has one or more retardations of 5 nm or more, it can be determined that the photomask substrate is manufactured according to this embodiment. For example, if the quartz glass substrate has one or more retardations of 5 nm or more at a measurement wavelength of 523 nm, it can be determined that the photomask substrate is manufactured according to this embodiment. The retardation magnitude can be 10 nm or more, 15 nm or more, or 20 nm or more. Since retardation can occur as many times as the number of recesses irradiated with laser, the number of retardations can be 2 or more, 5 or more, or 10 or more.

[0086] As mentioned above, used quartz glass substrates often have large scratches on the periphery due to contact with the photomask support of an exposure machine or peeling of the pecrylic layer. Therefore, the laser irradiation of the present embodiment may be performed on the scratches on the periphery to reduce their depth. Therefore, the photomask substrate according to this embodiment may have one or more retardations of 5 nm or more, particularly in a region of 50 mm or less from the periphery of the quartz glass substrate. This region may be 5 mm or more, 10 mm or more, or 15 mm or more from the periphery of the quartz glass substrate, or it may be 40 nm or less, or 30 nm or less from the periphery of the quartz glass substrate.

[0087] The photomask substrate according to this embodiment may have a PV (Peak-to-Valley) value of 5 μm or less. The PV value is the maximum height difference across the entire surface of the substrate (the warpage of the entire substrate). Having a small PV value can further improve the accuracy of pattern transfer in the photolithography process.

[0088] The upper limit of the PV value is preferably 30 μm, more preferably 20 μm, and even more preferably 10 μm. When it is desired to obtain a substrate with less warping, the smaller the PV value, the better, so the lower limit is not particularly limited. In addition, the PV value of the surface having retardation may be such a value.

[0089] <Method for Reusing Photomask Substrates> The method for reusing photomask substrates according to this embodiment allows used photomask substrates to be repeatedly reproduced into new photomask substrates by carrying out the method for manufacturing a photomask substrate according to this embodiment.

[0090] <Photomask Blanks and Manufacturing Method Thereof> The photomask blanks according to this embodiment have at least one type of film selected from a light-shielding film, a halftone film, and a phase shift film on the photomask substrate.

[0091] The photomask blanks according to this embodiment are manufactured by depositing at least one type of film selected from a light-shielding film, a halftone film, and a phase shift film on a photomask substrate produced by the above-described method for manufacturing a photomask substrate.

[0092] <Photomask and Manufacturing Method Thereof> The photomask according to this embodiment is obtained by forming a pattern on the above-described photomask blank.

[0093] The photomask according to this embodiment is manufactured by carrying out fine line circuit processing on the photomask blanks produced by the above-described method for manufacturing photomask blanks.

[0094] <Quartz Glass Substrate Processing Apparatus> As shown in FIG. 5, the quartz glass substrate processing apparatus 1 according to this embodiment is used for the above-mentioned photomask substrate, and has a laser unit 101 that irradiates the quartz glass substrate with a laser, and a moving unit 102 that moves the irradiation position on the quartz glass substrate by the laser unit 101.

[0095] The moving unit 102 may have any configuration as long as it can move the irradiation position on the quartz glass substrate by the laser unit 101. For example, it may be configured to move the laser unit 101, or it may be configured to move the irradiation position on the substrate by changing the angle of a galvanometer mirror that reflects the laser light irradiated from the laser unit 101, or a combination of these.

[0096] The quartz glass substrate processing device 1 according to this embodiment uses a laser unit 101 and a moving unit 102 to irradiate a laser onto an irradiation area including a recess on the quartz glass substrate, thereby melting at least a portion of the irradiation area and reducing the depth of the recess.

[0097] The quartz glass substrate processing apparatus 1 according to this embodiment further includes an intensity adjusting unit 103 that adjusts the intensity of the laser irradiated by the laser unit 101, and a temperature measuring unit 104 that measures the temperature at the irradiation position and obtains temperature information at the irradiation position.

[0098] The intensity adjusting unit 103 is controlled based on the temperature information. For example, the intensity adjusting unit 103 may be controlled so that the temperature of the irradiated area on the substrate is 1800° C. or higher and 2300° C. or lower during the laser irradiation period.

[0099] The quartz glass substrate processing apparatus 1 according to this embodiment may further include an imaging unit 105 that captures an image of the irradiation position and obtains imaging information of the irradiation position.

[0100] The present invention will be specifically described with reference to the following examples, but the present invention is not limited to these examples.

[0101] Example 1: Measurement Analysis of Depressions on Used Photomasks (Coordinates and Depth) Two used photomask substrates measuring 850 mm x 1200 mm were subjected to dissolution and removal of fine line patterns such as Cr, exposing the quartz glass substrate. After polishing to a thickness of several μm to remove any deposits, the number of depressions on each quartz glass substrate was counted using a scratch measurement device (model number: IGS, manufactured by Nikon) and the coordinates and depth of each depression were measured. The depression depth was measured as the depth of the deepest depression. A total of 318 or more depressions were detected within the exposure area on the surface (the side with the Cr pattern) of two quartz glass substrates. Of these, all 318 depressions were located within 30 mm of the substrate periphery. Figure 6 shows a bubble chart of the results. In Figure 6, the location of the bubbles indicates the location of the depressions, the area of ​​the bubbles indicates the depression depth, and the dotted line indicates the substrate periphery (850 mm x 1200 mm).

[0102] Example 2: Measurement results of step difference before and after carbon dioxide laser irradiation A line-shaped scratch with a depth of 100 μm or more present on a quartz glass substrate measuring 152 mm × 152 mm × 6.35 mm was irradiated with a carbon dioxide laser having a wavelength of 10.6 μm so that the temperature of the irradiated area was between 2000°C and 2100°C.

[0103] After irradiation with the carbon dioxide laser, the areas where scratches had been present on the lines were visually inspected and it was confirmed that the scratches had been removed. Using a 3D laser confocal microscope (manufactured by Keyence), the depth of the scratches after irradiation with the carbon dioxide laser was measured and found to be 10 μm or less. This demonstrates that laser irradiation can make deep recesses extremely shallow.

[0104] Example 3: Measurement of distortion due to carbon dioxide laser irradiation Using a 50 mm x 50 mm x 50 mm cubic quartz glass, the three-dimensional distribution of retardation (optical axis direction, side 1, side 2) was measured when a carbon dioxide laser was incident at a wavelength λ of 10.6 μm. From the obtained three-dimensional distribution data, a distortion of 255 nm was confirmed. Therefore, it was found that retardation occurs when quartz glass is irradiated with a laser, and that retardation can be used to identify the photomask substrate according to this embodiment.

[0105] From the above, it was found that the deep recesses found in the peripheral areas of used photomask substrates can be repaired by laser irradiation and polishing, and the substrate can be restored to a usable state. It was also found that the presence and degree of retardation can be used to determine whether the photomask substrate was manufactured according to this embodiment.

[0106] Examples 4 to 27: Measurement of recess depth (without carbon dioxide laser scanning) Artificial scratches (recesses) 50 to 100 μm deep were made in a quartz glass substrate. A carbon dioxide laser with a wavelength of 10.6 μm, a pulse width of 0.17 ms, a repetition frequency of 3000 Hz, a duty ratio of 50%, and an intensity distribution with a Gaussian distribution was irradiated at a fixed point without scanning to the irradiation area including the recesses. The depth of the recesses after laser irradiation was measured using a 3D interference microscope (manufactured by Keyence).

[0107] Examples 17 and 18: Measurement of recess depth after polishing A double-side polished sample was placed on a flat glass prototype, and monochromatic light was irradiated from the top side of the sample, and the generated interference fringes were observed from the top side of the sample. Concentric interference fringes (Newton's rings) were observed over the entire surface of the sample. The interference fringes (bright rings) occurred at locations that satisfied the following formula (1): 2d = (m + 1 / 2) λ (1) (λ is the wavelength of the monochromatic light, d is the gap distance between the prototype and the sample, and m is 0, 1, 2, etc.)

[0108] The interference fringes were observed to be slightly shifted near the recesses after polishing. The amount of shift was approximately 0.5 to 1 fringe depending on the sample. In equation (1), the depth of the recesses after polishing was calculated by substituting the amount of shift of the interference fringes into m, where d is the depth of the recesses after polishing.

[0109] Examples 19 to 27: Measurement of flatness after laser irradiation The unevenness over the entire surface of the substrate was measured using a laser interferometer, and the PV (peak-to-valley) value over the entire surface of the substrate was calculated to measure the flatness over the entire surface of the substrate after laser irradiation.

[0110] Table 1 shows the laser irradiation conditions and the depth of the recesses before and after laser irradiation for each of the examples and comparative examples.

[0111]

[0112] From the above, it was found that the depth of the recesses could be reduced under the irradiation conditions of Examples 4 to 27. Furthermore, it was found from Examples 17 and 18 that polishing could be performed without problems even when laser irradiation was performed, and the depth of the recesses could be further reduced. Therefore, by performing the recess processing step and the substrate surface processing step, the recesses in a substrate having recesses can be reduced, making it possible to reuse the substrate.

[0113] Of Examples 19 to 27, the flatness (PV value) of the entire substrate surface after laser irradiation was suppressed to 5 μm or less in Examples 19 to 22. Therefore, it was found that if it is desired to further suppress the warpage of the substrate, it is best to set the integrated amount of energy by laser irradiation to 4000 J or less.

[0114] Examples 28 to 33: Measurement of recess depth (with carbon dioxide laser scanning) An artificial scratch (recess) 100 μm deep was made in a quartz glass substrate. A carbon dioxide laser with a wavelength of 10.6 μm, a repetition rate of 3000 Hz, a duty ratio of 50%, and an intensity distribution of Gaussian was irradiated while scanning the irradiation area including the recess. The recess depth after laser irradiation was measured using a 3D interference microscope (manufactured by Keyence). Table 2 shows the laser irradiation conditions and the recess depth before and after laser irradiation for each example and comparative example.

[0115]

[0116] It was found from Examples 28 to 33 that even when the carbon dioxide laser was scanned, the depth of the recesses could be reduced by irradiating the carbon dioxide laser.

[0117] DESCRIPTION OF SYMBOLS 1... Glass substrate processing device 101... Laser unit 102... Moving unit 103... Intensity adjustment unit 104... Temperature measurement unit 105... Imaging unit

Claims

1. A method for manufacturing a photomask substrate from a quartz glass substrate, comprising: irradiating a region including recesses on the first surface of the quartz glass substrate with a peak wavelength of 9.2 μm to 12 μm, a pulse width of 1 ns to 100 ms, and an average power density of 50 W / cm ２ More than 700W / cm ２ A method for manufacturing a substrate for a photomask, comprising: a recess processing step of irradiating the substrate with the following laser light; and a substrate surface processing step of removing an area including the irradiated area from the surface of the first surface on which the recess processing step has been performed.

2. The method for manufacturing a photomask substrate according to claim 1, wherein the depth of the recess after the substrate surface processing step is performed is smaller than the depth of the recess before the substrate surface processing step is performed.

3. A method for manufacturing a photomask substrate according to claim 1 or 2, wherein the arithmetic mean height Sa of the first surface after the substrate surface processing step is performed is smaller than the arithmetic mean height Sa of the first surface before the substrate surface processing step is performed.

4. The peak power density of the laser light is 100 W / cm ２ More than 1400W / cm ２ The method for producing a photomask substrate according to any one of claims 1 to 3, wherein the method is as follows:

5. The intensity of the laser light in the center of the irradiation area is stronger than the intensity of the laser light in the peripheral area of ​​the irradiation area, and in the recess processing step, the average power density of the laser light is 100 W / cm ２ More than 700W / cm ２ The method for producing a photomask substrate according to any one of claims 1 to 4, wherein the method is as follows:

6. In the recess processing step, the peak power density of the laser light is 200 W / cm ２ More than 1400W / cm ２ The method for manufacturing a photomask substrate according to claim 5 , wherein:

7. The intensity of the laser light is constant within the irradiation range, and in the recess processing step, the average power density of the laser light is 50 W / cm ２ More than 350W / cm ２ The method for producing a photomask substrate according to any one of claims 1 to 4, wherein the method is as follows:

8. In the recess processing step, the peak power density of the laser light is 100 W / cm ２ More than 700W / cm ２ The method for manufacturing a photomask substrate according to claim 7 , wherein:

9. The method for manufacturing a photomask substrate according to any one of claims 1 to 8, wherein in the recess processing step, the repetition frequency of the laser light is 5 Hz or more and 50 MHz or less.

10. The method for manufacturing a photomask substrate according to any one of claims 1 to 9, wherein in the recess processing step, the duty ratio of the laser light is 5% or more and 90% or less.

11. The method for manufacturing a photomask substrate according to any one of claims 1 to 10, wherein in the recess processing step, the laser light is irradiated so that the irradiation range has a diameter of 100 μm or more and 30 mm or less.

12. The method for manufacturing a photomask substrate according to any one of claims 1 to 11, wherein in the recess processing step, the laser light is irradiated onto the irradiation area for 3 seconds to 30 minutes.

13. A method for manufacturing a photomask substrate according to any one of claims 1 to 12, wherein in the recess processing step, the laser light is irradiated so that the cumulative amount of energy imparted to the irradiation area by the laser light irradiation is 4000 J or less.

14. The pulse width is determined by a half-width, and the irradiation range is determined by a value where the intensity of the laser light is 1 / e of the peak intensity. ２ The method for manufacturing a photomask substrate according to any one of claims 1 to 13, wherein the range is the above.

15. The first surface further has another recess different from the recess, and the recess processing step is performed by irradiating a laser beam having a peak wavelength of 9.2 μm or more and 12 μm or less and a pulse width of 1 ns or more and 100 ms or less with an average power density of 50 W / cm ２ More than 700W / cm ２ 15. The method for manufacturing a photomask substrate according to claim 1, further comprising: irradiating another irradiation area at a position different from that of the irradiation area below, wherein the other irradiation area includes the other recess.

16. A method for manufacturing a photomask substrate as described in claim 15, wherein in the recess processing step, the laser light is irradiated so that the cumulative amount of energy imparted to the other irradiation area by the irradiation of the laser light is 4000 J or less.

17. A method for manufacturing a substrate for a photomask, comprising: a recess processing step of irradiating a laser onto a quartz glass substrate having a recess on a first surface to reduce the depth of the recess; and a substrate surface processing step of removing an area including the irradiated area from the surface of the first surface that has been subjected to the recess processing step, wherein in the recess processing step, the irradiated area of ​​the laser includes the recess, and at least a portion of the irradiated area is melted.

18. The method for manufacturing a photomask substrate according to claim 17, wherein in the recess processing step, the temperature of the irradiation area during the period when the laser is irradiated is 1800°C or higher and 2300°C or lower.

19. A method for manufacturing a photomask substrate according to any one of claims 1 to 18, wherein the substrate surface processing step removes the area including the irradiation range by scraping the surface of the first surface.

20. A method for manufacturing a photomask substrate according to any one of claims 1 to 19, wherein in the recess processing step, the composition of the irradiated area after irradiating with the laser light is silicon dioxide.

21. A method for manufacturing a substrate for a photomask according to any one of claims 1 to 20, comprising a recess position identifying step of acquiring position information of the recess on the first surface, and in the recess processing step, irradiating the quartz glass substrate with the laser light based on the position information.

22. The method for manufacturing a photomask substrate according to any one of claims 1 to 21, further comprising a layer forming step of forming a silicon dioxide layer on the first surface.

23. The method for manufacturing a photomask substrate according to claim 22, further comprising a layer planarization step of scraping the surface of the silicon dioxide layer, wherein the arithmetic mean height Sa of the silicon dioxide layer after the layer planarization step is performed is smaller than the arithmetic mean height Sa of the silicon dioxide layer before the layer planarization step is performed.

24. The method for manufacturing a photomask substrate according to claim 22 or 23, wherein the layer forming step forms the silicon dioxide layer on the first surface before the recess processing step is performed.

25. The method for manufacturing a photomask substrate according to any one of claims 22 to 24, wherein the layer forming step forms the silicon dioxide layer on the first surface after the recess processing step has been performed.

26. The method for manufacturing a photomask substrate according to any one of claims 1 to 25, wherein a second surface opposite to the first surface is subjected to the same treatment as that for the first surface.

27. A method for manufacturing a photomask substrate according to any one of claims 1 to 26, wherein the difference between the thickness of the thickest part of the quartz glass substrate before the recess processing step and the thickness of the photomask substrate is 0.2 mm or less.

28. The method for manufacturing a photomask substrate according to any one of claims 1 to 27, wherein in the recess processing step, the depth of the recess is set to 30 μm or less.

29. A method for manufacturing a photomask substrate according to any one of claims 1 to 28, wherein in the substrate surface processing step, the arithmetic mean height Sa of the first surface is set to 20 μm or less.

30. A method for manufacturing a photomask substrate according to any one of claims 1 to 29, wherein the quartz glass substrate is a used photomask from which the photomask pattern has been removed.

31. The method for producing a photomask substrate according to any one of claims 1 to 30, further comprising a pattern removal step of removing a photomask pattern from a used photomask to obtain the quartz glass substrate.

32. The method for manufacturing a photomask substrate according to claim 31, further comprising a photomask recovery step of recovering the used photomask.

33. A method for manufacturing photomask blanks, comprising depositing at least one type of film selected from a light-shielding film, a halftone film, and a phase shift film on a photomask substrate produced by the method for manufacturing a photomask substrate according to any one of claims 1 to 32, to produce a photomask blank.

34. A method for manufacturing a photomask, comprising carrying out fine line circuit processing on a photomask blank produced by the method for manufacturing a photomask blank according to claim 33, to manufacture a photomask.

35. A method for recycling photomask substrates, in which used photomask substrates are repeatedly reproduced into new photomask substrates by carrying out the method for producing photomask substrates according to any one of claims 1 to 32.

36. A photomask substrate manufactured by the method for manufacturing a photomask substrate according to any one of claims 1 to 32.

37. A photomask substrate comprising a quartz glass substrate, the photomask substrate having one or more retardations of 5 nm or more on the quartz glass substrate.

38. The photomask substrate according to claim 37, wherein the quartz glass substrate has one or more retardations of 5 nm or more in a region 50 mm or less from the outer periphery.

39. The photomask substrate according to claims 37 and 38, wherein the PV value of the surface having the retardation is 30 μm or less.

40. A photomask blank having at least one film selected from the group consisting of a light-shielding film, a halftone film, and a phase shift film on the photomask substrate according to any one of claims 36 to 39.

41. A photomask having a pattern formed on the photomask blank according to claim 40.

42. A processing device for a quartz glass substrate used as a photomask substrate, comprising: a laser unit that irradiates the quartz glass substrate with a laser; and a moving unit that moves the irradiation position on the quartz glass substrate by the laser unit, wherein the laser unit and the moving unit irradiate an irradiation range including a recess on the quartz glass substrate with the laser, melting at least a portion of the irradiation range and reducing the depth of the recess.

43. A quartz glass substrate processing device as described in claim 42, comprising an intensity adjustment unit that adjusts the intensity of the laser irradiated by the laser unit, and a temperature measurement unit that measures the temperature at the irradiation position and obtains temperature information about the irradiation position, and controls the intensity adjustment unit based on the temperature information.

44. The processing device for a silica glass substrate according to claim 42 or 43, further comprising an imaging unit for imaging the irradiation position and obtaining imaging information of the irradiation position.

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