Method for producing substrate for photomask, method for producing photomask blank, method for producing photomask, method for reusing substrate for photomask, substrate for photomask, photomask blank, photomask, apparatus for processing quartz glass substrate

Abstract

To provide a method for repeatedly regenerating a substrate for photomask without changing a thickness of a substrate for a photomask.SOLUTION: The method for producing a photomask substrate includes a recess processing step in which a laser is irradiated on a quartz glass substrate having recesses on the first surface to reduce the depth of the recesses, and a substrate flattening step in which the first surface subjected to the recess processing step is ground to reduce the arithmetic average height Sa of the first surface. In the recess processing step, the irradiation area of the laser includes the recesses and involves melting at least a part of the irradiation area.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[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. [Background technology]

[0002] Patent Document 1 discloses a photomask blank having a film on a photomask substrate. When a photomask substrate with 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. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-105158 Summary of the Invention

[0004] One aspect of the present invention is a method for manufacturing a substrate for a photomask, comprising: a recess processing step of irradiating a laser onto a quartz glass substrate having recesses on a first surface to reduce the depth of the recesses; and a substrate flattening step of polishing the first surface that has been subjected to the recess processing step to reduce the arithmetic mean height Sa of the first surface, wherein in the recess processing step, the irradiation range of the laser includes the recesses, and at least a portion of the irradiation range is melted.

[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.

[0009] Another aspect of the present invention is a photomask blank having at least one film selected from a light-shielding film, a halftone film, and a phase shift film on the above-mentioned photomask substrate.

[0010] Another aspect of the present invention is a photomask in which a pattern is formed on the above-mentioned photomask blank.

[0011] Another aspect of the present invention is an apparatus for processing a quartz glass substrate used as a substrate for a photomask, the apparatus having 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 the laser onto an irradiation range that includes a recess on the quartz glass substrate, melting at least a portion of the irradiation range and reducing the depth of the recess. [Brief explanation of the drawings]

[0012] [Figure 1] 1A to 1C are cross-sectional views schematically illustrating an example of a method for producing a photomask substrate (laser refining method) according to the present embodiment. [Figure 2]4 is a cross-sectional view schematically illustrating another example of the method for producing a photomask substrate (laser refining method) according to the present embodiment. FIG. [Figure 3] 1 is a cross-sectional view schematically illustrating an example of a method for producing a photomask substrate according to the present embodiment (laser refining method+CVD refining method). [Figure 4] FIG. 3 is a cross-sectional view schematically illustrating another example of the method for producing a photomask substrate according to the present embodiment (laser refining method+CVD refining method). [Figure 5] 1 is a block diagram of a processing apparatus for a quartz glass substrate according to an embodiment of the present invention. [Figure 6] 1 is a bubble chart showing coordinates and depths of recesses on quartz glass substrates recovered from used photomask substrates. [Figure 7] FIG. 10 is a diagram showing an image of how recesses become shallower due to carbon dioxide laser irradiation. DETAILED DESCRIPTION OF THE INVENTION

[0013] 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.

[0014] Typically, a photomask for a flat panel display (FPD) is a parallel plate substrate made of 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 disilicide is applied. 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.

[0015] Similarly, photomasks for semiconductor circuits refer to parallel flat substrates made of quartz glass with the first and second surfaces polished, on which thin patterns of light-shielding films such as chrome, half-tone films, and phase-shift films such as chrome and molybdenum silicide are formed. Manufacturers of semiconductor devices use reduced projection exposure machines to reduce and transfer the thin line patterns on photomasks onto various substrates for semiconductor devices.

[0016] Photomask substrates that have finished being used as photomasks by panel manufacturers and semiconductor device manufacturers are sometimes collected for recycling if they are in a state without any 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. Once the photopattern is dissolved and removed, the substrate, with the quartz glass exposed, typically contains scratches on its front and back surfaces. Therefore, the substrate cannot be used as a recycled photomask by forming the next 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 flattened again before the photomask can be formed.

[0017] This embodiment will be described in detail below.

[0018] <Method of manufacturing a photomask substrate> The method for manufacturing a photomask substrate according to this embodiment includes the steps of: a recess processing step of irradiating a laser beam onto a quartz glass substrate having a recess on a first surface thereof to reduce the depth of the recess; a substrate flattening step of polishing the first surface on which the recess processing step has been performed to reduce the arithmetic mean height Sa (surface roughness; ISO25178) of the first surface, In the recess processing step, the laser irradiation range includes the recess, and at least a part of the irradiation range is melted.

[0019] (i) Recess processing step In the recess processing step, for example, by irradiating a laser with a wavelength of 10.6 μm, the silica glass in and around the recess melts and flows into the recess, making it possible to reduce the depth of the recess as shown in Figure 7.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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 10.8 μm or less, rather than just 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 10.7 μm, more preferably 10.6 μm.

[0024] 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 ―1The wavelength is in the vicinity of 9.2 μm or more and 10.8 μm 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 10.8 μm or less. A carbon dioxide laser is an example of a typical laser oscillation device that can stimulate 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 oscillation device that can emit electromagnetic waves having a wavelength of 9.2 μm or more and 10.8 μm or less.

[0025] In the recess processing step, the temperature of the irradiation area during laser irradiation 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 area during laser irradiation is low, the quartz glass substrate tends to melt less, which reduces the efficiency of reducing the depth of the recess. If the temperature of the irradiation area during laser irradiation is too high, the quartz glass tends to sublimate significantly. In addition, the laser irradiation period can be appropriately selected depending on the laser energy fluence and the depth of the recess. For example, it can be 10 seconds or higher and 30 minutes or lower. By locally heating the recess in this way, the recess and its surroundings locally melt and flow into the recess, thereby further reducing the depth of the recess. Therefore, the temperature of the irradiation range during the laser irradiation period only needs to be a temperature at which the quartz glass can melt and flow, and even in the case of a relatively low temperature of 1800°C or higher and 1900°C or lower, it is possible to reduce the depth of the recess by making the laser irradiation time relatively long, for example, from 10 minutes to 120 minutes or lower.

[0026] (ii) Substrate planarization process The substrate planarization process is a process of reducing the substrate surface to a flat surface, and can be performed by polishing or precision polishing. In the polishing process, an abrasive such as cerium oxide with a particle diameter of approximately 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 approximately several μm. Either the polishing process or the precision polishing process may be used, or the precision polishing process may be performed after the polishing process.

[0027] In the substrate planarization 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 planarization step is preferably 7 μm, more preferably 5 μm, and even more preferably 3 μm. In particular, it is more preferable that the arithmetic mean height Sa (surface roughness; ISO 25178) of the entire first surface is set to 20 μm or less. The upper limit of the arithmetic mean height of the entire first surface after the substrate planarization step is preferably 7 μm, more preferably 5 μm, and even more preferably 3 μm.

[0028] (iii) Layer formation process 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.

[0029] 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. By doing so, 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.

[0030] The layer formation process uses at least one of plasma CVD (chemical vapor deposition), thermal CVD, laser ablation, sputtering, ion plating, and vacuum deposition. In particular, plasma CVD using tetraethoxysilane (TEOS) or a mixture of SiF4 and O2 gases can form silicon dioxide layers at rates of 1 μm / 10 min or faster. Furthermore, it is important to control the CVD conditions to minimize the difference in refractive index between the quartz glass substrate and the silicon dioxide layer, i.e., to ensure that the chemical composition and density of the quartz glass substrate and the silicon dioxide layer are approximately the same. This is because a large difference in refractive index between the quartz glass substrate and the silicon dioxide layer can adversely affect exposure performance when used as a photomask. The refractive index difference should be controlled to 0.01 or less, preferably 0.005, and even 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, and since the surface roughness of the recesses is reduced, it is possible to completely cover the recesses with the silicon dioxide layer without leaving any voids. Furthermore, 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 process to minimize the residual stress in the silicon dioxide layer in advance. Furthermore, two or more types of layers can be laminated in the layer formation process.

[0031] 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.

[0032] (iv) Layer planarization process 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; ISO25178) of the first surface on which the silicon dioxide layer is formed.

[0033] The layer planarization process is a process for reducing and flattening the silicon dioxide layer, and can be performed using a polishing process or a precision polishing process, similar to the substrate planarization process described above. In the polishing process, an abrasive such as cerium oxide with a particle diameter of approximately 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 approximately several μm. Either the polishing process or the precision polishing process can be used, or the precision polishing process can be performed after the polishing process.

[0034] Because the interface between the silicon dioxide layer and the quartz glass substrate is already assimilated to a nearly unrecognizable state in the layer formation process, there is no need to completely remove the silicon dioxide layer from the first surface of the quartz glass substrate in the layer planarization process. As long as it is within the upper and lower tolerance limits of the substrate thickness dimension, any remaining silicon dioxide layer will have no effect on the optical performance of the photomask. Planarization of the silicon dioxide layer makes the first surface 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 on the substrate until it reaches the quartz glass substrate before layer formation, and then performing a further substrate planarization process on the partially exposed quartz glass substrate.

[0035] 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.

[0036] (v) Smoothing process If fine irregularities exist on the inner surface of the recesses on the quartz glass substrate before the layer formation step (iii) is performed, the smoothing step can remove the fine irregularities that make up the surface roughness of the inner surface of the recesses on the quartz glass substrate, thereby smoothing the inner surface of the recesses. In other words, the surface roughness of the inner surface of the recesses (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 recesses, including irregularities, cracks, etc.

[0037] 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.

[0038] Solvent immersion or plasma dry etching is effective for the smoothing process. In solvent immersion, the inner surfaces of the recesses are immersed in at least one of a hydrofluoric acid solution, a buffered hydrofluoric acid solution, and a strong alkaline solution. This dissolves and removes the minute irregularities that make up the surface roughness of the inner surfaces of the recesses, resulting in a smooth inner surface of the recesses. Examples of strong alkaline solutions include aqueous sodium hydroxide and aqueous potassium hydroxide solutions. In plasma dry etching, the quartz glass substrate is placed in a low-pressure plasma generating chamber, and fluorocarbon gases such as CF4 and C2F6, or NF3 gas or SF6 gas are introduced. The pressure inside the chamber is controlled to a range of 0.1 Pa to 10 Pa to generate low-pressure plasma. The quartz glass substrate is etched by exposure to active fluorine-based radicals and ions, and the inner surfaces of the recesses, which are particularly prone to defects, are selectively etched, resulting in a smooth inner surface of the recesses.

[0039] 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.

[0040] Laser irradiation can also be used in the smoothing process. By irradiating a laser with a wavelength of 9.2 μm or more and 10.8 μm or more onto the recesses on the front or back surface of the quartz glass substrate and rapidly heating the recesses locally to approximately 1500°C or more and 1900°C or less, the inner surface of the recesses is locally melted, resulting in a smooth inner surface of the recesses. For example, 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 or more and 600 seconds or less.

[0041] 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.

[0042] (vi) Recess position identification 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.

[0043] (vii) Pattern removal process The pattern removal step is a step of removing the photomask pattern from the used photomask to obtain a quartz glass substrate.

[0044] (viii) Photomask recovery process The photomask recovery step is a step of recovering used photomasks.

[0045] 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.

[0046] Specific examples of the method for manufacturing a photomask substrate according to this embodiment will be described below with reference to Figures 1 to 4. The initial states (1)-1, (2)-1, (3)-1, and (4)-1 in each figure represent the state 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.

[0047] (1)-1 in Figure 1 shows an example of a location with one recess on the first surface. (2)-1, (3)-1, and (4)-1 in Figures 2 to 4 show examples of locations with two deep recesses on the periphery and three shallow recesses near the center. The deep recesses on the periphery in Figures 2 to 4 correspond to scratches that occur when the photomask contacts the photomask support of the exposure machine while being held in the exposure machine, or scratches that occur near the frame of a pellicle previously attached to the surface of the quartz glass substrate and are caused when the pellicle is peeled off using a tool. In other words, numerous large scratches were detected in the periphery 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. In Figures 2 to 4, deep recesses are, for example, 100 μm or less in depth, and shallow recesses are, for example, approximately 15 μm in depth. Furthermore, within all of the recesses shown in Figure 4, many finer irregularities exist.

[0048] In reality, there are at least 10 recesses, and sometimes as many as several dozen, on the quartz glass substrate in the initial state shown in each figure. Furthermore, in reality, multiple recesses exist not only on the first surface but also on the opposing second surface, just like on 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 cross over the recesses. This can cause the fine lines to be damaged in places that cross over 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.

[0049] <About Figure 1> 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 10.8 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).

[0050] 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 flattening process).

[0051] 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.

[0052] <About Figure 2> 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 10.8 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, resulting in state (2)-2 (recess processing step).

[0053] The quartz glass substrate in state (2)-2 is subjected to polishing and precision polishing until the shallow recess and the three shallow recesses in the center are flattened, thereby completing a photomask substrate in state (2)-3 (substrate flattening process).

[0054] 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 substrate thickness is limited to the depth of the recesses that have become shallower and the depth of 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 also be selectively irradiated onto recesses in the peripheral portion.

[0055] Additionally, it is effective to combine laser refining with CVD refining. CVD refining can repair shallow recesses more efficiently than polishing, thereby increasing the productivity of reused substrates. CVD refining does not remove all shallow recesses within the effective area of ​​used photomask substrates using polishing or precision polishing, but repairs them by smoothing the inner surfaces of the recesses and forming CVD-SiO2, and then flattens the entire surface using precision polishing. This method can even prevent any reduction in substrate thickness, making it possible to regenerate the substrate semi-permanently. CVD refining significantly reduces process time by at least partially replacing polishing and precision polishing with CVD, making mass production possible.

[0056] <About Figure 3> 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 10.8 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).

[0057] A silicon dioxide layer is formed on the quartz glass substrate in state (3)-2 by the CVD method to produce state (3)-3 (layer formation process). 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.

[0058] The silicon dioxide layer is polished and precision polished until the substrate in state (3)-3 is flat, completing the photomask substrate in state (3)-4 (layer planarization step). Note that a photomask substrate can also be manufactured by planarizing the silicon dioxide layer until it reaches the quartz glass substrate before layer formation, and then performing a further substrate planarization step on the partially exposed quartz glass substrate.

[0059] <About Figure 4> 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 10.8 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.

[0060] 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).

[0061] A silicon dioxide layer is formed on the quartz glass substrate in state (4)-3 by the CVD method to produce state (4)-4 (layer formation process). 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.

[0062] The silicon dioxide layer is polished or precision polished until the substrate in state (4)-4 is flat, thereby completing a photomask substrate in state (4)-5 (layer flattening step).

[0063] 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 by 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.

[0064] 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.

[0065] <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 light 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 laser, so the presence and degree of retardation can be used to determine whether the photomask substrate was manufactured according to this embodiment.

[0066] The retardation can be calculated by multiplying the phase difference when light leaves the sample by the measured wavelength λ. For example, the wave number in the sample is Fast axis: 6.3×λ / 2, slow axis: 8×λ / 2, If so, the difference between the two is 1.7×λ / 2, and if the measurement wavelength λ is 523 nm, the retardation is 1.7×523 nm / 2=444.6 nm.

[0067] 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.

[0068] As mentioned above, many large scratches caused by contact with the photomask support of the peripheral exposure machine or peeling of the pecrylic film are often found on used quartz glass substrates. Therefore, the laser irradiation of the present embodiment is sometimes performed on the scratches in the peripheral area 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 outer 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 outer periphery of the quartz glass substrate, or it may be 40 nm or less, or 30 nm or less from the outer periphery of the quartz glass substrate.

[0069] <How to reuse photomask substrates> The method for recycling 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.

[0070] <Photomask blanks and their manufacturing method> The photomask blank according to this embodiment has at least one type of film selected from a light-shielding film, a halftone film, and a phase shift film on the photomask substrate.

[0071] 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.

[0072] <Photomask and its manufacturing method> The photomask according to this embodiment is obtained by forming a pattern on the above-mentioned photomask blank.

[0073] 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.

[0074] <Quartz glass substrate processing equipment> As shown in FIG. 5, the quartz glass substrate processing apparatus 1 according to this embodiment is used for the above-mentioned photomask substrate, a laser unit 101 that irradiates a laser onto a quartz glass substrate; and a moving unit 102 that moves the irradiation position on the quartz glass substrate by the laser unit 101.

[0075] 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.

[0076] The quartz glass substrate processing apparatus 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.

[0077] 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.

[0078] 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.

[0079] 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. [Example]

[0080] The present invention will be specifically described with reference to the following examples, but the present invention is not limited to these examples.

[0081] Example 1: Measurement analysis of recesses in a used photomask (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, to expose the quartz glass substrate. After polishing to a thickness of several micrometers to remove any deposits, the number of recesses on each quartz glass substrate was counted using a scratch measurement device (model number: IGS, manufactured by Nikon) and their coordinates and depths were measured. The recess depth was measured as the depth of the deepest point. A total of 318 recesses were detected within the exposure area on the surface of the two quartz glass substrates (the side with the Cr pattern). Of these, all 318 recesses were located within 30 mm of the substrate perimeter. Figure 6 shows the results in a bubble chart. In Figure 6, the location of the bubbles indicates the location of the recesses, the area of ​​the bubbles indicates the depth of the recesses, and the dotted line indicates the outer perimeter of the substrate (850 mm x 1200 mm).

[0082] Example 2: Step measurement results before and after carbon dioxide laser irradiation A line-shaped scratch with a depth of 100 μm or more on a quartz glass substrate measuring 152 mm x 152 mm x 6.35 mm was irradiated with a carbon dioxide laser with a wavelength of 10.6 μm so that the temperature of the irradiated area was between 2000°C and 2100°C.

[0083] 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. When the depth of the scratches after irradiation with the carbon dioxide laser was measured using a 3D laser microscope (manufactured by Keyence), it was found that the depth of the scratches was 10 μm or less. This shows that laser irradiation can make deep depressions extremely shallow.

[0084] Example 3: Distortion measurement by carbon dioxide laser irradiation Using a 50mm x 50mm x 50mm 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 λ10.6μm. From the obtained three-dimensional distribution data, a distortion of 255nm 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.

[0085] 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. [Explanation of symbols]

[0086] 1. Glass substrate processing equipment 101 Laser section 102 Moving part 103 Strength adjustment part 104...Temperature measurement section 105 Imaging unit

Claims

1. a recess processing step of irradiating a laser beam onto a quartz glass substrate having a recess on a first surface thereof to reduce the depth of the recess; a substrate flattening step of polishing the first surface on which the recess processing step has been performed to reduce an arithmetic mean height Sa of the first surface, In the recess processing step, the laser irradiation area includes the recess, and at least a portion of the irradiation area is melted.

2. 2. The method for manufacturing a photomask substrate according to claim 1, wherein the recessed portion has a depth of 30 [mu]m or less in the recessed portion processing step.

3. 3. The method for manufacturing a photomask substrate according to claim 1, wherein the substrate planarizing step makes the arithmetic mean height Sa of the first surface 20 [mu]m or less.

4. 4. The method for manufacturing a photomask substrate according to claim 1, wherein in the recess processing step, the composition of the irradiated area after irradiating with the laser is silicon dioxide.

5. a recess position specifying step of acquiring position information of the recess on the first surface, 5. The method for manufacturing a photomask substrate according to claim 1, wherein in the recess processing step, the quartz glass substrate is irradiated with the laser based on the position information.

6. 6. The method for manufacturing a photomask substrate according to claim 1, wherein the recess processing step uses the laser having a wavelength of 9.2 μm or more and 10.8 μm or less.

7. 7. The method for manufacturing a photomask substrate according to claim 1, wherein in the recess processing step, the temperature of the irradiation area during the period of irradiation with the laser is 1800° C. or higher and 2300° C. or lower.

8. The method for manufacturing a photomask substrate according to claim 1 , further comprising a layer forming step of forming a silicon dioxide layer on the first surface.

9. 9. The method for manufacturing a photomask substrate according to claim 8, further comprising a layer planarization step of polishing the silicon dioxide layer to reduce an arithmetic mean height Sa of the first surface on which the silicon dioxide layer is formed.

10. 10. The method for manufacturing a photomask substrate according to claim 8, wherein the layer forming step forms the silicon dioxide layer on the first surface before the recess processing step is performed.

11. 10. The method for manufacturing a photomask substrate according to claim 8, wherein the layer forming step forms the silicon dioxide layer on the first surface after the recess processing step has been performed.

12. 12. The method for manufacturing a photomask substrate according to claim 1, wherein the depth of the recesses before being irradiated with the laser in the recess processing step is 15 μm or more.

13. 13. The method for manufacturing a photomask substrate according to claim 1, wherein a second surface opposite to the first surface is subjected to the same treatment as that for the first surface.

14. 14. The method for manufacturing a photomask substrate according to claim 1, wherein a 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.

15. The method for manufacturing a photomask substrate according to any one of claims 1 to 14, wherein the quartz glass substrate is a used photomask from which a photomask pattern has been removed.

16. The method for producing a photomask substrate according to any one of claims 1 to 15, further comprising a pattern removal step of removing a photomask pattern from a used photomask to obtain the quartz glass substrate.

17. The method for manufacturing a photomask substrate according to claim 16 , further comprising a photomask recovery step of recovering the used photomask.

18. A method for manufacturing a photomask blank, comprising forming at least one 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 17, to manufacture a photomask blank.

19. A method for producing a photomask, comprising carrying out fine line circuit processing on a photomask blank produced by the method for producing a photomask blank according to claim 18, to produce a photomask.

20. A method for recycling photomask substrates, which comprises repeatedly reproducing used photomask substrates into new photomask substrates by carrying out the method for producing a photomask substrate according to any one of claims 1 to 17.

21. A photomask substrate including a quartz glass substrate, A photomask substrate having at least one retardation of 5 nm or more on the quartz glass substrate.

22. 22. The photomask substrate according to claim 21, 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 thereof.

23. A photomask blank comprising the photomask substrate according to claim 21 or 22, and at least one film selected from the group consisting of a light-shielding film, a halftone film, and a phase shift film.

24. A photomask having a pattern formed on the photomask blank according to claim 23.

25. A processing device for a quartz glass substrate used as a photomask substrate, a laser unit that irradiates the quartz glass substrate with a laser; a moving unit that moves the irradiation position on the quartz glass substrate by the laser unit, The quartz glass substrate processing device irradiates an irradiation area including a recess on the quartz glass substrate with the laser by the laser unit and the moving unit, thereby melting at least a portion of the irradiation area and reducing the depth of the recess.

26. an intensity adjusting unit that adjusts the intensity of the laser emitted by the laser unit; a temperature measurement unit that measures the temperature of the irradiation position and obtains temperature information of the irradiation position, 26. The apparatus for processing a silica glass substrate according to claim 25, wherein the intensity adjusting unit is controlled based on the temperature information.

27. 27. The apparatus for processing a silica glass substrate according to claim 26, further comprising an imaging unit that images the irradiation position and obtains imaging information of the irradiation position.

Images