Substrate and method for manufacturing the same

Abstract

To provide a manufacturing method of a substrate in which recessed flaw having a depth of less than 5 nm is suppressed, and which is therefore suitable as a mask blank for EUVL.SOLUTION: A manufacturing method of a substrate is provided which performs final polishing using a polishing device having an upper surface plate comprising a polishing pad, the manufacturing method includes a step in which: the substrate is held on the polishing device in such a manner that a main surface of the substrate directs toward the upper surface plate side; the substrate is polished by rotating the upper surface plate while polishing-slurry is entrained by the main surface of the substrate; then the upper surface plate is detached from the main surface of the polished substrate by moving up the upper surface plate while rotating the upper surface plate.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a substrate and a method for manufacturing the same, and more specifically, to a glass substrate suitably used as a mask blank substrate and a method for manufacturing the same. [Background technology]

[0002] As photolithography patterns become finer, the quality requirements for glass substrates used as photomasks, such as defect density, defect size, surface roughness, and flatness, are becoming increasingly stringent. In particular, regarding defects on the substrate, even extremely minute defects that were not previously a problem can now disrupt pattern formation. Furthermore, improvements in the sensitivity of defect inspection machines have made it possible to detect such minute defects, and their reduction is therefore required.

[0003] In recent years, EUV lithography (hereinafter abbreviated as "EUVL"), an exposure technique using Extreme Ultra Violet (hereinafter abbreviated as "EUV") light, has attracted attention as a way to achieve even finer patterns than those produced by conventional ultraviolet photolithography. EUV light is light in the soft X-ray region or vacuum ultraviolet region with wavelengths of approximately 0.2 to 100 nm, and reflective masks are commonly used as transfer masks in EUVL. The surface quality required for the mask blanks substrates used in such reflective masks for EUVL is particularly stringent, as even concave defects with a depth of less than 5 nm can disrupt pattern formation during exposure.

[0004] The surface quality of such mask blank substrates is greatly influenced by the method of performing the final stage of the polishing process (hereinafter referred to as final polishing). For example, Patent Document 1 describes using a suede-type pad having a pad surface with a height difference of 50 μm or less between the maximum and minimum peaks on the surface, and polishing 1 to 60 g / cm². 2 A method has been proposed to achieve excellent surface smoothness by polishing a glass substrate with a polishing load such that the occurrence of concave defects is suppressed.

[0005] Furthermore, Patent Document 2 states that the area of ​​the abrasive cloth is S1(m²). 2 Let S2(m²) be the surface area of ​​the glass material. 2 A method has been proposed for manufacturing glass substrates for mask blanks, in which variation in the number of concave defects can be significantly suppressed by setting Q = N × S² / S1 to 0.05 or more and 0.2 or less when the number of glass materials to be polished is N, the polishing cloth is approximately circular with an outer diameter of D (m), the rotation speed of the polishing platen relative to the glass material is ω (rpm), and the supply amount of the polishing slurry is P (L / min), and setting A = (2π(D / 2)²ω) / P to 1 or more and 15 or less.

[0006] On the other hand, Patent Document 3 discloses a method for manufacturing a substrate in which a finishing polishing process is performed using a double-sided polishing apparatus that holds the substrate in a carrier while bringing the two main surfaces of the substrate into contact with polishing pads on a rotating upper platen and a lower platen, respectively. In this apparatus, foreign matter such as solids formed from solidified abrasive grains and processing fragments generated when the substrate is polished tends to accumulate on and inside the polishing pad of the lower platen of the double-sided polishing apparatus. Therefore, a method has been proposed to suppress the occurrence of new defects caused by the finishing polishing process by polishing the main surface of the substrate on the upper platen side of the double-sided polishing apparatus. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2009-012164 [Patent Document 2] Japanese Patent Publication No. 2017-134108 [Patent Document 3] Japanese Patent Publication No. 2017-170588 [Overview of the project] [Problems that the invention aims to solve]

[0008] However, as described in Patent Document 1, a suede-type pad having a pad surface with a height difference of 50 μm or less between the maximum and minimum peaks on the surface is used, and the load capacity is 1 to 60 g / cm². 2 While performing the final polishing with this polishing load can suppress the occurrence of concave defects with a half-width of 60-150 nm, which can be detected by conventional surface defect inspection machines for photomasks, it is insufficient to suppress the occurrence of concave defects with a depth of less than 5 nm.

[0009] Furthermore, controlling the ratio of the surface area of ​​the glass substrate to the area of ​​the polishing cloth and the slurry flow rate, as described in Patent Document 2, or performing finish polishing so that the main surface of the substrate faces the upper platen side of the double-sided polishing apparatus, as described in Patent Document 3, does not practically eliminate the presence of foreign matter that may come into contact with the main surface of the substrate during polishing and cause concave defects less than 5 nm deep. Therefore, these methods cannot be considered fundamental solutions.

[0010] This invention has been made in view of the above circumstances, and aims to provide a method for manufacturing a substrate, particularly a substrate in which concave defects with a depth of less than 5 nm are suppressed, and which is suitable for use as a mask blank for EUVL. [Means for solving the problem]

[0011] To solve the above problems, the inventors diligently studied the operation of the upper platen at the end of the final polishing stage (hereinafter abbreviated as "final polishing") in the finishing polishing process of a substrate in a polishing apparatus equipped with a polishing pad. As a result, they found that it is useful to hold the substrate in the polishing apparatus so that the main surface of the substrate faces the upper platen, rotate the upper platen to polish the substrate, and then lift the upper platen away from the polished main surface of the substrate while it is still rotating without stopping. They found that this method can reduce concave defects with a depth of less than 5 nm that occur on the substrate surface compared to the conventional processing method in which the rotation of the upper platen is stopped before lifting the polishing pad on the upper platen side away from the substrate surface, leading to the present invention.

[0012] In other words, the present invention is 1. A method for manufacturing a substrate, in which the final polishing is performed using a polishing apparatus having an upper platen equipped with a polishing pad, A method for manufacturing a substrate, comprising the steps of: holding the substrate in a polishing device so that the main surface faces the upper platen; polishing the substrate by rotating the upper platen while entraining the main surface of the substrate with polishing slurry; and then raising the upper platen while it is still rotating to separate the upper platen from the main surface of the polished substrate. 2. The method for manufacturing a substrate according to claim 1, wherein the rotation speed of the upper platen when lifting the upper platen away from the main surface of the polished substrate is 0.5 to 50 rpm. 3. A method for manufacturing a substrate according to claim 1 or 2, wherein the upward speed of the upper platen when lifting the upper platen away from the main surface of the polished substrate is 0.1 to 50 mm / second. 4. A method for manufacturing a substrate according to claim 1 or 2, wherein the viscosity of the polishing slurry at 20°C is 0.5 to 30 mPa·s. 5. The method for manufacturing a substrate according to claim 1 or 2, wherein the polishing slurry contains 5 to 50% by mass of abrasive particles. 6. A method for manufacturing a substrate according to claim 1 or 2, wherein the polishing slurry contains colloidal silica particles as an abrasive component. 7. A method for manufacturing a substrate according to 6, wherein the average primary particle diameter of the colloidal silica particles, calculated from the specific surface area measured by the gas adsorption method, is 5 nm or more and 50 nm or less. 8. A method for manufacturing a substrate according to claim 1 or 2, wherein the pH of the polishing slurry is 8 to 11. 9. A method for manufacturing a substrate according to claim 1 or 2, wherein the substrate is a glass substrate for mask blanks mainly composed of SiO2. 10.9 The power spectral density PSD(f,θ) in polar coordinate form, obtained by the manufacturing method described in 9 and by measuring the surface shape of a 1 μm × 1 μm region with an atomic force microscope, is obtained at a spatial frequency of 10 μm. -1 More than 100μm -1 The maximum value of PSD_AVE(θ) averaged within the following range is 0.05nm. 4 The following are glass substrates for mask blanks. To provide. [Effects of the Invention]

[0013] According to the present invention, compared with the conventional processing method of stopping the rotation of the upper platen and then separating the polishing pad on the upper platen side from the substrate surface, it is possible to reduce concave defects with a depth of less than 5 nm generated on the substrate surface, and a substrate having high surface quality, which is suitable as a substrate for a mask blank for EUVL, can be provided.

Brief Description of the Drawings

[0014] [Figure 1] It is a schematic view showing a double-sided polishing apparatus used in one embodiment of the method for manufacturing a substrate of the present invention.

Embodiments for Carrying Out the Invention

[0015] Hereinafter, the present invention will be described in detail. [Method for Manufacturing Substrate] In the method for manufacturing a substrate of the present invention, when performing the final polishing of the substrate using a polishing apparatus having an upper platen provided with a polishing pad, the substrate is held in the polishing apparatus such that the main surface faces the upper platen side, and after polishing the substrate by rotating the upper platen while accompanying the polishing slurry, the upper platen is raised while being rotated to separate the polishing pad of the upper platen from the main surface of the polished substrate. By this, the generation of very shallow concave defects with a depth of less than 5 nm can be reduced.

[0016] Here, in the present invention, the final polishing includes, for example, a rough polishing step for rough polishing the surface of a raw material substrate obtained by molding, annealing, slicing, chamfering, and lapping a synthetic quartz glass ingot, a flatness measurement step for measuring the flatness of the surface of the roughly polished substrate, a local polishing step for local polishing, and the final stage of polishing in the finishing polishing step for adjusting the surface roughness of the raw material substrate from which the scratches generated on the surface by local polishing have been removed.

[0017] (1) Polishing Apparatus The polishing apparatus used in the present invention is not particularly limited as long as it has an upper platen equipped with a polishing pad, and a mechanism for removing the polishing pad of the upper platen from the polished main surface of the substrate after the upper platen has been placed on the main surface of the substrate and the substrate has been polished. Examples include a single-sided polishing apparatus having an upper platen equipped with a polishing pad, and a double-sided polishing apparatus having an upper platen and a lower platen, each equipped with a polishing pad. However, a double-sided polishing apparatus is preferred from the viewpoint of polishing efficiency.

[0018] Hereinafter, an embodiment of the manufacturing method for the substrate of the present invention will be described with reference to the drawings. Figure 1 shows a double-sided polishing apparatus 10 used in a substrate manufacturing method according to one embodiment of the present invention. As shown in Figure 1, the polishing apparatus 10 has an upper platen 3 that has a rotating shaft 1 and a polishing pad 2 on its lower surface and is vertically movable up and down, and opposite to it is a lower platen 5 that has a rotating shaft 4 and a polishing pad (not shown) on its upper surface, and a plurality of carriers 6 are provided at equal intervals around the rotating shaft 4 of the lower platen 5. Each carrier has a plurality of work holes 8 formed therein for holding substrates (also called workpieces) 7, and one substrate is held in each work hole. The carrier 6 is formed to be thinner than the thickness of the substrate. The upper platen 3 is lowered, and the substrate 7 is sandwiched between the upper platen 3 and the lower platen 5. While supplying polishing slurry (not shown) between the upper and lower platens 3 and 5 and the substrate 7, the upper platen 3 is rotated at a predetermined rotational speed in the direction of the thick arrow a by the rotation axis 1 of the upper platen 3, the lower platen 5 is rotated in the direction of the thick arrow b by the rotation axis 4 of the lower platen 5, and the carrier 6 is rotated in the direction of the thin arrows c or d, respectively, thereby polishing the substrate 7. In this embodiment, the lower platen is provided with multiple carriers, but at least one is sufficient, and although multiple work holes are provided, at least one is sufficient. The number of carriers and work holes is not particularly limited and can be appropriately selected according to the size of the polishing device and the substrate. The upper platen 3 and the lower platen 5 may also be rotated in opposite directions. Furthermore, the order of rotation of the upper platen, attachment to the substrate, and polishing of the substrate is not particularly limited. For example, the upper platen3 First, rotate the plate, and then polish it at the same time as it is placed on top of the plate. 3 The rotation and placement of the plate may be performed simultaneously to allow for polishing, or the upper plate may be used. 3 The process may involve first attaching the material to the plate, followed by rotation and polishing, and can be modified as appropriate depending on the polishing equipment and the required degree of polishing.

[0019] In such a polishing mechanism, the main surface of the substrate during polishing is subjected to a resultant force consisting of two components: a vertical force due to the load from the upper platen and a horizontal force due to the rotation of the upper platen and carrier. When the rotation of the upper platen completely stops with the polishing pad on the upper platen side in contact with the main surface of the substrate at the end of polishing, the resultant vector of the forces applied to the main surface of the substrate will be biased from horizontal to vertical relative to the substrate as the rotational speed of the upper platen decreases. At this time, if there is some foreign matter between the main surface of the substrate and the polishing pad on the upper platen side that can grind the substrate surface with higher efficiency than the abrasive grains in the polishing slurry, the vertical component of the impulse applied to the main surface of the substrate by that foreign matter will be concentrated in a limited area within the main surface of the substrate, resulting in the leaving of a localized concave structure on the main surface of the substrate.

[0020] On the other hand, in the manufacturing method of the present invention, when polishing is completed, the polishing pad on the upper platen side is removed from the main surface of the substrate while the upper platen is still rotating. In this case, even if there is some foreign matter between the main surface of the substrate and the polishing pad on the upper platen side that can grind the substrate surface with higher efficiency than abrasive grains, the perpendicular component of the impulse applied to the main surface of the substrate by that foreign matter will not be concentrated in a limited area within the main surface of the substrate. Therefore, it is difficult to leave localized concave structures within the main surface of the substrate, and as a result, concave defects can be reduced.

[0021] The rotation speed of the upper platen when lifting it from the main surface of the substrate is not particularly limited, but from the viewpoint of minimizing the likelihood of scratching the substrate, it is preferably 0.5 to 50 rpm, more preferably 1 to 30 rpm, and even more preferably 5 to 20 rpm. The rotation direction of the upper platen is not particularly limited, but when using a double-sided polishing device, it is preferable to rotate it in the opposite direction to the rotation direction of the lower platen.

[0022] When separating the polishing pad on the upper platen from the main surface of the substrate at the end of polishing, the upward speed of the upper platen is preferably 0.1 to 50 mm / second, more preferably 0.5 to 20 mm / second, and even more preferably 1 to 10 mm / second, considering that if the upward speed is too slow, the polishing slurry will evaporate on the main surface of the substrate, resulting in convex defects, while if the upward speed is too fast, the substrate will tend to stick to the polishing pad on the upper platen.

[0023] Furthermore, before the upper platen is raised, i.e., during polishing, the rotational speed of the upper and lower platens, the polishing pressure, and other polishing conditions can be those of normal use.

[0024] (2) Polishing slurry The viscosity of the polishing slurry used in this invention is preferably 0.5 to 30 mPa·s, more preferably 0.5 to 10 mPa·s, and even more preferably 1 to 5 mPa·s at 20°C, considering that the abrasive particles in the polishing slurry should be spread more abundantly and uniformly between the main surface of the substrate and the polishing pad on the upper platen side, thereby facilitating the dispersion of the component perpendicular to the impulse received by the main surface of the substrate from foreign matter. The viscosity of the polishing slurry can be measured using a commercially available viscometer, for example, a TVC-7 viscometer manufactured by Toki Sangyo Co., Ltd.

[0025] The concentration of abrasive particles in the polishing slurry is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 20% by mass or more, considering that a larger number of abrasive particles in the polishing slurry are present between the main surface of the substrate and the polishing pad on the upper platen side, making it easier to obtain the effect of dispersing the component perpendicular to the impulse received by the main surface of the substrate from foreign matter. On the other hand, considering that concave defects are suppressed due to the formation of aggregates between abrasive particles, the concentration is preferably 50% by mass or less, more preferably 45% by mass or less, and even more preferably 40% by mass or less.

[0026] Colloidal silica particles are preferred as the abrasive component in the polishing slurry, and colloidal silica, in which these colloidal silica particles are dispersed in water, can be used as the raw material for the polishing slurry. Commercially available colloidal silica can be used, and examples of commercially available colloidal silica include the GP series, PL series, and BS series manufactured by Fuso Chemical Industries, Ltd. While there are no particular restrictions on the method of synthesizing colloidal silica particles, high-purity particles produced by hydrolysis of organic silicate compounds such as alkoxysilanes are preferred from the viewpoint of reducing metal contamination.

[0027] The average primary particle diameter of the colloidal silica particles described above is preferably 5 nm or larger, more preferably 10 nm or larger, more preferably 50 nm or smaller, and more preferably 30 nm or smaller, from the viewpoint of ease of removal of colloidal silica particles remaining in the polishing slurry on the substrate surface after polishing, and achieving both reduction of surface roughness and concave defects and polishing efficiency. The average primary particle diameter of the colloidal silica particles can be calculated from the specific surface area (e.g., BET specific surface area) measured by the gas adsorption method. In this case, the specific surface area can be measured using colloidal silica before it is made into a polishing slurry, with the colloidal silica particles in a dry state.

[0028] The pH of the polishing slurry described above is preferably 8 or higher, and more preferably 8.5 or higher, in order to obtain good dispersion stability of colloidal silica particles. On the other hand, from the viewpoint of suppressing the amount of etching of the substrate during polishing and suppressing the occurrence of concave defects, the pH of the polishing slurry is preferably 11 or lower, and more preferably 10.5 or lower.

[0029] (3) Polishing pad The polishing pad used in the manufacturing method of the present invention is not particularly limited, but from the viewpoint of emphasizing the surface quality of the substrate, a soft suede-type pad is preferred.

[0030] (4) Substrate to be polished In the manufacturing method of the present invention, there are no particular restrictions on the size or thickness of the substrate to be polished. However, when used for photomask blanks, considering use with current EUVL exposure equipment, a 6-inch square substrate, which is commonly used for photomask blanks, is preferred. For example, a 152mm x 152mm x 6.35mm rectangular 6025 substrate is preferred. For round substrates, 6-inch diameter, 8-inch diameter, and 12-inch diameter substrates are preferred.

[0031] If the substrate thickness is less than 5 mm, when the upper platen is raised at the end of polishing, the substrate tends to stick to the polishing pad on the upper platen side, and it may be difficult to separate the polishing pad on the upper platen side from the main surface of the substrate while the upper platen is rotating. On the other hand, if the substrate thickness is 5 mm or more, the substrate remains on the polishing pad on the lower platen side due to its own weight, making it preferable to apply the manufacturing method of the present invention. There is no particular upper limit to the thickness of the substrate, but it is preferably 10 mm or less, and more preferably 8 mm or less.

[0032] The substrate material to which the manufacturing method of the present invention is applied is not particularly limited, but when used in the exposure process in EUVL, it is necessary to use a substrate with a low coefficient of thermal expansion, so a glass substrate mainly composed of SiO2 is preferred. The glass substrate mainly composed of SiO2 is not particularly limited, but examples include a titania-doped synthetic quartz glass substrate obtained by doping synthetic quartz glass with titania at a ratio of 5 to 10 mass%. Furthermore, the manufacturing method of the present invention can also be applied to soda-lime glass substrates, silicon wafer substrates, sapphire substrates, gallium nitride substrates, lithium tantalate substrates, etc., which can be obtained by other similar methods. Glass substrates mainly composed of SiO2, in particular titania-doped synthetic quartz glass substrates, can be suitably used as glass substrates for mask blanks.

[0033] (5) Manufacturing process As described above, the manufacturing method of the present invention is applicable to a finishing polishing process that follows a rough polishing step of roughly polishing the surface of a raw material substrate obtained by molding, annealing, slicing, chamfering, and lapping a synthetic quartz glass ingot, a flatness measurement step of measuring the flatness of the surface of the roughly polished raw material substrate, and a local polishing step of performing local polishing. However, if scratches on the raw material substrate cannot be completely removed by the local polishing step in a single finishing polishing step, a preliminary polishing step for mirror-finishing the substrate surface may be performed between the local polishing step and the final polishing of the present invention to obtain a higher surface quality, resulting in multiple finishing polishing steps. The synthetic quartz glass ingot can be of a composition appropriate to the substrate to be manufactured. For example, when manufacturing a titania-doped synthetic quartz glass substrate, a synthetic quartz glass ingot doped with a predetermined concentration of titania can be used.

[0034] The rough polishing process can be carried out using a double-sided polishing machine that performs planetary motion, and using an abrasive containing, for example, cerium oxide particles, zirconium oxide particles, or colloidal silica particles as abrasive grains.

[0035] Following the rough polishing process, the flatness of the substrate surface is measured in the flatness measurement process. However, in order to reduce the processing time of the subsequent local polishing process, it is preferable that the flatness (TIR) ​​of a 142 mm × 142 mm area be in the range of 100 to 1000 nm after the rough polishing process is completed. The flatness can be measured using a commercially available photomask flatness tester, such as the UltraFlat manufactured by Tropel.

[0036] The local polishing process is not limited to any method that allows for the determination of the amount of polishing at each part of the substrate surface based on pre-measured surface data, and the amount of polishing at each part of the substrate surface to be controlled. For example, it can be selected from local polishing methods using small rotary processing tools, Magneto Rheological Finishing (MRF) methods using magnetic fluid containing abrasives, and methods using gas cracker ion beam (GCIB) or plasma etching. In local polishing methods using small rotary processing tools, the amount of polishing is controlled by the speed at which the tool moves. That is, if a large amount of polishing is desired, the speed at which the tool passes over the substrate surface should be slowed down, and if the target shape is already close and less polishing is needed, the amount of polishing should be controlled by increasing the speed at which the tool passes over the substrate surface.

[0037] The machining section of the aforementioned small rotary machining tool is not particularly limited, but it is preferable to use a rotary tool of the rotary type. Here, from the perspective of reducing polishing damage to the glass, the material of the rotary processing tool that comes into contact with the glass can be selected from polyurethane, felt buffs, rubber, cerium pads, etc., with a hardness of A50 to A75 (according to JIS K6253), but it is not limited to these types as long as it can grind the glass surface. Furthermore, the shape of the grinding section of the rotary machining tool is not particularly limited, and examples include circular, donut-shaped, cylindrical, bullet-shaped, disc-shaped, barrel-shaped, etc.

[0038] The flatness (TIR) of any 142 mm × 142 mm area on the substrate surface after the local polishing process is preferably 100 nm or less, and more preferably 50 nm or less. Also, its shape can be arbitrarily selected according to the specifications, such as convex or concave, depending on the conditions of the subsequent finishing polishing. After the local polishing process, a polished substrate can be obtained by performing the final polishing of the present invention in the finishing polishing process.

[0039] [Polished substrate] The substrate obtained by the present invention, by applying the above-described method for manufacturing the substrate of the present invention, has a polar coordinate form power spectral density PSD(f,θ) obtained by measuring the surface shape of an arbitrary 1 μm × 1 μm area with an atomic force microscope, at a spatial frequency of 10 μm -1 or more and 100 μm -1 The maximum value of PSD_AVE(θ) averaged within the following range is preferably 0.05 nm 4 or less. Such a substrate has reduced concave defects with a depth of less than 5 nm and is suitable as a substrate for EUVL mask blanks. Here, the atomic force microscope can be appropriately selected from conventionally known ones, and specific examples thereof include Cypher ES manufactured by Oxford Instruments.

[0040] The angular direction power spectral density is calculated from the discrete Fourier transform F(u,v) of the surface shape Z(Px,Py) of the glass substrate. F(u,v) is calculated by the following formula (1).

[0041]

Equation

[0042] Here, Nx and Ny are the number of measurement points in the x and y directions when measuring the surface shape of the glass substrate. Px and Py are integers indicating the position of each measurement point in the x and y directions, with Px taking values ​​of 0, 1, ..., Nx-1 and Py taking values ​​of 0, 1, ..., Ny-1. In contrast, u and v take values ​​of u = -1 / 2, -1 / 2 + 1 / Nx, ..., 1 / 2 and v = -1 / 2, -1 / 2 + 1 / Ny, ..., 1 / 2. The power spectral density P(u,v) can be obtained by normalizing F(u,v) using the measurement pitch Δx, Δy in the x,y directions and the area of ​​the measurement region A = (NxΔx) × (NyΔy) as shown in equation (2) below.

[0043]

number

[0044] Without this standardization, it would be impossible to simply compare power spectral densities calculated under different measurement range and measurement pitch conditions. On the other hand, the spatial frequency f(u,v) and the angle θ are expressed by the following equations (3) and (4), respectively.

[0045]

number

[0046]

number

[0047] The polar coordinate form PSD(f,θ) is obtained by transforming P(u,v) using equations (3) and (4). Furthermore, the PSD(f,θ) in polar coordinate form is given when the spatial frequency f is 10 μm -1 More than 100μm -1 The averaged PSD_AVE(θ) over the following range is expressed by the following equation (5).

[0048]

number

[0049] Here, Nf is the number of measurement points that satisfy the following equation (6).

[0050]

number

[0051] The maximum value of PSD_AVE(θ) is preferably 0.05 nm, from the viewpoint of avoiding the amplification of concave structures and the resulting concave defects that can be detected by defect inspection equipment when the main surface of the substrate is cleaned before film deposition after polishing. 4 The following, and more preferably 0.04 nm 4 The following applies: [Examples]

[0052] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0053] [Examples 1-4] Sliced ​​titania-doped synthetic quartz glass substrate material (6 inches square, 6.35 mm thick) was lapped using a planetary motion double-sided lapping machine, and then rough polished using a planetary motion double-sided polishing machine. The flatness of the surface of the roughly polished substrate was measured, and local polishing was performed using a small rotary processing tool. Finally, preliminary finish polishing was performed using a planetary motion double-sided polishing machine with an abrasive containing colloidal silica particles as abrasive material to prepare the raw substrate.

[0054] The raw substrate, which had undergone preliminary finishing polishing, was subjected to final polishing using a double-sided polishing apparatus with suede-type polishing cloth attached to the upper and lower polishing plates. In the final polishing process, a polishing slurry was used that contained 25% by mass of colloidal silica particles with an average primary particle diameter of 16 nm as the abrasive component, and whose pH was adjusted to 9.4. Ten substrates 7 were placed in the work holes 8 formed in the carrier 6 of the lower platen 5 of the polishing apparatus 10 shown in Figure 1, with their main surfaces facing the upper platen. Polishing was performed for 30 minutes, adjusting the load and the rotation speeds of the upper platen 3 and lower platen 5 as appropriate so that the polishing allowance of the main surface was 100 nm. After that, without stopping the rotation of the upper platen 3, it was raised while still rotating, and the polishing pad 2 on the upper platen 3 side was separated from the main surface of the polished substrates. The rotation speed of the upper platen 3, the raising speed, and the viscosity of the polishing slurry when the polishing pad 2 on the upper platen 3 side was separated from the main surface of the polished substrates are shown in Table 1 below.

[0055] After polishing, the substrates were cleaned and dried. Then, a defect inspection of the main surface of the substrate was performed using a defect inspection device for mask blanks substrates (manufactured by Lasertec Corporation). The locations of defects were observed using an atomic force microscope, and the number of concave defects with a depth of less than 5 nm was measured. Ten polished substrates were observed, and the average number of defects per substrate was determined. Furthermore, by measuring the surface shape of a 1 μm × 1 μm region within the main surface of the substrate using an atomic force microscope, the power spectral density PSD(f,θ) in polar coordinate form was obtained at a spatial frequency of 10 μm. -1 More than 100μm -1 The maximum value of PSD_AVE(θ) averaged within the following range was calculated. Ten polished substrates were measured, and the average of the maximum values ​​for each substrate was calculated. The results are shown in Table 1.

[0056] [Table 1]

[0057] [Comparative Examples 1-3] After polishing, the rotation of the upper platen was stopped, and with the upper platen stopped, it was raised to separate the polishing pad on the upper platen side from the main surface of the substrate. The final polishing of the substrate was then performed in the same manner as in Examples 1-4 and evaluated. The results are shown in Table 2.

[0058] [Table 2]

Claims

1. A method for manufacturing a substrate, which involves performing final polishing using a polishing apparatus having upper and lower platens equipped with polishing pads, A method for manufacturing a substrate, comprising the steps of: holding the substrate on a carrier provided on the lower platen of a polishing apparatus so that the main surface faces the upper platen; polishing the substrate by rotating the upper platen while entraining the main surface of the substrate with polishing slurry; and then raising the upper platen while it is still rotating to separate it from the main surface of the polished substrate. A method for manufacturing a substrate, wherein the upward speed of the upper platen when lifting the upper platen away from the main surface of the polished substrate is 0.1 to 50 mm / second, and the rotational speed is 0.5 to 50 rpm.

2. The method for manufacturing a substrate according to claim 1, wherein the viscosity of the polishing slurry at 20°C is 0.5 to 30 mPa·s.

3. The method for manufacturing a substrate according to claim 1 or 2, wherein the polishing slurry contains 5 to 50% by mass of abrasive components.

4. The method for manufacturing a substrate according to claim 1 or 2, wherein the polishing slurry contains colloidal silica particles as an abrasive component.

5. The method for manufacturing a substrate according to claim 4, wherein the average primary particle diameter of the colloidal silica particles, calculated from the specific surface area measured by the gas adsorption method, is 5 nm or more and 50 nm or less.

6. The method for manufacturing a substrate according to claim 1 or 2, wherein the pH of the polishing slurry is 8 to 11.

7. The aforementioned substrate is SiO 2 A method for manufacturing a substrate according to claim 1 or 2, wherein the substrate is a glass substrate for mask blanks, the main component of which is a glass substrate.

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