Glass plate processing method and EUVL mask blank manufacturing method

Abstract

This processing method for glass substrates comprises: preparing a protective layer-equipped glass substrate that has a glass substrate and a protective layer containing a resin layer which is in contact with the glass substrate; holding the protective layer-equipped glass substrate by means of a clamp placed against the protective layer; and, while the protective layer-equipped glass substrate is held by the clamp, etching a first main surface of the glass substrate by irradiating the first main surface with a gas cluster in the form of a beam.

Description

[Technical field]

[0001] The present disclosure relates to a method for processing a glass plate and a method for manufacturing a mask blank for EUVL. [Background technology]

[0002] Conventionally, photolithography technology has been used in the manufacture of semiconductor devices, in which an exposure apparatus irradiates a photomask pattern with light and transfers the photomask pattern onto a resist film.

[0003] Recently, in order to enable the transfer of fine patterns, the use of short-wavelength exposure light, for example, ArF excimer laser light, and further EUV (Extreme Ultra-Violet) light, has been considered.

[0004] Here, EUV light includes soft X-rays and vacuum ultraviolet light, and specifically refers to light with a wavelength of about 0.2 nm to 100 nm. At present, EUV light with a wavelength of about 13.5 nm is mainly considered as exposure light.

[0005] Patent Document 1 describes a method for producing a mask blank for EUVL (Extreme Ultra-Violet Lithography). The mask blank for EUVL includes a glass plate, a reflective film formed on the glass plate, and an absorbing film formed on the reflective film.

[0006] EUVL mask blanks require high flatness to improve the transfer accuracy of fine patterns. The flatness of EUVL mask blanks is determined mainly by the flatness of the glass plate that serves as the substrate, so the glass plate must have high flatness.

[0007] The manufacturing method described in Patent Document 1 includes a preliminary polishing step, a measuring step, and a corrective polishing step. In the preliminary polishing step, both main surfaces of the glass plate are pre-polished. In the measuring step, the maximum thickness distribution and flatness of the glass plate are measured. In the corrective polishing step, the main surface of the glass plate is locally polished based on the measurement results of the measuring step. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] International Publication No. 2011 / 115131 Summary of the Invention [Problem to be solved by the invention]

[0009] The local polishing of Patent Document 1 uses gas clusters and the like. The gas clusters are ionized by the impact of thermal electrons, then accelerated by an electric field, and irradiated toward the first main surface of the glass plate, locally etching the first main surface. As a result, the first main surface can be flattened.

[0010] The gas cluster irradiation is performed inside a vacuum vessel. Since the glass plate cannot be held by a vacuum chuck inside the vacuum vessel, the glass plate is held by a clamp. The clamp holds the glass plate in a detachable manner. Therefore, the clamp can be moved toward and away from the glass plate.

[0011] The glass plate is etched inside the vacuum chamber, generating particles. The particles are generated when gas clusters collide with the glass plate or the surrounding members of the glass plate. The particles are made of, for example, glass, metal, or resin. The generated particles may adhere to the clamp while it is waiting. If the clamp approaches the glass plate in this state, the particles will get caught between the clamp and the glass plate. As a result, defects will occur in the glass plate.

[0012] Defects can be concave scratches or convex deposits. These defects are caused by particles. Scratches are the traces of contact with particles, and deposits are the particles themselves.

[0013] One aspect of the present disclosure provides a technique that can suppress the occurrence of defects in a glass sheet due to contact with a clamp. [Means for solving the problem]

[0014] A method for processing a glass plate according to one embodiment of the present disclosure includes preparing a glass plate with a protective layer, the glass plate having a glass plate and a protective layer including a resin layer in contact with the glass plate; holding the glass plate with the protective layer with a clamp placed against the protective layer; and, while the glass plate with the protective layer is held by the clamp, irradiating a beam-shaped gas cluster onto a first main surface of the glass plate to etch the first main surface. Effect of the Invention

[0015] According to one aspect of the present disclosure, it is possible to suppress the occurrence of defects in a glass sheet due to contact with a clamp. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a flowchart showing a method for manufacturing an EUVL mask blank according to one embodiment. [Diagram 2] FIG. 2 is a cross-sectional view showing an example of a glass plate to be subjected to S1 in FIG. [Diagram 3] FIG. 3 is a plan view illustrating an example of the glass plate of FIG. [Figure 4] FIG. 4 is a cross-sectional view showing an EUVL mask blank according to an embodiment. [Diagram 5] FIG. 5 is a cross-sectional view showing an example of a photomask for EUVL. [Figure 6] FIG. 6 is a cross-sectional view showing a processing device according to an embodiment. [Figure 7]FIG. 7 is an enlarged cross-sectional view showing the glass plate and its peripheral parts in FIG. [Figure 8] FIG. 8 is a diagram showing the glass plate and its peripheral parts as viewed from the direction of irradiation of the gas clusters in FIG. [Figure 9] FIG. 9 is a view of the clamp and spacer of FIG. 7 from another angle. [Figure 10] FIG. 10 is a flowchart showing an example of S3 in FIG. [Figure 11] FIG. 11 is a cross-sectional view showing a clamp according to a first modified example. [Figure 12] FIG. 12 is a cross-sectional view showing a clamp according to a second modified example. [Figure 13] FIG. 13 is a cross-sectional view showing a clamp according to a third modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In each drawing, the same or corresponding configurations are denoted by the same reference numerals, and descriptions thereof may be omitted. In the specification, the symbol "~" indicating a numerical range means that the numerical values ​​before and after the symbol are included as the lower and upper limits.

[0018] As shown in FIG. 1, the method for manufacturing a mask blank for EUVL (Extreme Ultra-Violet Lithography) includes steps S1 to S7. A glass plate is used for manufacturing the mask blank. The glass of the glass plate is preferably quartz glass containing 90% or more by mass of SiO2. The upper limit of the SiO2 content in the quartz glass is 100% by mass. Compared to general soda-lime glass, the quartz glass has a smaller linear expansion coefficient and a smaller dimensional change due to temperature change. In addition to SiO2, the quartz glass may contain TiO2. The quartz glass may contain 90% to 95% by mass of SiO2 and 5% to 10% by mass of TiO2. When the TiO2 content is 5% to 10% by mass, the linear expansion coefficient is approximately zero near room temperature and there is almost no dimensional change near room temperature. The quartz glass may contain trace components other than SiO2 and TiO2, but it is preferable that the quartz glass does not contain trace components.

[0019] As shown in FIG. 2 and FIG. 3, the glass plate 2 includes a first main surface 21, a second main surface 22, four end surfaces 23, four first chamfered surfaces 24, and four second chamfered surfaces 25. The first main surface 21 is rectangular. In this specification, the rectangular shape includes a shape with chamfered corners. The rectangle also includes a square. The second main surface 22 faces in the opposite direction to the first main surface 21. The second main surface 22 is also rectangular like the first main surface 21. The end surface 23 is perpendicular to the first main surface 21 and the second main surface 22. The first chamfered surface 24 is formed at the boundary between the first main surface 21 and the end surface 23. The second chamfered surface 25 is formed at the boundary between the second main surface 22 and the end surface 23. In this embodiment, the first chamfered surface 24 and the second chamfered surface 25 are so-called C-chamfered surfaces, but may be R-chamfered surfaces.

[0020] The first main surface 21 of the glass plate 2 has a quality assurance region 26 shown by a dot pattern in Fig. 3. The quality assurance region 26 is a region that is processed to a desired flatness by S1 to S4. The quality assurance region 26 is a region excluding a peripheral region 27 within a distance L of, for example, 5 mm from the end face 23 when viewed from a direction perpendicular to the first main surface 21. Although not shown, the second main surface 22 of the glass plate 2 also has a quality assurance region and a peripheral region, similar to the first main surface 21.

[0021] First, in S1 of Fig. 1, the first main surface 21 and the second main surface 22 of the glass plate 2 are polished. The first main surface 21 and the second main surface 22 may be polished simultaneously by a double-sided polisher, or may be polished sequentially by a single-sided polisher. In S1, the glass plate 2 is polished while a polishing slurry is supplied between the polishing pad and the glass plate 2. The polishing slurry contains an abrasive. The abrasive is, for example, cerium oxide particles. The first main surface 21 and the second main surface 22 may be polished multiple times with abrasives of different materials or grain sizes.

[0022] The abrasive used in S1 is not limited to cerium oxide particles, and may be, for example, silicon oxide particles, aluminum oxide particles, zirconium oxide particles, titanium oxide particles, diamond particles, silicon carbide particles, or the like.

[0023] 1, the surface shapes of the first main surface 21 and the second main surface 22 of the glass plate 2 are measured. For example, a non-contact measuring device such as a laser interference type is used to measure the surface shape so as not to scratch the surface. The measuring device measures the surface shapes of the quality assurance area 26 of the first main surface 21 and the quality assurance area of ​​the second main surface 22.

[0024] 1, the first main surface 21 and the second main surface 22 of the glass plate 2 are processed with a gas cluster beam in order to improve the flatness by referring to the measurement result of S2. The first main surface 21 and the second main surface 22 are etched in order with the gas cluster. The order is not particularly limited and may be either first.

[0025] The gas clusters are ionized by the collision of the thermal electrons, then accelerated by an electric field, and after further neutralization, are irradiated toward the first main surface 21 or the second main surface 22. The collision of the gas clusters locally etches and flattens the first main surface 21 or the second main surface 22. Details of S3 will be described later.

[0026] Next, in S4 of Fig. 1, the first main surface 21 and the second main surface 22 of the glass plate 2 are finish-polished. The first main surface 21 and the second main surface 22 may be polished simultaneously by a double-sided polisher, or may be polished sequentially by a single-sided polisher. In S4, the glass plate 2 is polished while a polishing slurry is supplied between the polishing pad and the glass plate 2. The polishing slurry contains an abrasive. The abrasive is, for example, colloidal silica particles.

[0027] Next, in S5 of FIG. 1, a reflective film 3 shown in FIG. 4 is formed in the quality assurance area 26 of the first main surface 21 of the glass plate 2. The reflective film 3 reflects EUV light. The reflective film 3 may be, for example, a multilayer reflective film in which high-refractive index layers and low-refractive index layers are alternately laminated. The high-refractive index layers are made of, for example, silicon (Si), and the low-refractive index layers are made of, for example, molybdenum (Mo). The reflective film 3 is formed by a sputtering method such as an ion beam sputtering method or a magnetron sputtering method.

[0028] Next, in S6 of Fig. 1, an absorbing film 4 shown in Fig. 4 is formed on the reflective film 3 formed in S5. The absorbing film 4 absorbs EUV light. The absorbing film 4 is formed of, for example, a single metal, an alloy, a nitride, an oxide, an oxynitride, or the like containing at least one element selected from tantalum (Ta), chromium (Cr), and palladium (Pd). The absorbing film 4 is formed, for example, by sputtering.

[0029] Finally, in S7 of Fig. 1, a conductive film 5 shown in Fig. 4 is formed in the quality assurance area of ​​the second main surface 22 of the glass plate 2. The conductive film 5 is used to electrostatically attract a photomask with an electrostatic chuck of an exposure device. The conductive film 5 is made of, for example, chromium nitride (CrN). The conductive film 5 is formed by, for example, a sputtering method. Note that, although S7 is performed after S5 and S6 in this embodiment, it may be performed before S5 and S6.

[0030] The reflective film 3 and the conductive film 5 may be arranged inversely. That is, the conductive film 5 may be formed in the quality assurance area 26 of the first main surface 21 of the glass plate 2, and the reflective film 3 may be formed in the quality assurance area 22 of the second main surface 22 of the glass plate 2. The absorbing film 4 is formed on the reflective film 3.

[0031] By the above steps S1 to S7, an EUVL mask blank 1 shown in Fig. 4 is obtained. The EUVL mask blank 1 includes a glass plate 2, a reflective film 3, an absorbing film 4, and a conductive film 5. Note that the EUVL mask blank 1 does not necessarily include the conductive film 5. Furthermore, the EUVL mask blank 1 may further include another film.

[0032] For example, the EUVL mask blank 1 may further include a low-reflection film. The low-reflection film is formed on the absorbing film 4. The low-reflection film is used for inspecting the opening pattern 41 of the absorbing film 4 shown in FIG. 5, and has lower reflection characteristics with respect to inspection light than the absorbing film 4. The low-reflection film is formed of, for example, TaON or TaO. For example, a sputtering method is used as a method for forming the low-reflection film.

[0033] Moreover, the EUVL mask blank 1 may further include a protective film. The protective film is formed between the reflective film 3 and the absorbing film 4. The protective film protects the reflective film 3 so that the reflective film 3 is not etched when the absorbing film 4 is etched to form an opening pattern 41 in the absorbing film 4. The protective film is formed of, for example, Ru, Si, or TiO2. For example, a sputtering method is used as a method for forming the protective film.

[0034] 5, the EUVL photomask is obtained by forming an opening pattern 41 in an absorbing film 4. Photolithography and etching are used to form the opening pattern 41. Therefore, the resist film used to form the opening pattern 41 may be included in the EUVL mask blank 1.

[0035] Next, a processing apparatus used in S3 in Fig. 1 will be described with reference to Fig. 6. The processing apparatus 100 is a so-called GCIB (Gas Cluster Ion Beam) processing apparatus.

[0036] The processing apparatus 100 includes a vacuum vessel 101. The vacuum vessel 101 has a nozzle chamber 102, an ionization / acceleration chamber 103, and a processing chamber 104. The three chambers 102, 103, and 104 are connected to each other to form a passage for a gas cluster. The three chambers 102, 103, and 104 are evacuated by three vacuum pumps 105, 106, and 107, and are maintained at a desired vacuum level. The number of chambers and the number of vacuum pumps are not particularly limited.

[0037] The processing apparatus 100 includes a generation unit 110. The generation unit 110 generates gas clusters. The generation unit 110 includes, for example, a raw material tank 111, a pressure controller 113, a supply pipe 114, and a nozzle 116. The raw material tank 111 stores a raw material gas (for example, CF4 gas). The pressure controller 113 controls the supply pressure of the raw material gas supplied from the raw material tank 111 to the nozzle 116 via the supply pipe 114. The nozzle 116 is provided in the nozzle chamber 102, and injects the raw material gas into a vacuum to form a supersonic gas jet 118.

[0038] The source gas is cooled by adiabatic expansion in the gas jet 118. As a result, a part of the gas jet 118 condenses into gas clusters, each of which is an aggregate of several to several thousand atoms or molecules. Many gas clusters are contained near the center of the flow of the gas jet 118. Therefore, the gas clusters can be efficiently sent out by passing only the center of the flow of the gas jet 118 through the schema 119.

[0039] The source gas is not limited to CF4 gas, and may be SF6 gas, Ar gas, O2 gas, N2 gas, NF3 gas, N2O gas, CHF3 gas, C2F6 gas, C3F8 gas, C4F6 gas, SiF4 gas, COF2 gas, SeF6 gas, TeF6 gas, or WF6 gas. A plurality of gases may be selected from these gases, or a mixed gas may be used as the source gas. The source gas is preferably one that can create large-sized gas clusters and can be etched at a high rate, and specifically, one that contains fluorine.

[0040] The processing apparatus 100 includes an ionization section 120. The ionization section 120 ionizes at least a portion of the gas clusters in the gas jet 118. The ionization section 120 includes, for example, one or more hot filaments 124 and a cylindrical electrode 126. The hot filament 124 receives power (voltage V F ) generates heat and emits thermoelectrons. The cylindrical electrode 126 accelerates the thermoelectrons emitted from the thermal filament 124, and causes the accelerated thermoelectrons to collide with gas clusters. Collisions between the electrons and the gas clusters cause electrons to be emitted from some of the gas clusters, which then become positively ionized. Note that two or more electrons may be emitted, resulting in multiply charged ions. A voltage V from a power source 127 is applied between the cylindrical electrode 126 and the thermal filament 124. A This voltage V A The thermal electrons are accelerated by the electric field and collide with the gas clusters.

[0041] The processing apparatus 100 includes an acceleration section 130. The acceleration section 130 accelerates the gas clusters ionized in the ionization section 120 to form a GCIB 128. The acceleration section 130 includes, for example, a first electrode 132 and a second electrode 134. The second electrode 134 is grounded, and a positive voltage Vs is applied to the first electrode 132 from a power supply 135. The first electrode 132 and the second electrode 134 form an electric field that accelerates the positively ionized gas clusters. The accelerated gas clusters are extracted as a GCIB 128 from an opening in the second electrode 134. The power supply 136 applies an acceleration voltage Vs that biases the ionization section 120 with respect to the first electrode 132 and the second electrode 134.Acc and the total GCIB accelerating potential is V Acc V Acc is, for example, 1 kV to 200 kV, preferably 1 kV to 70 kV.

[0042] The processing apparatus 100 may include a neutralization section (not shown). The neutralization section neutralizes the GCIB 128 formed in the acceleration section 130 to form neutral gas clusters. Since the glass plate 2 is irradiated with neutral gas clusters, it is possible to prevent the glass plate 2 from being charged. Note that even if the glass plate 2 is irradiated with positively ionized gas clusters, it is possible to etch the glass plate 2.

[0043] The processing apparatus 100 includes an irradiation unit 150. The irradiation unit 150 irradiates the glass plate 2 with a beam-like gas cluster 129 to locally etch the glass plate 2. The diameter of the beam of the gas cluster 129 is, for example, 1 mm to 15 mm. The irradiation unit 150 includes, for example, a stage 151, a stage moving mechanism 152, and an aperture 153. The stage 151 is installed in the processing chamber 104 and holds the glass plate 2. The stage moving mechanism 152 moves the stage 151 two-dimensionally in the Y-axis direction and the Z-axis direction to move the irradiation point of the gas cluster 129 on the glass plate 2. By controlling the moving speed, the etching amount can be controlled and the glass plate 2 can be flattened. The stage moving mechanism 152 can also move the stage 151 in the X-axis direction. The aperture 153 is provided in the middle of the passage of the gas cluster 129 to increase the uniformity of the intensity of the gas cluster 129. The gas clusters 129 pass through the openings of the aperture 153 and are irradiated onto the glass plate 2 .

[0044] Next, the irradiation section 150 of the processing apparatus 100 will be described with reference to Figs. 7 to 9. In this specification, the X-axis direction, the Y-axis direction, and the Z-axis direction are perpendicular to each other. The X-axis direction and the Y-axis direction are horizontal directions, and the Z-axis direction is vertical. In the following description, the positive X-axis direction is the forward direction, and the negative X-axis direction is the backward direction. The irradiation direction of the gas cluster 129 shown by the arrow in Fig. 7 is the positive X-axis direction.

[0045] As shown in Fig. 7, the irradiation unit 150 irradiates beam-shaped gas clusters 129 forward, and the irradiated gas clusters 129 locally etch the first main surface 21 of the glass plate 2. The first main surface 21 is disposed facing backward and tilted obliquely upward. Since the first main surface 21 faces obliquely upward, the stage 151 can stably hold the glass plate 2 from below. Note that if the orientation of the glass plate 2 is reversed, it is naturally possible to locally etch the second main surface 22 of the glass plate 2.

[0046] 9, the stage 151 is disposed facing the second main surface 22 of the glass plate 2. The stage 151 is disposed in front of the glass plate 2. The stage 151 may hold the glass plate 2 via a spacer 155, for example. The spacer 155 forms a gap between the stage 151 and the glass plate 2. Compared to a case where the entire second main surface 22 of the glass plate 2 is in contact with the stage 151, the occurrence of contact scratches on the second main surface 22 can be suppressed.

[0047] Spacer 155 may have a tapered surface. If spacer 155 holds second chamfered surface 25 of glass plate 2 with the tapered surface, it does not come into contact with second main surface 22 at all, so that it is possible to reliably prevent the occurrence of contact scratches on second main surface 22. A part of spacer 155 is disposed on the outer side of glass plate 2 when viewed from the irradiation direction of gas cluster 129 as shown in FIG. 8.

[0048] In this embodiment, a part of the spacer 155 is disposed outside the glass plate 2 as viewed from the irradiation direction of the gas cluster 129, but it is also possible to dispose the entire spacer 155 inside the glass plate 2. In that case, the spacer 155 contacts not the second chamfered surface 25 of the glass plate 2 but the peripheral region of the second main surface 22 excluding the quality assurance region.

[0049] Furthermore, the stage 151 may hold the glass plate 2 via a clamp 156. The glass plate 2 can be stably held in a vacuum. The entire clamp 156 is disposed outside the glass plate 2 when viewed from the irradiation direction of the gas cluster 129. The clamp 156 holds, for example, the end surface 23 of the glass plate 2. A plurality of clamps 156 are provided at intervals along the periphery of the glass plate 2.

[0050] In this embodiment, the clamp 156 presses the edge surface 23 of the glass plate 2, but it may also press the peripheral region 27 of the first main surface 21 of the glass plate 2. The clamp 156 may also press the first chamfered surface 24 of the glass plate 2. In these cases, too, a part of the clamp 156 is disposed on the outer side of the glass plate 2 when viewed from the irradiation direction of the gas cluster 129.

[0051] Incidentally, irradiation of the gas cluster 129 is carried out inside the vacuum vessel 101. Inside the vacuum vessel 101, the glass plate 2 cannot be held by a vacuum chuck, so the glass plate 2 is held by a clamp 156. The clamp 156 holds the glass plate 2 in a detachable manner. Therefore, the clamp 156 can be moved toward and away from the glass plate 2.

[0052] The glass plate 2 is etched inside the vacuum vessel 101, and particles are generated. The particles are generated when the gas clusters 129 collide with the glass plate 2 or a peripheral member of the glass plate 2. The material of the particles is, for example, glass, metal, or resin. The generated particles may adhere to the clamp 156 in a standby state. When the clamp 156 approaches the glass plate 2 in this state, the particle becomes caught between the glass plate 2 and the clamp 156. As a result, conventionally, defects may occur in the glass plate 2.

[0053] Therefore, in this embodiment, a glass plate 7 with a protective layer is prepared. The glass plate 7 with a protective layer includes a glass plate 2 and a protective layer 6. The protective layer 6 includes a resin layer 61 that contacts the glass plate 2. The resin layer 61 may be a single layer or multiple layers. The resin layer 61 does not include filler or powder at least on the surface in contact with the glass plate 2. This is because filler and powder can cause dust generation or scratches. It is preferable that the resin layer 61 does not include filler or powder not only on the surface in contact with the glass plate 2 but also inside.

[0054] Examples of the resin for the resin layer 61 include vinyl acetate resin, ethylene-vinyl acetate copolymer resin, isobutene-maleic anhydride copolymer resin, acrylic copolymer resin, styrene-butadiene rubber copolymer, vinyl chloride resin, chloroprene rubber, nitrile rubber, epoxy resin, modified epoxy resin, silicone resin, modified silicone resin, urethane resin, EVA resin, ABS resin, polypropylene, high density polyethylene, low density polyethylene, polystyrene, polyester, polyamide, polyvinyl chloride, polycarbonate, PET (Poly Ethylene Terephthalate), POM (Poly Oxy Methylene), PBT (Poly Butylene Terephthalate), polyvinylidene chloride, PVA (Poly Vinyl Alcohol), and fluororesin. Also, PPSU (Poly Phenyl Sulfone), PSU (Poly Sulfone), PAR (Poly Arylate), PEI (Poly Ether Imide), PEEK (Poly Ethel Ethel Keton), PPS (Poly Phenylene Sulfide), PES (Poly Ethel Sulfone), PAI (Poly Amide Imide), LCP (Liquid Crystal Polymer), PTFE (Poly Tetra Fluoro Ethylene), PCTFE (Poly Chloro TriFluoro Ethylene), or PVDF (Poly Vinylidene DiFluoride) is used as the resin material of the shield plate 161. These resins can be removed by RCA cleaning or scrub cleaning, which will be described later.

[0055] Since the resin layer 61 is softer than the glass plate 2, it is softer than particles generated by etching the glass plate 2 and serves as a buffer material. That is, when a particle gets caught between the clamp 156 and the glass plate 2, the resin layer 61 deforms so as to absorb the particle. Therefore, the occurrence of defects in the glass plate 2 can be suppressed.

[0056] The thickness of the resin layer 61 is not particularly limited, but is, for example, 0.001 mm to 10 mm, and preferably 0.001 mm to 1 mm. If the thickness of the resin layer 61 is 0.001 mm or more, the thickness of the resin layer 61 is greater than the particle diameter of the particles, and therefore the resin layer 61 can function as a buffer material. If the thickness of the resin layer 61 is 10 mm or less, the shear deformation of the resin layer 61 is small when the clamp 156 holds the resin layer 61, and the positional deviation of the glass plate 2 is small. If the thickness of the resin layer 61 is 1 mm or less, the effect on processing accuracy is small.

[0057] In this embodiment, the protective layer 6 includes only the resin layer 61, but may include a metal layer or a ceramic layer in addition to the resin layer 61. The metal layer and the ceramic layer are disposed on the outside of the resin layer 61, that is, on the opposite side of the glass plate 2 with respect to the resin layer 61. The metal of the metal layer is aluminum, copper, iron, nickel, zinc, titanium, stainless steel, or brass. These metals can be removed by RCA cleaning, which will be described later. The ceramic of the ceramic layer is alumina, zirconia, aluminum nitride, silicon carbide, silicon nitride, forsterite, steatite, cordierite, sialon, machinable ceramic, barium titanate, lead zirconate titanate, ferrite, or mullite.

[0058] The protective layer 6 is formed, for example, on the edge surface 23 of the glass plate 2. A plurality of protective layers 6 are arranged at intervals along the periphery of the glass plate 2. This makes it easier to remove the protective layer 6 than when the protective layer 6 is arranged along the entire periphery of the glass plate 2. The protective layer 6 may be arranged in a position where the clamp 156 comes into contact.

[0059] As described above, if the orientation of the glass plate 2 is reversed, it is naturally possible to locally etch the second main surface 22 of the glass plate 2. In this case, the protective layer 6 also serves as a buffer material. That is, when a particle gets caught between the clamp 156 and the glass plate 2, the resin layer 61 deforms so as to absorb the particle. Therefore, the occurrence of defects in the glass plate 2 can be suppressed.

[0060] Next, S3 in Fig. 1 will be described in detail with reference to Fig. 10. S3 in Fig. 1 includes S31 to S36 shown in Fig. 10.

[0061] 10, a protective layer 6 is formed on the glass plate 2. For example, a liquid containing a material for the protective layer 6 is applied to the glass plate 2 and solidified to form the protective layer 6. Because the liquid has fluidity, it is possible to form a protective layer that follows the surface shape of the glass plate 2. The material for the protective layer 6 includes, for example, a thermosetting resin, a thermoplastic resin, or an ultraviolet curing resin.

[0062] Instead of applying a liquid containing the material of the protective layer 6 to the glass plate 2 and solidifying it, a tape-shaped protective layer 6 may be attached to the glass plate 2. Since a pre-solidified protective layer 6 is attached to the glass plate 2, the working time can be shortened. The material of the tape-shaped protective layer 6 includes a thermosetting resin, a thermoplastic resin, or an ultraviolet curing resin.

[0063] Also, instead of applying a liquid containing the material of the protective layer 6 to the glass plate 2 and solidifying it, a frame-shaped protective layer 6 as shown in FIG. 13 may be applied to cover the glass plate 2. The frame-shaped protective layer 6 includes, for example, a frame-shaped plate portion 65 and a rib portion 66 protruding from the entire periphery of the plate portion 65. The plate portion 65 has an opening 65a larger than the quality assurance region 26 of the first main surface 21 of the glass plate 2, and contacts the peripheral region 27. Meanwhile, the rib portion 66 contacts the end surface 23 of the glass plate 2. The frame-shaped protective layer 6 can be separated from the glass plate 2 in its original shape, and can be applied again to cover another glass plate 2.

[0064] In this embodiment, S31 in Fig. 10 is performed after S2 in Fig. 1, but it may be performed before S2 in Fig. 1, or may be performed before S1 in Fig. 1. However, S32 in Fig. 10 is performed after S2 in Fig. 1.

[0065] 10, a glass plate 7 with a protective layer is prepared. Specifically, for example, the glass plate 7 with a protective layer obtained in S31 is carried into a vacuum chamber 101 of a processing apparatus 100 shown in FIG.

[0066] 10, the glass plate 7 with the protective layer is held by a clamp 156 placed against the protective layer 6, as shown in FIGS. 7 to 9. The protective layer 6 serves as a buffer material. That is, when a particle is caught between the clamp 156 and the glass plate 2, the resin layer 61 deforms so as to absorb the particle. This makes it possible to suppress the occurrence of defects in the glass plate 2.

[0067] 10, the beam-like gas cluster 129 is irradiated onto the first main surface 21 of the glass plate 2. In order to move the irradiation point, the stage moving mechanism 152 moves the stage 151 two-dimensionally in the Y-axis direction and the Z-axis direction. By controlling the moving speed, the etching amount can be controlled, and the first main surface 21 can be flattened.

[0068] 10, the protective layer-coated glass plate 7 is released from the clamps 156. Thereafter, the protective layer-coated glass plate 7 is carried out from the vacuum chamber 101 of the processing apparatus 100 to the outside.

[0069] Next, in S36 of FIG. 10, the glass plate 7 with the protective layer is washed with a cleaning solution to remove the protective layer 6. The washing includes, for example, scrubbing. In scrubbing, the glass plate 7 with the protective layer is scrubbed with a brush or a sponge. The resin layer 61 and thus the protective layer 6 can be efficiently removed. In scrubbing, an alkaline solution containing a surfactant may be used as the cleaning solution. The removal efficiency can be improved by the action of the alkali. The scrubbing and ultrasonic cleaning may be used in combination. Furthermore, the scrubbing may be used as part of the RCA cleaning described below.

[0070] The cleaning of the protective layer-attached glass plate 7 may include RCA cleaning. The RCA cleaning may include, for example, SC-1 cleaning, dilute hydrofluoric acid cleaning, and SC-2 cleaning, in this order. In the SC-1 cleaning, a mixed aqueous solution of ammonium hydroxide (NH4OH) and hydrogen peroxide (H2O2) is used as the cleaning liquid. In the dilute hydrofluoric acid cleaning, dilute hydrofluoric acid is used as the cleaning liquid. In the SC-2 cleaning, a mixed aqueous solution of hydrochloric acid (HCl) and hydrogen peroxide is used as the cleaning liquid. The RCA cleaning may further include SPM cleaning. In the SPM cleaning, a mixed aqueous solution of sulfuric acid (H2SO4) and hydrogen peroxide is used as the cleaning liquid.

[0071] As described above, if the orientation of the glass plate 2 is reversed, it is naturally possible to locally etch the second main surface 22 of the glass plate 2. In this case, the resin layer 61 of the protective layer 6 also serves as a buffer material. That is, when a particle gets caught between the clamp 156 and the glass plate 2, the resin layer 61 deforms so as to absorb the particle. Therefore, the occurrence of defects in the glass plate 2 can be suppressed.

[0072] Next, a clamp 156 according to a first modified example will be described with reference to Fig. 11. The clamp 156 of this modified example presses the peripheral region 27 of the first main surface 21 of the glass plate 2. A protective layer 6 is formed in the peripheral region 27. When a particle gets caught between the clamp 156 and the glass plate 2, the resin layer 61 deforms so as to absorb the particle. Therefore, the occurrence of defects in the glass plate 2 can be suppressed.

[0073] The clamp 156 presses the glass plate 2 against the spacer 155. The protective layer 6 may be formed on the second chamfered surface 25 of the glass plate 2 and pressed against the spacer 155. When a particle gets caught between the spacer 155 and the glass plate 2, the resin layer 61 deforms so as to absorb the particle. Therefore, the occurrence of defects in the glass plate 2 can be suppressed.

[0074] A plurality of protective layers 6 are disposed at intervals along the periphery of the glass plate 2. The protective layers 6 are easier to remove than when the protective layers 6 are disposed along the entire periphery of the glass plate 2. The protective layers 6 may be disposed at positions where the spacers 155 or the clamps 156 come into contact.

[0075] As described above, the spacer 155 may press the peripheral region of the second main surface 22 instead of the second chamfered surface 25 of the glass plate 2. In this case, the protective layer 6 is formed on the peripheral region of the second main surface 22 of the glass plate 2 and pressed against the spacer 155.

[0076] Next, a clamp 156 according to a second modified example will be described with reference to Fig. 12. The clamp 156 of this modified example presses the first chamfered surface 24 of the glass plate 2. A protective layer 6 is formed on the first chamfered surface 24. When a particle gets caught between the clamp 156 and the glass plate 2, the resin layer 61 deforms so as to absorb the particle. Therefore, the occurrence of defects in the glass plate 2 can be suppressed.

[0077] The clamp 156 presses the glass plate 2 against the spacer 155. The protective layer 6 may be formed on the second chamfered surface 25 of the glass plate 2 and pressed against the spacer 155. When a particle gets caught between the spacer 155 and the glass plate 2, the resin layer 61 deforms so as to absorb the particle. Therefore, the occurrence of defects in the glass plate 2 can be suppressed.

[0078] A plurality of protective layers 6 are disposed at intervals along the periphery of the glass plate 2. The protective layers 6 are easier to remove than when the protective layers 6 are disposed along the entire periphery of the glass plate 2. The protective layers 6 may be disposed at positions where the spacers 155 or the clamps 156 come into contact.

[0079] As described above, the spacer 155 may press the peripheral region of the second main surface 22 instead of the second chamfered surface 25 of the glass plate 2. In this case, the protective layer 6 is formed on the peripheral region of the second main surface 22 of the glass plate 2 and pressed against the spacer 155. EXAMPLES

[0080] The experimental data will be described below. Example 1 below is an embodiment, and Example 2 below is a comparative example.

[0081] In Example 1, the first main surface 21 of the glass plate 2 was processed with beam-shaped gas clusters 129 by the processing apparatus 100 shown in Fig. 6. The processing conditions were as follows. Material of glass plate 2: Quartz glass containing TiO2 Raw material gas: CF4 gas Acceleration voltage V Acc :60kV Arrangement of protective layer 6: arrangement of FIG. Dimensions of protective layer 6: 15 mm x 6 mm x 0.35 mm thick Material of protective layer 6: Silicone resin Construction of clamp 156: Construction of FIG.

[0082] In Example 1, the clamp 156 pressed the edge surface 23 of the glass plate 2 via the protective layer 6, so that after the protective layer 6 was removed with a cleaning liquid, no defects were visually confirmed in the portion of the edge surface 23 of the glass plate 2 pressed by the clamp 156. This is because when a particle gets caught between the clamp 156 and the glass plate 2, the protective layer 6 deforms so as to prevent stress concentration.

[0083] In Example 2, the first main surface 21 of the glass plate 2 was processed with beam-like gas cluster 129 under the same processing conditions as in Example 1, except that the protective layer 6 was not used. In Example 2, the clamp 156 contacted the edge surface 23 of the glass plate 2, and defects were visually confirmed in the portion of the edge surface 23 of the glass plate 2 pressed by the clamp 156.

[0084] The results of Examples 1 and 2 show that the clamps 156 pressing the edge surface 23 of the glass sheet 2 through the protective layer 6 can suppress the occurrence of defects in the glass sheet 2 due to contact with the clamps 156.

[0085] The glass plate processing method and EUVL mask blank manufacturing method according to the present disclosure have been described above, but the present disclosure is not limited to the above-mentioned embodiments. Various changes, modifications, substitutions, additions, deletions, and combinations are possible within the scope of the claims. These naturally fall within the technical scope of the present disclosure.

[0086] For example, the use of the glass plate processed by the processing method of the present disclosure is not limited to EUVL. The use of the glass plate may be any use that requires high flatness, such as a medical device. The glass composition of the glass plate may be any use that corresponds to the use of the glass plate.

[0087] This application claims priority based on Japanese Patent Application No. 2020-084730, filed with the Japan Patent Office on May 13, 2020, the entire contents of which are incorporated herein by reference. [Explanation of symbols]

[0088] 1. Mask blanks for EUVL 2 Glass plate 21 First main surface 22 Second main surface 23 End face 24 1st chamfer surface 25 2nd chamfer 3 Reflective film 4. Absorbing membrane 6 Protective layer 61 Resin layer 7 Glass plate with protective layer 100 Processing equipment 129 Gas Cluster 151 Stages 155 Spacer 156 Clamp

Claims

1. Preparing a glass plate with a protective layer, the glass plate having a glass plate and a protective layer including a resin layer in contact with the glass plate; holding the glass plate with the protective layer by a clamp applied to the protective layer; and irradiating a first main surface of the glass plate with a beam of gas clusters while the glass plate with the protective layer is held by the clamp, thereby etching the first main surface.

2. 2. The processing method according to claim 1, wherein the protective layer is formed on an edge surface perpendicular to the first main surface of the glass plate, a first chamfered surface formed at a boundary between the first main surface and the edge surface, or a peripheral region within 5 mm from the edge surface of the first main surface.

3. The glass plate further includes a second main surface facing opposite to the first main surface, and a second chamfered surface formed at a boundary between the second main surface and the edge surface, the protective layer is further formed on a peripheral region within 5 mm from the end face of the second main surface of the glass plate or on the second chamfered surface, and is pressed against a spacer by the clamp; The processing method according to claim 2 , wherein the spacer forms a gap between the glass plate and a stage disposed opposite the second main surface of the glass plate.

4. The processing method according to claim 1 , further comprising removing the protective layer after releasing the holding of the protective layer-coated glass plate by the clamps.

5. The method of claim 4 , wherein the protective layer is removed by scrubbing.

6. The method according to claim 4 or 5, wherein the protective layer is removed with an alkaline solution containing a surfactant.

7. The processing method according to any one of claims 1 to 6, further comprising applying a liquid containing a material of the protective layer to the glass plate and solidifying the liquid to form the protective layer.

8. The processing method according to any one of claims 1 to 6, further comprising attaching the protective layer in a tape form to the glass plate.

9. The processing method according to any one of claims 1 to 6, further comprising detachably covering the glass plate with the protective layer in a frame shape.

10. Planarizing the first main surface of the glass plate by using the processing method according to any one of claims 1 to 9; forming a reflective film that reflects EUV light on the first main surface of the glass plate; forming an absorbing film on the reflective film that absorbs EUV light; The method for producing an EUVL mask blank comprises the steps of:

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