Ultrasonic cleaning head, substrate cleaning method, substrate cleaning apparatus, substrate manufacturing method, and EUVL mask blank manufacturing method

Abstract

This ultrasonic cleaning head has a vibration surface that faces the upper surface of a substrate with a gap therebetween, and contacts a liquid film formed on the upper surface of the substrate. The vibration surface has a surface density of Ce element of 30×1010atoms / cm2 as detected by a total reflection X-ray fluorescence analysis.

Description

[Technical Field]

[0001] This disclosure relates to an ultrasonic cleaning head, a substrate cleaning method, a substrate cleaning apparatus, a method for manufacturing a substrate, and a method for manufacturing a mask blank for EUVL. [Background technology]

[0002] In recent years, with the miniaturization of semiconductor devices, EUV lithography (EUVL), a lithography technique using extreme ultraviolet (EUV) light, has been developed. EUV includes soft X-rays and vacuum ultraviolet light, specifically light with wavelengths of approximately 0.2 nm to 100 nm. Currently, EUV with a wavelength of approximately 13.5 nm is being primarily studied.

[0003] In EUVL (Extreme Ultraviolet Light) lithography, a reflective mask is used. The reflective mask comprises, in this order, a substrate such as a glass substrate, a multilayer reflective film that reflects EUV light, and an absorbing film that absorbs EUV light. An aperture pattern is formed on the absorbing film. In EUVL, the aperture pattern of the absorbing film is transferred to a target substrate such as a semiconductor substrate. This transfer includes the transfer at a reduced size.

[0004] During the manufacturing process of EUVL mask blanks, the glass substrate or the functional film formed on the glass substrate may need to be cleaned. One method of cleaning for this purpose is ultrasonic cleaning.

[0005] The cleaning method described in Patent Document 1 involves spraying a cleaning solution pre-treated with ultrasonic waves onto the upper surface of a rotating substrate from a nozzle. The cleaning method described in Patent Document 2 involves supplying a cleaning solution between the upper surface of a rotating substrate and the lower surface of an ultrasonic cleaning head, and cleaning the upper surface of the substrate by applying ultrasonic waves to this cleaning solution from the lower surface of the ultrasonic cleaning head. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2013-158664 [Patent Document 2] Japanese Patent Application Publication No. 2001-87725 [Overview of the project] [Problems that the invention aims to solve]

[0007] Even when using the cleaning method described in Patent Document 1, the number of particles adhering to the substrate could not be sufficiently reduced. The inventors of the present invention investigated the particles adhering to the substrate after ultrasonic cleaning and found that cerium oxide particles were one of the causes of the particles. They also found that cerium oxide particles adhering to the ultrasonic cleaning head detached during cleaning and adhered to the substrate, which was the source of the cerium oxide particles. Since cerium oxide particles are commonly used in mechanical polishing, it is thought that they adhered during the manufacturing process of the ultrasonic cleaning head. The manufacturing process of the ultrasonic cleaning head includes, for example, cutting and mechanical polishing. Cutting involves shaping the diaphragm into a desired form. Mechanical polishing involves polishing the diaphragm with cerium oxide particles.

[0008] One aspect of this disclosure provides a technique for reducing the number of particles adhering to a substrate by ultrasonic cleaning. [Means for solving the problem]

[0009] An ultrasonic cleaning head according to one aspect of this disclosure has a vibrating surface that is spaced apart from the upper surface of a substrate and in contact with a liquid film formed on the upper surface of the substrate. The vibrating surface has a surface density of Ce element detected by total internal reflection X-ray fluorescence analysis of 30 × 10 10 atoms / cm 2 The following applies: [Effects of the Invention]

[0010] An ultrasonic cleaning head according to one aspect of the present disclosure has a surface density of Ce elements on the vibrating surface of 30 × 10 10 atoms / cm 2Since it is as follows, the areal density of cerium oxide particles adhering to the vibration surface is low. Therefore, the number of particles detaching from the vibration surface of the ultrasonic cleaning head can be reduced, and the number of particles adhering to the substrate by ultrasonic cleaning can be reduced.

Brief Description of the Drawings

[0011] [Figure 1] FIG. 1 is a side view showing a substrate cleaning apparatus according to an embodiment. [Figure 2] FIG. 2 is a cross-sectional view showing an example of the internal structure of the cleaning head. [Figure 3] FIG. 3 is a cross-sectional view showing another example of the internal structure of the cleaning head. [Figure 4] FIG. 4 is a plan view showing an example of the movement locus of the cleaning head. [Figure 5] FIG. 5 is a cross-sectional view showing an example of the pre-treatment of the cleaning head. [Figure 6] FIG. 6 is a cross-sectional view showing another example of the pre-treatment of the cleaning head. [Figure 7] FIG. 7 is a diagram showing an example of the relationship between the number of processed dummy substrates and the number of particles. [Figure 8] It is a flowchart showing a method for manufacturing a mask blank for EUVL according to an embodiment. [Figure 9] FIG. 9 is a cross-sectional view showing an example of a substrate. [Figure 10] FIG. 10 is a plan view of the substrate of FIG. 9. [Figure 11] FIG. 11 is a cross-sectional view showing an example of a mask blank for EUVL. [Figure 12] FIG. 12 is a cross-sectional view showing an example of a mask for EUVL.

Embodiments for Carrying Out the Invention

[0012] The embodiments for implementing this disclosure will be described below with reference to the drawings. In each drawing, the same or corresponding components will be denoted by the same reference numeral, and their descriptions may be omitted. In the specification, the numeral "~" indicating a numerical range means that the numbers written before and after it are included as the lower and upper limits, respectively.

[0013] Referring to Figures 1 to 4, a substrate cleaning apparatus 1 according to one embodiment will be described. The substrate cleaning apparatus 1 cleans a substrate W by applying ultrasonic vibrations to a liquid film F formed on the substrate W. It can remove particles adhering to the substrate W. The substrate cleaning apparatus 1 comprises a holding unit 10, a nozzle 20, a cleaning head 30, a rotating unit 40, a first moving unit 50, a second moving unit 60, and a control unit 90. The cleaning head 30 is an example of an ultrasonic cleaning head.

[0014] The holding part 10 holds the substrate W horizontally. When viewed from above, the substrate W is rectangular (see Figure 4), but may also be circular. The substrate W includes a glass substrate, a silicon wafer, or a compound semiconductor wafer. The substrate W may also include a functional film formed on a glass substrate or the like. The functional film is, for example, a light-reflective film, a light-absorbing film, a conductive film, or an insulating film.

[0015] The holding portion 10 includes a plurality of pins 11 arranged at intervals along the periphery of the substrate W, as shown in Figure 1, for example. The plurality of pins 11 hold the periphery of the substrate W. The substrate W is placed on the plurality of pins 11. Since there is space beneath the substrate W, it is also possible to attach a sensor to the underside of the substrate W. The holding portion 10 may also hold the substrate W by suction.

[0016] The nozzle 20 forms a liquid film F by supplying cleaning fluid to the upper surface Wa of the substrate W held by the holding unit 10. The upper surface Wa of the substrate W is also referred to as the substrate upper surface Wa. For example, the nozzle 20 supplies cleaning fluid to the vicinity of the center of the substrate upper surface Wa. The substrate W is rotating, and the cleaning fluid on the substrate W spreads from the center to the periphery due to centrifugal force. As a result, a liquid film F is formed over the entire substrate upper surface Wa. The nozzle 20 may be provided outside the cleaning head 30 as shown in Figure 1, or it may be provided inside the cleaning head 30, although this is not shown.

[0017] The nozzle 20 is connected to a cleaning fluid supply source 22 via a supply line 21. A valve 23 is provided in the middle of the supply line 21. The valve 23 opens and closes the flow path of the supply line 21. When the valve 23 opens the flow path of the supply line 21, cleaning fluid is supplied from the supply source 22 to the nozzle 20, and the nozzle 20 discharges the cleaning fluid. When the valve 23 closes the flow path of the supply line 21, the nozzle 20 stops discharging the cleaning fluid.

[0018] The cleaning solution may be, for example, pure water (e.g., deionized water), a mixture of pure water and X (at least one component selected from the group consisting of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, formic acid, and acetic acid), a mixture of pure water and Y (at least one component selected from the group consisting of ammonia, tetramethylammonium hydroxide, triethanolamine, choline, sodium hydroxide, potassium hydroxide, and cesium hydroxide), a mixture of pure water and Z (at least one component selected from the group consisting of hydrogen peroxide, perchlorate ions, and periodate ions), a mixture of pure water and X and Z, or a mixture of pure water and Y and Z.

[0019] The cleaning solution may contain at least one gas selected from the group consisting of H2 gas, CO2 gas, N2 gas, O2 gas, O3 gas, and Ar gas. By controlling the amount of dissolved gas, the efficiency of cavitation generation can be improved, and the efficiency of particle removal can be improved. The gas dissolved in the cleaning solution is preferably H2 gas, CO2 gas, or N2 gas, and more preferably CO2 gas.

[0020] As shown in Figure 2, the cleaning head 30 includes a vibrating surface 31a that contacts the liquid film F and an ultrasonic transducer 32 that vibrates the vibrating surface 31a. The cleaning head 30 also includes a diaphragm 31. The diaphragm 31 has a downward-facing vibrating surface 31a that contacts the liquid film F and an upward-facing mounting surface 31b to which the ultrasonic transducer 32 is attached.

[0021] The vibrating surface 31a is installed parallel to the upper surface Wa of the substrate. The size of the vibrating surface 31a is, for example, smaller than the size of the upper surface Wa of the substrate. The shape of the vibrating surface 31a is, for example, circular. When the nozzle 20 is provided inside the cleaning head 30, the discharge port of the nozzle 20 is formed on the vibrating surface 31a.

[0022] The mounting surface 31b may be installed parallel to the vibration surface 31a, as shown in Figure 2, or it may be installed at an angle to the vibration surface 31a, as shown in Figure 3. In Figure 3, θ is the angle between the normal to the vibration surface 31a and the normal to the mounting surface 31b. The direction of the normal to the mounting surface 31b is the vibration direction of the ultrasonic transducer 32.

[0023] The ultrasonic transducer 32 applies ultrasonic vibrations to the liquid film F by vibrating its vibrating surface 31a, thereby applying sound pressure to the substrate W. This allows particles adhering to the upper surface Wa of the substrate to be removed. The output of the ultrasonic transducer 32 is controlled by the control unit 90. When the distance D between the cleaning head 30 and the substrate W is constant, the sound pressure acting on the substrate W increases as the output of the ultrasonic transducer 32 increases.

[0024] The rotating part 40 rotates the substrate W together with the holding part 10. The rotational centerline 10R of the holding part 10 is set vertically. The holding part 10 holds the substrate W such that its rotational centerline 10R passes through the center of the substrate W. The rotating part 40 includes, for example, a servo motor 41. The rotational driving force of the servo motor 41 may be transmitted to the holding part 10 via pulleys and belts or gears (not shown). The servo motor 41 transmits information about the rotational position of the holding part 10 to the control unit 90. The rotational position of the holding part 10 is expressed as a rotation angle. A stepping motor may be used instead of the servo motor 41.

[0025] The first moving unit 50 moves the cleaning head 30 in a horizontal direction perpendicular to the rotation centerline 10R of the holding unit 10. The cleaning head 30 is moved, for example, between a position directly above the center of the substrate W and a position directly above the periphery of the substrate W. The first moving unit 50 includes, for example, a servo motor 51. The servo motor 51 transmits information regarding the horizontal position of the cleaning head 30 to the control unit 90. A stepping motor may be used instead of the servo motor 51.

[0026] The first moving unit 50 moves the cleaning head 30 in a horizontal direction perpendicular to the rotation centerline 10R of the holding unit 10, for example, by rotating the pivot axis 52. The pivot axis 52 is fixed to one end of the pivot arm 53, and the cleaning head 30 is fixed to the other end of the pivot arm 53. The rotation centerline 30R of the cleaning head 30 is set vertically.

[0027] Although not shown in the diagram, the first moving unit 50 may move the cleaning head 30 in a horizontal direction perpendicular to the rotational centerline 10R of the holding unit 10 along a horizontal guide rail.

[0028] The second moving unit 60 moves the cleaning head 30 vertically. For example, the second moving unit 60 moves the cleaning head 30 vertically by moving the pivot axis 52 vertically. The second moving unit 60 includes a servo motor 61. The second moving unit 60 may also include a ball screw that converts the rotational motion of the servo motor 61 into linear motion. The servo motor 61 transmits information regarding the vertical position of the cleaning head 30 to the control unit 90. A stepping motor may be used instead of the servo motor 61. The second moving unit 60 may move the cleaning head 30 vertically using an air cylinder instead of a motor.

[0029] Although not shown in the diagram, the second moving part 60 may move the holding part 10 vertically instead of moving the cleaning head 30 vertically. In either case, the distance D between the substrate W and the cleaning head 30 can be changed.

[0030] The control unit 90 controls the valve 23, the ultrasonic transducer 32, the rotating part 40, the first moving part 50, and the second moving part 60. The control unit 90 is, for example, a computer and comprises a CPU (Central Processing Unit) 91 and a storage medium 92 such as memory. The storage medium 92 stores programs that control various processes performed in the substrate cleaning apparatus 1. The control unit 90 controls the operation of the substrate cleaning apparatus 1 by causing the CPU 91 to execute the programs stored in the storage medium 92.

[0031] Next, the operation of the substrate cleaning apparatus 1, that is, the substrate cleaning method, will be explained. First, a transport robot (not shown) enters the substrate cleaning apparatus 1 and passes the substrate W it is holding to the holding unit 10. After the holding unit 10 holds the substrate W horizontally, the transport robot exits the substrate cleaning apparatus 1. In this way, the substrate W is transported.

[0032] Next, the rotating part 40 rotates the substrate W together with the holding part 10, and the nozzle 20 supplies cleaning liquid to the vicinity of the center of the substrate W. The cleaning liquid on the substrate W spreads outwards from the center to the periphery due to centrifugal force. As a result, a liquid film F is formed over the entire upper surface Wa of the substrate. The amount of cleaning liquid supplied is, for example, 0.1 L / min to 5.0 L / min, preferably 0.8 L / min to 1.6 L / min.

[0033] Next, the first moving unit 50 adjusts the horizontal position of the cleaning head 30 so that the vibrating surface 31a of the cleaning head 30 contacts the liquid film F, while the second moving unit 60 adjusts the vertical position of the cleaning head 30. A desired gap is formed between the cleaning head 30 and the substrate W. This gap is, for example, 0.1 mm to 5.0 mm, preferably 1.0 mm to 4.0 mm.

[0034] Next, the ultrasonic transducer 32 vibrates the vibrating surface 31a of the cleaning head 30, thereby applying ultrasonic vibrations to the liquid film F and sound pressure to the upper surface Wa of the substrate.

[0035] Next, the first moving unit 50 moves the cleaning head 30 in a horizontal direction perpendicular to the rotation centerline 10R of the holding unit 10. The cleaning head 30 is moved back and forth between a position directly above the center of the substrate W and a position directly above the periphery of the substrate W. The substrate W is rotating, and the entire upper surface Wa of the substrate is cleaned.

[0036] Next, the second moving unit 60 raises the cleaning head 30, and then the first moving unit 50 moves the horizontal position of the cleaning head 30 to the standby position. When viewed from above, the standby position is outside the periphery of the substrate W. At the same time, the ultrasonic transducer 32 stops vibrating the vibrating surface 31a, and the nozzle 20 stops supplying the cleaning fluid.

[0037] Next, with the nozzle 20 stopping the supply of cleaning fluid, the rotating part 40 rotates the substrate W together with the holding part 10, causing the cleaning fluid on the substrate W to be shaken off from the periphery of the substrate W by centrifugal force. The liquid film F is removed from the substrate W, and the substrate W is dried.

[0038] Next, a transport robot (not shown) enters the substrate cleaning apparatus 1 and receives the substrate W from the holding unit 10. After the transport robot holds the substrate W, the transport robot exits the substrate cleaning apparatus 1. In this way, the substrate W is removed.

[0039] Next, an example of pre-treatment of the cleaning head 30 will be described with reference to Figures 5 and 6. Pre-treatment of the cleaning head 30 is performed before the cleaning head 30 is assembled into the substrate cleaning device 1. After the cleaning head 30 is assembled into the substrate cleaning device 1, a dummy substrate is cleaned by the substrate cleaning device 1, and then the actual product substrate W is cleaned. Note that pre-treatment of the cleaning head 30 only needs to be performed before cleaning the dummy substrate, and it is also possible to perform it after the cleaning head 30 has been assembled into the substrate cleaning device 1.

[0040] The dummy substrate is constructed in the same way as the actual substrate W and is cleaned in the same way as the substrate W. Specifically, although not shown in the diagram, the dummy substrate is cleaned by applying ultrasonic vibrations from the vibrating surfaces 31a to the liquid film F while forming a liquid film F between the vibrating surfaces 31a of the opposing cleaning heads 30 and the upper surface of the dummy substrate. Hereinafter, the cleaning of the dummy substrate will also be referred to as dummy cleaning. Dummy cleaning is performed to suppress dust generation from the cleaning heads 30.

[0041] As shown in Figures 5 and 6, particles P adhere to the vibrating surface 31a of the cleaning head 30. The distance between the vibrating surface 31a of the cleaning head 30 and the upper surface of the dummy substrate is short, making it easy for particles P detached from the vibrating surface 31a of the cleaning head 30 to adhere to the upper surface of the dummy substrate. It is practically difficult to reduce the number of adhering particles P to zero.

[0042] Dummy cleaning is performed repeatedly while replacing the dummy substrates. As shown in Figure 7, the more dummy substrates are processed, that is, the longer the dummy cleaning time, the more dust generation from the cleaning head 30 is suppressed, and the number of particles P adhering to the dummy substrates by ultrasonic cleaning decreases.

[0043] As shown in Figure 7, after a certain amount of time has passed since the dummy cleaning, the number of particles P adhering to the dummy substrate settles to a constant value. Subsequently, the actual product substrate W is cleaned. The number of particles P adhering to the substrate W is approximately the same as the number of particles P adhering to the final dummy substrate.

[0044] Incidentally, the fewer particles P attached to the vibrating surface 31a of the cleaning head 30 before dummy cleaning, the shorter the time it takes for the number of particles P attached to the dummy substrate to settle to a constant value, and the smaller that constant value becomes. Therefore, the fewer particles P attached to the vibrating surface 31a of the cleaning head 30 before dummy cleaning, the fewer particles P attached to the substrate W.

[0045] The inventors of this application investigated the cause of particle P adhering to the vibrating surface 31a of the cleaning head 30. It is believed that particle P adheres during one of the manufacturing, packaging, or transportation processes of the cleaning head 30. The inventors of this application focused on cerium oxide particles used in the manufacturing process of the cleaning head 30.

[0046] The vibrating surface 31a of the cleaning head 30 is formed on the diaphragm 31, as shown in Figures 2 and 3. The material of the diaphragm 31 is, for example, quartz glass (SiO2). The material of the diaphragm 31 may also be sapphire glass (Al2O3). Furthermore, the material of the diaphragm 31 may be either crystalline or amorphous.

[0047] The manufacturing process for the cleaning head 30 includes, as an example, cutting and mechanical polishing. Cutting involves shaping the diaphragm 31 into a desired form. After cutting, mechanical polishing involves polishing the diaphragm 31 with cerium oxide particles. It is assumed that the cerium oxide particles adhere to the diaphragm 31 during mechanical polishing. The manufacturing process for the cleaning head 30 may also include flame polishing between cutting and mechanical polishing, as an example.

[0048] The inventors of this application considered removing cerium oxide particles adhering to the diaphragm 31 by supplying at least one of the first chemical solution L1 and the second chemical solution L2, described later, to the diaphragm 31 before dummy cleaning. Removing cerium oxide particles not only shortens the time it takes for the number of particles P adhering to the dummy substrate to settle at a constant value, but also reduces that constant value.

[0049] The first chemical solution L1 removes cerium oxide particles attached to the diaphragm 31 by dissolving them. The first chemical solution L1 is not particularly limited as long as it dissolves cerium oxide, but for example, it is an aqueous mixture of sulfuric acid (H2SO4) and hydrogen peroxide (H2O2) (so-called SPM), or an aqueous solution containing sulfuric acid. The first chemical solution L1 may be heated to promote the dissolution of cerium oxide.

[0050] The first chemical solution L1 is stored in the first chemical solution tank 101, for example, as shown in Figure 5. The first chemical solution L1 can be supplied to the diaphragm 31 by immersing the diaphragm 31 in the first chemical solution L1 stored in the first chemical solution tank 101. The method of supplying the first chemical solution L1 is not particularly limited. For example, the first chemical solution L1 may be sprayed onto the diaphragm 31 using a sprayer.

[0051] The second chemical solution L2 dissolves the surface of the diaphragm 31, thereby removing cerium oxide particles from the diaphragm 31. The second chemical solution L2 is appropriately selected depending on the material of the diaphragm 31, but for example, it is an aqueous solution containing hydrofluoric acid (HF) or an aqueous solution containing an alkaline detergent. The aqueous solution containing an alkaline detergent preferably has a pH of 9 or higher. If the pH is 9 or higher, the Si-O bond can be broken and SiO2 can be etched. The alkaline detergent contains, for example, NaOH or KOH. The second chemical solution L2 may be heated to promote the dissolution of the cleaning head 30.

[0052] The second chemical solution L2 is stored in the second chemical solution tank 102, for example, as shown in Figure 6. The second chemical solution L2 can be supplied to the diaphragm 31 by immersing it in the second chemical solution L2 stored in the second chemical solution tank 102. The method of supplying the second chemical solution L2 is not particularly limited. For example, the second chemical solution L2 may be sprayed onto the diaphragm 31 using a sprayer.

[0053] The first chemical solution L1 and the second chemical solution L2 may be supplied not only to the vibrating surface 31a of the diaphragm 31 but also to the side surface 31c. Furthermore, although not shown, if the discharge port of the nozzle 20 is formed on the vibrating surface 31a of the diaphragm 31, it is preferable to supply the first chemical solution L1 and the second chemical solution L2 to the inside of the nozzle 20 as well. It is preferable to supply the first chemical solution L1 and the second chemical solution L2 to the portion of the diaphragm 31 that comes into contact with the cleaning solution.

[0054] Either the first chemical solution L1 or the second chemical solution L2 may be used, but it is preferable to use both. When using both the first chemical solution L1 and the second chemical solution L2, it is preferable to supply the first chemical solution L1 to the diaphragm 31 first, and then supply the second chemical solution L2 to the diaphragm 31.

[0055] If the first chemical solution L1 is supplied to the diaphragm 31, and then the second chemical solution L2 is supplied to the diaphragm 31, surface roughness of the diaphragm 31 can be suppressed compared to when the order is reversed. This is because if the particles P adhering to the surface of the diaphragm 31 are dissolved first, the surface of the diaphragm 31 can be dissolved uniformly.

[0056] After supplying an acidic solution as the first solution L1 or second solution L2 to the diaphragm 31, it is preferable to supply an alkaline solution to the diaphragm 31. The alkaline solution can adjust the zeta potential of both the cleaning head 30 and the particles P to the same polarity (e.g., negative), thereby suppressing the re-adhesion of particles P. The alkaline solution is, for example, an aqueous solution containing an alkaline detergent, or a mixed aqueous solution of ammonium hydroxide (NH4OH) and hydrogen peroxide (H2O2) (so-called SC-1).

[0057] After supplying the first chemical solution L1 or the second chemical solution L2 to the diaphragm 31, it is preferable to supply a rinsing solution to the diaphragm 31 to remove any remaining chemical residue. Pure water such as DIW (deionized water) is used as the rinsing solution.

[0058] Furthermore, it is also possible to remove cerium oxide particles from the diaphragm 31 by dry etching the surface of the diaphragm 31. For example, fluorine plasma can be used for dry etching the diaphragm 31.

[0059] The number of cerium oxide particles adhering to the vibrating surface 31a of the cleaning head 30 can be expressed by the surface density of Ce element detected by total reflection X-ray fluorescence (TXRF) analysis of the vibrating surface 31a. The lower the surface density of Ce element, the fewer the number of cerium oxide particles.

[0060] The inventor of the present application will explain in detail in the column of the embodiments. When the areal density of the Ce element detected by the TXRF method on the vibration surface 31a of the cleaning head 30 using the chemical solution is 30×10 10 atoms / cm 2 or less, it has been found that the number of particles P adhering to the substrate W can be reduced by ultrasonic cleaning.

[0061] When the areal density of the Ce element on the vibration surface 31a of the cleaning head 30 is 30×10 10 atoms / cm 2 or less, the areal density of the cerium oxide particles adhering to the vibration surface 31a is low. Therefore, the number of particles P detaching from the vibration surface 31a of the cleaning head 30 can be reduced, and the number of particles P adhering to the substrate W by ultrasonic cleaning can be reduced.

[0062] In addition, the method of making the areal density of the Ce element on the vibration surface 31a of the cleaning head 30 30×10 10 atoms / cm 2 or less is not limited to the method of supplying at least one of the first chemical solution L1 and the second chemical solution L2 to the diaphragm 31. For example, the density of the cerium oxide particles may be within a predetermined range by scrub cleaning using a brush or a sponge.

[0063] From the viewpoint of reducing the number of particles P adhering to the substrate W by ultrasonic cleaning, the areal density of the Ce element on the vibration surface 31a of the cleaning head 30 is preferably 10×10 10 atoms / cm 2 or less, more preferably 1×10 10 atoms / cm 2 or less. The areal density of the Ce element on the vibration surface 31a of the cleaning head 30 may be 0 atoms / cm 2 or more.

[0064] The vibrating surface 31a of the cleaning head 30 preferably has a surface density of 1.0% or less for all elements excluding the most abundant element among the elements with atomic numbers 13-30 and 33-72 detected by the TXRF method, with the surface density of the most abundant element being taken as 100%. If the material of the vibrating surface 31a is SiO2, the most abundant element is Si. If the material of the vibrating surface 31a is Al2O3, the most abundant element is Al. The atomic number of Ce is 58.

[0065] The element with atomic number 13 is Al. The element with atomic number 30 is Zn. The element with atomic number 33 is As. The element with atomic number 72 is Hf. Here, it is assumed that a tungsten (W) beam will be used as the X-ray source for the TXRF method. When using a W beam, Ga (atomic number 31) and Ge (atomic number 32) are difficult to detect.

[0066] If the sum of the surface densities of all elements except the most abundant element is 1.0% or less, then the number of particles P adhering to the vibrating surface 31a will be small. Therefore, the number of particles P detached from the vibrating surface 31a of the cleaning head 30 can be reduced, and the number of particles P adhering to the substrate W by ultrasonic cleaning can be reduced.

[0067] The sum of the surface densities of all elements except the most abundant element is preferably 0.5% or less, from the viewpoint of reducing the number of particles P adhering to the substrate W. The sum of the surface densities of all elements except the most abundant element may be 0.0% or more, but from the viewpoint of productivity, it is preferably 0.1% or more.

[0068] Next, with reference to Figure 8, a method for manufacturing the EUVL mask blank 200 shown in Figure 11 will be described. The method for manufacturing the EUVL mask blank 200 includes steps S101 to S107. For example, the substrate 210 shown in Figures 9 and 10 is prepared in advance. Steps S101 to S104 are included in the manufacturing method of the substrate.

[0069] The substrate 210 includes a first main surface 211 and a second main surface 212 facing the opposite direction to the first main surface 211. The first main surface 211 is rectangular. In this specification, a rectangular shape includes a shape with chamfered corners. A rectangle also includes a square. The second main surface 212 faces the opposite direction to the first main surface 211. The second main surface 212 is also rectangular, similar to the first main surface 211.

[0070] The substrate 210 also includes four end faces 213, four first chamfered faces 214, and four second chamfered faces 215. The end faces 213 are perpendicular to the first main face 211 and the second main face 212. The first chamfered faces 214 are formed at the boundary between the first main face 211 and the end face 213. The second chamfered faces 215 are formed at the boundary between the second main face 212 and the end face 213. In this embodiment, the first chamfered faces 214 and the second chamfered faces 215 are so-called C-chamfered faces, but they may also be R-chamfered faces.

[0071] The substrate 210 is, for example, a glass substrate. Preferably, the glass of the substrate 210 is quartz glass containing TiO2. Compared to general soda-lime glass, quartz glass has a smaller coefficient of thermal expansion and less dimensional change due to temperature changes. The quartz glass may contain 80% to 95% by mass of SiO2 and 4% to 17% by mass of TiO2. When the TiO2 content is 4% to 17% by mass, the coefficient of thermal expansion at room temperature is approximately zero, and there is almost no dimensional change at room temperature. The quartz glass may also contain third components or impurities other than SiO2 and TiO2.

[0072] In a plan view, the dimensions of the substrate 210 are, for example, 152 mm in length and 152 mm in width. The length and width dimensions may be greater than 152 mm.

[0073] The substrate 210 has a central region 211A and a peripheral region 211B on its first main surface 211. The central region 211A is a square region excluding the rectangular frame-shaped peripheral region 211B that surrounds the central region 211A, and is the region that is processed to the desired flatness by steps S101 to S104, and is the quality assurance region. The quality assurance region has a size of, for example, 142 mm in length and 142 mm in width. The four sides of the central region 211A are parallel to the four end faces 213. The center of the central region 211A coincides with the center of the first main surface 211.

[0074] Although not shown in the figures, the second main surface 212 of the substrate 210 also has a central region and a peripheral region, similar to the first main surface 211. The central region of the second main surface 212 is a square region, similar to the central region of the first main surface 211, and is the region that is processed to the desired flatness by steps S101 to S104 in Figure 8, and is the quality assurance region. The quality assurance region has dimensions of, for example, 142 mm in length and 142 mm in width.

[0075] Step S101 includes polishing the first main surface 211 and the second main surface 212 of the substrate 210. In this embodiment, the first main surface 211 and the second main surface 212 are polished simultaneously using a double-sided polishing machine (not shown), but they may also be polished sequentially using a single-sided polishing machine (not shown). In step S101, the substrate 210 is polished while supplying polishing slurry between the polishing pad and the substrate 210.

[0076] As polishing pads, for example, urethane-based polishing pads, nonwoven fabric-based polishing pads, or suede-based polishing pads can be used. The polishing slurry contains an abrasive and a dispersion medium. The abrasive is, for example, cerium oxide particles. The dispersion medium is, for example, water or an organic solvent. The first main surface 211 and the second main surface 212 may be polished multiple times with abrasives of different materials or particle sizes.

[0077] The abrasive used in step S101 is not limited to cerium oxide particles, but may also be silicon oxide particles, aluminum oxide particles, zirconium oxide particles, titanium oxide particles, diamond particles, or silicon carbide particles, for example.

[0078] Step S102 includes measuring the surface shapes of the first main surface 211 and the second main surface 212 of the substrate 210. For measuring the surface shapes, a non-contact measuring instrument such as a laser interferometry instrument is used so as not to damage the surface. The measuring instrument measures the surface shapes of the central region 211A of the first main surface 211 and the central region of the second main surface 212.

[0079] Step S103 includes referring to the measurement results from step S102 and locally machining the first main surface 211 and the second main surface 212 of the substrate 210 in order to improve flatness. The first main surface 211 and the second main surface 212 are locally machined in sequence. The order in which they are machined does not matter and is not particularly limited.

[0080] For localized machining, at least one of the following methods may be used: GCIB (Gas Cluster Ion Beam) method, PCVM (Plasma Chemical Vaporization Machining) method, magnetic fluid polishing method, and polishing with a rotary polishing tool.

[0081] Step S104 includes performing finish polishing on the first main surface 211 and the second main surface 212 of the substrate 210. In this embodiment, the first main surface 211 and the second main surface 212 are polished simultaneously using a double-sided polishing machine (not shown), but they may be polished sequentially using a single-sided polishing machine (not shown). In step S104, the substrate 210 is polished while supplying polishing slurry between the polishing pad and the substrate 210. The polishing slurry contains an abrasive. The abrasive is, for example, colloidal silica particles.

[0082] Step S105 includes forming a conductive film 240, as shown in Figure 11, in the central region of the second main surface 212 of the substrate 210. The conductive film 240 is used to attract the EUVL mask to the electrostatic chuck of the exposure apparatus. The conductive film 240 is formed of, for example, chromium nitride (CrN). For example, sputtering can be used as a method for forming the conductive film 240.

[0083] Step S106 includes forming a multilayer reflective film 220, as shown in Figure 11, on the central region 211A of the first main surface 211 of the substrate 210. The multilayer reflective film 220 reflects EUV light. The multilayer reflective film 220 is formed by alternately stacking high refractive index layers and low refractive index layers. The high refractive index layers are formed from silicon (Si), for example, and the low refractive index layers are formed from molybdenum (Mo), for example. As a method for depositing the multilayer reflective film 220, sputtering methods such as ion beam sputtering and magnetron sputtering are used.

[0084] Step S107 includes forming an absorption film 230, as shown in Figure 11, on the multilayer reflective film 220 formed in step S106. The absorption film 230 absorbs EUV. The absorption film 230 may also be a phase-shift film, which may shift the phase of EUV. The absorption film 230 is formed from a single metal, alloy, nitride, oxide, oxynitride, etc., containing at least one element selected from tantalum (Ta), chromium (Cr), and palladium (Pd). For example, sputtering can be used as a method for depositing the absorption film 230.

[0085] In this embodiment, steps S106 to S107 are performed after step S105, but they may also be performed before step S105.

[0086] By following the steps S101 to S107 described above, the EUVL mask blank 200 shown in Figure 11 is obtained. The EUVL mask blank 200 has a conductive film 240, a substrate 210, a multilayer reflective film 220, and an absorption film 230 in this order. In addition to the conductive film 240, substrate 210, multilayer reflective film 220, and absorption film 230, the EUVL mask blank 200 may also include another film.

[0087] For example, the EUVL mask blank 200 may further include a low-reflection film. The low-reflection film is formed on the absorption film 230. Subsequently, an aperture pattern 231 is formed on both the low-reflection film and the absorption film 230. The low-reflection film is used to inspect the aperture pattern 231 and has lower reflectivity than the absorption film 230 with respect to inspection light. The low-reflection film is formed, for example, from TaON or TaO. For example, sputtering can be used as a method for depositing the low-reflection film.

[0088] Furthermore, the EUVL mask blank 200 may also include a protective film. The protective film is formed between the multilayer reflective film 220 and the absorption film 230. The protective film protects the multilayer reflective film 220 from being etched when the absorption film 230 is etched to form an aperture pattern 231 in the absorption film 230. The protective film is formed of, for example, Ru, Si, or TiO2. For example, sputtering can be used as a method for depositing the protective film.

[0089] As shown in Figure 12, the EUVL mask 201 is obtained by forming an aperture pattern 231 in the absorption film 230 of the EUVL mask blank 200. Photolithography and etching methods are used to form the aperture pattern 231. Therefore, the resist film used to form the aperture pattern 231 may be included in the EUVL mask blank 200.

[0090] Incidentally, during the manufacturing process of the EUVL mask blank 200, the substrate 210 or various functional films formed on the substrate 210 may be cleaned. Cleaning methods include those utilizing chemical reactions with acids or alkalis, those utilizing physical actions, or combinations thereof. Cleaning methods utilizing physical actions include ultrasonic cleaning, scrubbing, or two-fluid cleaning. Two-fluid cleaning involves spraying a cleaning solution and gas while mixing them.

[0091] Ultrasonic cleaning is performed using, for example, the substrate cleaning apparatus 1 shown in Figure 1. Preferably, ultrasonic cleaning is performed at least one of the following steps: between steps S104 and S105, between steps S105 and S106, between steps S106 and S107, or after step S107. Although not shown, ultrasonic cleaning may also be performed before or after the application of a low-reflection film, hard mask film, or protective film. [Examples]

[0092] The experimental data is described below. Example 1 below is a comparative example, and Examples 2 to 4 below are examples of the actual cases. The experimental conditions and evaluation results for Examples 1 to 4 are shown in Table 1.

[0093] [Table 1]

[0094] In Examples 1 to 4, the cleaning head was pre-treated by supplying the various cleaning solutions listed in Table 1 to the cleaning head's diaphragm in the order of the numbers listed in Table 1. After that, dummy cleaning was performed, followed by substrate cleaning. The material of the cleaning head's diaphragm was quartz glass. The diaphragm was pre-treated by cutting and mechanical polishing in that order. For mechanical polishing, cerium oxide particles were used to polish the diaphragm.

[0095] In Table 1, the "surface density of Ce" and the "surface density of all elements except Si" were measured using the TXRF method after pretreatment of the cleaning head and before dummy cleaning. A tungsten (W) beam was used as the X-ray source for the TXRF method, and the surface densities of elements with atomic numbers 13-30 and 33-72 were measured. Si was the most abundant element. The "surface density of all elements except Si" is the sum of the surface densities of all elements except Si, with the surface density of Si set to 100%. The detection limit (lower detection limit) of the measuring device used to measure the surface density of various elements by the TXRF method is 0.8 × 10⁻⁶. 10 atoms / cm 2 That was the case.

[0096] Furthermore, since measuring the surface density of various elements on the vibrating surface of the cleaning head using the TXRF method would destroy the cleaning head, a quartz glass plate was prepared separately from the cleaning head. The quartz glass plate was pre-processed by cutting and mechanical polishing in the same order as the vibrating surface of the cleaning head. For mechanical polishing, cerium oxide particles were used to polish the quartz glass plate. After supplying the various cleaning solutions listed in Table 1 to the quartz glass plate in the order of the numbers listed in Table 1, the surface density of various elements on the surface of the quartz glass plate was measured using the TXRF method.

[0097] In Table 1, "dummy cleaning time" is the time it takes for the number of particles adhering to the dummy substrate by ultrasonic cleaning to settle at a constant value. The number of particles adhering to the dummy substrate by ultrasonic cleaning was measured by measuring the number of particles on the dummy substrate before and after ultrasonic cleaning and calculating the difference.

[0098] In Table 1, "Substrate Particle Count" is the average number of particles adhering to the substrate by ultrasonic cleaning after dummy cleaning. The number of particles adhering to the substrate by ultrasonic cleaning was measured by measuring the number of particles on the substrate before and after ultrasonic cleaning and calculating the difference.

[0099] The particle count was measured using Lasertec's MAGICS series. The particle count represents the number of defects converted to a 40nm size SiO2 particle.

[0100] As shown in Table 1, in Example 1, neither the first chemical solution (a chemical solution that dissolves cerium oxide) nor the second chemical solution (a chemical solution that dissolves quartz glass) was supplied to the diaphragm of the cleaning head during the pretreatment of the cleaning head, resulting in a long "dummy cleaning time" and a high "number of particles on the substrate." The surface of the quartz glass plate subjected to the same pretreatment as the cleaning head had a "surface density of Ce" of 30 × 10⁶. 10 atoms / cm 2 It exceeded this value, and the "surface density of all elements except Si" exceeded 1.0%.

[0101] On the other hand, in Example 2, "HF" was supplied to the diaphragm of the cleaning head during the pretreatment of the cleaning head, resulting in a shorter "dummy cleaning time" and fewer "particles on the substrate." "HF" corresponds to the second chemical solution (a chemical solution that dissolves quartz glass). The surface of the quartz glass plate subjected to the same pretreatment as the cleaning head had a "surface density of Ce" of 30 × 10⁻¹⁶. 10 atoms / cm 2 The results were as follows:

[0102] In Example 3, "SPM" and "HF" were supplied to the cleaning head's diaphragm in this order during the pretreatment of the cleaning head, resulting in a shorter "dummy cleaning time" and a lower "number of particles on the substrate." "SPM" corresponds to the first chemical solution (a chemical solution that dissolves cerium oxide), and "HF" corresponds to the second chemical solution (a chemical solution that dissolves quartz glass). The surface of a quartz glass plate subjected to the same pretreatment as the cleaning head had a "surface density of Ce" of 1 × 10⁻⁶. 10 atoms / cm 2 The following conditions were met, and the "surface density of all elements except Si" was 1.0% or less.

[0103] In Example 4, "SPM" and "alkaline detergent" were supplied to the diaphragm of the cleaning head in this order during the pretreatment of the cleaning head. "SPM" corresponds to the first chemical solution (a chemical solution that dissolves cerium oxide), and "alkaline detergent" corresponds to the second chemical solution (a chemical solution that dissolves quartz glass). The surface of the quartz glass plate that underwent the same pretreatment as the cleaning head had a "surface density of Ce" of 10 × 10⁻¹⁴. 10 atoms / cm 2 The following conditions were met, and the "surface density of all elements except Si" was 1.0% or less.

[0104] The following additional information is disclosed regarding the above-described embodiment. [Note 1] An ultrasonic cleaning head having a vibrating surface that is positioned opposite the upper surface of a substrate at a distance from it and in contact with a liquid film formed on the upper surface of the substrate, The aforementioned vibrating surface has a surface density of Ce element detected by total internal reflection X-ray fluorescence analysis of 30 × 10⁻¹⁰ 10 atoms / cm 2The ultrasonic cleaning head is as follows. [Note 2] The aforementioned vibrating surface has a surface density of Ce element detected by total internal reflection X-ray fluorescence analysis of 10 × 10 10 atoms / cm 2 The ultrasonic cleaning head is as follows, as described in Appendix 1. [Note 3] The aforementioned vibrating surface has a surface density of Ce element detected by total internal reflection X-ray fluorescence analysis of 1 × 10⁻¹⁶ 10 atoms / cm 2 The ultrasonic cleaning head is as follows, as described in Appendix 2. [Note 4] The vibrating surface is an ultrasonic cleaning head as described in any one of the appendices 1 to 3, wherein, when the surface density of the most abundant element among elements with atomic numbers 13 to 30 and 33 to 72 detected by total internal reflection X-ray fluorescence analysis is taken as 100%, the sum of the surface densities of all elements excluding the most abundant element is 1.0% or less. [Note 5] The ultrasonic cleaning head described in Appendix 4, wherein the most abundant element is Si. [Note 6] The ultrasonic cleaning head according to Appendix 4 or 5, wherein the material of the vibrating surface is SiO2. [Note 7] By supplying at least one of a first chemical solution that dissolves cerium oxide and a second chemical solution that dissolves the vibrating surface of an ultrasonic cleaning head, the surface density of the element Ce detected by total internal reflection X-ray fluorescence analysis of the vibrating surface is increased to 30 × 10⁻¹⁰. 10 atoms / cm 2 Do the following, The surface density of the element Ce detected by total internal reflection X-ray fluorescence analysis of the vibrating surface is 30 × 10 10 atoms / cm 2 After the following, a liquid film is formed between the vibrating surfaces of the opposing ultrasonic cleaning heads and the upper surface of the substrate, while vibration is applied from the vibrating surfaces to the liquid film. A substrate cleaning method having the following characteristics. [Note 8] A substrate cleaning apparatus comprising an ultrasonic cleaning head as described in any one of the appendices 1 to 6, a holding unit for holding the substrate horizontally, and a nozzle for forming the liquid film on the upper surface of the substrate held by the holding unit. [Note 9] A method for manufacturing a substrate, comprising cleaning the substrate using the substrate cleaning apparatus described in Appendix 8. [Note 10] A method for manufacturing an EUVL mask blank, comprising cleaning a glass substrate or a functional film formed on the glass substrate using the substrate cleaning apparatus described in Appendix 8.

[0105] The ultrasonic cleaning head, substrate cleaning method, substrate cleaning apparatus, substrate manufacturing method, and EUVL mask blank manufacturing method described above have been explained, but this disclosure is not limited to the embodiments described above. Various changes, modifications, substitutions, additions, deletions, and combinations are possible within the scope of the claims. These also naturally fall within the technical scope of this disclosure.

[0106] This application claims priority based on Japanese Patent Application No. 2022-032933, filed with the Japan Patent Office on March 3, 2022, and the entire contents of Japanese Patent Application No. 2022-032933 are incorporated herein by reference. [Explanation of Symbols]

[0107] 30. Cleaning head (ultrasonic cleaning head) 31a Vibration surface W board Wa substrate top surface F liquid film

Claims

1. An ultrasonic cleaning head having a vibrating surface that is positioned opposite the upper surface of a substrate at a distance from it and in contact with a liquid film formed on the upper surface of the substrate, The aforementioned vibrating surface has a surface density of Ce element detected by total internal reflection X-ray fluorescence analysis of 30 × 10⁻¹⁰ １０ atoms / cm ２ The ultrasonic cleaning head is as follows.

2. The aforementioned vibrating surface has a surface density of Ce element detected by total internal reflection X-ray fluorescence analysis of 10 × 10 １０ atoms / cm ２ The ultrasonic cleaning head according to claim 1, which is as follows:

3. The aforementioned vibrating surface has a surface density of Ce element detected by total internal reflection X-ray fluorescence analysis of 1 × 10⁻¹⁶ １０ atoms / cm ２ The ultrasonic cleaning head according to claim 2, which is as follows:

4. The ultrasonic cleaning head according to any one of claims 1 to 3, wherein the vibrating surface has a surface density of 1.0% or less when the surface density of the most abundant element among elements with atomic numbers 13 to 30 and 33 to 72 detected by total internal reflection X-ray fluorescence analysis is taken as 100%.

5. The ultrasonic cleaning head according to claim 4, wherein the most abundant element is Si.

6. The material of the vibrating surface is SiO ２ The ultrasonic cleaning head according to claim 4.

7. By supplying at least one of a first chemical solution that dissolves cerium oxide and a second chemical solution that dissolves the vibration surface to the vibration surface of the ultrasonic cleaning head, the surface density of Ce element detected by total reflection X-ray fluorescence analysis of the vibration surface is reduced to 30×10 １０ atoms / cm ２ or less, and The surface density of the Ce element detected by total internal reflection X-ray fluorescence analysis of the vibrating surface is 30 × 10 １０ atoms / cm ２ After the following, a liquid film is formed between the vibrating surfaces of the opposing ultrasonic cleaning heads and the upper surface of the substrate, while vibration is applied from the vibrating surfaces to the liquid film. A substrate cleaning method having the following characteristics.

8. A substrate cleaning apparatus comprising: an ultrasonic cleaning head according to any one of claims 1 to 3; a holding unit for holding the substrate horizontally; and a nozzle for forming the liquid film on the upper surface of the substrate held by the holding unit.

9. A method for manufacturing a substrate, comprising cleaning the substrate using the substrate cleaning apparatus described in claim 8.

10. A method for manufacturing an EUVL mask blank, comprising cleaning a glass substrate or a functional film formed on the glass substrate using the substrate cleaning apparatus described in claim 8.

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