Ultrasonic cleaning device, substrate cleaning method, and method for manufacturing mask blank for euvl

Abstract

To provide a technique for measuring a parameter that is an alternative to the spacing between a cleaning head and a substrate, or an acoustic pressure acting on the substrate.SOLUTION: An ultrasonic cleaning device includes a cleaning head equipped with a holding unit for holding a substrate horizontally, a nozzle for forming a liquid film on the upper surface of the substrate held by the holding unit, a vibration surface in contact with the liquid film, and an ultrasonic transducer for vibrating the vibration surface, an ultrasonic oscillator that is electrically connected to the ultrasonic transducer via wiring, and a measurement unit for measuring at least one of incident power from the ultrasonic oscillator toward the ultrasonic transducer and reflected power returning from the ultrasonic transducer to the ultrasonic oscillator in the wiring.SELECTED DRAWING: Figure 14

Description

[Technical field]

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

[0002] In recent years, with the miniaturization of semiconductor devices, EUV lithography (EUVL), an exposure technology using extreme ultraviolet (EUV) light, has been developed. EUV 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 with a wavelength of about 13.5 nm is mainly being considered.

[0003] In EUVL, a reflective mask is used. A reflective mask has, in this order, a substrate such as a glass substrate, a multilayer reflective film that reflects EUV, and an absorbing film that absorbs EUV. An aperture pattern is formed in the absorbing film. In EUVL, the aperture pattern in the absorbing film is transferred to a target substrate such as a semiconductor substrate. Transferring includes reducing and transferring.

[0004] During the manufacturing process of EUVL mask blanks, the glass substrate or the functional film formed on the glass substrate may be cleaned. One of the cleaning methods is ultrasonic cleaning.

[0005] The cleaning method described in Patent Document 1 includes spraying a cleaning liquid to which ultrasonic waves have been applied from a nozzle onto the upper surface of a rotating substrate.The cleaning method described in Patent Document 2 includes supplying a cleaning liquid between the upper surface of the rotating substrate and the lower surface of a cleaning head, and applying ultrasonic waves to the cleaning liquid from the lower surface of the cleaning head, thereby cleaning the upper surface of the substrate.

[0006] In the cleaning method of Patent Document 2, when cleaning the upper surface of a substrate, a cleaning head is moved in a direction perpendicular to the center line of rotation of the substrate while rotating the substrate. The cleaning head is moved horizontally between a position directly above the center of the upper surface of the substrate and a position directly above the periphery of the upper surface of the substrate. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2013-158664 A [Patent Document 2] JP 2001-087725 A Summary of the Invention [Problem to be solved by the invention]

[0008] When the distance between the cleaning head and the substrate fluctuates, the sound pressure acting on the substrate fluctuates. Therefore, in order to suppress the fluctuation of the sound pressure, it is conceivable to measure the distance between the cleaning head and the substrate or the sound pressure acting on the substrate. However, it may be difficult to measure the distance between the cleaning head and the substrate or the sound pressure acting on the substrate. For example, it is difficult to measure the distance between the cleaning head and the substrate when the space between the cleaning head and the substrate is filled with cleaning liquid. Also, while it is easy to measure the sound pressure acting on the center of the substrate, it is difficult to measure the sound pressure acting on the periphery of the substrate.

[0009] One aspect of the present disclosure provides a technique for measuring a parameter that is a proxy for the spacing between the cleaning head and the substrate, or the acoustic pressure acting on the substrate. [Means for solving the problem]

[0010] An ultrasonic cleaning device according to one embodiment of the present disclosure includes a holding unit that holds a substrate horizontally, a nozzle that forms a liquid film on the upper surface of the substrate held by the holding unit, a cleaning head including a vibration surface that contacts the liquid film and an ultrasonic transducer that vibrates the vibration surface, an ultrasonic oscillator that is electrically connected to the ultrasonic transducer via wiring, and a measurement unit that measures at least one of the incident power directed from the ultrasonic oscillator to the ultrasonic transducer and the reflected power returning from the ultrasonic transducer to the ultrasonic transducer in the wiring. Effect of the Invention

[0011] According to one aspect of the present disclosure, at least one of the incident power from the ultrasonic generator to the ultrasonic transducer and the reflected power from the ultrasonic transducer back to the ultrasonic generator can be measured as a parameter replacing the distance between the cleaning head and the substrate or the sound pressure acting on the substrate. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a side view showing an ultrasonic cleaning device according to one embodiment. [Diagram 2] FIG. 2 is a cross-sectional view showing an example of the internal structure of the cleaning head. [Diagram 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 a movement trajectory of the cleaning head. [Diagram 5] FIG. 5 is a diagram showing an example of the relationship between the output of an ultrasonic transducer and the sound pressure acting on a substrate. [Figure 6] FIG. 6 is a cross-sectional view showing an example of a standing wave formed between the cleaning head and the substrate. [Figure 7] FIG. 7 is a diagram showing an example of the relationship between the distance between the cleaning head and the substrate and the sound pressure acting on the substrate. [Figure 8] FIG. 8 is a plan view showing an example of points at which the distance between the cleaning head and the substrate is measured. [Figure 9] FIG. 9 is a diagram showing an example of the inclination of the center line of rotation of the cleaning head. [Figure 10] FIG. 10 is a diagram showing an example of variation in the distance between the cleaning head and the substrate due to the inclination of the center line of rotation of the cleaning head. [Figure 11] FIG. 11 is a diagram showing an example of the inclination of the normal to the upper surface of the substrate. [Figure 12] FIG. 12 is a diagram showing an example of variation in the distance between the cleaning head and the substrate due to the inclination of the normal to the upper surface of the substrate. [Figure 13]FIG. 13 is a diagram showing an example of variation in the distance between the cleaning head and the substrate due to the inclination of the rotation center line of the cleaning head and the inclination of the normal line to the upper surface of the substrate. [Figure 14] FIG. 14 is a diagram showing an example of an ultrasonic oscillator, an ultrasonic transducer, and a measuring unit. [Figure 15] FIG. 15 is a diagram showing an example of the relationship between the distance between the cleaning head and the substrate, the sound pressure acting on the substrate, and the reflected power. [Figure 16] FIG. 16 is a diagram showing an example of the correlation between the sound pressure and the reflected power shown in FIG. [Figure 17] FIG. 17 is a diagram showing an example of the difference in frequency spectrum between the presence and absence of gap control. [Figure 18] FIG. 18 is a diagram showing an example of the difference in the number of defects depending on whether or not gap control is performed. [Figure 19] FIG. 19 is a flowchart showing a method for manufacturing an EUVL mask blank according to an embodiment. [Figure 20] FIG. 20 is a cross-sectional view showing an example of a substrate. [Figure 21] FIG. 21 is a plan view of the substrate of FIG. [Figure 22] FIG. 22 is a cross-sectional view showing an example of an EUVL mask blank. [Diagram 23] FIG. 23 is a cross-sectional view showing an example of an EUVL mask. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In each drawing, the same or corresponding components are denoted by the same reference numerals, and the description may be omitted. In the specification, the symbol "~" indicating a range of values ​​means that the values ​​before and after the symbol are included as the lower and upper limits.

[0014] An ultrasonic cleaning apparatus 1 according to one embodiment will be described with reference to Fig. 1 to Fig. 4. The ultrasonic cleaning apparatus 1 cleans the substrate W by applying ultrasonic vibrations to a liquid film F formed on the substrate W. Particles adhering to the substrate W can be removed. The ultrasonic cleaning apparatus 1 includes 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.

[0015] The holder 10 holds the substrate W horizontally. When viewed from above, the substrate W is rectangular (see FIG. 4), but may be circular. The substrate W includes a glass substrate, a silicon wafer, or a compound semiconductor wafer. The substrate W may include a functional film formed on a glass substrate or the like. The functional film is, for example, a light reflecting film, a light absorbing film, a conductive film, or an insulating film.

[0016] The holder 10 includes a plurality of pins 11 arranged at intervals along the periphery of the substrate W, as shown in Fig. 1 for example. The pins 11 hold the periphery of the substrate W. The substrate W is placed on the pins 11. Since there is a space below the substrate W, it is also possible to attach a sensor to the underside of the substrate W, as described below. The holder 10 may hold the substrate W by suction.

[0017] The nozzle 20 forms a liquid film F by supplying a cleaning liquid to the upper surface Wa of the substrate W held by the holder 10. The upper surface Wa of the substrate W is also referred to as the substrate upper surface Wa. The nozzle 20 supplies the cleaning liquid, for example, near the center of the substrate upper surface Wa. The substrate W is rotating, and the cleaning liquid on the substrate W spreads from the center to the periphery of the substrate W due to centrifugal force. As a result, a liquid film F is formed on the entire substrate upper surface Wa. The nozzle 20 may be provided outside the cleaning head 30 as shown in FIG. 1, or may be provided inside the cleaning head 30 (not shown).

[0018] The nozzle 20 is connected to a supply source 22 of the cleaning liquid 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, the cleaning liquid is supplied from the supply source 22 to the nozzle 20, and the nozzle 20 ejects the cleaning liquid. When the valve 23 closes the flow path of the supply line 21, the nozzle 20 stops ejecting the cleaning liquid.

[0019] The cleaning liquid is, 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, X, and Z, or a mixture of pure water, Y, and Z.

[0020] The cleaning liquid may have at least one gas dissolved therein 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, it is possible to improve the efficiency of cavitation generation and the efficiency of particle removal. The gas dissolved in the cleaning liquid is preferably H2 gas, CO2 gas, or N2 gas, and more preferably CO2 gas.

[0021] 2, the cleaning head 30 includes a vibration surface 31a that contacts the liquid film F, and an ultrasonic vibrator 32 that vibrates the vibration surface 31a. The cleaning head 30 includes a vibration plate 31. The vibration plate 31 has a downward vibration surface 31a that contacts the liquid film F, and an upward mounting surface 31b to which the ultrasonic vibrator 32 is attached.

[0022] The vibration surface 31a is disposed parallel to the substrate upper surface Wa. The size of the vibration surface 31a is, for example, smaller than the size of the substrate upper surface Wa. The shape of the vibration surface 31a is, for example, circular. When the nozzle 20 is provided inside the cleaning head 30, the nozzle 20 has an outlet formed on the vibration surface 31a.

[0023] The mounting surface 31b may be disposed parallel to the vibration surface 31a as shown in Fig. 2, or may be disposed obliquely to the vibration surface 31a as shown in Fig. 3. In Fig. 3, θ is the angle between the normal line of the vibration surface 31a and the normal line of the mounting surface 31b. The normal direction of the mounting surface 31b is the vibration direction of the ultrasonic transducer 32.

[0024] The ultrasonic transducer 32 vibrates the vibration surface 31a to apply ultrasonic vibrations to the liquid film F and sound pressure to the substrate W. This makes it possible to peel off particles adhering to the upper surface Wa of the substrate. The output of the ultrasonic transducer 32 is controlled by the control unit 90. When the distance G between the cleaning head 30 and the substrate W is constant, the greater the output PW of the ultrasonic transducer 32, the greater the sound pressure SP acting on the substrate W (see FIG. 5). In this specification, the sound pressure SP does not refer to an instantaneous value but to an effective value.

[0025] The relationship between the output PW of the ultrasonic transducer 32 and the sound pressure SP acting on the substrate W (for example, the relationship shown in FIG. 5) is stored in advance in the storage unit 92 of the control unit 90. The relationship between the distance G between the cleaning head 30 and the substrate W and the sound pressure SP acting on the substrate W (for example, the relationship shown in FIG. 7) is also stored in advance in the storage unit 92 of the control unit 90. The relationship between the distance G and the sound pressure SP will be described later.

[0026] As shown in FIG. 1, the rotating unit 40 rotates the substrate W together with the holding unit 10. The rotation center line 10R of the holding unit 10 is installed vertically. The holding unit 10 holds the substrate W so that the rotation center line 10R passes through the center of the substrate W. The rotating unit 40 includes a servo motor 41. The rotational driving force of the servo motor 41 may be transmitted to the holding unit 10 via a pulley and belt or gears (not shown). The servo motor 41 transmits information regarding the rotational position of the holding unit 10 to the control unit 90. The rotational position of the holding unit 10 is represented by a rotation angle.

[0027] The first moving unit 50 moves the cleaning head 30 in a horizontal direction perpendicular to the rotation center line 10R of the holder 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 a servo motor 51. The servo motor 51 transmits information regarding the horizontal position of the cleaning head 30 to the control unit 90.

[0028] The first moving unit 50 moves the cleaning head 30 in a horizontal direction perpendicular to the rotation center line 10R of the holder 10, for example by rotating a rotation shaft 52. The rotation shaft 52 is fixed to one end of a rotation arm 53, and the cleaning head 30 is fixed to the other end of the rotation arm 53. The rotation center line 30R of the cleaning head 30 is installed vertically.

[0029] Although not shown, the first moving part 50 may move the cleaning head 30 in a horizontal direction perpendicular to the rotation center line 10R of the holder 10 along a horizontal guide rail.

[0030] The second movement unit 60 moves the cleaning head 30 in the vertical direction. For example, the second movement unit 60 moves the rotating shaft 52 in the vertical direction to move the cleaning head 30 in the vertical direction. The second movement unit 60 includes a servo motor 61. The second movement unit 60 may 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.

[0031] Although not shown, the second moving part 60 may move the holder 10 in the vertical direction instead of moving the cleaning head 30 in the vertical direction. In either case, the distance G between the cleaning head 30 and the substrate W can be changed.

[0032] The control unit 90 controls the valve 23, the ultrasonic transducer 32, the rotating unit 40, the first moving unit 50, and the second moving unit 60. The control unit 90 is, for example, a computer, and includes an arithmetic unit 91 such as a CPU (Central Processing Unit), and a storage unit 92 such as a memory. The storage unit 92 stores programs that control various processes executed in the ultrasonic cleaning device 1. The control unit 90 controls the operation of the ultrasonic cleaning device 1 by having the arithmetic unit 91 execute the programs stored in the storage unit 92.

[0033] Next, the operation of the ultrasonic cleaning apparatus 1, that is, the substrate cleaning method, will be described. First, a transfer robot (not shown) enters the inside of the ultrasonic cleaning apparatus 1 and delivers the substrate W held by the transfer robot to the holder 10. After the holder 10 holds the substrate W horizontally, the transfer robot exits the ultrasonic cleaning apparatus 1. In this manner, the substrate W is carried in.

[0034] Next, the rotating unit 40 rotates the substrate W together with the holder 10, and the nozzle 20 supplies the cleaning liquid near the center of the substrate W. The cleaning liquid on the substrate W spreads from the center to the periphery of the substrate W due to centrifugal force. As a result, a liquid film F is formed on the entire substrate upper surface Wa. The supply rate of the cleaning liquid is, for example, 0.1 L / min to 5.0 L / min, and preferably 0.8 L / min to 1.6 L / min.

[0035] Next, the first moving unit 50 adjusts the horizontal position of the cleaning head 30, and the second moving unit 60 adjusts the vertical position of the cleaning head 30, so that the vibration surface 31a of the cleaning head 30 contacts the liquid film F. A desired gap G is formed between the cleaning head 30 and the substrate W. The gap G is, for example, 0.1 mm to 5.0 mm, and preferably 1.0 mm to 4.0 mm.

[0036] Next, the ultrasonic vibrator 32 vibrates the vibration surface 31a of the cleaning head 30 to impart ultrasonic vibration to the liquid film F, thereby applying sound pressure to the upper surface Wa of the substrate.

[0037] Next, the first moving part 50 moves the cleaning head 30 in a horizontal direction perpendicular to the rotation center line 10R of the holder 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 substrate upper surface Wa is cleaned.

[0038] Next, after the second moving unit 60 raises the cleaning head 30, 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 a position outside the periphery of the substrate W. In addition, the ultrasonic vibrator 32 stops vibrating the vibration surface 31a, and the nozzle 20 stops supplying the cleaning liquid.

[0039] Next, in a state where the nozzle 20 stops supplying the cleaning liquid, the rotating unit 40 rotates the substrate W together with the holder 10, so that the cleaning liquid on the substrate W is 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.

[0040] Next, a transfer robot (not shown) enters the inside of the ultrasonic cleaning apparatus 1 and receives the substrate W from the holder 10. After the transfer robot holds the substrate W, the transfer robot exits the ultrasonic cleaning apparatus 1. In this manner, the substrate W is unloaded.

[0041] Next, the relationship between the distance G between the cleaning head 30 and the substrate W and the sound pressure SP acting on the substrate W will be described with reference to Figs. 6 to 7. As shown in Fig. 6, between the cleaning head 30 and the substrate W, ultrasonic waves emitted from the vibration surface 31a and ultrasonic waves reflected by the upper surface Wa of the substrate are superimposed to form a standing wave. In Fig. 6, A n corresponds to the position of the nth (n: integer greater than or equal to 1) antinode of the standing wave, and B n corresponds to the position of the nth node of the standing wave. Note that the reflection of the ultrasonic wave is a free end reflection.

[0042] When the output PW of the ultrasonic transducer 32 is constant, the sound pressure SP acting on the substrate W varies according to the distance G, as shown in FIG. 7. When the substrate upper surface Wa is located at the antinode position of the standing wave, the sound pressure SP becomes maximum. When the substrate upper surface Wa is located at the node position of the standing wave, the sound pressure SP becomes minimum. The larger the distance G, the smaller the maximum value of the sound pressure SP becomes. The sound pressure SP is measured, for example, by a sound pressure sensor 70 shown in FIG. 6. The sound pressure sensor 70 is attached to the lower surface of the substrate W.

[0043] At the position of the antinode of the standing wave, the sound pressure SP acting on the substrate upper surface Wa is high, cavitation is likely to occur, and particle removal efficiency is good. When the distance G satisfies the following formula (1), the substrate upper surface Wa is at the position of the antinode of the standing wave or a position close to it. Therefore, when the distance G satisfies the following formula (1), particle removal efficiency is good.

[0044]

number

[0045]

number

[0046] Incidentally, when cleaning the substrate upper surface Wa, that is, when forming a liquid film F on the substrate upper surface Wa and applying ultrasonic vibration to the liquid film F, the ultrasonic cleaning device 1 moves the cleaning head 30 in a direction perpendicular to the rotation center line 10R of the holder 10 while rotating the substrate W together with the holder 10. The cleaning head 30 is moved horizontally between a position directly above the center of the substrate upper surface Wa and a position directly above the periphery of the substrate upper surface Wa. When the distance G between the cleaning head 30 and the substrate W varies depending on the horizontal position of the cleaning head 30 and the rotational position of the substrate W, the sound pressure SP acting on the substrate W varies as is clear from FIG. 7.

[0047] With reference to FIG. 8, an example of points P1 to P16 for measuring the distance G between the cleaning head 30 and the substrate W will be described. Each of the points P1 to P16 is set on the substrate upper surface Wa. The distance G at each of the points P1 to P16 is the distance between each of the points P1 to P16 and the center of the vibration surface 31a when the center of the vibration surface 31a reaches directly above each of the points P1 to P16. A plurality of points P1 to P8 are set at equal intervals on a first circle C1, and another plurality of points P9 to P16 are set at equal intervals on a second circle C2. The first circle C1 and the second circle C2 are concentric circles, and their centers coincide with the center of the substrate upper surface Wa. The second circle C2 is set outside the first circle C1.

[0048] Next, an example of variation in the gap G between the cleaning head 30 and the substrate W due to the inclination of the rotation center line 30R of the cleaning head 30 will be described with reference to Figures 9 and 10. When the rotation center line 30R is inclined with respect to the rotation center line 10R as shown in Figure 9, the gap G varies depending on the horizontal position of the cleaning head 30. Note that in Figure 9, the normal line N to the substrate upper surface Wa coincides with the rotation center line 10R.

[0049] In this case, as shown in Fig. 10, the interval G does not depend on the rotational position of the holding part 10. The intervals G at each of the points P1 to P8 on the first circle C1 are the same interval G1. In addition, the intervals G at each of the points P9 to P16 on the second circle C2 are also the same interval G2. However, the intervals G1 and G2 are different. Either the interval G1 or the interval G2 may be larger.

[0050] The absolute value of the difference ΔG (ΔG=G2-G1) between the gaps G1 and G2 varies according to the inclination angle α (α>0) of the pivot center line 30R of the cleaning head 30 relative to the rotation center line 10R of the holder 10. The larger the inclination angle α, the larger the absolute value of the difference ΔG. Therefore, the magnitude of the inclination angle α can be determined from the absolute value of the difference ΔG. Furthermore, the inclination direction of the pivot center line 30R can be determined from the positive or negative value of the difference ΔG.

[0051] Next, an example of the variation in the gap G between the cleaning head 30 and the substrate W due to the inclination of the normal line N to the upper surface Wa of the substrate will be described with reference to Fig. 11 and Fig. 12. When the normal line N is inclined with respect to the rotation center line 10R as shown in Fig. 11, the gap G varies according to the rotation position of the holder 10. The rotation position of the holder 10 is expressed by the rotation angle. In Fig. 11, the pivot center line 30R is parallel to the rotation center line 10R.

[0052] In this case, as shown in FIG. 12, the variation of the interval G at each point P1-P8 on the first circle C1 is represented by a first sine curve S1, and the variation of the interval G at each point P9-P16 on the second circle C2 is represented by a second sine curve S2. The interval G2 corresponding to the vibration center line of the second sine curve S2 coincides with the interval G1 corresponding to the vibration center line of the first sine curve S1. The amplitude A2 of the second sine curve S2 is larger than the amplitude A1 of the first sine curve S1. In FIG. 12, RP is the rotation position corresponding to the maximum value of the first sine curve S1 and the second sine curve S2.

[0053] The difference ΔA (ΔA=A2-A1>0) between the amplitudes A1 and A2 varies according to the inclination angle β (β>0) of the normal N of the substrate upper surface Wa relative to the rotation center line 10R of the holding part 10. The larger the inclination angle β, the larger the difference ΔA. Therefore, the magnitude of the inclination angle β can be determined from the difference ΔA. Furthermore, the inclination direction of the normal N can be determined from the rotation position RP.

[0054] 13, an example of variation in the gap G between the cleaning head 30 and the substrate W due to the inclination of the rotation center line 30R of the cleaning head 30 and the inclination of the normal line N to the upper surface Wa of the substrate will be described. When the normal line N is inclined with respect to the rotation center line 10R and the rotation center line 30R is inclined with respect to the rotation center line 10R, the gap G varies depending on both the horizontal position of the cleaning head 30 and the rotational position of the holder 10.

[0055] In this case, as shown in FIG. 13, the variation of the interval G at each point P1-P8 on the first circle C1 is represented by the first sine curve S1, and the variation of the interval G at each point P9-P16 on the second circle C2 is represented by the second sine curve S2. The interval G2 corresponding to the vibration center line of the second sine curve S2 is different from the interval G1 corresponding to the vibration center line of the first sine curve S1. Either the interval G1 or the interval G2 may be larger. On the other hand, the amplitude A2 of the second sine curve S2 is larger than the amplitude A1 of the first sine curve S1. In FIG. 12, RP is the rotation position corresponding to the maximum value of the first sine curve S1 and the second sine curve S2.

[0056] The absolute value of the difference ΔG (ΔG = G2 - G1) between the gaps G1 and G2 varies according to the inclination angle α (α > 0). The larger the inclination angle α, the larger the absolute value of the difference ΔG. Therefore, the magnitude of the inclination angle α can be determined from the absolute value of the difference ΔG. Furthermore, the inclination direction of the turning center line 30R can be determined from the positive or negative value of the difference ΔG. Furthermore, the difference ΔA (ΔA = A2 - A1 > 0) between the amplitudes A1 and A2 varies according to the inclination angle β (β > 0). The larger the inclination angle β, the larger the difference ΔA. Therefore, the magnitude of the inclination angle β can be determined from the difference ΔA. Furthermore, the inclination direction of the normal N can be determined from the rotation position RP.

[0057] It is not realistic to set the tilt angles α and β to completely zero. Therefore, the distance G between the cleaning head 30 and the substrate W may vary depending on the horizontal position of the cleaning head 30 and the rotational position of the substrate W. When the distance G varies, the sound pressure SP varies. Therefore, the control unit 90, for example, keeps the distance G within an allowable range in order to keep the sound pressure SP within the allowable range. Keeping the distance G within the allowable range includes correcting the vertical position of at least one of the cleaning head 30 and the substrate W.

[0058] For example, before cleaning the substrate W, the control unit 90 may measure the distance G between the cleaning head 30 and the second substrate at each of multiple points P1 to P16 on the upper surface of the second substrate while the second substrate, which is prepared separately from the substrate W, is held by the holder 10. Alternatively, instead of measuring the distance G between the cleaning head 30 and the second substrate, it may be possible to measure the sound pressure acting on the second substrate. The measurement results are stored in the memory unit 92 of the control unit 90. Based on the measurement results, the vertical position of at least one of the cleaning head 30 and the substrate W is corrected, thereby controlling the distance G to be constant.

[0059] As described above, it is conceivable to measure the distance G or the sound pressure SP using a second substrate separate from the substrate W before cleaning the substrate W. However, there are cases where it is difficult to measure the distance G or the sound pressure SP. For example, it is difficult to measure the distance G in a state where a cleaning liquid is filled between the cleaning head 30 and the substrate W. In addition, while it is easy to measure the sound pressure SP acting on the center of the substrate W, it is difficult to measure the sound pressure SP acting on the periphery of the substrate W.

[0060] Therefore, the present inventors have investigated parameters that can be substituted for the gap G or the sound pressure SP, and have found that it is possible to control the sound pressure SP by measuring the reflected power returning from the ultrasonic transducer 32 to the ultrasonic oscillator 80 as shown in Fig. 14. The ultrasonic oscillator 80 is a power source that outputs power, and the ultrasonic transducer 32 is a load that consumes power. If there is a discrepancy between the impedance on the power source side and the impedance on the load side, the power is returned to the power source without being consumed by the load. Therefore, it is estimated that the greater the reflected power, the lower the sound pressure SP.

[0061] The power reflected by the ultrasonic transducer 32 returns to the ultrasonic generator 80, and a portion of it is reflected again and input to the ultrasonic transducer 32. Therefore, in a steady state, the reflected power also contributes to the incident power, i.e., the power traveling from the ultrasonic generator 80 to the ultrasonic transducer 32. Therefore, information on the reflected power can be obtained by measuring the incident power.

[0062] In order to improve the control accuracy of the sound pressure SP, it is preferable to calculate an index value that indicates the difference between the impedance on the power supply side and the impedance on the load side. The index value preferably includes at least one of the standing wave ratio (SWR), reflection coefficient, and return loss. The standing wave ratio, reflection coefficient, and return loss are calculated by a general formula.

[0063] Next, an example of an ultrasonic oscillator 80, an ultrasonic transducer 32, and a measuring unit 82 will be described with reference to Fig. 14. The ultrasonic cleaning device 1 includes a measuring unit 82 that measures at least one of incident power and reflected power in a wiring 81 that electrically connects the ultrasonic oscillator 80 and the ultrasonic transducer 32. The incident power is a traveling wave traveling from the ultrasonic oscillator 80 toward the ultrasonic transducer 32. The reflected power is a reflected wave returning from the ultrasonic transducer 32 to the ultrasonic oscillator.

[0064] For example, a directional coupler 83 is provided in the middle of the wiring 81. The directional coupler 83 extracts the incident power and the reflected power separately. The measurement unit 82 has at least one of a first measurement unit 82A that measures the incident power and a second measurement unit 82B that measures the reflected power. Each of the first measurement unit 82A and the second measurement unit 82B includes, for example, a power sensor.

[0065] The ultrasonic cleaning device 1 may include a calculation unit 84. The calculation unit 84 calculates an index value representing a difference between the impedance of the ultrasonic oscillator 80 and the impedance of the ultrasonic transducer 32. The index value preferably includes at least one of a standing wave ratio, a reflection coefficient, and a return loss. The calculation unit 84 transmits the calculated index value to the control unit 90. The calculation unit 84 may be a part of the control unit 90.

[0066] Next, an example of the correlation between the distance G between the cleaning head 30 and the substrate W, the sound pressure SP acting on the substrate W, and the reflected power will be described with reference to Figures 15 and 16. The data shown in Figures 15 and 16 was measured by changing the distance G while maintaining the amplitude and frequency of the incident power constant, with the center of the vibration surface 31a of the cleaning head 30 positioned directly above the center of the substrate upper surface Wa. From Figure 15, it can be seen that the sound pressure SP varies depending on the distance G. Furthermore, from Figures 15 and 16, it can be seen that there is a correlation between the sound pressure SP and the reflected power, and the smaller the reflected power, the greater the sound pressure SP.

[0067] For example, before cleaning the substrate W, the control unit 90 holds a second substrate prepared separately from the substrate W by the holder 10 and measures the reflected power in a state in which the center of the vibration surface 31a of the cleaning head 30 is located directly above each of the multiple points P1 to P16 on the upper surface of the second substrate. The reflected power has a correlation with the distance G. Therefore, by measuring the reflected power, it is possible to determine the magnitude of the tilt angle α, the tilt direction of the rotation center line 30R, the magnitude of the tilt angle β, and the tilt direction of the normal line N.

[0068] The control unit 90 stores the results of measuring the reflected power in the memory unit 92. The information to be stored may be the reflected power measured at each of the points P1 to P16 itself, or the magnitude of the tilt angle α, the tilt direction of the turning center line 30R, the magnitude of the tilt angle β, and the tilt direction of the normal line N, which are calculated from the reflected power measured at each of the points P1 to P16.

[0069] When cleaning the substrate W, the control unit 90 controls the distance G based on the result of measuring the reflected power before cleaning the substrate W. For example, the control unit 90 controls the vertical position of the cleaning head 30 so that the distance G satisfies formula (1). This makes it possible to maintain a high sound pressure SP over the entire upper surface Wa of the substrate, and to evenly clean the entire upper surface Wa of the substrate.

[0070] An example of the difference between the presence and absence of gap control will be described with reference to Figures 17 and 18. In Figures 17 and 18, gap control refers to controlling the gap G to be constant by correcting the vertical position of the cleaning head 30 based on the result of measuring the reflected power before cleaning the substrate W. Figure 17 shows a frequency spectrum obtained by performing a fast Fourier transform on the reflected power. Also, Figure 18 shows the number of defects classified by the circle equivalent diameter of the defects.

[0071] Without gap control, the gap G fluctuates with each rotation of the substrate W as shown in Figures 12 and 13, and an amplitude peak was observed at the frequency corresponding to the rotation speed of the substrate W as shown in Figure 17. On the other hand, with gap control, no amplitude peak was observed at the frequency corresponding to the rotation speed of the substrate W as shown in Figure 17. Furthermore, with gap control, the sound pressure SP can be maintained high over the entire upper surface Wa of the substrate compared to without gap control, and therefore the number of defects was smaller as shown in Figure 18.

[0072] The control unit 90 may measure at least one of the incident power and the reflected power while holding a second substrate prepared separately from the substrate W by the holding unit 10 and locating the center of the vibration surface 31a of the cleaning head 30 directly above each of the multiple points P1 to P16 on the upper surface of the second substrate. The control unit 90 may use the index value as a result of the measurement.

[0073] In addition, when cleaning the substrate W, in this embodiment, the control unit 90 controls (a) the distance G between the cleaning head 30 and the substrate W, but may control other parameters. Examples of other parameters include: (b) the moving speed of the cleaning head 30 in a horizontal direction perpendicular to the rotation center line 10R of the holder 10; (c) the rotation speed of the substrate W; (d) the amplitude of the incident power from the ultrasonic generator to the ultrasonic transducer 32; (e) the frequency of the incident power; The control unit 90 only needs to control at least one of the above (a) to (e).

[0074] The control unit 90 can keep the sound pressure SP within the allowable range at each of the multiple points P1 to P16 by controlling at least one of the above (a), (d), and (e). Furthermore, the control unit 90 can keep the time integral value of the sound pressure SP within the allowable range at each of the multiple points P1 to P16 by controlling at least one of the above (b) and (c). Even if the sound pressure SP does not fall within the allowable range, as long as the time integral value of the sound pressure SP falls within the allowable range, the entire upper surface Wa of the substrate can be evenly cleaned.

[0075] In this embodiment, before cleaning the substrate W, the control unit 90 holds a second substrate prepared separately from the substrate W in the holding unit 10, and measures at least one of the incident power and the reflected power while positioning the center of the vibration surface 31a of the cleaning head 30 directly above each of the multiple points P1 to P16 on the upper surface of the second substrate, and stores the measurement results in the memory unit 92, but the technology of the present disclosure is not limited to this.

[0076] For example, the control unit 90 may measure at least one of the incident power and the reflected power while holding the substrate W on the holder 10 and positioning the center of the vibration surface 31a of the cleaning head 30 directly above each of the points P1 to P16 on the substrate upper surface Wa, and store the measurement results. When measuring the reflected power, a cleaning liquid is filled between the cleaning head 30 and the substrate W.

[0077] Specifically, the control unit 90 may alternately repeat the following (S201) and (S202) when rotating the substrate W and moving the cleaning head 30 in the horizontal direction while applying ultrasonic vibrations to the liquid film F from the vibration surface 31a of the cleaning head 30. (S201) Measure at least one of the incident power and the reflected power at a desired point on the substrate upper surface Wa. (S202) Based on the measurement result, control at least one selected from the above (a) to (e).

[0078] Incidentally, the ultrasonic cleaning device 1 repeatedly cleans the substrate W while replacing the substrate W held by the holder 10. When the substrate W is replaced, the thickness of the substrate W may change, and the distance G between the substrate W and the cleaning head 30 may change. When the distance G changes, the sound pressure SP changes.

[0079] Therefore, the control unit 90 may measure the thickness of the substrate W. The thickness of the substrate W may be measured before the substrate W is held by the holding unit 10, or may be measured while the substrate W is held by the holding unit 10. The thickness of the substrate W is measured using a general thickness meter. The thickness meter may be of either a contact type or a non-contact type. The thickness meter may transmit the measurement results to the control unit 90. The measurement results of the thickness of the substrate W are stored in the memory unit 92 of the control unit 90.

[0080] When cleaning the substrate W, the control unit 90 controls at least one selected from the above (a) to (e) based on the thickness of the substrate W. This allows the time integral value of the sound pressure SP acting on the substrate W to be within an allowable range, thereby suppressing uneven cleaning between substrates.

[0081] Next, with reference to Fig. 19, a method for manufacturing an EUVL mask blank 200 shown in Fig. 22 will be described. The method for manufacturing an EUVL mask blank 200 has steps S101 to S107. For example, a substrate 210 shown in Fig. 20 and Fig. 21 is prepared in advance. When the substrate 210 is a glass substrate, steps S101 to S104 are included in the method for manufacturing a glass substrate.

[0082] The substrate 210 includes a first main surface 211 and a second main surface 212 facing opposite 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 opposite to the first main surface 211. The second main surface 212 is also rectangular, like the first main surface 211.

[0083] The substrate 210 also includes four end surfaces 213, four first chamfered surfaces 214, and four second chamfered surfaces 215. The end surfaces 213 are perpendicular to the first main surface 211 and the second main surface 212. The first chamfered surface 214 is formed at the boundary between the first main surface 211 and the end surfaces 213. The second chamfered surface 215 is formed at the boundary between the second main surface 212 and the end surfaces 213. In this embodiment, the first chamfered surface 214 and the second chamfered surface 215 are so-called C-chamfered surfaces, but may be R-chamfered surfaces.

[0084] The substrate 210 is, for example, a glass substrate. The glass of the substrate 210 is preferably quartz glass containing TiO2. Quartz glass has a smaller linear expansion coefficient and smaller dimensional change due to temperature change than general soda-lime glass. 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 linear expansion coefficient is approximately zero near room temperature, and almost no dimensional change occurs near room temperature. Quartz glass may contain a third component or impurities other than SiO2 and TiO2.

[0085] The size of the substrate 210 in plan view is, for example, 152 mm in length and 152 mm in width. The length and width may be greater than or equal to 152 mm.

[0086] The substrate 210 has a central region 211A and a peripheral region 211B on the first main surface 211. The central region 211A is a square region excluding a rectangular frame-shaped peripheral region 211B surrounding the central region 211A, and is a region that is processed to a desired flatness in steps S101 to S104, and is a 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.

[0087] Although not shown, 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 a region that is processed to a desired flatness by steps S101 to S104 in Fig. 19, and is a quality assurance region. The quality assurance region has a size of, for example, 142 mm in length and 142 mm in width.

[0088] 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 by a double-sided polisher (not shown), but may be polished sequentially by a single-sided polisher (not shown). In step S101, the substrate 210 is polished while supplying a polishing slurry between a polishing pad and the substrate 210.

[0089] The polishing pad may be, for example, a urethane-based polishing pad, a nonwoven fabric-based polishing pad, or a suede-based polishing pad. 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 grain sizes.

[0090] The abrasive used in step S101 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.

[0091] Step S102 includes measuring the surface shapes of the first main surface 211 and the second main surface 212 of the substrate 210. 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 central region 211A of the first main surface 211 and the central region of the second main surface 212.

[0092] Step S103 includes locally processing the first main surface 211 and the second main surface 212 of the substrate 210 to improve flatness with reference to the measurement result of step S102. The first main surface 211 and the second main surface 212 are locally processed in that order. The order in which they are processed may be either first or second, and is not particularly limited.

[0093] For the local processing, for example, at least one method selected from a gas cluster ion beam (GCIB) method, a plasma chemical vaporization machining (PCVM) method, a polishing method using a magnetic fluid, and polishing using a rotary polishing tool is used.

[0094] Step S104 includes performing finish polishing of 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 by a double-sided polisher (not shown), but may be polished sequentially by a single-sided polisher (not shown). In step S104, the substrate 210 is polished while a polishing slurry is supplied between the polishing pad and the substrate 210. The polishing slurry contains an abrasive. The abrasive is, for example, colloidal silica particles.

[0095] Step S105 includes forming a conductive film 240 shown in FIG. 22 in a central region of the second main surface 212 of the substrate 210. The conductive film 240 is used to attach the EUVL mask to an electrostatic chuck of an exposure tool. The conductive film 240 is made of, for example, chromium nitride (CrN). The conductive film 240 is formed by, for example, sputtering.

[0096] Step S106 includes forming a multilayer reflective film 220 shown in FIG. 22 in the central region 211A of the first main surface 211 of the substrate 210. The multilayer reflective film 220 reflects EUV. The multilayer reflective film 220 is formed by alternately laminating, for example, high refractive index layers and low refractive index layers. The high refractive index layers are formed of, for example, silicon (Si), and the low refractive index layers are formed of, for example, molybdenum (Mo). The multilayer reflective film 220 is formed by a sputtering method such as an ion beam sputtering method or a magnetron sputtering method.

[0097] Step S107 includes forming an absorbing film 230 shown in FIG. 22 on the multilayer reflective film 220 formed in step S106. The absorbing film 230 absorbs EUV. The absorbing film 230 may be a phase shift film and may shift the phase of EUV. The absorbing film 230 is formed of a single metal, an alloy, a nitride, an oxide, an oxynitride, or the like containing at least one element selected from, for example, tantalum (Ta), chromium (Cr), ruthenium (Ru), iridium (Ir), and palladium (Pd). The absorbing film 230 is formed, for example, by sputtering.

[0098] In this embodiment, steps S106 to S107 are performed after step S105, but may be performed before step S105.

[0099] 22 is obtained by the above steps S101 to S107. The EUVL mask blank 200 has, in this order, a conductive film 240, a substrate 210, a multilayer reflective film 220, and an absorbing film 230. Note that the EUVL mask blank 200 may include another film in addition to the conductive film 240, the substrate 210, the multilayer reflective film 220, and the absorbing film 230.

[0100] For example, the EUVL mask blank 200 may further include a low-reflection film. The low-reflection film is formed on the absorbing film 230. Then, an opening pattern 231 is formed in both the low-reflection film and the absorbing film 230. The low-reflection film is used for inspecting the opening pattern 231, and has lower reflection characteristics with respect to inspection light than the absorbing film 230. 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.

[0101] The EUVL mask blank 200 may further include a protective film. The protective film is formed between the multilayer reflective film 220 and the absorbing film 230. The protective film protects the multilayer reflective film 220 so that the multilayer reflective film 220 is not etched when the absorbing film 230 is etched to form an opening pattern 231 in the absorbing film 230. The protective film is formed of, for example, Ru, Si, Rh, TiO2, or the like. The protective film is formed by, for example, a sputtering method.

[0102] 23, the EUVL mask 201 is obtained by forming an opening pattern 231 in an absorbing film 230 of an EUVL mask blank 200. Photolithography and etching are used to form the opening pattern 231. Therefore, the EUVL mask blank 200 may include a resist film used to form the opening pattern 231.

[0103] 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 using a chemical reaction with acid or alkali, cleaning using a physical action, or a combination of these may be performed. Cleaning using a physical action includes ultrasonic cleaning, scrubbing cleaning, and two-fluid cleaning. In two-fluid cleaning, a cleaning liquid and a gas are mixed and sprayed.

[0104] The ultrasonic cleaning is performed, for example, using an ultrasonic cleaning device 1 shown in Fig. 1. The ultrasonic cleaning is preferably performed at least one of between steps S104 and S105, between steps S105 and S106, between steps S106 and S107, and after step S107. Although not shown, the ultrasonic cleaning may be performed before or after a low reflection film, a hard mask film, or a protective film.

[0105] The ultrasonic cleaning apparatus, the substrate cleaning method, and the method for manufacturing an EUVL mask blank 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. [Explanation of symbols]

[0106] 1. Ultrasonic cleaning equipment 10 Holding part 30 cleaning heads 31a Vibration surface 32 Ultrasonic transducer 80 Ultrasonic Oscillator 81 Wiring 82 Measuring part W substrate F liquid film

Claims

1. a holding portion for holding the substrate horizontally; a nozzle for forming a liquid film on an upper surface of the substrate held by the holding part; a cleaning head including a vibration surface that contacts the liquid film and an ultrasonic vibrator that vibrates the vibration surface; an ultrasonic oscillator electrically connected to the ultrasonic transducer via a wiring; A measurement unit that measures at least one of an incident power from the ultrasonic oscillator toward the ultrasonic transducer and a reflected power from the ultrasonic transducer back to the ultrasonic oscillator in the wiring; An ultrasonic cleaning device comprising:

2. 2. The ultrasonic cleaning device according to claim 1, further comprising a calculation unit that calculates an index value representing a deviation between an impedance of the ultrasonic oscillator and an impedance of the ultrasonic vibrator based on at least one of the measurement results of the incident power and the reflected power.

3. The ultrasonic cleaning apparatus of claim 2 , wherein the index value includes at least one of a standing wave ratio, a reflection coefficient, and a return loss.

4. A rotating unit that rotates the holding unit; a first moving unit that moves the cleaning head in a horizontal direction perpendicular to a rotation center line of the holding unit; a second moving unit that adjusts a distance between the cleaning head and the substrate by moving the holding unit or the cleaning head in a vertical direction; A control unit that controls the ultrasonic oscillator, the rotation unit, the first movement unit, and the second movement unit; having The ultrasonic cleaning device according to any one of claims 1 to 3, wherein the control unit controls at least one of a distance between the cleaning head and the substrate, a moving speed of the cleaning head in the horizontal direction, a rotation speed of the substrate, an amplitude of the incident power, and a frequency of the incident power based on at least one measurement result of the incident power and the reflected power.

5. 1. A substrate cleaning method comprising: holding a substrate horizontally with a holder; forming a liquid film on an upper surface of the substrate held by the holder; bringing a vibration surface of a cleaning head into contact with the liquid film; and vibrating the vibration surface by an ultrasonic vibrator, A substrate cleaning method comprising measuring at least one of an incident power directed from the ultrasonic oscillator to the ultrasonic oscillator and a reflected power returning from the ultrasonic oscillator to the ultrasonic oscillator in a wiring electrically connecting the ultrasonic oscillator and the ultrasonic oscillator.

6. 6. The substrate cleaning method according to claim 5, further comprising: calculating an index value representing a difference between an impedance of the ultrasonic oscillator and an impedance of the ultrasonic transducer based on at least one of the measurement results of the incident power and the reflected power.

7. The method of cleaning a substrate according to claim 6 , wherein the index value includes at least one of a standing wave ratio, a reflection coefficient, and a return loss.

8. measuring at least one of the incident power and the reflected power at each of a plurality of points on an upper surface of a second substrate, the second substrate being prepared separately from the substrate, in a state in which the second substrate is held by the holding unit; while rotating the substrate and moving the cleaning head in a horizontal direction perpendicular to a center line of rotation of the substrate while the substrate is held by the holder, controlling at least one of a distance between the cleaning head and the substrate, a moving speed of the cleaning head in the horizontal direction, a rotation speed of the substrate, an amplitude of the incident power, and a frequency of the incident power based on at least one measurement result of the incident power and the reflected power; The method for cleaning a substrate according to any one of claims 5 to 7, comprising:

9. measuring at least one of the incident power and the reflected power at each of a plurality of points on an upper surface of the substrate while the substrate is held by the holding unit; while rotating the substrate and moving the cleaning head in a horizontal direction perpendicular to a center line of rotation of the substrate while the substrate is held by the holder, controlling at least one of a distance between the cleaning head and the substrate, a moving speed of the cleaning head in the horizontal direction, a rotation speed of the substrate, the incident power, and a frequency of the incident power based on a measurement result of at least one of the incident power and the reflected power; The method for cleaning a substrate according to any one of claims 5 to 7, comprising:

10. A method for producing a mask blank for EUVL, comprising cleaning a glass substrate or a functional film formed on the glass substrate by the method for cleaning a substrate according to any one of claims 5 to 7.

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