Substrate cleaning method, glass substrate manufacturing method, EUVL mask blank manufacturing method, and substrate cleaning apparatus

Abstract

This substrate cleaning method has the following steps (A) to (G): (A) holding a substrate horizontally with a holding part; (B) forming a liquid film on an upper surface of the substrate held by the holding part; (C) bringing a vibrating surface of a cleaning head into contact with the liquid film; (D) vibrating the vibrating surface with an ultrasonic vibrator; (E) rotating the substrate together with the holding part and moving the cleaning head in a horizontal direction perpendicular to the rotation center line of the holding part; (F) measuring the distance between a second substrate, which was prepared separately from the substrate, and the cleaning head or the sound pressure acting on the second substrate in a state in which the second substrate is held by the holding part; and (G) controlling at least one selected from the vertical position of the cleaning head or the holding part, the output of the ultrasonic vibrator, the rotational speed of the holding part, and the moving speed of the cleaning head in the horizontal direction on the basis of the measured results.

Description

Technical Field

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

Background Art

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

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

[0004] During the manufacturing process of a mask blank for EUVL, it may be necessary to clean a glass substrate or a functional film formed on the glass substrate. As one of the cleaning methods, ultrasonic cleaning may be performed.

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

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

[0007] The cleaning method described in Patent Document 2 involves moving an ultrasonic cleaning head perpendicular to the rotational centerline of the substrate while rotating the substrate when cleaning the upper surface of the substrate. The ultrasonic 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.

[0008] Conventionally, the distance between the ultrasonic cleaning head and the substrate could fluctuate depending on the horizontal position of the ultrasonic cleaning head and the rotational position of the substrate, which could result in uneven sound pressure acting on the substrate. As a result, uneven cleaning of the substrate could occur.

[0009] One aspect of this disclosure provides a technique for uniformly cleaning the entire surface of a substrate. [Means for solving the problem]

[0010] A substrate cleaning method according to one aspect of the present disclosure comprises the following (A) to (G): (A) The substrate is held horizontally by a holding unit. (B) A liquid film is formed on the upper surface of the substrate held by the holding unit. (C) The vibrating surface of the cleaning head is brought into contact with the liquid film. (D) The vibrating surface is vibrated by an ultrasonic transducer. (E) The substrate is rotated together with the holding unit, and the cleaning head is moved in a horizontal direction perpendicular to the rotation center line of the holding unit. (F) With a second substrate, prepared separately from the first substrate, held by the holding unit, the distance between the second substrate and the cleaning head, or the sound pressure acting on the second substrate, is measured at each of several points on the upper surface of the second substrate. (G) While rotating the substrate and moving the cleaning head in the horizontal direction, ultrasonic vibrations are applied to the liquid film from the vibrating surface of the cleaning head, and at least one selected from the following is controlled based on the measured results: the vertical position of the cleaning head or the holding part, the output of the ultrasonic transducer, the rotational speed of the holding part, and the horizontal movement speed of the cleaning head. [Effects of the Invention]

[0011] According to one aspect of this disclosure, the distance between the second substrate and the cleaning head or the sound pressure acting on the second substrate is measured at each of several points on the upper surface of the second substrate, and the upper surface of the substrate is cleaned using the measurement results. As a result, the time integral value of the sound pressure at each of the several points on the upper surface of the substrate can be kept within an acceptable range, and the entire upper surface of the substrate can be cleaned uniformly. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a side view showing a substrate cleaning apparatus according to one embodiment. [Figure 2] Figure 2 is a cross-sectional view showing an example of the internal structure of a washing head. [Figure 3] Figure 3 is a cross-sectional view showing another example of the internal structure of a washing head. [Figure 4] Figure 4 is a plan view showing an example of the movement trajectory of the cleaning head. [Figure 5]FIG. 5 is a diagram showing an example of the relationship between the output of the ultrasonic transducer and the sound pressure acting on the 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 measurement points on the upper surface of the second substrate. [Figure 9] FIG. 9 is a diagram showing an example of the inclination of the rotation center line of the cleaning head. [Figure 10] FIG. 10 is a diagram showing an example of the variation in the distance between the second substrate and the cleaning head due to the inclination of the rotation center line of the cleaning head. [Figure 11] FIG. 11 is a diagram showing an example of the inclination of the normal line on the upper surface of the second substrate. [Figure 12] FIG. 12 is a diagram showing an example of the variation in the distance between the second substrate and the cleaning head due to the inclination of the normal line on the upper surface of the second substrate. [Figure 13] FIG. 13 is a diagram showing an example of the variation in the distance between the second substrate and the cleaning head due to the inclination of the rotation center line of the cleaning head and the inclination of the normal line on the upper surface of the second substrate. [Figure 14] It is a flowchart showing a method for manufacturing a mask blank for EUVL according to an embodiment. [Figure 15] FIG. 15 is a cross-sectional view showing an example of a substrate. [Figure 16] FIG. 16 is a plan view of the substrate of FIG. 15. [Figure 17] FIG. 17 is a cross-sectional view showing an example of a mask blank for EUVL. [Figure 18] FIG. 18 is a cross-sectional view showing an example of a mask for EUVL.

BEST MODE FOR CARRYING OUT THE INVENTION

[0013] 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.

[0014] 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.

[0015] 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.

[0016] 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, as will be described later. The holding portion 10 may also hold the substrate W by suction.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] The ultrasonic transducer 32 applies ultrasonic vibration 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 greater the output PW of the ultrasonic transducer 32, the greater the sound pressure SP acting on the substrate W (see Figure 5). In this specification, sound pressure SP refers to the effective value, not the instantaneous 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 Figure 5) is pre-stored in the storage medium 92 of the control unit 90. Similarly, the relationship between the distance D 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 Figure 7) is also pre-stored in the storage medium 92 of the control unit 90. The relationship between distance D and sound pressure SP will be described later.

[0026] As shown in Figure 1, 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 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 regarding 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.

[0027] 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 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 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] Next, with reference to Figures 6 and 7, the relationship between the distance D between the cleaning head 30 and the substrate W and the sound pressure SP acting on the substrate W will be explained. As shown in Figure 6, between the cleaning head 30 and the substrate W, ultrasonic waves emitted from the vibrating surface 31a and ultrasonic waves reflected from the upper surface Wa of the substrate are superimposed, forming a standing wave. In Figure 6, A n This corresponds to the position of the nth antinode (n: an integer greater than or equal to 1) of the standing wave, and B n This corresponds to the position of the nth node of the standing wave. Note that the reflection of ultrasound 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 with distance D, as shown in Figure 7. The sound pressure SP is at its maximum when the top surface Wa of the substrate is located at the antinode of the standing wave. The sound pressure SP is at its minimum when the top surface Wa of the substrate is located at the node of the standing wave. The larger the distance D, the smaller the maximum value of the sound pressure SP becomes. The sound pressure SP is measured by a sound pressure sensor 70, for example, as shown in Figure 6. The sound pressure sensor 70 is attached to the bottom surface of the substrate W.

[0043] At the antinodes of standing waves, the sound pressure SP acting on the substrate surface Wa is high, making cavitation more likely and resulting in good particle removal efficiency. When the distance D satisfies equation (1) below, the substrate surface Wa is at or near the antinode of the standing wave. Therefore, when the distance D satisfies equation (1) below, particle removal efficiency is good.

[0044]

number

[0045]

number

[0046] Incidentally, when the substrate cleaning apparatus 1 cleans the upper surface Wa of the substrate, that is, when forming a liquid film F on the upper surface Wa of the substrate and applying ultrasonic vibrations to the liquid film F, it rotates the substrate W together with the holding unit 10 and moves the cleaning head 30 in a direction perpendicular to the rotation centerline 10R of the holding unit 10. The cleaning head 30 is moved horizontally between a position directly above the center of the upper surface Wa of the substrate and a position directly above the periphery of the upper surface Wa of the substrate. As is clear from Figure 7, when the distance D between the cleaning head 30 and the substrate W changes according to the horizontal position of the cleaning head 30 and the rotation position of the substrate W, unevenness occurs in the sound pressure SP acting on the substrate W.

[0047] Therefore, before cleaning the substrate W, the control unit 90 holds the second substrate W2 (see Figure 8), which is prepared separately from the substrate W, in the holding unit 10, and stores the results of measuring the distance D between the second substrate W2 and the cleaning head 30 at each of several points P1 to P16 on the upper surface W2a of the second substrate W2. For measuring the distance D, for example, a laser displacement meter 80 as shown in Figure 1 is used. The laser displacement meter 80 is fixed to the cleaning head 30 or the swivel arm 53 and moves vertically and horizontally together with the cleaning head 30.

[0048] The upper surface W2a of the second substrate W2 is also referred to as the upper surface W2a of the second substrate. The distance D at each point P1 to P16 on the upper surface W2a of the second substrate is the distance between each point P1 to P16 and the center of the vibration surface 31a when the center of the vibration surface 31a reaches directly above each point P1 to P16. Multiple points P1 to P8 are set at equal intervals on the first circle C1, and another set of multiple points P9 to P16 are set at equal intervals on the second circle C2. The first circle C1 and the second circle C2 are concentric circles, and their centers coincide with the center of the upper surface W2a of the second substrate. The second circle C2 is set outside the first circle C1.

[0049] Next, with reference to Figures 9 and 10, an example of variation in the distance D between the second substrate W2 and the cleaning head 30 due to the inclination of the rotation centerline 30R of the cleaning head 30 will be described. As shown in Figure 9, when the rotation centerline 30R is inclined with respect to the rotation centerline 10R, the distance D fluctuates according to the horizontal position of the cleaning head 30. Note that in Figure 9, the normal N of the upper surface W2a of the second substrate coincides with the rotation centerline 10R.

[0050] In this case, as shown in Figure 10, the distance D does not depend on the rotational position of the holding part 10. The distance D at each point P1 to P8 on the first circle C1 is the same distance D1. Similarly, the distance D at each point P9 to P16 on the second circle C2 is the same distance D2. However, distances D1 and D2 are different. Either distance D1 or D2 can be larger.

[0051] The absolute value of the difference ΔD (ΔD = D2 - D1) between distances D1 and D2 varies depending on the inclination angle α (α > 0) of the rotational centerline 30R of the cleaning head 30 relative to the rotational centerline 10R of the holding unit 10. The larger the inclination angle α, the larger the absolute value of the difference ΔD. Therefore, the magnitude of the inclination angle α can be determined from the absolute value of the difference ΔD. Also, the direction of the inclination of the rotational centerline 30R can be determined from the sign of the difference ΔD.

[0052] Next, with reference to Figures 11 and 12, an example of variation in the distance D between the second substrate W2 and the cleaning head 30 due to the inclination of the normal N of the upper surface W2a of the second substrate will be described. As shown in Figure 11, when the normal N is inclined with respect to the rotation centerline 10R, the distance D fluctuates according to the rotational position of the holding unit 10. The rotational position of the holding unit 10 is expressed as the rotation angle. Note that in Figure 11, the pivot centerline 30R is parallel to the rotation centerline 10R.

[0053] In this case, as shown in Figure 12, the variation in distance D at points P1 to P8 on the first circle C1 is represented by the first sine curve S1, and the variation in distance D at points P9 to P16 on the second circle C2 is represented by the second sine curve S2. The distance D2 corresponding to the vibration centerline of the second sine curve S2 coincides with the distance D1 corresponding to the vibration centerline of the first sine curve S1. The amplitude A2 of the second sine curve S2 is greater than the amplitude A1 of the first sine curve S1. In Figure 12, RP is the rotational position corresponding to the maximum value of the first sine curve S1 and the second sine curve S2.

[0054] The difference ΔA between amplitudes A1 and A2 (ΔA = A2 - A1 > 0) varies depending on the inclination angle β (β > 0) of the normal N of the upper surface W2a of the second substrate with respect to the rotation centerline 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. In addition, the inclination direction of the normal N can be determined from the rotation position RP.

[0055] Next, referring to Figure 13, an example of variation in the distance D between the second substrate W2 and the cleaning head 30 due to the inclination of the pivot centerline 30R of the cleaning head 30 and the inclination of the normal N of the upper surface W2a of the second substrate will be described. When the normal N is inclined with respect to the rotation centerline 10R, and the pivot centerline 30R is also inclined with respect to the rotation centerline 10R, the distance D will vary according to both the horizontal position of the cleaning head 30 and the rotational position of the holding unit 10.

[0056] In this case, as shown in Figure 13, the variation in distance D at points P1 to P8 on the first circle C1 is represented by the first sine curve S1, and the variation in distance D at points P9 to P16 on the second circle C2 is represented by the second sine curve S2. The distance D2 corresponding to the vibration centerline of the second sine curve S2 is different from the distance D1 corresponding to the vibration centerline of the first sine curve S1. Either distance D1 or D2 can 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 Figure 12, RP is the rotational position corresponding to the maximum value of the first sine curve S1 and the second sine curve S2.

[0057] The absolute value of the difference ΔD (ΔD = D2 - D1) between distances D1 and D2 varies depending on the inclination angle α (α > 0). The larger the inclination angle α, the larger the absolute value of the difference ΔD. Therefore, the magnitude of the inclination angle α can be determined from the absolute value of the difference ΔD. Also, the direction of inclination of the rotation centerline 30R can be determined from the sign of the difference ΔD. Furthermore, the difference ΔA (ΔA = A2 - A1 > 0) between amplitudes A1 and A2 varies depending on 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. Also, the direction of inclination of the normal vector N can be determined from the rotation position RP.

[0058] It is not practical to make the inclination angles α and β completely zero. Therefore, before cleaning the substrate W, the control unit 90 holds the second substrate W2, which is prepared separately from the substrate W, in the holding unit 10, and stores the results of measuring the distance D between the second substrate W2 and the cleaning head 30 at each of several points P1 to P16 on the upper surface W2a of the second substrate W2. The information to be stored may be the distance D at each point P1 to P16, or it may be the magnitude of the inclination angle α, the inclination direction of the pivot center line 30R, the magnitude of the inclination angle β, and the inclination direction of the normal N, which are calculated from the distance D at each point P1 to P16.

[0059] Alternatively, instead of storing the measurement results of the distance D between the second substrate W2 and the cleaning head 30 at each of the multiple points P1 to P16 on the upper surface W2a of the second substrate W2 before cleaning the substrate W, the control unit 90 may store the measurement results of the sound pressure SP acting on the second substrate W2. Since the distance D and the sound pressure SP have a certain relationship (see Figure 7), it is possible to determine the magnitude of the inclination angle α, the inclination direction of the pivot centerline 30R, the magnitude of the inclination angle β, and the inclination direction of the normal N regardless of which is measured. The sound pressure SP is measured, for example, by a sound pressure sensor 70 shown in Figure 6. Multiple sound pressure sensors 70 are attached to the lower surface of the second substrate W2.

[0060] When cleaning the substrate W (more specifically, when rotating the substrate W and moving the cleaning head 30 horizontally while applying ultrasonic vibrations to the liquid film F from the vibrating surface 31a of the cleaning head 30), the control unit 90 controls the vertical position of the cleaning head 30 based on the measured results so that the distance D between the substrate W and the cleaning head 30 is within an acceptable range. In this case, for example, before cleaning the substrate W, the control unit 90 determines the vertical position of the cleaning head 30 to keep the distance D within an acceptable range based on the measured results.

[0061] As described above, when cleaning the substrate W, the control unit 90 controls the vertical position of the cleaning head 30 based on the measured results so that the distance D between the substrate W and the cleaning head 30 is within an acceptable range. This allows the sound pressure SP at each of the multiple points on the substrate surface Wa to be kept within an acceptable range, and the entire substrate surface Wa can be cleaned evenly. When the distance D satisfies the above equation (1), the sound pressure SP acting on the substrate surface Wa is high, and the particle removal efficiency is good.

[0062] Alternatively, instead of controlling the vertical position of the cleaning head 30 based on the measured results, the control unit 90 may control the vertical position of the holding unit 10 so that the distance D between the substrate W and the cleaning head 30 is within an acceptable range. In this case as well, the sound pressure SP can be kept within an acceptable range at each of the multiple points on the substrate surface Wa, and the entire substrate surface Wa can be cleaned evenly.

[0063] The control unit 90 may, when cleaning the substrate W, control the output PW of the ultrasonic transducer 32 based on the measured results so that the sound pressure SP acting on the substrate W remains within an acceptable range. In this case, before cleaning the substrate W, the control unit 90 stores the relationship between the output PW and the sound pressure SP (see Figure 5) and the relationship between the distance D and the sound pressure SP (Figure 7), and determines the output PW necessary to keep the sound pressure SP within an acceptable range based on the stored relationships and the measured results.

[0064] To clean the entire surface Wa of the substrate evenly, it is sufficient to keep the time integral value of the sound pressure SP at each of the multiple points on the substrate surface Wa within an acceptable range; it is not necessary for the sound pressure SP to be outside the acceptable range. For example, when cleaning the substrate W, the control unit 90 may control the rotation speed of the holding unit 10 or the movement speed of the cleaning head 30 so that the time integral value of the sound pressure SP at each of the multiple points on the substrate surface Wa falls within an acceptable range.

[0065] When cleaning the substrate W, the control unit 90 only needs to control at least one selected from the following: the vertical position of the cleaning head 30 or the holding unit 10, the output PW of the ultrasonic transducer 32, the rotational speed of the holding unit 10, and the movement speed of the cleaning head 30 in the horizontal direction perpendicular to the rotational center line 10R of the holding unit 10, so that the time integral value of the sound pressure SP at each of the multiple points on the upper surface Wa of the substrate falls within an acceptable range.

[0066] The control unit 90 stores the results of measuring the distance D between the second substrate W2 and the cleaning head 30, or the sound pressure SP acting on the second substrate W2, at each of the multiple points P1 to P16 on the upper surface W2a of the second substrate W2, while the second substrate W2 is held by the holding unit 10 before cleaning the substrate W. However, the technology of this disclosure is not limited thereto.

[0067] For example, the control unit 90 may store the results of measuring the distance D between the substrate W and the cleaning head 30 at each of several points P1 to P16 on the upper surface Wa of the substrate W, while the substrate W is held by the holding unit 10, that is, before ultrasonic vibration is applied to the liquid film F from the vibrating surface 31a of the cleaning head 30. In this case as well, the time integral value of the sound pressure SP can be kept within an acceptable range at each of the multiple points on the upper surface Wa of the substrate, and the entire upper surface Wa of the substrate can be cleaned uniformly.

[0068] Alternatively, the control unit 90 may measure the distance D between the substrate W and the cleaning head 30, or the sound pressure SP acting on the substrate W, at each of the multiple points P1 to P16 on the upper surface Wa of the substrate W while cleaning the substrate W. In this case as well, the time integral value of the sound pressure SP can be kept within an acceptable range at each of the multiple points on the upper surface Wa of the substrate, and the entire upper surface Wa of the substrate can be cleaned uniformly.

[0069] Specifically, when cleaning the substrate W (more specifically, when rotating the substrate W and moving the cleaning head 30 horizontally while applying ultrasonic vibrations to the liquid film F from the vibrating surface 31a of the cleaning head 30), the control unit 90 may repeatedly perform the following (A) and (B): (A) Measure the distance D or sound pressure SP at a desired point on the upper surface Wa of the substrate. (B) Based on the measured result, control at least one selected from the vertical position of the cleaning head 30 or the holding unit 10, the output of the ultrasonic transducer 32, the rotation speed of the holding unit 10, and the movement speed of the cleaning head 30 in the horizontal direction perpendicular to the rotation center line 10R of the holding unit 10.

[0070] Incidentally, the substrate cleaning device 1 repeatedly cleans the substrate W while replacing the substrate W held in the holding unit 10. When the substrate W is replaced, the thickness of the substrate W may change, and the distance D between the substrate W and the cleaning head 30 may change. When the distance D changes, the sound pressure SP acting on the substrate W changes, as is clear from Figure 7.

[0071] Therefore, the control unit 90 stores the result of measuring the thickness of the substrate W before, for example, holding the substrate W in the holding unit 10. The thickness of the substrate W is measured using a general thickness gauge. The thickness gauge may be contact type or non-contact type. The thickness gauge may transmit the measured result to the control unit 90.

[0072] When cleaning the substrate W, the control unit 90 controls at least one selected from the following based on the measured substrate thickness: the vertical position of the cleaning head 30 or the holding unit 10, the output PW of the ultrasonic transducer 32, the rotational speed of the holding unit 10, and the movement speed of the cleaning head 30 in the horizontal direction perpendicular to the rotational center line 10R of the holding unit 10. This allows the time integral value of the sound pressure SP acting on the substrate W to be kept within an acceptable range, thereby suppressing uneven cleaning between substrates.

[0073] The control unit 90 stores the result of measuring the thickness of the substrate W before holding the substrate W in the holding unit 10, but the technology of this disclosure is not limited to this. In other words, the thickness of the substrate W may be measured while the substrate W is held in the holding unit 10. The thickness of the substrate W may be measured before cleaning the substrate W, or it may be measured while cleaning the substrate W. In this case as well, the time integral value of the sound pressure SP acting on the substrate W can be kept within an acceptable range, and uneven cleaning between substrates can be suppressed.

[0074] Next, with reference to Figure 14, a method for manufacturing the EUVL mask blank 200 shown in Figure 17 will be described. The method for manufacturing the EUVL mask blank 200 includes steps S101 to S107. For example, a substrate 210 shown in Figures 15 and 16 is prepared in advance. If the substrate 210 is a glass substrate, steps S101 to S104 are included in the method for manufacturing the glass substrate.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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 14, and is the quality assurance region. The quality assurance region has dimensions of, for example, 142 mm in length and 142 mm in width.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] Step S105 includes forming a conductive film 240, as shown in Figure 17, 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.

[0089] Step S106 includes forming a multilayer reflective film 220, as shown in Figure 17, 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.

[0090] Step S107 includes forming an absorption film 230, as shown in Figure 17, 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.

[0091] In this embodiment, steps S106 to S107 are performed after step S105, but they may also be performed before step S105.

[0092] By following the steps S101 to S107 described above, the EUVL mask blank 200 shown in Figure 17 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.

[0093] 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.

[0094] 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.

[0095] As shown in Figure 18, 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.

[0096] 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.

[0097] 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.

[0098] The above describes the substrate cleaning apparatus, substrate cleaning method, glass substrate manufacturing method, and EUVL mask blank manufacturing method related to this disclosure. However, 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.

[0099] This application claims priority based on Japanese Patent Application No. 2022-013019, filed with the Japan Patent Office on January 31, 2022, and the entire contents of Japanese Patent Application No. 2022-013019 are incorporated herein by reference. [Explanation of symbols]

[0100] 10 Holding part 30 Cleaning Heads 31a Vibration surface 32 Ultrasonic transducer W board W2 Second Board F liquid film

Claims

1. A method for cleaning a substrate, comprising: holding the substrate horizontally in a holding part; forming a liquid film on the upper surface of the substrate held in the holding part; contacting the vibrating surface of a cleaning head with the liquid film; vibrating the vibrating surface with an ultrasonic transducer; and rotating the substrate together with the holding part and moving the cleaning head in a horizontal direction perpendicular to the rotation center line of the holding part, With a second substrate, prepared separately from the aforementioned substrate, held in the holding unit, the distance between the second substrate and the cleaning head, or the sound pressure acting on the second substrate, is measured at each of several points on the upper surface of the second substrate. While applying ultrasonic vibrations to the liquid film from the vibrating surface of the cleaning head, the substrate is rotated and the cleaning head is moved in the horizontal direction, and at least one selected from the following is controlled based on the measured results: the vertical position of the cleaning head or the holding part, the output of the ultrasonic transducer, the rotational speed of the holding part, and the horizontal movement speed of the cleaning head. A substrate cleaning method having the following characteristics.

2. With the second substrate held by the holding part, the distance between the second substrate and the cleaning head is measured at each of several points on the upper surface of the second substrate, When rotating the substrate and moving the cleaning head in the horizontal direction while applying ultrasonic vibrations to the liquid film from the vibrating surface of the cleaning head, the vertical position of the cleaning head or the holding part is controlled based on the measured results so that the distance between the substrate and the cleaning head satisfies the following formula (1). A substrate cleaning method according to claim 1, comprising: [Math 1] In the above formula (1), D is the distance between the substrate and the cleaning head, n is an integer of 1 or more, λ is the wavelength of the ultrasonic waves applied to the liquid film from the cleaning head in the liquid film, m is an integer of 5 or more, and Θ is a value that satisfies the following formula (2) when v is the velocity of the ultrasonic waves in the liquid film and v1 is the velocity of the ultrasonic waves in the diaphragm forming the vibrating surface. [Math 2] In the above equation (2), θ is the angle between the normal to the vibrating surface of the diaphragm that is in contact with the liquid film and the normal to the mounting surface of the diaphragm to which the ultrasonic transducer is attached.

3. With the second substrate held by the holding part, the distance between the second substrate and the cleaning head is measured at each of several points on the upper surface of the second substrate, When rotating the substrate and moving the cleaning head horizontally while applying ultrasonic vibrations to the liquid film from the vibrating surface of the cleaning head, the output of the ultrasonic transducer is controlled based on the measured results so that the sound pressure acting on the substrate remains within an acceptable range. A substrate cleaning method according to claim 1, comprising:

4. A method for cleaning a substrate, comprising: holding the substrate horizontally in a holding part; forming a liquid film on the upper surface of the substrate held in the holding part; contacting the vibrating surface of a cleaning head with the liquid film; vibrating the vibrating surface with an ultrasonic transducer; and rotating the substrate together with the holding part and moving the cleaning head in a horizontal direction perpendicular to the rotation center line of the holding part, Before applying ultrasonic vibrations to the liquid film from the vibrating surface of the cleaning head, the distance between the substrate and the cleaning head is measured at each of several points on the upper surface of the substrate while the substrate is held by the holding part. While applying ultrasonic vibrations to the liquid film from the vibrating surface of the cleaning head, the substrate is rotated and the cleaning head is moved in the horizontal direction, and at least one selected from the following is controlled based on the measured results: the vertical position of the cleaning head or the holding part, the output of the ultrasonic transducer, the rotational speed of the holding part, and the horizontal movement speed of the cleaning head. A substrate cleaning method having the following characteristics.

5. When rotating the substrate and moving the cleaning head in the horizontal direction while applying ultrasonic vibrations to the liquid film from the vibrating surface of the cleaning head, the vertical position of the cleaning head or the holding part is controlled based on the measured results so that the distance between the substrate and the cleaning head satisfies the following formula (1). A substrate cleaning method according to claim 4, comprising: [Math 3] In the above formula (1), D is the distance between the substrate and the cleaning head, n is an integer of 1 or more, λ is the wavelength of the ultrasonic waves applied to the liquid film from the cleaning head in the liquid film, m is an integer of 5 or more, and Θ is a value that satisfies the following formula (2) when v is the velocity of the ultrasonic waves in the liquid film and v1 is the velocity of the ultrasonic waves in the diaphragm forming the vibrating surface. [Math 4] In the above equation (2), θ is the angle between the normal to the vibrating surface of the diaphragm that is in contact with the liquid film and the normal to the mounting surface of the diaphragm to which the ultrasonic transducer is attached.

6. When rotating the substrate and moving the cleaning head horizontally while applying ultrasonic vibrations to the liquid film from the vibrating surface of the cleaning head, the output of the ultrasonic transducer is controlled based on the measured results so that the sound pressure acting on the substrate remains within an acceptable range. A substrate cleaning method according to claim 4, comprising:

7. A method for cleaning a substrate, comprising: holding the substrate horizontally in a holding part; forming a liquid film on the upper surface of the substrate held in the holding part; contacting the vibrating surface of a cleaning head with the liquid film; vibrating the vibrating surface with an ultrasonic transducer; and rotating the substrate together with the holding part and moving the cleaning head in a horizontal direction perpendicular to the rotation center line of the holding part, The thickness of the substrate is measured before the substrate is held in the holding part, While applying ultrasonic vibrations to the liquid film from the vibrating surface of the cleaning head, the substrate is rotated and the cleaning head is moved in the horizontal direction, and at least one selected from the vertical position of the cleaning head or the holding part, the output of the ultrasonic transducer, the rotational speed of the holding part, and the horizontal movement speed of the cleaning head is controlled based on the measured plate thickness. A substrate cleaning method having the following characteristics.

8. A method for cleaning a substrate, comprising: holding the substrate horizontally in a holding part; forming a liquid film on the upper surface of the substrate held in the holding part; contacting the vibrating surface of a cleaning head with the liquid film; vibrating the vibrating surface with an ultrasonic transducer; and rotating the substrate together with the holding part and moving the cleaning head in a horizontal direction perpendicular to the rotation center line of the holding part, While applying ultrasonic vibrations to the liquid film from the vibrating surface of the cleaning head, the substrate is rotated and the cleaning head is moved in the horizontal direction, The distance between the substrate and the cleaning head, or the sound pressure acting on the substrate, is measured at a desired point on the upper surface of the substrate. Based on the measured results, control at least one selected from the following: the vertical position of the cleaning head or the holding part, the output of the ultrasonic transducer, the rotational speed of the holding part, and the horizontal movement speed of the cleaning head. A circuit board cleaning method that involves repeatedly performing the following steps.

9. While applying ultrasonic vibrations to the liquid film from the vibrating surface of the cleaning head, the substrate is rotated and the cleaning head is moved in the horizontal direction, The distance between the substrate and the cleaning head is measured at a desired point on the upper surface of the substrate, Based on the measured results, the vertical position of the cleaning head or the holding part is controlled so that the distance between the substrate and the cleaning head satisfies the following formula (1). The substrate cleaning method according to claim 8, wherein the above is repeated. 【Number 5】 In the above formula (1), D is the distance between the substrate and the cleaning head, n is an integer of 1 or more, λ is the wavelength of the ultrasonic waves applied to the liquid film from the cleaning head in the liquid film, m is an integer of 5 or more, and Θ is a value that satisfies the following formula (2) when v is the velocity of the ultrasonic waves in the liquid film and v1 is the velocity of the ultrasonic waves in the diaphragm forming the vibrating surface. [Math 6] In the above equation (2), θ is the angle between the normal to the vibrating surface of the diaphragm that is in contact with the liquid film and the normal to the mounting surface of the diaphragm to which the ultrasonic transducer is attached.

10. While applying ultrasonic vibrations to the liquid film from the vibrating surface of the cleaning head, the substrate is rotated and the cleaning head is moved in the horizontal direction, The distance between the substrate and the cleaning head is measured at a desired point on the upper surface of the substrate, Based on the measured results, the output of the ultrasonic transducer is controlled so that the sound pressure acting on the substrate remains within an acceptable range. The substrate cleaning method according to claim 8, wherein the above is repeated.

11. A method for cleaning a substrate, comprising: holding the substrate horizontally in a holding part; forming a liquid film on the upper surface of the substrate held in the holding part; contacting the vibrating surface of a cleaning head with the liquid film; vibrating the vibrating surface with an ultrasonic transducer; and rotating the substrate together with the holding part and moving the cleaning head in a horizontal direction perpendicular to the rotation center line of the holding part, The thickness of the substrate is measured while the substrate is held in the holding part, While applying ultrasonic vibrations to the liquid film from the vibrating surface of the cleaning head, the substrate is rotated and the cleaning head is moved in the horizontal direction, and at least one selected from the vertical position of the cleaning head or the holding part, the output of the ultrasonic transducer, the rotational speed of the holding part, and the horizontal movement speed of the cleaning head is controlled based on the measured plate thickness. A substrate cleaning method having the following characteristics.

12. A method for manufacturing a glass substrate, comprising cleaning the glass substrate using the substrate cleaning method described in any one of claims 1 to 11.

13. 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 method according to any one of claims 1 to 11.

14. A substrate cleaning apparatus comprising: a holding part for holding a substrate; a nozzle for forming a liquid film on the upper surface of the substrate held by the holding part; a cleaning head including a vibrating surface that contacts the liquid film and an ultrasonic transducer for vibrating the vibrating surface; a rotating part for rotating the holding part; a first moving part for moving the cleaning head in a horizontal direction perpendicular to the rotation center line of the holding part; a second moving part for moving the holding part or the cleaning head in a vertical direction; and a control unit for controlling the ultrasonic transducer, the rotating part, the first moving part, and the second moving part, The control unit is a substrate cleaning apparatus that performs the substrate cleaning method according to any one of claims 1 to 11.

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