Single-wafer ultrasonic substrate cleaning machine and vibrating unit therefor

Abstract

This invention provides a single-wafer ultrasonic substrate cleaning machine that can improve cleaning performance by enabling ultrasonic cleaning at high power and high frequency. The cleaning machine 11 includes a vibrating unit 12 with a structure in which a piezoelectric element 41 that generates ultrasonic waves is housed in a case 30, an oscillation circuit 14 that generates ultrasonic waves by applying high-frequency power to the piezoelectric element 41, and a control device 15 that controls the oscillation circuit 14. The piezoelectric element 41 has a plurality of comb-tooth electrodes 42A and 42B formed on a first main surface 41a, and a second main surface 41b is joined to the inner surface of the bottom 32 of the case 30. Leakage surface acoustic waves are generated by applying high-frequency power to the plurality of comb-tooth electrodes 42A and 42B. The control device 15 can drive the piezoelectric element 41 by selecting one of the resonance frequencies of the fundamental wave of the leakage surface acoustic wave and a resonance frequency higher than that frequency. (Selected Figure: Figure 1)

Description

Technical Field

[0001] The present invention relates to a single-sheet ultrasonic substrate cleaning machine and a vibrating body unit used therefor.

Background Art

[0002] Conventionally, a single-sheet ultrasonic substrate cleaning machine that cleans a substrate by irradiating ultrasonic waves while supplying a cleaning liquid into the gap between the substrate and a vibrating body unit in a state where the substrate to be cleaned is rotated is well known (see, for example, Patent Document 1). In recent years, a vibrating body unit in which a plurality of comb-shaped electrodes (IDT electrodes) are formed on a piezoelectric element constituting the vibrating body unit has been proposed (see, for example, Patent Document 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Disclosure of the Invention

Problems to be Solved by the Invention

[0004] By the way, the driving frequency of the piezoelectric element during substrate cleaning was conventionally about several hundred kHz to 1 MHz, but in order to improve the cleaning performance, it is desirable to increase the driving frequency. However, in order to vibrate the piezoelectric element at a high frequency, it is necessary to reduce the thickness of the piezoelectric element or, when using comb-shaped electrodes, etc. Narrowing the spacing of the comb-tooth electrodes [[ID=4l]]Therefore, it becomes difficult to manufacture the vibrating body unit. Further, even if the vibrating body unit as described above can be manufactured, structurally, the withstand voltage becomes small and the current capacity also becomes small. Therefore, in order to avoid destruction of the vibrating body unit, it is necessary to use the piezoelectric element without applying too high power, and there is a problem that a high cleaning effect cannot be expected.

[0005] The present invention has been made in view of the above problems, and its objective is to provide a single-wafer ultrasonic substrate cleaning machine and a vibrating unit therefor, which can improve cleaning performance by enabling ultrasonic cleaning at high power and high frequency. [Means for solving the problem]

[0006] To solve the above problems, the invention described in claim 1 is a single-wafer ultrasonic substrate cleaning machine comprising a vibrating body unit having a structure in which a piezoelectric element that generates ultrasonic waves is housed in a case, an oscillation circuit that generates ultrasonic waves by applying high-frequency power to the piezoelectric element, and a control device that controls the oscillation circuit, wherein the substrate, which is the object to be cleaned, is rotated and a cleaning liquid is supplied to the gap between the substrate and the vibrating body unit while ultrasonic waves are irradiated, the piezoelectric element being a plate-shaped member having a first main surface and a second main surface, the first main surface It is composed of a comb tooth pattern with a line / space of 0.15 mm or more. The gist of this invention is a single-wafer ultrasonic substrate cleaning machine characterized in that a plurality of comb-tooth electrodes are formed, the second main surface is joined to the inner surface of the bottom of the case, a leakage surface acoustic wave is generated by applying high-frequency power to the plurality of comb-tooth electrodes, and the control device can drive the piezoelectric element by selecting one of the resonance frequencies from the fundamental frequency of the leakage surface acoustic wave and a resonance frequency higher than the resonance frequency of the fundamental frequency.

[0007] Therefore, according to the invention described in claim 1, the piezoelectric element can be driven not only at the resonant frequency of the fundamental wave of the leakage surface acoustic wave, but also at a higher resonant frequency. As a result, the spacing between the multiple comb-tooth electrodes can be narrowed and the thickness of the piezoelectric element can be reduced. Thin Without modification, high-frequency ultrasonic cleaning is possible through high-power drive, thereby improving cleaning performance.

[0008] The invention described in claim 2 is characterized in that, in claim 1, the piezoelectric element generates a leakage surface acoustic wave having a fundamental resonance frequency of 3 MHz or higher, and is capable of generating leakage surface acoustic waves in multiple wavelength ranges including resonance frequencies that are three times or more higher than the fundamental resonance frequency.

[0009] Therefore, according to the invention described in claim 2, the piezoelectric element can be driven not only at the fundamental wave resonant frequency of 3 MHz or higher, but also at resonant frequencies higher than that, thus enabling ultrasonic cleaning at higher frequencies than conventional methods.

[0010] The invention described in claim 3 is characterized in that, in claim 2, the control device drives the piezoelectric element at a relatively low resonant frequency in the initial stage of cleaning, and then switches to a relatively high resonant frequency to drive the piezoelectric element.

[0011] Therefore, according to the invention described in claim 3, dirt adhering to the substrate can first be loosened at a relatively low frequency, and then the loosened dirt can be efficiently removed at a relatively high frequency. Thus, cleaning performance can be improved.

[0012] The invention described in claim 4 is characterized in that, in the case of cleaning the substrate using a plurality of types of cleaning liquids in claim 2, the control device drives the piezoelectric element by switching the resonant frequency for each type of cleaning liquid.

[0013] Therefore, according to the invention described in claim 4, the piezoelectric element can be driven at a suitable resonant frequency depending on the type and application of each cleaning solution. Thus, cleaning performance can be improved.

[0014] The invention described in claim 5 is characterized in that, in any one of claims 1 to 4, the bottom of the case has a flat bottom surface and is formed in a substantially circular shape when viewed from a direction perpendicular to the bottom surface.

[0015] Therefore, according to the invention described in claim 5, if the bottom of the case has such an external shape, even if the vibrator unit is swung horizontally during substrate cleaning, it is less likely to splash up the cleaning fluid. Thus, it is possible to prevent the cleaning fluid from entering the case through the seal portion.

[0016] The invention according to claim 6 is characterized in that, in any one of claims 1 to 4, the case includes a bottomed concave quartz case body having the bottom and an upper opening, and a cover body that liquid-tightly closes the upper opening.

[0017] The invention according to claim 7 is a vibrating body unit used in a single-sheet ultrasonic substrate cleaning machine, having a structure in which a piezoelectric element that generates ultrasonic waves is housed in a case. The piezoelectric element is a plate-like member having a first main surface and a second main surface. On the first main surface It is composed of a comb tooth pattern with a line / space of 0.15 mm or more. a plurality of comb-shaped electrodes are formed, the second main surface is joined to the inner surface of the bottom of the case, and by applying high-frequency power to the plurality of comb-shaped electrodes, leaky surface acoustic waves having a fundamental wave resonance frequency of 3 MHz or more are generated, and leaky surface acoustic waves in a plurality of wavelength regions including a resonance frequency three times or more higher than the frequency of the fundamental wave can be generated. The gist of the invention is a vibrating body unit for a single-sheet ultrasonic substrate cleaning machine.

Effect of the Invention

[0018] As described in detail above, according to the inventions of claims 1 to 7, ultrasonic cleaning at high power and high frequency is possible, so the cleaning performance can be improved.

Brief Description of the Drawings

[0019] [Figure 1] Schematic diagram showing a single-sheet ultrasonic substrate cleaning machine according to an embodiment embodying the present invention. [Figure 2] Schematic cross-sectional view showing a vibrating body unit in the single-sheet ultrasonic substrate cleaning machine of the embodiment. [Figure 3] Bottom view showing the above vibrating body unit. [Figure 4] Plan view showing a piezoelectric element included in the above vibrating body unit. [Figure 5] Graph for explaining the vibration characteristics of the piezoelectric element of the embodiment. ​​​​A plan view showing a piezoelectric element included in a vibrator unit of another embodiment.

Best Mode for Carrying Out the Invention

[0020] Hereinafter, a single-sheet ultrasonic substrate cleaning machine 11 according to an embodiment embodying the present invention will be described in detail based on FIGS. 1 to 5.

[0021] FIG. 1 is a schematic view showing the single-sheet ultrasonic substrate cleaning machine 11 of the present embodiment. FIG. 2 is a schematic cross-sectional view showing the vibrator unit 12 in the substrate cleaning machine 11. FIG. 3 is a bottom view showing the vibrator unit 12. FIG. 4 is a plan view showing a piezoelectric element 41 included in the vibrator unit 12.

[0022] This single-sheet ultrasonic substrate cleaning machine 11 is a device for cleaning substrates B1, which are objects to be cleaned, one by one using a cleaning liquid L1. More specifically, this single-sheet ultrasonic substrate cleaning machine 11 is a device for cleaning the substrate B1 by irradiating ultrasonic waves while supplying the cleaning liquid L1 to the rotating substrate B1. The substrate B1 is not limited, but as a preferred example, for example, a disk-shaped semiconductor wafer B1 can be cited. In the present embodiment, the semiconductor wafer B1 after removing relatively large particles through CMP processing and scrub cleaning is used as the object to be cleaned. In such a semiconductor wafer B1, relatively fine particles still remain unremoved, so ultrasonic cleaning is performed for the purpose of completely removing the fine particles. In addition, trace amounts of organic contamination, metal contamination, oil and grease generated during the manufacturing process, and natural oxide films generated by contact with the atmosphere are also targets to be removed by ultrasonic cleaning.

[0023] As shown in Figure 1, this single-wafer ultrasonic substrate cleaning machine 11 comprises a substrate rotation mechanism 2, a cleaning fluid supply nozzle 4, a vibrator unit mounting jig 3, a vibrator unit 12, and a control unit 13. The substrate rotation mechanism 2 has a circular stage 2a for horizontally placing a semiconductor wafer B1, and a rotating shaft 2b that supports the stage 2a by being connected to the center of the lower surface of the stage 2a. The rotating shaft 2b is driven by a motor (not shown) and is configured to rotate when driven by the motor.

[0024] The cleaning solution supply nozzle 4 is positioned diagonally downward on the upper surface of the stage 2a, and supplies cleaning solution L1 to the upper surface of the semiconductor wafer B1 from its tip. The cleaning solution L1 is not particularly limited as long as it is a liquid that can clean the surface of the semiconductor wafer B1, and may be either pure water or a chemical solution. Examples of chemical solutions include aqueous solutions of hydrofluoric acid, nitric acid, phosphoric acid, sulfuric acid, hydrochloric acid, acetic acid, ammonia, and hydrogen peroxide. The chemical solution is selected appropriately depending on the object to be cleaned. The number of cleaning solution supply nozzles 4 is not particularly limited, but if multiple types of cleaning solution L1 are used, it is desirable to provide a cleaning solution supply nozzle 4 for each type.

[0025] The vibrating unit mounting jig 3 is positioned above the stage 2a, and the vibrating unit 12 can be attached to the lower surface of its tip. The vibrating unit mounting jig 3 is supported by a rocking mechanism (not shown) and is configured to rock along the direction of the upper surface of the stage 2a when driven by the rocking mechanism. The control unit 13 comprises an oscillation circuit 14 and a control device 15, and is connected to the vibrating unit 12 via a cable 27. The oscillation circuit 14 is a circuit for generating ultrasonic waves by applying high-frequency power to the piezoelectric element 41 of the vibrating unit 12, which will be described later. The control device 15 is a device for controlling the operation of the oscillation circuit 14.

[0026] As shown in Figures 1 and 2, the vibrating unit 12 has a structure in which a piezoelectric element 41 that generates ultrasonic waves is housed in a case 30, and its upper side is attached to the vibrating unit mounting jig 3. The case 30 that constitutes the vibrating unit 12 comprises a case body 31 and a cover body 21.

[0027] The case body 31 of this embodiment is a quartz member having a circular cross-section and a bottomed concave shape, and has a bottom portion 32 and a side wall portion 34. The bottom portion 32 is circular when viewed from a direction perpendicular to the bottom surface 32a (see Figure 3), and the side wall portion 34 is integrally formed on the outer circumference of the bottom portion 32. The thickness of the bottom portion 32 is uniform, and both the inner surface 32b and the outer surface 32a of the bottom portion are flat and smooth surfaces. The thickness of the bottom portion 32 is arbitrary and not particularly limited, but is set to approximately 1.0 mm to 2.0 mm (1.7 mm in this embodiment). An upper flange portion 33 is integrally formed on the upper opening 35 of the case body 31, i.e., the upper edge of the side wall portion 34. The case body 31 serves as a container for housing the piezoelectric element 41, and also serves as an acoustic matching layer that efficiently transmits ultrasonic vibrations generated by the piezoelectric element 41 to the outside. In this embodiment, the case body 31 is made of quartz, but it may of course be made of other materials (for example, ceramics such as silicon carbide, or metals such as stainless steel or aluminum).

[0028] The cover body 21 is a component that liquid-tightly seals the upper opening 35 to prevent cleaning fluid L1 from entering the case body 31. The cover body 21 is composed of two components: an upper cover 22 and a lower cover 23. Both the upper cover 22 and the lower cover 23 are made of resin material, and in this embodiment, they are made of fluororesin, which has excellent chemical resistance and heat resistance. The lower cover 23 is a component formed in the shape of a circular ring and is positioned to surround approximately half of the upper part of the side wall portion 34 of the case body 31. The upper cover 22 is a component formed in the shape of a circular lid and is positioned to cover the upper opening 35 completely. The upper end surface of the lower cover 23 is positioned flush with the upper surface of the upper flange portion 33, and the lower outer circumference of the upper cover 22 is positioned to be in surface contact with both the upper end surface of the lower cover 23 and the upper surface of the upper flange portion 33. Multiple bolt insertion holes 22c are formed through the outer circumference of the upper cover 22 and the lower cover 23 at various locations. Bolts 25 are inserted through these bolt insertion holes 22c to secure the upper cover 22 and the lower cover 23 to each other. In other words, the upper cover 22 and the lower cover 23 are fixed to the case body 31 by sandwiching the upper flange portion 33 from above and below.

[0029] Furthermore, a sealing member 24 is provided at the interface between at least one of the upper cover 22 and the lower cover 23 and the upper flange portion 33. Specifically in this embodiment, a circular sealing retaining groove 22a is provided on the outer circumference of the lower surface of the upper cover 22, and a silicone rubber O-ring, which is the sealing member 24, is held within the sealing retaining groove 22a. The sealing retaining groove 22a and the sealing member 24 are provided corresponding to the position on the upper surface of the flange portion 33. Therefore, when the upper cover 22 is installed, the sealing member 24 is positioned at the interface between the upper cover 22 and the upper flange portion 33. This sealing structure prevents the ingress of cleaning fluid L1 through the interface.

[0030] As shown in Figures 1 to 4, the piezoelectric element 41 is a plate-shaped member with a circular shape in plan view, having a first main surface 41a and a second main surface 41b, and is a ceramic sintered body formed using a piezoelectric ceramic material. The piezoelectric ceramic material is not particularly limited, but in this embodiment, for example, PZT is used. The thickness of the piezoelectric element 41 is not particularly limited and can be arbitrary, but for example, it is set to a thickness of about 1 / 3 to 1 / 2 of the thickness of the bottom 32 (0.64 mm in this embodiment). This piezoelectric element 41 occupies approximately the same area as the inner surface 32b of the bottom 32 of the case body 31, specifically occupying 95% or more of the area. The second main surface 41b of the piezoelectric element 41 is bonded to the inner surface 32b of the bottom 32 with an adhesive.

[0031] As shown in Figure 4, a pair of comb-tooth electrodes 42A and 42B are formed on the first main surface 41a of the piezoelectric element 41. One comb-tooth electrode 42A is composed of a strip-shaped base pattern 43 and numerous linear comb-tooth patterns 44 that are narrower than the base pattern 43 and extend parallel to the short direction of the base pattern 43. The other comb-tooth electrode 42B is composed of a strip-shaped base pattern 43 and numerous linear comb-tooth patterns 45 that are narrower than the base pattern 43 and extend parallel to the short direction of the base pattern 43. The comb-tooth patterns 44 and 45 are arranged alternately at regular intervals. In Figure 4, for illustrative purposes, the number of comb-tooth patterns 44 and 45 is depicted in a simplified manner with a considerably reduced number, but in reality, there are 20 or more comb-tooth patterns 44 and 45 each (approximately 50 each in this embodiment). Furthermore, the line / space of the comb tooth patterns 44 and 45 are equal, for example, set to approximately 0.15 mm to 0.30 mm each (0.16 mm each in this embodiment). The pair of comb tooth electrodes 42A and 42B are formed in an area of ​​more than half of the first main surface 41a of the piezoelectric element 41, preferably in an area of ​​50% to 95% of the first main surface 41a. The method for forming the comb tooth patterns 44 and 45 is not particularly limited, and appropriate methods such as attaching metal conductive foil, printing and firing metal conductive paste, sputtering of metal conductors, and etching of metal conductive layers can be used.

[0032] As shown in Figure 2, the wiring 29 inside the cable 27 is electrically connected to the pair of comb-tooth electrodes 42A and 42B by soldering or the like. A cable insertion hole 22b is provided in the center of the upper cover 22. The cable 27 is led out to the outside of the case 30 through this cable insertion hole 22b. A nut member 26 is provided in the center of the upper surface of the upper cover 22, corresponding to the cable insertion hole 22b. A sealing member 28 is provided around the cable insertion hole 22b in the center of the upper surface of the upper cover 22. This sealing member 28 is interposed between the nut member 26 and the upper cover 22, preventing the cleaning fluid L1 from entering through the cable insertion hole 22b.

[0033] As shown in Figure 2, the vibrating unit 12 further comprises a backing material 52 and a resin molded portion 51. The backing material 52 is, for example, a sheet-like porous material, and is placed on the first main surface 41a of the piezoelectric element 41 to attenuate and absorb ultrasonic vibrations emitted from the first main surface 41a side. The resin molded portion 51 is provided so as to fill the lower half of the internal space of the case body 31.

[0034] As shown in Figure 1, the cable 27 extending from the case 30 is electrically connected to the oscillation circuit 14 in the control unit 13. The oscillation circuit 14 generates a predetermined high frequency based on a command from the control device 15 and outputs high-frequency power to a pair of comb-tooth electrodes 42A and 42B of the piezoelectric element 41 through the wiring 29 in the cable 27. The pair of comb-tooth electrodes 42A and 42B then generate leakage surface acoustic waves when high-frequency power is applied. In particular, the piezoelectric element 41 of this embodiment generates leakage surface acoustic waves with a fundamental wave resonance frequency of 3 MHz or higher when high-frequency power is applied to the pair of comb-tooth electrodes 42A and 42B. Furthermore, the piezoelectric element 41 of this embodiment is capable of generating leakage surface acoustic waves in multiple wavelength ranges, including resonance frequencies that are three times or more higher than the frequency of its fundamental wave.

[0035] The control device 15 is a device for controlling the oscillation circuit 14 and consists of a personal computer including a CPU, ROM, RAM, etc. The ROM of the control device 15 stores a predetermined control program, and the CPU is configured to read the control program from the ROM and execute various processes. The control device 15 then outputs a command signal to the oscillation circuit 14 to generate a predetermined high frequency, thereby driving the piezoelectric element 41 to vibrate at the resonant frequency of the fundamental wave of the leakage surface acoustic wave, or a resonant frequency higher than that frequency. Input devices such as a keyboard and display devices such as a display are electrically connected to the control device 15.

[0036] Next, the method of using the single-wafer ultrasonic substrate cleaning machine 11 of this embodiment will be described. First, the substrate B1 is placed horizontally on the stage 2a of the substrate rotation mechanism 2, and the semiconductor wafer B1 is held in place by suction on the upper surface of the stage 2a using a chuck mechanism (not shown). Next, the motor is driven to rotate the rotation shaft 2b and the stage 2a, and at the same time, cleaning liquid L1 is supplied from the cleaning liquid supply nozzle 4 to the upper surface of the semiconductor wafer B1. Next, the vibrating body unit 12, which is attached to the vibrating body unit mounting jig 3, is positioned with a gap 7 between it and the upper surface of the semiconductor wafer B1. At this time, the size of the gap 7 is set to, for example, about 1 mm to 5 mm. Subsequently, the oscillation mechanism is driven to oscillate the vibrating body unit 12, and the piezoelectric element 41 is driven by the supply of high-frequency power from the oscillation circuit 14. Then, the pair of comb-tooth electrodes 42A and 42B generate leakage surface acoustic waves when high-frequency power is applied, and the entire piezoelectric element 41 vibrates ultrasonically. These ultrasonic vibrations are transmitted through the bottom 32 of the case body 31 and radiated to the outside of the vibrating unit 12, causing the cleaning liquid L1 filling the gap 7 to vibrate. In this case, the leaking surface acoustic waves propagate along the alignment direction of the comb tooth patterns 44 and 45 of the pair of comb-tooth electrodes 42A and 42B, resulting in the discharge and removal of fine particles adhering to the semiconductor wafer B1.

[0037] Figure 5 is a graph illustrating the vibration characteristics of the piezoelectric element 41 of this embodiment. The vertical axis represents the impedance value (Ω), and the horizontal axis represents the frequency (MHz). This graph shows that there is a region around 3.2 MHz where the impedance is minimal. The frequency corresponding to this minimum is the resonance frequency rp1 of the fundamental wave of the leakage surface acoustic wave, and its impedance value is approximately 0.5 Ω. Furthermore, according to this graph, in the frequency range higher than the resonance frequency rp1 of the fundamental wave, there are several regions where the impedance value is the same as or less than that of the resonance frequency rp1 of the fundamental wave. Specifically, the impedance minimums are located around 4.5 MHz, 5.3 MHz, 6.2 MHz, 7.5 MHz, 8.0 MHz, 9.1 MHz, 9.7 MHz, 10.5 MHz, and 11.6 MHz.

[0038] The minimum value around 4.5MHz indicates a resonant frequency approximately 1.4 times higher than the fundamental resonant frequency rp1 (second resonant frequency rp2). The minimum value around 5.3MHz indicates a resonant frequency approximately 1.6 times higher than the fundamental resonant frequency rp1 (third resonant frequency rp3). The minimum value around 6.2MHz indicates a resonant frequency approximately 1.9 times higher than the fundamental resonant frequency rp1 (fourth resonant frequency rp4). The minimum value around 7.5MHz indicates a resonant frequency approximately 2.3 times higher than the fundamental resonant frequency rp1 (fifth resonant frequency rp5). The minimum value around 8.0MHz indicates a resonant frequency approximately 2.5 times higher than the fundamental resonant frequency rp1 (sixth resonant frequency rp6). The minimum value around 9.1MHz indicates a resonant frequency approximately 2.8 times higher than the fundamental resonant frequency rp1 (seventh resonant frequency rp7). The minimum value around 9.7MHz indicates a resonant frequency approximately 3.0 times higher than the fundamental resonant frequency rp1 (8th resonant frequency rp8). The minimum value around 10.5MHz indicates a resonant frequency approximately 3.3 times higher than the fundamental resonant frequency rp1 (9th resonant frequency rp9). The minimum value around 11.6MHz indicates a resonant frequency approximately 3.6 times higher than the fundamental resonant frequency rp1 (10th resonant frequency rp10).

[0039] When using the single-wafer ultrasonic substrate cleaning machine 11 in manual mode, for example, the user can specify and select one or more resonant frequencies from the above 10 types of resonant frequencies rp1 to rp10 using the input device. For example, if the user specifies and selects the fundamental resonant frequency rp1, the control device 15 outputs a command to the oscillation circuit 14 to generate a high frequency of approximately 3.2 MHz. In response, the oscillation circuit 14 outputs a high frequency of approximately 3.2 MHz to the piezoelectric element 41, causing the piezoelectric element 41 to vibrate ultrasonically at approximately 3.2 MHz, which is the fundamental resonant frequency rp1. Furthermore, the user can also specify and select a resonant frequency that is three times or more higher than the fundamental resonant frequency rp1. For example, if the user specifies and selects the ninth resonant frequency rp9, the control device 15 outputs a command to the oscillation circuit 14 to generate a high frequency of approximately 10.5 MHz. In response, the oscillation circuit 14 outputs a high frequency of approximately 10.5 MHz to the piezoelectric element 41, causing the piezoelectric element 41 to vibrate ultrasonically at approximately 10.5 MHz, which is the ninth resonant frequency rp9.

[0040] As described above, ultrasonic cleaning may be performed in manual mode, where the user appropriately switches the resonant frequency to drive the piezoelectric element 41 through their own operation. However, in the single-wafer ultrasonic substrate cleaning machine 11 of this embodiment, it is also possible to select other modes. Specifically, ultrasonic cleaning can be performed in automatic mode, where the control device 15 automatically switches the resonant frequency to drive the piezoelectric element 41. When the single-wafer ultrasonic substrate cleaning machine 11 is used, for example, in automatic mode, the control device 15 first drives the piezoelectric element 41 at a relatively low resonant frequency (e.g., rp1) in the initial stage of the cleaning process using a predetermined cleaning solution L1. At this time, the dirt adhering to the semiconductor wafer B1 is loosened. After a predetermined time has elapsed, the control device 15 switches to a relatively high resonant frequency (e.g., rp9) to drive the piezoelectric element 41. At this time, the loosened dirt is efficiently removed. Here, an example of switching the resonant frequency in two stages (rp1→rp9) is shown, but it may also be switched in three stages (e.g., rp1→rp4→rp9) or in four stages (e.g., rp1→rp4→rp7→rp10).

[0041] Therefore, according to this embodiment, the following effects can be obtained.

[0042] (1) The single-wafer ultrasonic substrate cleaning machine 11 of this embodiment includes a vibrating unit 12 having a structure in which a piezoelectric element 41 is housed in a case 30, an oscillation circuit 14 that generates ultrasonic waves by applying high-frequency power to the piezoelectric element 41, and a control device 15 that controls the oscillation circuit 14. A pair of comb-tooth electrodes 42A and 42B are formed on the first main surface 41a of the piezoelectric element 41 of the vibrating unit 12, and the second main surface 41b is joined to the bottom inner surface 32b of the case 30. The piezoelectric element 41 generates leakage surface acoustic waves by applying high-frequency power to the pair of comb-tooth electrodes 42A and 42B. The control device 15 is capable of driving the piezoelectric element 41 by selecting one of the resonance frequencies rp2 to rp10, which are higher than the fundamental resonance frequency rp1 of the leakage surface acoustic wave.

[0043] With this configuration, the piezoelectric element 41 can be driven not only at the fundamental resonance frequency rp1 of the leakage surface acoustic wave, but also at higher resonance frequencies rp2 to rp10. As a result, the spacing between the pair of comb-tooth electrodes 42A and 42B can be narrowed, and the thickness of the piezoelectric element 41 can be reduced. Thin Without modification, high-frequency ultrasonic cleaning is possible by driving with high power, thereby improving cleaning performance. In addition, the spacing between the pair of comb-tooth electrodes 42A and 42B and the thickness of the piezoelectric element 41 can be narrowed. Thin Since chemical processing is unnecessary, the vibrating unit 12 becomes easier to manufacture, and its withstand voltage and current capacity are increased. Therefore, the piezoelectric element 41 is less likely to be damaged even when high power is applied. In addition, since the ultrasonic substrate cleaning machine 11 of this embodiment is a single-wafer type, the amount of cleaning solution L1 used can be reduced compared to batch type or flowing water type machines. Furthermore, it is possible to prevent the re-adhesion of dirt to the semiconductor wafer B1.

[0044] (2) In this embodiment, the control device 15 drives the piezoelectric element 41 at a relatively low resonant frequency in the initial stage of cleaning, and then switches to a relatively high resonant frequency to drive the piezoelectric element 41. This allows the dirt adhering to the semiconductor wafer B1 to be loosened first at a relatively low frequency, and then the loosened dirt to be efficiently removed at a relatively high frequency. In addition, by switching the frequency during the cleaning process, the generation of standing waves is prevented, and uneven cleaning is less likely to occur. As a result, the cleaning performance can be improved.

[0045] (3) In this embodiment, the bottom 32 of the case 30 has a flat bottom surface 32a and is formed in a substantially circular shape when viewed from a direction perpendicular to the bottom surface 32a. With the bottom 32 of the case 30 having such an external shape, even when the transducer unit 12 is oscillated horizontally while the semiconductor wafer B1 is rotated during cleaning of the semiconductor wafer B1, it becomes difficult to stir up the cleaning liquid L1. Thus, it is possible to prevent the cleaning liquid L1 from entering the case 30 through the seal portion.

[0046] (4) In particular, the case 30 of this embodiment comprises a bottomed concave quartz case body 31 having a bottom 32 and an upper opening 35, and a cover body 21 that liquid-tightly seals the upper opening 35. The cover body 21 is composed of an upper cover 22 and a lower cover 23 made of fluororesin. The upper flange portion 33 formed in the upper opening 35 of the case body 31 is sandwiched from above and below by the upper cover 22 and the lower cover 23. An O-ring, which is a sealing member 24, is provided at the interface between the upper cover 22 and the upper flange portion 33. With this configuration, the intrusion path of the cleaning liquid L1 through the upper opening 35 of the case body 31 is lengthened, and the intrusion path is almost completely blocked, so that the intrusion of the cleaning liquid L1 into the case 30 can be prevented more reliably.

[0047] The embodiments of the present invention may be modified as follows.

[0048] In the above embodiment of the vibrating body unit 12, the bottom 32 of the case body 31 was formed in a circular shape in plan view, so the aspect ratio defined by the maximum diameter / minimum diameter was 1, but it is not limited to this. For example, as in the vibrating body unit 12A of another embodiment shown in Figure 6, the bottom 32 of the case body 31 may be formed in an elliptical shape in plan view. That is, the aspect ratio defined by the maximum diameter / minimum diameter of the bottom 32 of the case body 31 may be 2 or less (preferably 1.5 or less). In addition, an elliptical piezoelectric element 41B may be provided in conjunction with this.

[0049] In the above embodiment, the numerous comb tooth patterns 44 and 45 on the pair of comb-tooth electrodes 42A and 42B are formed linearly, but the embodiment is not limited to this. For example, as in the piezoelectric element 41A of another embodiment shown in Figure 7, the numerous comb tooth patterns 44 and 45 may be formed in a semicircular shape and arranged concentrically overall. This configuration makes it easier to form the pair of comb-tooth electrodes 42A and 42B over a wide area on the first main surface 41a of the piezoelectric element 41A.

[0050] In the above embodiment, the control device 15 drives the piezoelectric element 41 at a relatively low resonant frequency in the initial stage of cleaning, and then switches to a relatively high resonant frequency to drive the piezoelectric element 41 (e.g., rp1 → rp9), but is not limited to this. For example, the piezoelectric element 41 may be driven by switching to the resonant frequency in the opposite direction (e.g., rp9 → rp1). Also, in a cleaning process using a predetermined cleaning solution L1, the piezoelectric element 41 may be driven by repeatedly switching between high and low resonant frequencies (e.g., rp1 → rp9 → rp1 → rp9). Alternatively, the piezoelectric element 41 may be driven by randomly switching the resonant frequency (e.g., rp1 → rp5 → rp3 → rp9 → rp7).

[0051] In the above embodiment, the single-wafer ultrasonic substrate cleaning machine 11 was used for cleaning after the CMP process, but it is not limited to this. For example, in another embodiment, the single-wafer ultrasonic substrate cleaning machine 11 may be used for cleaning after the film formation process, after the etching process, or after the resist stripping process.

[0052] • In the above embodiment, an example was shown in which the control device 15 drives the piezoelectric element 41 by switching the resonant frequency in the middle of the cleaning process when cleaning the semiconductor wafer B1 using one type of cleaning solution L1, but the embodiment is not limited to this. For example, in another embodiment, when cleaning the semiconductor wafer B1 using multiple types of cleaning solutions L1, the control device 15 may drive the piezoelectric element 41 by switching the resonant frequency for each type of cleaning solution L1. To give a specific example, suppose a series of cleaning processes consists of a first process using a chemical solution mixed with sulfuric acid and hydrogen peroxide, a second process using a chemical solution mixed with ammonia and hydrogen peroxide, a third process using a chemical solution mixed with fluorine and pure water, a fourth process using a chemical solution mixed with hydrochloric acid and hydrogen peroxide, and a fifth process using pure water. In this case, for example, the resonant frequency may be switched for each process, such as rp1→rp8→rp4→rp10→rp2, to drive the piezoelectric element 41. According to this, the piezoelectric element 41 can be driven at a suitable resonant frequency depending on the type and application of each cleaning solution L1, thereby improving cleaning performance.

[0053] • In the above embodiment, a semiconductor wafer B1 was used as an example of the object to be cleaned, but the embodiment is not limited to this. In another embodiment, a substrate other than a semiconductor wafer B1 (such as a ceramic substrate or various wiring substrates) may be used as the object to be cleaned.

[0054] Next, in addition to the technical ideas described in the claims, the technical ideas that can be grasped by the embodiments described above are listed below.

[0055] (1) In claim 1, etc., the plurality of comb-tooth electrodes are formed in an area of ​​more than half (preferably 50% to 95%) of the first main surface of the piezoelectric element. (2) In claim 1, etc., the bottom of the case has an aspect ratio defined by the maximum diameter / minimum diameter of 2 or less (preferably 1.5 or less). (3) In claim 6, the cover body comprises an upper cover and a lower cover made of fluororesin. (4) In claim 6, the cover body comprises an upper cover and a lower cover made of fluororesin, an upper flange portion is formed at the upper opening of the case body, the upper flange portion is sandwiched from above and below by the upper cover and the lower cover, and a sealing member is provided at the interface between at least one of the upper cover and the lower cover and the upper flange portion. [Explanation of Symbols]

[0056] 7: Gap 11: Single-wafer ultrasonic substrate cleaning machine 12, 12A: Vibrating Unit 14: Oscillator Circuit 15: Control device 21: Cover body 30: Case 31: Case body 32: Bottom 32b: Bottom inner surface 32a: Bottom surface (bottom outer surface) 35: Upper opening 41, 41A, 41B: Piezoelectric element 41a: First main surface 41b: Second main surface 42A, 42B: Comb electrode B1: Semiconductor wafer as a substrate L1: Cleaning solution rp1~rp10: Resonance frequency

Claims

1. A vibrating unit having a structure in which a piezoelectric element that generates ultrasonic waves is housed in a case, An oscillation circuit that generates ultrasonic waves by applying high-frequency power to the piezoelectric element, A control device that controls the oscillation circuit and A single-wafer ultrasonic substrate cleaning machine comprising the following components, which cleans a substrate by rotating the substrate and supplying cleaning fluid to the gap between the substrate and the vibrating unit while irradiating the substrate with ultrasonic waves, The piezoelectric element is a plate-shaped member having a first main surface and a second main surface, wherein a plurality of comb-tooth electrodes, each having a comb-tooth pattern with a line / space of 0.15 mm or more, are formed on the first main surface, the second main surface is joined to the inner surface of the bottom of the case, and leakage surface acoustic waves are generated by applying high-frequency power to the plurality of comb-tooth electrodes. The control device can drive the piezoelectric element by selecting one of the resonant frequencies from the fundamental frequency of the leakage surface acoustic wave and a resonant frequency higher than the fundamental frequency. A single-wafer ultrasonic substrate cleaning machine characterized by the following features.

2. The piezoelectric element generates the leakage surface acoustic wave whose fundamental frequency is 3 MHz or higher, It is possible to generate leakage surface acoustic waves in multiple wavelength ranges, including resonant frequencies that are three times or more higher than the resonant frequency of the fundamental wave. A single-wafer ultrasonic substrate cleaning machine according to claim 1, characterized in that...

3. The single-wafer ultrasonic substrate cleaning machine according to claim 2, characterized in that the control device drives the piezoelectric element at a relatively low resonant frequency in the initial stage of cleaning, and then switches to a relatively high resonant frequency to drive the piezoelectric element.

4. When cleaning the substrate using multiple types of cleaning solutions, The control device drives the piezoelectric element by switching the resonant frequency for each type of cleaning fluid. A single-wafer ultrasonic substrate cleaning machine according to claim 2, characterized in that...

5. The single-wafer ultrasonic substrate cleaning machine according to any one of claims 1 to 4, characterized in that the bottom of the case has a flat bottom surface and is formed in a substantially circular shape when viewed from a direction perpendicular to the bottom surface.

6. The single-wafer ultrasonic substrate cleaning machine according to any one of claims 1 to 4, characterized in that the case comprises a bottomed concave quartz case body having the bottom and top openings, and a cover body that liquid-tightly seals the top opening.

7. A vibrating unit used in a single-wafer ultrasonic substrate cleaning machine, comprising a structure in which a piezoelectric element that generates ultrasonic waves is housed in a case, The piezoelectric element is It is a plate-like member having a first main surface and a second main surface, Multiple comb-tooth electrodes, each having a comb-tooth pattern with a line / space of 0.15 mm or more, are formed on the first main surface, and the second main surface is joined to the inner surface of the bottom of the case. By applying high-frequency power to multiple comb-tooth electrodes, it is possible to generate leakage surface acoustic waves with a fundamental resonance frequency of 3 MHz or higher, and to generate leakage surface acoustic waves in multiple wavelength ranges, including resonance frequencies that are three times or more higher than the fundamental resonance frequency. A vibrating unit for a single-wafer ultrasonic substrate cleaning machine, characterized by the following features.

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