Single-wafer ultrasonic substrate cleaning machine and vibrator unit for same

Abstract

Provided is a single-wafer ultrasonic substrate cleaning machine that can perform ultrasonic cleaning at high power and high frequency and is thus capable of improving the cleaning performance. The cleaning machine 11 includes: a vibrator unit 12 having a structure in which a piezoelectric element 41 for generating ultrasonic waves is accommodated in a case 30; an oscillation circuit 14 for generating ultrasonic waves by applying high-frequency power to the piezoelectric element 41; and a control device 15 for controlling the oscillation circuit 14. In the piezoelectric element 41, a plurality of comb-tooth electrodes 42A, 42B are formed on a first main surface 41a, a second main surface 41b is joined to the inner surface of a bottom portion 32 of the case 30, and a leakage surface acoustic wave is generated by applying high-frequency power to the plurality of comb-tooth electrodes 42A, 42B. The control device 15 can drive the piezoelectric element 41 by selecting one of a resonance frequency of a fundamental wave of the leakage surface acoustic wave and a resonance frequency higher than the resonance frequency of the fundamental wave.

Description

Single-sheet ultrasonic substrate cleaning machine and vibrating unit therefor

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

[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 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 unit having a plurality of comb electrodes (IDT electrodes) formed on a piezoelectric element has been proposed (see, for example, Patent Document 2).

[0003] Japanese Patent Application Laid-Open No. 2011-115717, Japanese Patent Application Laid-Open No. 11-169441

[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 to reduce the thickness of the piezoelectric element when using comb electrodes, which makes it difficult to manufacture the vibrating unit. Further, even if a vibrating unit as described above can be manufactured, the withstand voltage is structurally reduced and the current capacity is also reduced. Therefore, in order to avoid destruction of the vibrating 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 an object thereof is to provide a single-sheet ultrasonic substrate cleaning machine capable of ultrasonic cleaning at high power and high frequency and thus improving the cleaning performance, and a vibrating unit therefor.

[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, a plurality of comb-tooth electrodes formed on the first main surface, the second main surface being joined to the bottom inner surface of the case, generating leakage surface acoustic waves by applying high-frequency power to the plurality of comb-tooth electrodes, and the control device being able to select one from the resonant frequency of the fundamental wave of the leakage surface acoustic wave and a resonant frequency higher than the resonant frequency of the fundamental wave to drive the piezoelectric element.

[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, ultrasonic cleaning at high frequency by driving with high power becomes possible without narrowing the spacing of the multiple comb-tooth electrodes or increasing the thickness of the piezoelectric element, 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 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 before.

[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, it is difficult to splash up the cleaning fluid even when the vibrator unit is swung horizontally during substrate cleaning. Thus, it is possible to prevent the cleaning fluid from entering the case through the seal portion.

[0016] The invention described in claim 6 is characterized in that, in any one of claims 1 to 4, 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.

[0017] The invention described in claim 7 is a vibrating body unit for a single-wafer ultrasonic substrate cleaning machine, comprising a structure in which a piezoelectric element that generates ultrasonic waves is housed in a case, wherein the piezoelectric element is a plate-shaped member having a first main surface and a second main surface, a plurality of comb-tooth electrodes are formed on the first main surface, 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-tooth electrodes, leakage surface acoustic waves having a fundamental wave resonance frequency of 3 MHz or higher are generated, and leakage surface acoustic waves in multiple wavelength ranges including resonance frequencies three times or more higher than the frequency of the fundamental wave are also generated.

[0018] As detailed above, according to the inventions described in claims 1 to 7, ultrasonic cleaning at high power and high frequency is possible, thereby improving cleaning performance.

[0019] A schematic diagram showing a single-wafer ultrasonic substrate cleaning machine according to one embodiment of the present invention. A schematic cross-sectional view showing the vibrating unit in the single-wafer ultrasonic substrate cleaning machine of the embodiment. A bottom view showing the vibrating unit. A plan view showing the piezoelectric element provided in the vibrating unit. A graph for explaining the vibration characteristics of the piezoelectric element of the embodiment. A bottom view showing the vibrating unit of another embodiment. A plan view showing the piezoelectric element provided in the vibrating unit of another embodiment.

[0020] Hereinafter, a single-wafer ultrasonic substrate cleaning machine 11, which embodies one embodiment of the present invention, will be described in detail with reference to Figures 1 to 5.

[0021] Figure 1 is a schematic diagram showing a single-wafer ultrasonic substrate cleaning machine 11 according to this embodiment. Figure 2 is a schematic cross-sectional view showing a vibrating unit 12 in the substrate cleaning machine 11. Figure 3 is a bottom view showing the vibrating unit 12. Figure 4 is a plan view showing a piezoelectric element 41 provided in the vibrating unit 12.

[0022] This single-wafer ultrasonic substrate cleaning machine 11 is a device that cleans substrates B1 one by one using a cleaning solution L1. More specifically, this single-wafer ultrasonic substrate cleaning machine 11 is a device that cleans substrates B1 by supplying cleaning solution L1 to a rotating substrate B1 while irradiating it with ultrasound. The substrate B1 is not limited, but a preferred example is a disc-shaped semiconductor wafer B1. In this embodiment, the semiconductor wafer B1 to be cleaned is one that has undergone CMP treatment and scrubbing to remove relatively large particles. Since relatively fine particles still remain on such a semiconductor wafer B1, ultrasonic cleaning is performed with the aim of completely removing these fine particles. In addition, trace amounts of organic and metallic contamination, oils and greases generated during the manufacturing process, and natural oxide films formed by contact with the atmosphere are also targets for removal by ultrasonic cleaning.

[0023] As shown in Figure 1, this single-wafer ultrasonic substrate cleaning machine 11 includes 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 appropriately selected 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 surface 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 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 materials other than quartz (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 about 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 periphery of the upper cover 22 and the lower cover 23. Bolts 25 are inserted through these bolt insertion holes 22c to fix 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 a number of 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 a number of 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 a certain interval. In Figure 4, for the sake of illustration, the number of comb-tooth patterns 44 and 45 is depicted in a schematic manner with a considerably reduced number, but in reality, there are 20 or more comb-tooth patterns 44 and 45 each (about 50 each in this embodiment). Furthermore, the line / space of the comb tooth patterns 44 and 45 are equal, and are 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 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 appropriately employed.

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

[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, we have shown an example of switching the resonant frequency in two stages (rp1 → rp9), but it is also possible to switch in three stages (for example, rp1 → rp4 → rp9), or even four stages (for example, 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 rp1 of the fundamental wave of the leakage surface acoustic wave and resonance frequencies rp2 to rp10 that are higher than the resonance frequency rp1 of the fundamental 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, high-frequency ultrasonic cleaning with high-power drive becomes possible without narrowing the spacing of the pair of comb-tooth electrodes 42A and 42B or increasing the thickness of the piezoelectric element 41, thereby improving cleaning performance. Furthermore, since narrowing the spacing of the pair of comb-tooth electrodes 42A and 42B and increasing the thickness of the piezoelectric element 41 are unnecessary, the vibrating body 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 flow-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 resonance frequency in the initial stage of cleaning, and then switches to a relatively high resonance frequency to drive the piezoelectric element 41. According to this, first, the dirt attached to the semiconductor wafer B1 is floated at a relatively low frequency, and then the floated dirt can be efficiently removed at a relatively high frequency. Also, by switching the frequency in the cleaning process, the generation of standing waves is prevented, and uneven cleaning is less likely to occur. As a result of the above, the cleaning performance can be improved.

[0045] (3) In this embodiment, the bottom portion 32 of the case 30 has a flat bottom surface 32a and is formed in a substantially circular shape when viewed from a direction orthogonal to the bottom surface 32a. And when the bottom portion 32 of the case 30 has such an outer shape, even when the vibrator unit 12 is swung in the horizontal direction while rotating the semiconductor wafer B1 during cleaning of the semiconductor wafer B1, it becomes difficult to lift up the cleaning liquid L1. Therefore, it is possible to prevent the intrusion of the cleaning liquid L1 into the case 30 through the seal portion.

[0046] (4) In particular, the case 30 of this embodiment includes a bottomed concave quartz case body 31 having a bottom portion 32 and an upper opening 35, and a cover body 21 that liquid-tightly closes the upper opening 35. This cover body 21 is configured to include an upper cover 22 and a lower cover 23 made of a fluororesin. The upper flange portion 33 formed at 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. And an O-ring, which is a seal member 24, is disposed at the interface between the upper cover 22 and the upper flange portion 33. According to this configuration, the intrusion path of the cleaning liquid L1 through the upper opening 35 of the case body 31 becomes longer, and the intrusion path is almost completely cut off, so that the intrusion of the cleaning liquid L1 into the case 30 can be more reliably prevented.

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

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

[0049] ・In the above embodiment, a large number of comb tooth patterns 44 and 45 in the pair of comb electrodes 42A and 42B were formed linearly, respectively, but it is not limited thereto. For example, like the piezoelectric element 41A of another embodiment shown in FIG. 7, a large number of comb tooth patterns 44 and 45 may be formed in a semicircular shape and arranged in an overall concentric shape. According to this configuration, it becomes easier to form the pair of comb electrodes 42A and 42B in 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 resonance frequency in the initial stage of cleaning and then switches to a relatively high resonance frequency to drive the piezoelectric element 41 (for example, rp1 → rp9), but it is not limited thereto. For example, conversely, the resonance frequency may be switched to drive the piezoelectric element 41 (for example, rp9 → rp1). Also, in the cleaning process using a predetermined cleaning liquid L1, the piezoelectric element 41 may be driven by repeatedly switching between high and low resonance frequencies (for example, rp1 → rp9 → rp1 → rp9). Alternatively, the piezoelectric element 41 may be driven by randomly switching the resonance frequency (for example, rp1 → rp5 → rp3 → rp9 → rp7).

[0051] ・In the above embodiment, the single - sheet ultrasonic substrate cleaning machine 11 was used for the cleaning performed after the CMP process, but it is not limited thereto. For example, in another embodiment, the single - sheet ultrasonic substrate cleaning machine 11 may be used for the cleaning performed after the film - forming process, may be used for the cleaning performed after the etching process, or may be used for the cleaning performed 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 of 2 or less (preferably 1.5 or less) defined by the maximum diameter / minimum diameter. (3) In claim 6, the cover body is composed of an upper cover and a lower cover made of fluororesin. (4) In claim 6, the cover body is composed of an upper cover and a lower cover made of fluororesin, an upper flange portion is formed in 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 disposed at the interface between at least one of the upper cover and the lower cover and the upper flange portion.

[0056] 7: Gap 11: Single-wafer ultrasonic substrate cleaning machine 12, 12A: Vibrating unit 14: Oscillation circuit 15: Control device 21: Cover 30: Case 31: Case body 32: Bottom 32b: Inner surface of bottom 32a: Bottom surface (outer surface of bottom) 35: Top opening 41, 41A, 41B: Piezoelectric element 41a: First main surface 41b: Second main surface 42A, 42B: Comb-tooth electrode B1: Semiconductor wafer as substrate L1: Cleaning solution rp1 to rp10: Resonant frequency

Claims

1. A single-wafer ultrasonic substrate cleaning machine comprising: 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; and a control device that controls the oscillation circuit, wherein the substrate is cleaned by supplying cleaning liquid to the gap between the substrate and the vibrating unit while the substrate is rotating and irradiating ultrasonic waves, wherein the piezoelectric element is a plate-shaped member having a first main surface and a second main surface, a plurality of comb-tooth electrodes formed on the first main surface, the second main surface being joined to the inner surface of the bottom of the case, and generating leakage surface acoustic waves by applying high-frequency power to the plurality of comb-tooth electrodes, and the control device being capable of driving the piezoelectric element by selecting one from the resonant frequency of the fundamental wave of the leakage surface acoustic wave and a resonant frequency higher than the resonant frequency of the fundamental wave.

2. The single-wafer ultrasonic substrate cleaning machine according to claim 1, characterized in that the piezoelectric element generates a leakage surface acoustic wave having a fundamental frequency of 3 MHz or higher, and is capable of generating leakage surface acoustic waves in multiple wavelength ranges including a resonance frequency three times or more higher than the fundamental frequency.

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. In the case of cleaning the substrate using multiple types of cleaning solutions, the control device is characterized in that it switches the resonant frequency for each type of cleaning solution to drive the piezoelectric element, as described in claim 2.

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 body unit for a single-wafer ultrasonic substrate cleaning machine, comprising a structure in which a piezoelectric element that generates ultrasonic waves is housed in a case, wherein the piezoelectric element is a plate-shaped member having a first main surface and a second main surface, a plurality of comb-tooth electrodes are formed on the first main surface, 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-tooth electrodes, a leakage surface acoustic wave having a fundamental resonance frequency of 3 MHz or higher is generated, and the leakage surface acoustic wave is capable of generating multiple wavelength ranges including resonance frequencies three times or more higher than the fundamental resonance frequency.

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