JP2019153638A - Ultrasonic cleaning apparatus, cleaning method and oscillator - Google Patents

Abstract

To provide a technology capable of accommodating further micronization of an object to be cleaned and structure complexity.SOLUTION: The ultrasonic cleaning apparatus includes: an oscillator for generating ultrasonic vibration by a surface acoustic wave using a piezoelectric element with an interdigital electrode; an ultrasonic wave oscillator for driving the oscillator; and a cleaning tank used to set an object to be cleaned and filled with cleaning fluid. By supplying high-frequency power from the ultrasonic wave oscillator, this technology generates, at the oscillator, a sound flow generated in cleaning fluid or ultrasonic vibration transmitted to the cleaning fluid and the inside of the cleaning fluid.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to an ultrasonic cleaning apparatus and a cleaning method for performing a cleaning process by irradiating ultrasonic vibration on a finely processed product such as a semiconductor wafer that is a cleaning target.

  As a cleaning device, an ultrasonic cleaning device (see Japanese Patent Application Laid-Open No. 2011-115717) for processing an ultrasonic vibration surface close to the surface of an object to be cleaned, or an ultrasonic cleaning device for reducing damage to an object to be cleaned (Japanese Patent Application Laid-Open No. 2013). -86059) has been proposed.

JP 2011-115717 A JP 2013-86059 A

  As the object to be cleaned is further miniaturized and the structure is complicated, there is a problem that fine foreign substances cannot be removed by the ultrasonic cleaning apparatus.

  The objective of this invention is providing the technique which can respond to the further refinement | miniaturization and structural complexity of the washing | cleaning target object.

  According to one aspect of the present invention, there is provided a vibrator that generates ultrasonic vibrations by a surface acoustic wave using a piezoelectric element having a comb-shaped electrode, an ultrasonic oscillator that drives the vibrator, and an object to be cleaned. A cleaning tank that is installed and filled with a cleaning liquid, and by supplying high-frequency power from an ultrasonic oscillator, an acoustic flow generated in the cleaning liquid or an ultrasonic vibration transmitted in the cleaning liquid and the cleaning liquid is used as a vibrator. Techniques for generating are provided.

  According to the ultrasonic cleaning apparatus, it is possible to remove fine foreign matters on the object to be cleaned by the synergistic effect of the acoustic flow generated in the cleaning liquid or the ultrasonic vibration transmitted to the cleaning liquid and the cleaning liquid.

It is the schematic which shows an example of the ultrasonic cleaning apparatus which is embodiment of this invention. It is a figure which shows notionally the structure of the comb-shaped electrode 4 of FIG. It is a figure which shows notionally the other structure of the comb-shaped electrode 4 of FIG. It is the schematic which shows an example of the vibrator | oscillator which comprises the some comb-shaped electrode which is embodiment of this invention. It is the schematic which shows another example of the vibrator | oscillator which comprises the several comb-shaped electrode which is embodiment of this invention. It is the schematic which shows an example of the surface acoustic wave radiated | emitted in the washing | cleaning liquid from the several comb-shaped electrode which is embodiment of this invention. It is the graph which showed the result of having calculated the adhesion force and the removal force in an ultrasonic wave with the theoretical calculation model with respect to the magnitude | size of the fine foreign material to remove. It is a graph which shows the result of having calculated the ultrasonic intensity per unit area, and the cavitation generation threshold value by the frequency by the theoretical calculation model. (A) It is the schematic which shows an example of the washing | cleaning method in the washing | cleaning apparatus which irradiates an ultrasonic wave from the back surface of the washing | cleaning target object which is an application example of embodiment of this invention. (B) It is detail drawing which shows an example of the washing | cleaning method in the washing | cleaning apparatus which irradiates an ultrasonic wave from the back surface of the washing | cleaning target object which is an application example of embodiment of this invention. FIG. 6 is a schematic diagram illustrating an example of a cleaning method in a cleaning apparatus that is an application example of the embodiment of the present invention and transmits vibrations by directly contacting a vibrator with an object to be cleaned. It is an application example of an embodiment of the present invention, and is a detailed view showing an example of a cleaning method in a cleaning apparatus that transmits vibrations by directly contacting a vibrator with an object to be cleaned. It is an application example of an embodiment of the present invention, and is a detailed view showing an example of a cleaning method in a cleaning apparatus that transmits ultrasonic waves or a substance that propagates ultrasonic vibrations directly to the object to be transmitted and transmits the vibrations. It is the schematic which shows the vibrator | oscillator which is the application example of embodiment of this invention, and was attached with the cooler which suppresses heat_generation | fever of a piezoelectric element.

  Hereinafter, embodiments will be described with reference to the drawings. However, in the following description, the same components may be denoted by the same reference numerals and repeated description may be omitted. In order to clarify the description, the drawings may be schematically represented with respect to the width, thickness, shape, etc. of each part as compared to the actual embodiment, but are merely examples, and the interpretation of the present invention is not limited to them. It is not limited.

(Embodiment)
First, the request | requirement and subject regarding an ultrasonic cleaning apparatus and the cleaning method are demonstrated.

  In order to reduce damage caused by ultrasonic irradiation to a microfabricated product such as a semiconductor wafer, it is necessary to increase the frequency so that cavitation generated in the cleaning liquid due to ultrasonic waves is less likely to occur. Here, cavitation is generated by expanding and compressing the cleaning liquid with ultrasonic waves, and the force depends on the frequency and intensity of the ultrasonic waves.

  A general piezoelectric element used for a vibrator for an ultrasonic cleaning device is a PZT element made of lead zirconate titanate (hereinafter, PZT). In order to further increase the frequency of the PZT element from a high frequency (around 1 to 2 MHz), it is necessary to further reduce the thickness of the PZT element due to the characteristics of the PZT element. In this case, since the mechanical strength of the PZT element is lowered, there is a possibility that the PZT element may be broken because the PZT element cannot withstand practically applied power and vibration.

  Further, the PZT element has an impedance characteristic that the impedance becomes lower as the frequency becomes higher. When high power is applied to the PZT element, the influence of the impedance change caused by the change in the surrounding environment such as the cleaning liquid increases, and the current fluctuation also increases, which may cause damage to the ultrasonic cleaning apparatus. For this reason, it is necessary to reduce the power applied to the PZT element, and the resulting cleaning effect may be reduced.

  Hereinafter, embodiments will be described with reference to the drawings.

  The ultrasonic cleaning apparatus 100 shown in FIG. 1 has the following configuration. That is, reference numeral 1 denotes a finely processed cleaning object such as a semiconductor wafer, and reference numeral 2 denotes a finely processed object to which fine foreign matters formed on the surface of the cleaning object 1 are attached. Reference numerals 3 and 4 denote the vibrator 101 in this embodiment, 3 denotes a piezoelectric element, and 4 denotes a comb-shaped electrode. Reference numeral 5 denotes an ultrasonic oscillator that supplies high-frequency power to the vibrator 101 and is connected by a high-frequency coaxial cable 102. Reference numeral 6 denotes a cleaning tank for cleaning, and the cleaning tank 6 is filled with a cleaning liquid 7. When the vibrator 101 is driven by the ultrasonic oscillator 5, an acoustic flow or ultrasonic vibration is generated in the cleaning liquid 7 from the portion of the comb-shaped electrode 4 as indicated by 8, and fine foreign matter adhering to the cleaning target 1 is removed. Remove.

  FIG. 2 is a diagram conceptually showing the configuration of the comb-shaped electrode 4 of FIG. This example shows a vibrator 101 in which one comb electrode 4 is formed on the upper surface of one piezoelectric element 3. The comb-shaped electrode 4 has one comb-shaped electrode E1 and the other electrode E2 which are formed on the upper surface of the piezoelectric element 3 and mesh with each other. The electrode E1 is connected to the + (HOT) pole of the high-frequency coaxial cable 102, the electrode E2 is connected to the-(GND) pole of the high-frequency coaxial cable 102, and the high-frequency power generated from the ultrasonic oscillator 5 is applied to the electrode E1 and the electrode E2. To be supplied.

  FIG. 3 is a diagram conceptually showing another configuration of the comb electrode 4 of FIG. This example shows a vibrator 101 in which two comb-shaped electrodes 4_1 and 4_2 are formed on the upper surface of one piezoelectric element 3. FIG. Each of the comb-shaped electrodes 4_1 and 4_2 has one comb-shaped electrode E1 and the other electrode E2 that mesh with each other, as in FIG. As in FIG. 2, the electrode E1 is connected to the + (HOT) pole of the high-frequency coaxial cable 102, and the electrode E2 is connected to the − (GND) pole of the high-frequency coaxial cable 102. Since the vibrator 101 shown in FIG. 3 can increase the power that can be supplied as compared with the vibrator 101 shown in FIG. 2, a more sufficient cleaning effect can be obtained. Therefore, it is preferable to select the optimal vibrator 101 according to the type of fine foreign matter adhering to the surface of the cleaning object 1. Although FIG. 3 shows an example in which two comb-shaped electrodes 4_1 and 4_2 are provided in one piezoelectric element 3, the present invention is not limited to this. The number of comb-shaped electrodes may be three or four.

  FIG. 4 is a diagram showing a configuration example when four comb-shaped electrodes are installed.

  On the surface of the piezoelectric element 3, four comb-shaped electrodes 4a, 4b, 4c, and 4d are disposed at equal intervals from the center point between the four poles of the comb-shaped electrodes 4a to 4d at intervals of 90 °. The acoustic flows or ultrasonic vibrations 8a, 8b, 8c, and 8d radiated into the cleaning liquid 7 from the comb electrodes 4a to 4d are directional, and they are synthesized at the focal point 10 shown in FIG. The ultrasonic vibration can also be called a surface acoustic wave.

  FIG. 5 is a modification of the vibrator 101 shown in FIG. In FIG. 5, each of the four comb electrodes 4a, 4b, 4c, and 4d is formed on the upper surface of the corresponding piezoelectric element 3a, 3b, 3c, and 3d, and four independent vibrators 101a, 101b, 101c, and 101d are formed. Composed. The four vibrators 101a, 101b, 101c, and 101d are installed on the surface of the power supply wiring board PCB based on the same idea as the four comb-shaped electrodes 4a, 4b, 4c, and 4d described in FIG. The power supply wiring board PCB has first electrode pairs P1 and P2 and second electrode pairs P3 and P4 as terminals to which high-frequency power from the ultrasonic oscillator 5 is supplied. The first electrode pair P1 and P2 are connected to the electrodes E1 and E2 of the comb-shaped electrode 4d and the electrodes E1 and E2 of the comb-shaped electrode 4b via the wirings L1 and L2, respectively. The second electrode pair P3, P4 is connected to the electrodes E1, E2 of the comb-shaped electrode 4a via the wirings L3, L4, and is connected to the electrodes E1, E2 of the comb-shaped electrode 4c via the wirings L5, L6. Is done. In this way, high frequency power from the ultrasonic oscillator 5 is supplied to each of the transducers 101a, 101b, 101c, and 101d. The connection portions between the vibrators 101a, 101b, 101c, and 101d and the wirings L1-L6 of the power supply wiring board PCB and the front and back surfaces of the power supply wiring board PCB are waterproofed.

  Therefore, the vibrators 101b and 101d are supplied with the same high-frequency power from the first electrode pair P1 and P2, and the vibrators 101a and 101c are supplied with the same high-frequency power from the second electrode pair P3 and P4. . If the same high-frequency power is supplied to the first electrode pair P1, P2 and the second electrode pair P3, P4, the vibrators 101a, 101b, 101c, 101d generate the same acoustic flow or ultrasonic vibration. . On the other hand, if high-frequency power is supplied only to the first electrode pair P1, P2, acoustic flow or ultrasonic vibration is generated from the transducers 101b, 101d. Further, if high frequency power is supplied only to the second electrode pair P3, P4, an acoustic flow or ultrasonic vibration is generated from the transducers 101a, 101c. Further, the high frequency power supplied to the first electrode pair P1 and P2 and the high frequency power supplied to the second electrode pair P3 and P4 are not the same but can be different. That is, according to the embodiment of FIG. 5, it is possible to finely control the generated acoustic flow or ultrasonic vibration.

  In FIG. 6, FIG. 6 (A) is a diagram depicting the comb-shaped electrodes 4a to 4d of FIG. 4 or 5 from the front. FIG. 6B shows the traveling direction of acoustic waves or surface acoustic waves (8a, 8c) radiated from two comb-shaped electrodes 4a, 4c disposed facing each other vertically (perpendicular to the wave front of the dense wave of interest). FIG. FIG. 6C is a diagram in which the traveling direction of the acoustic flow or the surface acoustic waves (8b, 8d) radiated from the two comb-shaped electrodes 4b, 4d disposed opposite to the left and right are drawn from directly above. .

  Referring to FIG. 6A, as described in FIG. 4 or FIG. 5, the comb electrodes 4a, 4b, 4c, and 4d are separated from the center point C0 between the four poles of the comb electrodes 4a to 4d. In (B) and FIG. 6 (C), they are installed equidistantly and at intervals of 90 ° as indicated by 12. On the surface of the piezoelectric element 3, acoustic flows or surface acoustic waves (8a, 8c) radiated from the two comb-shaped electrodes 4a, 4c disposed facing each other up and down, and two disposed facing the left and right Each of the acoustic flows or the surface acoustic waves (8b, 8d) radiated from the comb electrodes 4b, 4d is synthesized at the focal point 10.

  FIG. 6 shows an example in which lithium niobate (LiNbO3: Lithium Niobate) is used as the piezoelectric element 3 (3a, 3b, 3c, 3d). In FIG. 6, the angle 11 of the acoustic flow or the surface acoustic wave (8 a-8 d) radiated from the piezoelectric element 3 (3 a, 3 b, 3 c, 3 d) into the pure water as the cleaning liquid 7 is perpendicular to the piezoelectric element 3. With respect to the direction or horizontal direction, the angle is approximately 22 ° on one side, and the center part (Ca, Cb, Cc, Cd) of the comb-shaped electrodes (4a, 4b, 4c, 4d) serving as the radiation center part is approximately in both directions. It shows that it becomes 44 degree radiation.

  Also, from the center point C0 between the two opposing comb electrodes ((4a and 4c) or (4b and 4d)), the center points (C4a, C4b, When the distance 12 to C4c, C4d) is 4 mm, the acoustic flow or ultrasonic vibration (8a-8d) radiated into the cleaning liquid 7 from the respective comb electrodes (4a, 4b, 4c, 4d) is synthesized. The distance 13 to the focal point 10 is from the center point ((C4a and C4c) or (C4b and C4d)) between the two opposing comb electrodes ((4a and 4c) or (4b and 4d)). It indicates that the distance is approximately 9.9 mm in the front vertical direction or the front horizontal direction.

  FIG. 7 is a graph showing the results of calculating the adhesion force and the ultrasonic removal force with a theoretical calculation model with respect to the size of the fine foreign matter to be removed. In FIG. 7, the vertical axis indicates the adhesion force (Adhesion force [N]) and the removal force (Removal force [N]), and the horizontal axis indicates the size of the fine foreign matter (Particle Size [nm]). Yes. Here, N is Newton and nm is nanometer. In the theoretical calculation model of FIG. 7, only the intermolecular force is considered as the adhesion force, and the removal force is, for example, a frequency of 5 MHz and a power of 50 W is applied to each electrode area 1 cm 2 of the comb electrodes 4a to 4d. It is calculated as a case.

  FIG. 7 shows that in the case where the frequency is 5 MHz and the ultrasonic intensity per unit area to be applied is 50 W / cm 2, it is theoretically possible to remove fine foreign matters having a size of 20 nm or more. In this theoretical calculation model, the smaller the frequency and the higher the ultrasonic intensity per unit area to be applied, the smaller the fine foreign matter can be removed. However, since there is a concern about damage to the object to be cleaned due to the occurrence of cavitation described above, it is desirable to use the frequency and applied electric power that is a cavitation-free region for the size of the fine foreign matter to be removed.

  FIG. 8 is a graph showing the results of calculating the ultrasonic intensity per unit area and the cavitation generation threshold value depending on the frequency using a theoretical calculation model. In FIG. 8, the vertical axis indicates the ultrasonic intensity (Ultrasonic intensity (W / cm 2)), and the vertical axis indicates the frequency (Frequency (Hz)). The threshold value (Threshold) for occurrence of cavitation is shown as an example in FIG. 8 in the case of air saturated water. As shown in FIG. 8, when high applied power (that is, high detergency) is required, in order not to generate cavitation, it is necessary to use a higher frequency, and the frequency of 5 MHz, which is an example of FIG. Thus, it can be said that cavitation does not occur even at a sufficiently high applied power of about 1000 W / cm 2.

  The theoretical calculation model used in the graphs of FIGS. 7 and 8 is an example. In actual use, the conversion efficiency when radiating the vibration generated by the surface acoustic wave generated by the piezoelectric element used into the cleaning liquid, the properties of the cleaning liquid, and the ultrasonic intensity generated when propagating through the cleaning liquid due to the frequency of the ultrasonic waves. It is necessary to consider attenuation and the like. In consideration of these, the acoustic flow or ultrasonic vibration that actually reaches the object to be cleaned is smaller than the ultrasonic intensity shown in FIGS. 7 and 8, and thus high applied electric power in consideration of this is required.

  FIG. 9A is a conceptual configuration diagram of the ultrasonic cleaning apparatus 100a, and FIG. 9B is an enlarged view of the cleaning object 1 and the vibrator 101 in FIG. 9A. It is.

  In the cleaning method shown in FIGS. 9 (A) and 9 (B), the cleaning object having the property of transmitting the ultrasonic wave 8 in the cleaning liquid 7 filled in the cleaning tank 6 of the ultrasonic cleaning apparatus 100a. The vibrator 101 is installed on the back surface 1r side of 1. The vibrator 101 has a structure in which a liquid-resistant protective film 14 is applied to the piezoelectric element 3 having the comb-shaped electrode 4 and stored in a waterproof case 15. The protective film 14 is formed so as to cover the comb-shaped electrode 4 formed on the surface of the piezoelectric element 3 and the surface of the piezoelectric element 3 on which the comb-shaped electrode 4 is not formed. Note that the surface of the protective film 14 is uneven depending on the presence or absence of the comb-shaped electrode 4, but in FIG. 9B, it is drawn as a flat shape for the sake of simplicity of the drawing.

  In order to bring the electrode surface of the comb electrode 4 or the main surface Ms side of the substrate Sub of the piezoelectric element 3 into close contact with the opening 15o of the waterproof case 15, on the back surface Rs side facing the main surface Ms of the substrate Sub of the piezoelectric element 3, A feeding point 16 to the comb electrode 4 is provided. The substrate Sub of the piezoelectric element 3 is provided with a through electrode 16 a connected to the feeding point 16, and the high frequency coaxial cable 102 is connected to the feeding point 16 to feed power from the through electrode 16 a to the comb electrode 4. When the vibrator 101 is driven by the ultrasonic oscillator 5, an acoustic flow or ultrasonic vibration (8) is generated in the cleaning liquid 7 from the comb-shaped electrode 4, and the object 1 to be cleaned is caused by the ultrasonic transmission characteristics. Ultrasound is transmitted.

  That is, when the ultrasonic wave 8 is transmitted through the object 1 to be cleaned, the object 1 to be cleaned causes ultrasonic vibration, and the vibration causes a direct stress on the fine workpiece formed on the surface of the object 1 to be cleaned. Thus, the fine foreign matter 2 attached to the fine workpiece can be removed without any damage that can be caused by the above.

  However, in this application example, in addition to the parameters necessary for the above-described consideration, it is necessary to consider attenuation due to the ultrasonic transmittance depending on the density and thickness of the cleaning object 1 and the incident angle of the ultrasonic wave. It becomes.

  A cleaning apparatus 100b illustrated in FIG. 10 includes a stage STG on which the cleaning object 1 can be placed. In the stage STG, the vibrator 101 is embedded, and the back surface (1r) of the cleaning object 1 can be brought into direct contact with the main surface (Ms) of the vibrator 101. Since other structures are the same as those in FIGS. 1 and 9A, description thereof is omitted.

  FIG. 11 is an enlarged view of the cleaning object 1 and the vibrator 101 shown in FIG. In the cleaning method shown in FIG. 11, the vibrator 101 is brought into direct contact with one end 1e on the back surface 1r side (or the main surface 1m side facing the back surface 1r) of the object 1 to be cleaned. It is a method of installing so that it may be embedded in the provided recessed part.

  The vibrator 101 is applied with a liquid-resistant protective film 14 on the piezoelectric element 3 having the comb-shaped electrode 4 and is waterproof, for example, by housing the side surface and the back surface of the piezoelectric element 3 in a waterproof case 15. The treatment is applied and embedded in a recess provided in the stage STG.

  One end 101e of the vibrator 101 is installed so as to be in direct contact with one end 1e on the back surface 1r side (or main surface 1m side) of the cleaning object 1. In order to avoid interference with the object 1 to be cleaned, a feeding point 16 to the comb electrode 4 is provided on the back surface Rs side of the substrate Sub of the piezoelectric element 3. The substrate Sub of the piezoelectric element 3 is provided with a through electrode 16 a connected to the feeding point 16. In the waterproof case 15, the high-frequency coaxial cable 102 is connected to the feeding point 16. With this configuration, power is supplied from the through electrode 16 a to the comb electrode 4.

  The vibrator 101 is driven by the ultrasonic oscillator 5 connected to the high-frequency coaxial cable 102, and the piezoelectric element 3 vibrates by the surface acoustic wave 17 generated from the comb electrode 4, and the vibration of the piezoelectric element 3 directly acts on the object 1 to be cleaned. Thus, the ultrasonic vibration 18 is also generated in the cleaning object 1. By the ultrasonic vibration 18, the fine foreign matter 2 attached to the fine workpiece formed on the surface of the cleaning object 1 can be removed.

  In the cleaning method shown in FIG. 12, one end on the back surface 1r side (or the main surface 1m side) of the object 1 to be cleaned is passed through the vibrator 101 through the propagation material 19 capable of propagating ultrasonic waves or ultrasonic vibrations. It is a method of installing so that it may touch.

  In the cleaning apparatus 100c, the vibrator 101 fixes the piezoelectric element 3 including the comb-shaped electrode 4 and the one end 19e side of the propagation material 19 by bonding with an adhesive layer 20 such as an adhesive. The other end 19o side of the propagation material 19 is brought into direct contact with one end on the back surface 1r side (or the main surface 1m side) of the cleaning object 1. Similarly to FIG. 11, the vibrator 101 is subjected to waterproofing treatment such as being housed in the waterproof case 15, and is embedded in a recess provided in the stage STG.

  The propagation material 19 is preferably made of a material that has high ultrasonic wave propagation properties and does not cause dust generation due to use deterioration or elution of material components. For example, quartz glass can be used.

  In order to avoid interference with the propagation material 19, a feeding point 16 for the comb-shaped electrode 4 is provided on the back side 101 a of the substrate of the piezoelectric element 3. A through electrode 16 a connected to the feeding point 16 is provided on the substrate of the piezoelectric element 3, and the high frequency coaxial cable 102 is connected to the feeding point 16 in the waterproof case 15. With this configuration, power is supplied from the through electrode 16 a to the comb electrode 4.

  When the vibrator 101 is driven by the ultrasonic oscillator 5, the piezoelectric element 3 is vibrated by the surface acoustic wave 17 generated by the comb-shaped electrode 4, and the propagation material 19 is ultrasonically or ultrasonically vibrated (8 ) Is transmitted, and the ultrasonic vibration 18 is also generated in the cleaning object 1. By the ultrasonic vibration 18, the fine foreign matter 2 attached to the fine workpiece formed on the surface of the cleaning object 1 can be removed. In the cleaning method shown in FIG. 12, it is also possible to install the propagation material 19 in the vicinity of the cleaning object 1 without bringing the propagation material 19 into direct contact with the cleaning object 1. The cleaning method in which the propagation material 19 is installed in the vicinity of the cleaning object 1 can be regarded as an application example of the cleaning method shown in FIG. 9 and is effective as a cleaning method.

  The piezoelectric element 3 including the comb electrode 4 as the vibrator 101 shown in FIG. 13 generates heat when driven by the ultrasonic oscillator 5. In order to dissipate the heat generated in the piezoelectric element 3 having the comb-shaped electrode 4, the cooler 21 is closely attached to the vibrator 101 by heat radiation grease 22 or the like. The cooler 21 enables heat dissipation necessary to prevent the piezoelectric element 3 from being damaged by heat. For example, a metal heat sink processed into a required size, a thermo module using a Peltier element, or the like. Can be used. As a result, it is possible to suppress deterioration and breakage of the vibrator 101 caused by heat generated by application of high-frequency power or vibration. The vibrator 101 can be regarded as a surface acoustic wave element. The vibrator 101 shown in FIG. 13 can be used, for example, as the vibrator shown in FIGS. 2, 3, 5, 9, 11, and 12.

  In any method, in order to obtain a finer cleaning effect with a higher frequency band than before, a cleaning device equipped with a vibrator that can be driven with a high frequency and high power is required. The application can be realized depending on the form. That is, in this embodiment, delicate cleaning at a high frequency that does not generate cavitation corresponding to further miniaturization and structural complexity of the object to be cleaned is enabled.

  In general, if the ultrasonic intensity is the same, the higher the frequency, the smaller the displacement (amplitude) of the ultrasonic wave, resulting in weak cavitation. On the other hand, if the cavitation is weak, the cleaning power is also weakened. For this reason, a low frequency is used for cleaning applications that require strong cleaning without concern for damage to the object to be cleaned, and a high frequency for cleaning applications that require delicate cleaning to suppress damage to the object to be cleaned. Is used. That is, it is necessary to select a frequency suitable for the cleaning application. The cavitation generation area depends on the properties of the liquid used, the ultrasonic intensity (W / cm2) per unit area of the piezoelectric element used in the vibrator, and the frequency (Hz). The higher the frequency, the less cavitation occurs. The area extends to high ultrasonic intensity.

  As a cleaning apparatus using a cleaning liquid by a PZT element that is currently in practical use, a frequency of about 2 MHz is used as an upper limit. For example, in the case of air saturated water, the non-occurrence region of cavitation at 2 MHz is about 10 W / cm 2 or less as the ultrasonic intensity per unit area of a practical PZT element, considering a safety margin from theoretical calculation values. Limited to use in range.

  However, in this embodiment, the comb-shaped electrode 4 that generates surface acoustic waves can be designed from 2 MHz to several GHz, and can be used in a region where cavitation does not occur even with higher applied power (FIG. 8). reference).

  Further, when the cleaning effect is insufficient with one comb-shaped electrode 4, the piezoelectric elements 3 (3a, 3b, 3c, 3d) having a plurality of comb-shaped electrodes 4a-4d are used, whereby the comb-shaped electrodes 4a-4d are used. By combining the acoustic flow generated by the surface acoustic wave generated from each of the above or the ultrasonic vibration transmitted in the cleaning liquid at the focal point 10 determined from the radiation characteristics of the surface acoustic wave in the liquid, the cleaning effect at the synthetic focal point is obtained. This can be improved (see FIGS. 4 and 6).

  The radiation characteristics of surface acoustic waves in liquid are known to be emitted at a certain angle from the comb-shaped electrodes (4, 4a-4d) installed on the piezoelectric element 3, and the radiation angle is determined by the piezoelectric element 3 It depends on the Rayleigh wave velocity of the surface acoustic wave generated above and the propagation velocity of the liquid.

  For example, the angle radiated into the pure water by the piezoelectric element 3 using the LiNbO3 element is approximately 22 ° on one side with respect to the vertical direction of the piezoelectric element 3 and approximately 44 ° on both sides from the radiation center. . The focal point 10 (positional relationship from the piezoelectric elements 3a, 3b, 3c, and 3d) of the emitted ultrasonic wave can be obtained from the angle and the interval between the central portions of the plurality of comb-shaped electrodes 4a to 4d. (See FIG. 6).

  Further, by using an element having a material characteristic different from that of LiNbO 3 in the piezoelectric element 3, the Rayleigh wave velocity of the surface acoustic wave is also different. Therefore, the piezoelectric element 3 can be used at another angle suitable for the application.

  The surface acoustic wave generated from the piezoelectric element 3 (3a, 3b, 3c, 3d) having the comb-shaped electrode 4 (4a-4d) has already been established for high-frequency power filter use. It is possible to easily design an electrode applied to the frequency used in the present invention and the required element size.

  For example, it is known that the propagation speed of the surface acoustic wave generated by the comb electrodes (4_1, 4_2, 4a-4d) depends on the pitch and frequency between the comb electrodes (4_1, 4_2, 4a-4d).

  Further, as an application example of the cleaning method, by applying ultrasonic waves from the back surface side of the cleaning object 1, the fine foreign matter 2 on the surface side of the cleaning object 1 is removed, and the direct stress on the fine workpiece is applied. It is possible to avoid possible damage.

  Further, by using the piezoelectric element 3 (3a, 3b, 3c, 3d) having the comb electrodes (4, 4a-4d) that can be driven at a high frequency, the application range of the applied frequency is wider than that of the conventional PZT element. It is possible to set with the application of the acoustic flow by controlling the applied power or the response performance of ultrasonic vibration transmitted in the cleaning liquid, and not only for cleaning applications but also for various applications due to the ultrasonic effect in the liquid. Is possible.

  According to the present embodiment, one or more of the following effects can be obtained.

  1) The vibrator 101 uses the piezoelectric element 3 having comb-shaped electrodes (4, 4a-4d) that can be driven in a high frequency band in which cavitation that causes damage to the object to be cleaned does not occur.

  2) The cleaning effect can be obtained by the synergistic effect of the acoustic flow in the cleaning liquid caused by the surface acoustic wave generated by the vibrator 101 or the ultrasonic vibration transmitted to the cleaning liquid and the cleaning liquid.

  3) The material of the piezoelectric element 3 is a material that is efficient in generating surface acoustic waves and emitting ultrasonic waves to the cleaning liquid. For example, niobic acid, which is commonly used as a filter for high-frequency power using surface acoustic waves, is used. A lithium (LiNbO3) element or the like is used.

  4) In the vibrator 101, when one comb-shaped electrode (4) cannot obtain a sufficient cleaning effect due to the power that can be supplied, a plurality of comb-shaped electrodes (4_1, 4_2, or 4a-4d) are arranged at regular intervals. It is installed, and supply power is simultaneously applied to each comb-shaped electrode (4a-4d), and a plurality of ultrasonic waves radiated from the piezoelectric elements 3a-3d are synthesized at a specific focal point 10 by the radiation characteristics of surface acoustic waves in the liquid. . Thereby, the cleaning effect at the focal point 10 can be improved as compared with the case where one comb-shaped electrode is used.

  5) In response to damage to the fine workpiece formed on the surface of the cleaning object 1, the cleaning object 1 through which the ultrasonic wave is transmitted is irradiated with ultrasonic waves from the nearest side of the back surface of the cleaning object 1 in the cleaning liquid. The fine foreign matter 2 on the cleaning target 1 is removed by the vibration of the cleaning target 1 itself generated when ultrasonic waves are transmitted and the water flow generated in the cleaning liquid. Thereby, the damage which may be generated when an ultrasonic wave directly hits the fine workpiece formed on the surface of the cleaning object 1 can be avoided.

  As mentioned above, the invention made by the present inventor has been specifically described based on the examples. However, the present invention is not limited to the above-described embodiments and examples, and needless to say, various modifications can be made. .

  As another application example of the present invention, by using the vibrator 101 according to the present invention, the application range of the applied frequency can be designed in a wide range up to a frequency band higher than that of the PZT element, and vibration can be achieved. Utilizing response performance to acoustic flow or ultrasonic vibration transmitted in the cleaning liquid by high-frequency power oscillation control (continuous oscillation, intermittent oscillation, power fluctuation, etc.) from the ultrasonic oscillator 5 side that drives the child 101, and limited to cleaning applications Furthermore, application to various uses expected for the ultrasonic effect generated in the liquid is also possible.

  For example, the higher the frequency, the shorter the wavelength, so it is possible for ultrasonic waves to enter the fine gap, and for the fine gap that could not be realized at low frequencies, such as removal of fine foreign matter adhering to the complicated gap. All ultrasonic effects can be expected.

  In addition, the present invention can be applied to applications using the characteristics of ultrasonic propagation in the air with the action expected of high-frequency ultrasonic waves regardless of the liquid.

  In the above-described embodiment, the ultrasonic cleaning apparatus and the cleaning method for performing the cleaning process on the microfabricated product such as the semiconductor wafer have been described. However, the present invention is limited to the semiconductor manufacturing apparatus and the semiconductor device manufacturing method. For example, the present invention is also applicable to an ultrasonic cleaning apparatus and a cleaning method for performing a cleaning process on a glass substrate such as a liquid crystal display (LCD) apparatus.

  The present invention is applicable not only to cleaning applications, but also to stirring applications, liquid flow applications, pump applications, atomization applications, fountain applications, object transport applications, particle separation applications, particle aggregation applications, heating applications, etc. is there.

(Preferred embodiment of the present invention)
Hereinafter, preferred embodiments of the present invention will be additionally described.

(Appendix 1)
The ultrasonic cleaning apparatus according to claim 1, wherein the ultrasonic oscillator is configured to supply high frequency power having a transmission frequency exceeding 2 MHz to the vibrator.

(Appendix 2)
The ultrasonic cleaning apparatus according to (Appendix 1), wherein the transmission frequency is 2 MHz to several GHz.

(Appendix 3)
2. The ultrasonic cleaning apparatus according to claim 1, wherein the piezoelectric element is a lithium niobate element.

(Appendix 4)
The ultrasonic cleaning apparatus according to (Appendix 3), wherein the radiation angle emitted from the comb-shaped electrode installed on the piezoelectric element is 22 ° to 44 °.

(Appendix 5)
The ultrasonic cleaning apparatus according to (Appendix 3), wherein the radiation angle is determined according to a material of the piezoelectric element.

(Appendix 6)
In the ultrasonic cleaning apparatus according to (Appendix 3), the position of the piezoelectric element and the object to be cleaned is determined based on the radiation angle and the focal point of the ultrasonic wave radiated according to the interval between the plurality of comb-shaped electrode centers. An ultrasonic cleaning device configured to be in position.

(Appendix 7)
2. The ultrasonic cleaning apparatus according to claim 1, wherein a propagation speed of the surface acoustic wave generated by the comb electrodes depends on a pitch and a frequency between the comb electrodes.

1: Cleaning object 3: Piezoelectric element 4, 4a, 4b, 4c, 4d: Comb electrode 5: Ultrasonic oscillator 6: Cleaning tank 7: Cleaning liquid 100: Ultrasonic cleaning device 101: Vibrator

Claims (5)

A vibrator that generates ultrasonic vibrations by surface acoustic waves using a piezoelectric element having a comb-shaped electrode;
An ultrasonic oscillator for driving the vibrator;
A cleaning tank in which an object to be cleaned is installed and filled with a cleaning liquid,
The ultrasonic oscillator is configured to generate an acoustic flow generated in the cleaning liquid or the ultrasonic vibration transmitted to the cleaning liquid and the cleaning liquid in the vibrator by supplying high-frequency power. Sonic cleaning device. The ultrasonic cleaning apparatus according to claim 1,
A plurality of the piezoelectric elements;
An ultrasonic cleaning apparatus characterized by synthesizing an acoustic flow generated by a surface acoustic wave generated from each of the comb-shaped electrodes or the ultrasonic vibration transmitted to the cleaning liquid. The ultrasonic cleaning apparatus according to claim 1,
The vibrator is installed on the back side of the object to be cleaned,
An ultrasonic cleaning apparatus that vibrates the cleaning object by irradiating ultrasonic waves from the back side of the cleaning object and transmitting the ultrasonic waves radiated from the vibrator to the cleaning object. . A vibrator that generates ultrasonic vibrations by surface acoustic waves using a piezoelectric element having a comb-shaped electrode, an ultrasonic oscillator that drives the vibrator, and a cleaning object that is filled with a cleaning liquid A cleaning method using an ultrasonic cleaning device comprising a tank,
A cleaning method characterized by causing the vibrator to generate an acoustic flow generated in the cleaning liquid or the ultrasonic vibration transmitted to the cleaning liquid and the cleaning liquid by supplying high-frequency power from the ultrasonic oscillator. . A substrate constituting a piezoelectric element having a comb-shaped electrode;
A feeding point provided on the back surface of the substrate;
A through electrode provided on the substrate so as to connect the comb electrode and the feeding point;
And a protective film provided to cover the comb-shaped electrode.

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