JP2010241612A - Etching apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an etching apparatus capable of precisely controlling the thickness of a glass substrate which is etched. <P>SOLUTION: The etching apparatus includes a treatment tank 10 which stores an etching solution E and immerses a processing substrate X in the etching solution E, a circulation device 30 which makes the etching solution E in the treatment tank 10 flow, and an ultrasonic vibration generator 20 which is installed in the treatment tank 10 and has an ultrasonic vibrator 22 which makes the etching solution E facing the processing substrate X generate ultrasonic vibration and a control means 24 which controls driving of the ultrasonic vibrator 22. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an etching apparatus.

  With the diversification of information equipment, there is a growing need for flat panel displays that consume less power and are lighter. Thin-screen liquid crystal displays and organic electroluminescence devices with organic light-emitting layers are actively researched and developed. Has been.

  In such display devices, various glass substrates are often used in consideration of chemical stability and gas barrier properties against moisture and oxygen in the air. However, since the glass substrate is disadvantageous in terms of weight, it is disadvantageous for reducing the weight of the entire apparatus. Therefore, in general, the thickness of the glass substrate is reduced to reduce the weight of the entire apparatus.

Usually, a wet etching method is used for thinning a glass substrate. In order to reduce the thickness of the glass substrate using the wet etching method, for example, using an apparatus as shown in Patent Document 1, a method of immersing the entire glass substrate in a chemical solution and dissolving the substrate over the entire surface is employed. In such an apparatus, the etching amount is usually controlled by the concentration and temperature of the etching solution, the stirring rate of the etching solution, and the like. In such an apparatus, N ₂ is fed from the bottom of the etching apparatus for bubbling in order to agitate the chemical solution or prevent the impurities generated by etching from adhering to the substrate.

JP 2002-87844 A

However, in the conventional apparatus that stirs the chemical solution by bubbling, the stirring is likely to be uneven, and it is difficult to keep the thickness of the etched glass substrate constant. Further, it is known that etching is promoted by polishing the substrate surface with N ₂ bubbles generated by bubbling, but etching where many bubbles are localized tends to proceed near the generation source. For this reason, a difference in the degree of progress of etching tends to occur within the substrate surface, making it difficult to control the desired thickness.

  This invention is made | formed in view of such a situation, Comprising: It aims at providing the etching apparatus which can control the thickness of the glass substrate etched to high precision.

In order to solve the above-described problems, an etching apparatus of the present invention includes a processing tank in which an etching solution is stored and a substrate to be processed is immersed in the etching solution, and a flow unit that causes the etching solution in the processing tank to flow. Ultrasonic vibration generation, comprising: an ultrasonic vibrator that is provided in the processing tank and generates ultrasonic vibration in the etching solution facing the substrate to be processed; and a control unit that controls driving of the ultrasonic vibrator. And means.
According to this configuration, the amount of etching is controlled in addition to the normally known factors such as the concentration and temperature of the etchant, the stirring speed of the etchant, and the supply time of the ultrasonic vibration and the vibration frequency of the ultrasonic vibration. By doing so, control becomes possible. Therefore, the etching conditions can be set in more detail than in the conventional apparatus, and the thickness can be controlled more precisely. Further, since the etching solution is flowing by the flow means, the concentration of the etching solution is uniform throughout, and there is no concentration unevenness. Therefore, it is possible to provide an etching apparatus that can control the thickness of the substrate to be processed with high accuracy.

In the present invention, it is desirable that the ultrasonic vibration generating means is provided so as to face the substrate to be processed, and applies ultrasonic vibration propagating from the normal direction of the substrate to be processed to the substrate to be processed.
According to this configuration, since the ultrasonic vibration supplied from the normal direction of the substrate to be processed causes a straight flow in the propagation direction of the ultrasonic wave, the etching liquid is directed to the substrate to be processed in addition to the flow by the flow means. A flow occurs. Therefore, the replacement of the etching solution is actively performed in the vicinity of the substrate to be processed, so that the dissolution of the substrate to be processed can be promoted and etching can be suitably performed.

In the present invention, it is desirable that the ultrasonic vibration generating means has a cooling means for cooling the ultrasonic vibrator.
According to this configuration, since the ultrasonic transducer that generates heat by driving can be cooled, it is possible to provide an etching apparatus that can be stably driven while preventing damage to the apparatus.

In the present invention, it is desirable to have temperature control means for controlling the temperature of the etching solution.
According to this configuration, it is possible to prevent the etching solution from being heated and to change the etching rate by supplying the ultrasonic vibration, and to control the thickness of the substrate to be processed with high accuracy.

In the present invention, the processing tank has a partition partitioning the inside, and is divided into a first processing tank and a second processing tank by the partition, and the etching solution stored in the first processing tank is subjected to ultrasonic waves. First ultrasonic vibration generating means for applying vibration, and second ultrasonic vibration generating means for applying ultrasonic vibration to the etching solution stored in the second processing tank, and as the partition, It is desirable to use a substrate.
According to this configuration, an etching apparatus capable of simultaneously and accurately etching both surfaces of the substrate to be processed can be realized.

In the present invention, two stacked substrates to be processed are used as the partition walls, and the two substrates to be processed face the first processing tank and the second processing tank, respectively. It is desirable.
According to this configuration, the two substrates to be processed can be individually etched in the first processing tank and the second processing tank which are independent from each other, and productivity can be improved.

In the present invention, it is desirable that the first ultrasonic vibration generating means and the second ultrasonic vibration generating means can be independently controlled.
According to this configuration, it is possible to perform etching under different etching conditions in the first processing tank and the second processing tank which are independent of each other.

It is the schematic explaining the etching apparatus of 1st Embodiment of this invention. It is explanatory drawing of the etching process using the etching apparatus of 1st Embodiment. It is the schematic explaining the etching apparatus of 2nd Embodiment of this invention. It is explanatory drawing of the to-be-processed substrate used with the etching apparatus of 2nd Embodiment. It is explanatory drawing of the to-be-processed substrate arrange | positioned at the etching apparatus of 2nd Embodiment. It is explanatory drawing of the etching process using the etching apparatus of 2nd Embodiment.

[First Embodiment]
Hereinafter, an etching apparatus according to a first embodiment of the present invention will be described with reference to FIGS. In all the drawings below, the film thicknesses and dimensional ratios of the constituent elements are appropriately changed in order to make the drawings easy to see.

  FIG. 1 is a schematic diagram illustrating an etching apparatus 1 according to this embodiment. As shown in the figure, an etching apparatus 1 stores an etching solution E and holds a substrate X to be processed therein, and is provided outside the processing bath 10. The etching apparatus 1 stores the etching solution E in the processing bath 10. An ultrasonic vibration generator (ultrasonic vibration generating means) 20 for applying ultrasonic vibration, an etching liquid E circulation device (flow means) 30, a rinse liquid circulation device 40, and a treatment provided outside the processing tank 10. And a temperature control tank (temperature control means) 50 for controlling the temperature of the etching solution E in the tank 10. Each configuration will be described below.

  The processing tank 10 is provided with a substrate processing unit 14 provided at an upper portion and a chemical solution cooling unit 16 provided at a lower portion, and a substrate X to be processed is held on the inner side wall of the substrate processing unit 14. It has the holding part 12 to do. The substrate to be processed X disposed in the substrate processing unit 14 is etched by ultrasonic vibration supplied to the etching solution E as described later. In addition, a temperature adjustment tank 50 is disposed outside the chemical liquid cooling unit 16 to cool the etching liquid E in the treatment tank 10 that is heated by being supplied with ultrasonic vibration.

  An ultrasonic vibration generator 20 is disposed outside the substrate processing unit 14 of the processing tank 10. The ultrasonic vibration generator 20 includes an ultrasonic vibrator 22 that generates ultrasonic vibration in the etching solution E, and a control device (control means) 24 that controls driving of the ultrasonic vibrator 22. Further, in order to cool the ultrasonic transducer 22 that generates heat by driving, a water-cooled cooling means 26 is provided so as to enclose the ultrasonic transducer 22. The ultrasonic vibration generator 20 of the present embodiment can perform a dual mode operation of 70 KHz and 120 KHz.

  The ultrasonic vibration generator 20 is disposed at a position facing the substrate to be processed X disposed therein, and is provided so that ultrasonic vibration is uniformly applied to the entire surface of the substrate X to be processed.

  The etching solution E in the processing tank 10 is supplied from a circulating device 30 for the etching solution E provided in the processing tank 10. The circulation device 30 extends from the side wall of the chemical solution cooling unit 16 of the processing tank 10, and includes a chemical solution line 32 disposed up to the upper portion of the substrate processing unit 14 and a chemical solution tank connected to the chemical solution line 32 via the side pipe 33. 34, a filter 36 provided in the middle of the chemical liquid line 32, and a circulation pump 37 that circulates the etching liquid E in the chemical liquid line 32.

  The circulation device 30 supplies the etching solution E stored in the chemical solution tank 34 into the processing tank 10 through the chemical solution line 32 as necessary. Further, the etching solution E is circulated from the chemical solution cooling unit 16 to the substrate processing unit 14 by the action of the circulation pump 37. The filter 36 provided in the middle of the chemical liquid line 32 removes reaction products generated by etching and prevents reattachment to the substrate X to be processed. Further, when the etching is completed, the etching solution E is discharged from the processing tank 10.

The etching solution E is not particularly limited. For example, when a glass substrate is used as the substrate to be processed X, a mixed aqueous solution of hydrofluoric acid (HF) and sulfuric acid (H ₂ SO ₄ ) can be used. As the etching of the substrate X to be processed proceeds, the concentration of the etching solution E changes. Therefore, a concentration sensor (not shown) is provided in the circulation device 30, and when the concentration of the etching solution E falls below the reference value, a new one is added from the chemical solution tank 34. It is good also as performing control which supplies the etching liquid E and makes density | concentration constant.

  When the etching liquid E is discharged from the processing tank 10, the rinsing liquid is supplied from the rinsing liquid circulation device 40 provided in the processing tank 10. For example, pure water can be used as the rinse liquid. The circulation device 40 extends from the side wall of the chemical solution cooling unit 16 of the processing tank 10 and is connected to the rinse solution line 42 via the side tube 43 and the rinse solution line 42 disposed up to the upper portion of the substrate processing unit 14. A rinse liquid tank 44, a filter 46 provided in the middle of the rinse liquid line 42, and a circulation pump 47 that circulates the rinse liquid in the rinse liquid line 42 are provided.

The circulation device 40 supplies the rinse liquid via the rinse liquid line 42 into the treatment tank 10 after the etching is completed. In addition, the rinse liquid is circulated from the chemical liquid cooling unit 16 to the substrate processing unit 14 by the operation of the circulation pump 47. A filter 46 provided in the middle of the rinsing liquid line 42 removes reaction products generated by etching and prevents re-adhesion to the substrate X to be processed.
The etching apparatus 1 of this embodiment has the above configuration.

  Next, an etching process using the etching apparatus 1 will be described with reference to FIG. As shown in FIG. 2A, first, the substrate to be processed X that has been transferred into a single wafer is placed in the processing tank 10 filled with the etching solution E, and the inside of the processing tank 10 is passed through the chemical liquid line 32 by the circulation device 30. The etching solution E is circulated. Further, ultrasonic vibration is supplied to the etching solution E from the ultrasonic vibration generator 20.

  Here, an etching process using ultrasonic vibration will be described. First, when ultrasonic vibration is supplied into the etching solution E, the ultrasonic vibration that is a longitudinal wave works as a force that repeatedly reduces and compresses the etching solution E. If a decompression force is applied to the etching solution E in this repeated process, a vacuum cavity is generated in the etching solution E, and the gas dissolved in the etching solution E or the evaporating etching solution E is taken in, so that innumerable bubbles are generated. . However, at the next moment, the compressive force acts on the bubbles, so that they are crushed and the bubbles disappear. At this time, a shock wave is generated in the etching solution E because the solutions surrounding the bubbles collide with each other. The surface of the substrate X to be processed is polished by this shock wave.

  Further, in the etching apparatus 1 of the present embodiment, a straight flow is generated in the ultrasonic propagation direction by the ultrasonic vibration supplied from the normal direction of the substrate X to be processed, and therefore the etching liquid E is circulated by the circulation device 30. In addition to the direction, microscopically, a flow toward the substrate to be processed X is also generated. Therefore, replacement of the etching solution E is actively performed in the vicinity of the substrate to be processed X, and the dissolution of the substrate to be processed X is promoted.

In the conventional bubbling with N ₂ blowing, the generation source of bubbles is, for example, the bottom of the processing tank. However, when ultrasonic vibration is used, the vicinity of the substrate to be processed X becomes a generation source of bubbles. Air bubbles uniformly strike the surface of the substrate X facing the ultrasonic vibration generator 20. Therefore, the polishing of the substrate X to be processed by the above-described mechanism proceeds evenly within the substrate surface, and the difference in etching progress is less likely to occur. Moreover, the etching amount per unit time (etching rate) can be controlled by controlling the supply time of ultrasonic waves and the vibration frequency.

  In the etching process, the concentration of the etching solution E changes. However, since the etching solution E is circulated by the circulation device 30 and the concentration is controlled, the etching solution E has a uniform concentration as a whole. Further, when ultrasonic vibration is supplied to the etching solution E, the temperature of the etching solution E rises and the etching rate may change. However, the temperature of the etching solution E is cooled and maintained by the action of the temperature control tank 50. In addition, there is no etching rate shift due to temperature changes. Therefore, it becomes easy to etch the substrate X to be processed to a desired thickness.

  For example, in etching using a conventional etching apparatus, the amount of etching is controlled by the immersion time of the substrate to be processed X in the etching solution based on the etching rate determined by the concentration and temperature of the etching solution, the stirring speed of the etching solution, and the like. I was going. Compared with such a method, when the etching apparatus 1 of this embodiment is used, the etching amount can be controlled also by controlling the supply time and the vibration frequency of the ultrasonic vibration. Can be set in detail, and more precise thickness control becomes possible.

  When performing etching processing on a plurality of substrates to be processed, as usual, etching is performed in advance using a dummy substrate to be processed, and conditions for obtaining a desired etching amount are determined. It is good to keep.

When etching is performed until the substrate to be processed X has a desired thickness, the etching liquid is discharged from the processing tank 10 and pure water is supplied using a rinsing liquid circulation device 40 as shown in FIG. Supply and circulate. At that time, it is preferable to supply ultrasonic vibration to the pure water from the ultrasonic vibration generator 20 because the reaction product adhering to the surface of the substrate X to be processed and the etching solution can be easily removed. The ultrasonic vibration supplied at this time may be the same frequency as that during etching, or may be one with a reduced frequency.
As described above, the etching process using the etching apparatus 1 of the present embodiment is completed.

  According to the etching apparatus 1 configured as described above, it is possible to provide an etching apparatus that can set etching conditions in more detail than the conventional apparatus and can control the thickness of the substrate to be processed with high accuracy. Can do.

  In the present embodiment, the ultrasonic vibration generator 20 is disposed at a position facing the substrate to be processed X. However, if ultrasonic vibration is generated in the substrate processing unit 14, the processing target is processed. Since bubbles are generated in the etching solution E facing the substrate X and etching is promoted, the position does not have to be opposed to the substrate X to be processed.

  In the present embodiment, the ultrasonic vibration generator 20 has the water-cooled cooling means 26, but it may be an air-cooled type or other type of cooling method. In addition, although the continuous usable time is shortened, even if the ultrasonic vibration generator 20 does not have the cooling means 26, an etching apparatus capable of accurately controlling the thickness of the substrate X to be processed can be obtained. Is possible.

  In the present embodiment, the temperature control tank 50 disposed outside the chemical liquid cooling unit 16 cools the etching liquid E inside the chemical liquid cooling unit 16 to prevent the etching rate from being shifted. For example, a temperature control unit that changes to the temperature control tank 50 may be provided in the middle of the chemical solution line 32 to control the temperature of the circulating etching solution E. Although the continuous usable time is shortened, it is possible to provide an etching apparatus that can accurately control the thickness of the substrate X to be processed even if the temperature control tank 50 is not provided.

[Second Embodiment]
3 to 6 are explanatory views of the etching apparatus 2 according to the second embodiment of the present invention. The etching apparatus 2 of the present embodiment is partially in common with the etching apparatus 1 of the first embodiment. The difference is that the treatment tank is divided into two treatment tanks, a first treatment tank and a second treatment tank, and an ultrasonic vibration generator is provided for each treatment tank. Therefore, in this embodiment, the same code | symbol is attached | subjected about the component which is common in 1st Embodiment, and detailed description is abbreviate | omitted.

  FIG. 3 is a schematic diagram illustrating the etching apparatus 2 of the present embodiment, and corresponds to FIG. 1 of the first embodiment.

  As shown in the figure, the etching apparatus 2 stores an etching solution E, and the processing tank 60 is divided into a first processing tank 60A and a second processing tank 60B by a partition wall 80, and the first processing tank 60A and the first processing tank 60A. 2 Ultrasonic vibration generators 20A and 20B provided outside the processing tank 60B, the circulating device 30 for the etching liquid E, the circulating device 40 for the rinsing liquid, and the temperature control tank provided outside the processing tank 10 50. Each configuration will be described below.

  The first processing tank 60A and the second processing tank 60B of the processing tank 60 are each provided with a substrate processing unit 64 provided at the upper part and a chemical solution cooling part 66 provided at the lower part. Further, the first processing tank 60A and the second processing tank 60B are separated by two substrates to be processed X arranged in the processing tank 60, that is, a support portion 67 provided at the bottom of the processing tank 60. And the to-be-processed substrate X hold | maintained at the board | substrate holder 62 has played the role of the partition 80 which isolate | separates 60 A of 1st process tanks, and the 2nd process tank 60B.

  The ultrasonic vibration generators 20A and 20B can be controlled by supplying different drive signals from the respective control devices 24A and 24B to the respective ultrasonic transducers 22A and 22B, thereby making the drive conditions different. it can. By doing so, different ultrasonic vibrations are generated in the first processing tank 60A and the second processing tank 60B, and the etching amount of the substrate Xa to be processed and the etching amount of the substrate Xb to be processed can be made different. it can. When the driving conditions are different between the ultrasonic vibration generators 20A and 20B, the amount of heat generated in the ultrasonic vibrators 22A and 22B is also different, so that the amount of water passing through the cooling means 26A and 26B is varied to appropriately remove heat. Good to do.

  The chemical liquid line 32 included in the circulation device 30 extends from the walls of the chemical liquid cooling units 66 of the first processing tank 60 </ b> A and the second processing tank 60 </ b> B and is disposed up to the upper part of the processing tank 60. Similarly, the rinsing liquid line 42 included in the circulation device 40 extends from the walls of the chemical liquid cooling units 66 of the first processing tank 60 </ b> A and the second processing tank 60 </ b> B and is disposed up to the upper part of the processing tank 60.

  In the upper part of the processing tank 60, the chemical liquid line 32 and the rinsing liquid line 42 are connected to a switching valve 70, and a branch nozzle 72 is connected to the switching valve 70 via a pipe 71. The switching valve 70 selects either the chemical liquid line 32 or the rinsing liquid line 42 according to the type of liquid supplied to the processing tank 60, and the branch nozzle 72 supplies the etching liquid or rinsing liquid supplied via the pipe 71 to the first position. It branches and supplies to both 1st processing tank 60A and 2nd processing tank 60B.

  FIG. 4 is an explanatory view of the substrate to be processed X used in the etching apparatus 2 shown in FIG. The two substrates to be processed X are sandwiched while being fitted into the groove portions 63 of the frame-shaped substrate holders 62A and 62B. By holding the two substrates to be processed Xa and Xb together in this way, the etching apparatus 2 can simultaneously perform etching on the two substrates to be processed X. Of course, the etching may be performed while holding only one substrate X to be processed.

  FIG. 5 is an explanatory diagram for explaining the substrate to be processed X disposed in the processing tank 60 of the etching apparatus 2. As shown in FIG. 4, the substrate to be processed X held by the substrate holder 62 is inserted into a rail-like support portion 68 provided on the side wall of the processing bath 60 and placed on the support portion 67. The substrate X to be processed functions as a partition wall 80 that divides the processing tank 60 into two parts, a first processing tank 60A and a second processing tank 60B.

  FIG. 6 is an explanatory diagram of an etching process using the etching apparatus 2 of the present embodiment, and corresponds to FIG. 2 of the first embodiment.

  As shown in FIG. 6A, first, the two substrates to be processed Xa and Xb held by the substrate holder 62 are placed in the processing bath 60.

  Next, as shown in FIG. 6B, the switching valve 70 is switched to the circulation device 30 side to fill the etching solution E into the first processing tank 60A and the second processing tank 60B, and process the chemical solution through the chemical liquid line 32. The etching solution E in the tank 60 is circulated. The circulating etching solution E is distributed to the first processing tank 60A and the second processing tank 60B through the branch nozzle 72. The two substrates to be processed Xa and Xb arranged in the processing tank 60 are arranged facing the first processing tank 60A and the second processing tank 60B, respectively.

  From the ultrasonic vibration generators 20A and 20B, ultrasonic vibration is supplied to the etching solution E in the first processing tank 60A and the second processing tank 60B, respectively. At that time, the surface of the substrate to be processed Xa is polished by the ultrasonic vibration supplied from the ultrasonic vibration generator 20A, and the surface of the substrate to be processed Xb is polished by the ultrasonic vibration supplied from the ultrasonic vibration generator 20B. Thus, an etching process is performed on each substrate to be processed.

When etching is performed until the substrates to be processed Xa and Xb each have a desired thickness, the etching solution is discharged from the processing tank 60, and the switching valve 70 is connected to the circulation device 40 side as shown in FIG. The pure water is filled in the first treatment tank 60A and the second treatment tank 60B, and the pure water is circulated through the rinse liquid line 42. At that time, it is preferable to supply ultrasonic vibration to the pure water from the ultrasonic vibration generator 20 because the reaction product adhering to the surface of the substrate X to be processed and the etching solution can be easily removed. The ultrasonic vibration supplied at this time may be the same frequency as that during etching, or may be one with a reduced frequency.
As described above, the etching process using the etching apparatus 2 of this embodiment is completed.

  According to the etching apparatus 2 configured as described above, an etching apparatus capable of simultaneously and accurately etching both surfaces of the substrate to be processed X constituting the partition wall 80 can be obtained.

  The preferred embodiments of the present invention have been described above with reference to the accompanying drawings, but it goes without saying that the present invention is not limited to such examples. Various shapes, combinations, and the like of the constituent members shown in the above-described examples are examples, and various modifications can be made based on design requirements and the like without departing from the gist of the present invention.

DESCRIPTION OF SYMBOLS 1, ... Etching apparatus 10, 60 ... Processing tank, 20 ... Ultrasonic vibration generator (ultrasonic vibration generating means), 20A ... Ultrasonic vibration generator (first ultrasonic vibration generating means), 20B ... Ultrasonic Vibration generator (second ultrasonic vibration generating means), 22, 22A, 22B ... ultrasonic transducer, 24, 24A, 24B ... control device (control means), 26, 26A, 26B ... cooling means, 30 ... circulation device (Flowing means), 50 ... temperature control means, 60A ... first treatment tank, 60B ... second treatment tank, 80 ... partition wall, E ... etching solution, X, Xa, Xb ... substrate to be treated,

Claims (7)

A treatment tank in which an etching solution is stored, and the substrate to be treated is immersed in the etching solution;
Fluid means for fluidizing the etching solution in the treatment tank;
Ultrasonic vibration generation, comprising: an ultrasonic vibrator that is provided in the processing tank and generates ultrasonic vibration in the etching solution facing the substrate to be processed; and a control unit that controls driving of the ultrasonic vibrator. And an etching apparatus.   The ultrasonic vibration generating means is provided to face the substrate to be processed, and applies ultrasonic vibration that propagates from the normal direction of the substrate to be processed to the substrate to be processed. Etching equipment.   The etching apparatus according to claim 1, wherein the ultrasonic vibration generating unit includes a cooling unit that cools the ultrasonic transducer.   The etching apparatus according to any one of claims 1 to 3, further comprising a temperature adjusting unit that controls a temperature of the etching solution. The treatment tank has a partition partitioning the inside, and is divided into a first treatment tank and a second treatment tank by the partition,
First ultrasonic vibration generating means for applying ultrasonic vibration to the etching solution stored in the first processing tank; and second ultrasonic vibration for applying ultrasonic vibration to the etching liquid stored in the second processing tank. Generating means, and
The etching apparatus according to claim 1, wherein the substrate to be processed is used as the partition wall. As the partition wall, two stacked substrates to be processed are used,
The etching apparatus according to claim 5, wherein the two substrates to be processed face the first processing tank and the second processing tank, respectively.   The etching apparatus according to claim 5 or 6, wherein the first ultrasonic vibration generating means and the second ultrasonic vibration generating means can be controlled independently of each other.

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