JP2013086059A - Ultrasonic cleaning apparatus - Google Patents

Abstract

An ultrasonic cleaning apparatus capable of uniformly cleaning an object to be cleaned and reducing damage.
An ultrasonic cleaning apparatus includes a cleaning tank 2 in which an object to be cleaned 8 is immersed in a cleaning liquid 7, a plurality of ultrasonic vibration elements 302 that are disposed on a bottom surface of the cleaning tank 2 and vibrate the cleaning liquid 7. Based on the resonance frequency for each element stored in the memory unit 409 by randomly switching the memory unit 409 that stores the resonance frequency for each element, the oscillation unit 402 that can switch the oscillation frequency, and the element 302. And a control unit 401 that controls the oscillation unit 402 and supplies high-frequency power to the element.
[Selection] Figure 1

Description

  The present invention relates to an ultrasonic cleaning apparatus used for precision cleaning of semiconductor wafers and the like.

  High-frequency ultrasonic cleaning devices are used for precision cleaning of finely processed products such as semiconductor wafers, glass for liquid crystals, and hard disks. The dirt is particles of less than 1 μm, and the dirt is peeled off by the ultrasonic vibration transmitted through the cleaning liquid filled in the cleaning tank or by the synergistic effect of the cleaning liquid and the ultrasonic vibration.

JP-A-9-47733

  However, the performance of semiconductor cleaning is diversifying year after year, and the particle shape of dirt varies in size, the state of adhesion and particle material varies, and the precision of the object to be cleaned has increased dramatically, resulting in uneven cleaning. The damage to the object to be cleaned is remarkable. For this reason, in the ultrasonic cleaning apparatus, the stability of the cleaning performance is particularly emphasized.

  The present invention has been made paying attention to the above circumstances, and an object of the present invention is to provide an ultrasonic cleaning apparatus capable of reducing unevenness in cleaning and damage to an object to be cleaned.

  In order to achieve the above object, a first aspect of an ultrasonic cleaning apparatus according to the present invention includes: a cleaning tank in which an object to be cleaned is immersed in a cleaning liquid; and a plurality of vibrators that are disposed on a bottom surface of the cleaning tank and vibrate the cleaning liquid. An ultrasonic vibration element, a storage unit that stores a resonance frequency for each element, an oscillation unit that can switch an oscillation frequency, and the resonance frequency for each element stored in the storage unit by randomly switching the elements. And a control unit that controls the oscillation unit based on the above and supplies high-frequency power to the element.

  According to the first aspect, even when the characteristics of the ultrasonic vibration element vary, each vibration element vibrates with maximum efficiency by supplying high-frequency power from the oscillator in accordance with the specific resonance frequency of each element. To do. When this is switched at random, when viewed on a time average basis, all the vibration elements vibrate uniformly. Therefore, it is possible to realize an ultrasonic cleaning apparatus that can uniformly clean the object to be cleaned and can reduce damage.

According to a second aspect of the present invention, there is provided the setting means for setting at least one of the element switching interval and the output power value of the high-frequency power in the first aspect.
According to the second aspect, for example, the element switching interval can be adjusted to a time interval that does not generate a standing wave in the cleaning liquid. By doing in this way, generation | occurrence | production of a standing wave is suppressed and the washing | cleaning without a nonuniformity is attained.

Furthermore, a third aspect of the present invention is the method according to the first aspect, wherein high-frequency power of a plurality of oscillation frequencies is supplied to the element by the oscillating unit, and a frequency having a minimum current measurement value is detected as a resonance frequency The detection means to further comprise.
According to the third aspect, the resonance frequency for each ultrasonic vibration element can be automatically detected. Resonance measures the voltage value and current value of the high-frequency power, and the phase difference is zero, that is, the efficiency is maximum. When the efficiency is low, that is, when the phase is shifted, the current value naturally increases, so that it can be said that the efficiency is maximum = current value minimum. Further, if the current value is minimum, there is an advantage that the loss of the transmission line is also reduced.

  That is, according to the present invention, it is possible to provide an ultrasonic cleaning device that can reduce cleaning unevenness and damage to an object to be cleaned.

1 is a block diagram showing a configuration of an ultrasonic cleaning apparatus according to a first embodiment of the present invention. The figure which shows the vibration characteristic of an ultrasonic vibration element. The figure which shows the memory table memorize | stored in the memory | storage part of an ultrasonic vibration module. The figure which shows an example of a control value setting screen. The figure which shows the frequency switching process of an ultrasonic oscillator. The flowchart which shows the resonant frequency detection process of the ultrasonic cleaning apparatus of FIG. The figure which shows the memory table memorize | stored in the memory | storage part of an ultrasonic vibration module. The block diagram which shows the structure of the ultrasonic cleaning apparatus which concerns on 2nd Embodiment of this invention. The flowchart which shows the resonant frequency detection process of the ultrasonic cleaning apparatus of FIG.

Embodiments of an ultrasonic cleaning apparatus according to the present invention will be described below with reference to the drawings.
(First embodiment)
FIG. 1 is a block diagram showing the configuration of the ultrasonic cleaning apparatus according to the first embodiment of the present invention.
The ultrasonic cleaning apparatus stores a quartz tank (cleaning tank) 2 filled with a cleaning liquid 7 for immersing an object to be cleaned such as a semiconductor wafer 8 to be cleaned, and the quartz tank 2 in a state where pure water 6 is filled. It has an outer tub 1. The ultrasonic cleaning apparatus further includes an ultrasonic vibration module 3, an ultrasonic oscillator 4, and a control value setting terminal (PC) 5.

  The ultrasonic vibration module 3 includes an ultrasonic vibration plate 301, ultrasonic vibration elements 302-1 to 302-n, a storage unit 303, and a plug unit 304. The ultrasonic vibration plate 301 is disposed on the bottom surface of the outer tub 1, and the ultrasonic vibration elements 302-1 to 302-1 are connected to the ultrasonic vibration plate 301. High-frequency power is supplied from the ultrasonic oscillator 4 to the ultrasonic vibration elements 302-1 to 302-n via the plugs 304.

  FIG. 2 shows the vibration characteristics of the ultrasonic vibration elements 302-1 to 302-n, where the horizontal axis represents frequency [kHz] and the vertical axis represents vibration efficiency [%]. The frequency at which the vibration efficiency is maximized (resonance frequency) is the optimum value of the oscillation frequency. As shown in FIG. 2, the ultrasonic vibration elements 302-1 to 30-n have “variation” in the resonance frequency and vibration efficiency. Therefore, the resonance frequency of each ultrasonic vibration element 302-1 to n is automatically detected by a method described later, and the resonance frequency [kHz] and vibration efficiency [%] for each ultrasonic vibration element 302-1 to n are stored. The stored memory table is stored in the storage unit 303. FIG. 3 shows an example of the memory table. The storage unit 303 may be configured with a wireless IC tag (RFID: Radio Frequency Identification) or the like.

  The ultrasonic oscillator 4 includes an oscillator 402, an amplifier unit 403, a matching unit 404, a current measuring unit 405, a power measuring unit 406, and plugging units 411 and 412 and a control unit 401 that controls the operation of each unit. Electric power is supplied to the ultrasonic vibration module 3. Further, a display unit 407, an operation unit 408 such as an operation switch, and a memory unit 409 are connected to the control unit 401. The display unit 407 displays the power value measured by the power measuring unit 406 and the like. The operation unit 408 is used for setting operations such as a power value and an oscillation frequency.

The PC 5 includes a control unit 501, a display unit 502, an operation unit 503, and a plug unit 504, and sets various control values of the control unit 401 of the ultrasonic oscillator 4.
FIG. 4 is an example of the control value setting screen 11 displayed on the display unit 502 of the PC 5. The user can set various control values for each of the ultrasonic vibration elements 302-1 to 302-1 through this screen. In FIG. 4, the “resonance frequency (kHz)” is set to the same value as the memory table of FIG. “Initial amplification factor (times) of the amplifier unit” is an initial value for controlling the amplifier unit 403 so that the output power reaches a predetermined power (for example, 500 W) in a short time when the oscillation frequency is switched. . The “oscillation time” is a value that controls the switching frequency of the oscillation frequency, and is determined in advance in consideration of cleaning efficiency and the like. The “oscillation order” is a value that controls the oscillation order of the ultrasonic transducer elements 302-1 to 302-n. For example, the oscillation order is controlled using a random number or determined in advance using a random number. These settings are input to the ultrasonic oscillator 4 through the plug portion 504 and stored in the memory unit 409.

  Next, the operation of the ultrasonic cleaning apparatus configured as described above will be described. FIG. 5 is a diagram showing a frequency switching process of the ultrasonic oscillator 4. The control unit 401 sequentially switches the oscillation unit 402, the amplifier unit 403, and the matching unit 404 based on the setting contents (resonance frequency, initial amplification factor of the amplifier unit, oscillation order, and oscillation time) stored in the memory unit 409. The ultrasonic vibration elements 302-1 to 30-n are oscillated by supplying the set high frequency power.

  Here, the principle of the standing wave generation and the method for suppressing the standing wave will be described with reference to FIG. In the standing wave, the ultrasonic wave oscillated by the ultrasonic vibration plate 301 travels as a traveling wave in the cleaning liquid of the quartz tank 2, and this traveling wave is reflected by the liquid surface to become a reflected wave. It occurs when the vibration position stops moving due to the overlapping phases. When the standing wave is generated in the cleaning liquid, the ultrasonic vibration energy in the cleaning liquid is suppressed, and the cleaning effect of the article to be cleaned 8 is greatly reduced.

  Therefore, in this embodiment, the oscillation frequency is switched until the ultrasonic wave vibrated by the ultrasonic vibration plate 301 reaches the liquid surface of the cleaning liquid 7 in order to suppress the standing wave in the cleaning liquid. By switching the oscillation frequency at such timing, it is possible to suppress the interference between the traveling wave of the ultrasonic wave and the reflected wave, and to prevent the cleaning effect from being lowered.

Hereinafter, an embodiment of the switching time of the oscillation frequency will be described.
The water depth of the cleaning liquid 7 in the quartz tank 2 is a1, the ultrasonic water velocity is v1, and the time for the ultrasonic wave to reach the water surface from the bottom surface is s1. The underwater velocity v1 of the ultrasonic wave is about 1530 m / s regardless of the ultrasonic frequency.

The arrival time s1 of the ultrasonic wave can be obtained from the following equation.
s1 = a1 / v1
Here, when the water depth a1 is 0.5 m, the arrival time s1 is 33.3 ms (0.0333 seconds). In order to suppress the standing wave in the cleaning liquid 7, the oscillation frequency switching time s2 is set to 33.3 ms or less.
s2 ≦ s1
FIG. 6 is a flowchart for automatically detecting the resonance frequency of each ultrasonic vibration element of the ultrasonic vibration module 3. In the configuration shown in FIG. 1, since the ultrasonic vibration elements 302-1 to 30-n are connected in parallel, the resonance frequency of each element cannot be directly detected. For this reason, the ultrasonic vibration module 3 is regarded as one ultrasonic vibration element, and the resonance frequency is automatically detected assuming that the element has a plurality of resonance frequencies.

  In step S11, the control unit 401 performs initial setting. Specifically, an oscillation frequency range input (minimum frequency fmin = 950 kHz, maximum frequency fmax = 1100 kHz), variable width input (fstep = 0.1 kHz), input of the number of ultrasonic vibration elements n, and current value threshold Enter “ith”.

  In step S12, the control unit 401 controls the oscillation frequency f of the oscillation unit 402 to the minimum frequency fmin, and applies a predetermined voltage to the ultrasonic vibration element by the amplifier unit 403 and the matching unit 404. The control unit 401 measures the current value i using the current measurement unit 405 and writes the oscillation frequency f and the measured current value i in the memory unit 409 as a pair.

  In step S <b> 13, the control unit 401 controls the oscillation unit 402 so that the oscillation frequency f = the minimum frequency fmin + the variable width fstep. The control unit 401 repeats the processes of steps S12 and S13 until the oscillation frequency f exceeds the maximum frequency fmax (step S14).

  When the oscillation frequency f exceeds the maximum frequency fmax (step S14: YES), the control unit 401 selects n ultrasonic vibration elements from the data in the memory unit 409 in ascending order of the current value i (step S15). If the current value i does not exceed the current value threshold value ith (step S16: NO), it is removed from the selected current value i (step S17). When the current value i is greater than or equal to the current value threshold value ith (step S16: YES), the vibration efficiency is calculated from the selected current value i or selected from a table, and as shown in FIG. The vibration efficiency of the frequency is written in the storage unit 303 of the ultrasonic vibration module 3 (step S18).

(Second Embodiment)
FIG. 8 is a block diagram showing a configuration of an ultrasonic cleaning apparatus according to the second embodiment of the present invention. The difference from FIG. 1 in the first embodiment is that power is directly supplied to each of the ultrasonic transducer elements 302-1 to 302-n. Therefore, a switching unit 413 is added to the ultrasonic oscillator 4, and the plug part 412 </ b> A and the plug part 304 </ b> A have connection terminals corresponding to the switch unit 413. In FIG. 8, the same parts as those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted.

FIG. 9 is a follow chart for automatically detecting the resonance frequency of each ultrasonic vibration element of the ultrasonic vibration module 3. Unlike the case of FIG. 6, the configuration of FIG. 8 can directly detect the resonance frequency of each of the ultrasonic transducer elements 302-1 to 302-n.
In step S21, the control unit 401 performs initial setting. Specifically, an oscillation frequency range input (minimum frequency fmin = 950 kHz, maximum frequency fmax = 1100 kHz), variable width input (fstep = 0.1 kHz), and number n of ultrasonic vibration elements are input. In step S22, the control unit 401 initializes the ultrasonic vibration element number N = 0.

In step S23, the control unit 401 sets the oscillation frequency f of the oscillation unit 402 to the minimum frequency fmin, and increments the ultrasonic vibration element number N by one.
In step S <b> 25, the control unit 401 applies a predetermined voltage to the ultrasonic vibration element by the amplifier unit 403 and the matching unit 404. The control unit 401 measures the current value by the current measurement unit 405 and writes the ultrasonic vibration element number N, the oscillation frequency f, and the measured current value in the memory unit 409 in association with each other.

  In step S <b> 26, the control unit 401 controls the oscillation unit 402 so that the oscillation frequency f = the minimum frequency fmin + the variable width fstep. The control unit 401 repeats the processes of steps S25 and S26 until the oscillation frequency f exceeds the maximum frequency fmax (step S27).

When the oscillation frequency f exceeds the maximum frequency fmax (step S27: YES), the control unit 401 selects, from the data in the memory unit 409, the frequency with the minimum current value as the resonance frequency. The vibration efficiency of the element is calculated from the current value or selected from the table, and the element number, resonance frequency, and vibration efficiency are written in the storage unit 303 of the ultrasonic vibration module 3 (step S28).
Thereafter, the process proceeds to step S23, and the above processing is repeated for each element. In step S24, the ultrasonic vibration element number N exceeds the number n of ultrasonic vibration elements, and the resonance frequency is detected for all elements, and the process is terminated.

As described above, according to the first and second embodiments, it is possible to realize an ultrasonic cleaning apparatus that can uniformly clean an object to be cleaned and can reduce damage.
In general, in an ultrasonic cleaning machine, a plurality of vibration elements are used, and each vibration element has a specific resonance frequency. Usually, however, selection is performed so that each is as close as possible. As a result, each vibration element vibrates uniformly and can be cleaned without unevenness. However, the selection has a limit due to cost. In the present embodiment, the characteristics of the vibration element are measured in advance, and when oscillating, high-frequency power is supplied from the oscillator in accordance with the information, so that each vibration element vibrates with maximum efficiency. By switching these sequentially, when viewed on a time average, all the vibration elements vibrate uniformly.

  The cleaning tank is filled with the cleaning liquid, but the ultrasonic wave irradiated from the vibration surface is reflected by the liquid surface. At this time, there is a component returning to the vibration surface at a certain rate, and a standing wave may be generated due to interference between the traveling wave and the reflected wave. When a standing wave is generated, since nodes and bellies are alternately present, cleaning unevenness occurs in a striped manner at that portion. The condition for generating the standing wave occurs when the wavelength of the ultrasonic wave determined by the sound speed and frequency in water and the liquid depth have a certain relationship. The liquid level constantly fluctuates, and the speed of sound in water tends to change depending on the liquid temperature and the properties of the cleaning liquid. Thus, standing waves may occur, disappear, or remain unstable.

  On the other hand, in the above-described embodiment, control is performed so as to oscillate by always changing the frequency so that a standing wave does not constantly occur. The frequency does not need to be changed continuously, and can oscillate intermittently within a certain frequency range as programmed in advance, or can oscillate at random with random numbers. In the program, it is possible to determine by performing an experiment by the user himself so that the cleaning effect is optimum.

  The resonance is a state in which the voltage value and current value of the high-frequency power are measured and the phase difference is zero, that is, the efficiency is maximum. When the efficiency is low, that is, when the phase is shifted, the current value naturally increases, so that it can be said that the efficiency is maximum = current value minimum. Further, if the current value is minimum, there is an advantage that the loss of the transmission line is also reduced.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Further, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine suitably the component covering different embodiment.

  DESCRIPTION OF SYMBOLS 1 ... Outer tank, 2 ... Quartz tank (cleaning tank), 3 ... Ultrasonic vibration module, 4 ... Ultrasonic oscillator, 5 ... Terminal for control value setting (PC), 6 ... Pure water, 7 ... Cleaning liquid, 8 ... Covered Cleaning object (semiconductor wafer), 301 ... ultrasonic vibration plate, 302 ... ultrasonic vibration element, 303 ... storage part, 304 ... plugging part, 401 ... control part, 402 ... oscillation part, 403 ... amplifier part, 404 ... matching 405 ... Current measuring unit, 406 ... Power measuring unit, 407 ... Display unit, 408 ... Operating unit, 409 ... Memory unit, 411, 412 ... Connecting unit, 501 ... Control unit, 502 ... Display unit, 503 ... Operation Part, 504 .. plug part.

Claims (3)

A cleaning tank in which an object to be cleaned is immersed in a cleaning liquid;
A plurality of ultrasonic vibration elements arranged on the bottom surface of the cleaning tank and vibrating the cleaning liquid;
A storage unit for storing a resonance frequency for each element;
An oscillation unit capable of switching the oscillation frequency;
A control unit that switches the elements at random, controls the oscillation unit based on a resonance frequency for each element stored in the storage unit, and supplies high-frequency power to the element. Sonic cleaning device.   The ultrasonic cleaning apparatus according to claim 1, further comprising setting means for setting at least one of the element switching interval and the output power value of the high-frequency power.   2. The super-unit according to claim 1, further comprising detection means for supplying high-frequency power of a plurality of oscillation frequencies to each element by the oscillation unit and detecting a frequency having a minimum measured current value as a resonance frequency. Sonic cleaning device.

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