JPH0924349A - Ultrasonic washing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the washing effect of an ultrasonic washing device by respectively specifying the angle of inclination of the base of the inside tank of a device constituted by inclining the base of the inside tank from horizontal and inclining the base of an outside tank mounted with an ultrasonic vibrator transducer so as to nearly parallel this base with the base of the inside tank, the plate thickness of the tanks as well as the frequency of the transducer. SOLUTION: The base of the inside tank 4 is inclined at an angle of inclination of 3 to 20 deg. from horizontal. As a result, air bubbles are risen rightward and upward by their own buoyancy and are not longer stagnated at the rear surface of the inside tank 4 as soon as the air bubbles are generated. Then, the reflection of ultrasonic energy by the air bubbles is prevented. Further, the base of the outside tank 1, on which the transducer 3 is mounted, is so inclined as to parallel with the base of the inside tank 4. As a result, the base of the inside tank 4 is perpendicularly irradiated with the ultrasonic vibrations radiated from the transducer 3 of 500kHz to 1.5MHz. Then, the transmittance of the ultrasonic vibration at the base of the inside tank 4 is enhanced to approximately 100% and the washing effect is improved. The inside tank is made of quartz glass having a half wavelength of ±10% of the ultrasonic frequency in the plate width.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for cleaning silicon wafers of compound semiconductor substrates, compound semiconductor wafers, etc., and performs precision cleaning without adhesion of metal ions.
The present invention relates to an ultrasonic cleaning device having a double tank structure that uses a high frequency of 00 kHz or more.

[0002]

2. Description of the Related Art Most of dirt adhering to semiconductor material wafers and semiconductor devices has small particles of 0.1 μm to 10 μm, and generally has weak adhesion and can be peeled off by ultrasonic cleaning. On the other hand, the materials to be cleaned are fragile, and conventional ultrasonic cleaning devices of 20 kHz to 50 kHz are liable to damage (scratch, defect, etc.) by the action of ultrasonic waves. Sound waves have been applied.

[0003] Furthermore, there is a problem that metal ions eluted from a stainless steel or other metal cleaning tank or diaphragm adhere to the object to be cleaned. A washing apparatus having a double tank structure using a beaker made of aluminum is used.

FIG. 3 is a cross-sectional view of a conventional ultrasonic cleaning apparatus, which is an ultrasonic cleaning apparatus having a double tank structure using a quartz glass beaker as an inner tank. In the figure, 10 is an outer tank, 1
1 is a beaker, 2 is an ultrasonic medium liquid, 3 is an ultrasonic transducer, 5
Is a cleaning liquid.

The plate thickness of the quartz glass beaker 11 used as the inner tank varies depending on the size and structure of the apparatus.
Approximately 5 mm is used. Generally, as the size of the beaker increases, more mechanical strength is required,
The plate thickness increases. The beaker for 2 cassettes with a wafer size of 6 inches is slightly smaller in size, and the plate thickness is often 3 mm. A plate thickness of 4 mm is often used.

Ultrasonic vibrations radiated upward from the ultrasonic vibrator 3 attached to the bottom surface of the outer tank 10 are transmitted to the medium liquid 2 and penetrate the bottom surface of the beaker 11 to be cleaned in the beaker 11. It is transmitted to things. In this case, the frequency of the ultrasonic transducer is set so that the thickness of the bottom surface of the beaker 11 is half the wavelength ± 10%. That is, the ultrasonic frequency that matches the natural frequency of the thickness vibration of the bottom surface of the beaker 11 is selected. For example, if the thickness is 3 mm, the ultrasonic frequency is 1M.
Hz and 730 kHz for 4 mm.

However, as shown in FIG. 3, bubbles 1 generated by the ultrasonic action in the ultrasonic medium liquid 2 in the outer tank 10
2 adheres to the lower surface of the beaker 11 to hinder the transmission of ultrasonic waves. FIG. 4 is a cross-sectional view showing another structure of the conventional ultrasonic cleaning device. This structural example is an example in which the bottom surface of the beaker 4 is provided with an inclination θ so that the bubbles 12 are removed by the action of the buoyancy of the bubbles 12. This inclination θ is more effective as the angle increases, but is practically about 3 ° to 20 ° due to other restrictions such as the size and structure of the device.

[0008]

FIG. 5 is a characteristic example diagram showing the transmittance of ultrasonic vibration energy with respect to the inclination angle of the beaker bottom surface. The angle θ between the beaker 4 in FIG. 4 and the ultrasonic wave generation surface, that is, the mounting surface of the vibrator 3 on the bottom surface of the outer tank 10.
Indicates that the transmittance is 100% when θ = 0 to 2 °, that is, when they are substantially parallel, the transmittance decreases as the angle θ increases.

From the above, the conventional structure shown in FIGS. 3 and 4 has the following problems. (1) In the case of FIG. 3, since the bottom surface of the beaker 11 and the mounting surface of the vibrator 3 are parallel to each other, the conditions under which the ultrasonic vibration energy is transmitted to the beaker are good.
There is a drawback in that the transmission of ultrasonic waves is hindered because 2 is attached. (2) In the case of FIG. 4, air bubbles do not adhere to the bottom surface of the beaker, but since the bottom surface of the beaker 4 is inclined with respect to the mounting surface of the vibrator 3, as shown in FIG. There is a drawback in that the transmittance of the ultrasonic energy is reduced and the ultrasonic energy transmitted inside the beaker 4 is reduced.

(3) Further, in the case of FIG. 3, the holder for the wafer, which is called a cassette or carrier, has a structure in which the lower portion is slightly narrowed to prevent the wafer from falling in order to hold the wafer. Furthermore, the transmission of high-frequency ultrasonic waves of 500 kHz or more is not a broad directivity but a substantially parallel beam, so the transmission of ultrasonic waves is blocked by the narrowed portion at the bottom of this cassette. A dead zone is created, and a cleaning failure occurs. FIG. 6 is a sectional view showing a state in which the cassette 9 is put in the conventional apparatus shown in FIG. The inclined portion in the cassette 9 becomes a dead zone 13 and ultrasonic energy is not transmitted.

The object of the invention described in claim 1 of the present invention is to solve the drawbacks of the above-mentioned conventional structure. To prevent bubbles from adhering to the lower surface of the inner tank, ultrasonic energy is applied. Another object of the present invention is to provide an ultrasonic cleaning device having an improved cleaning effect by improving the transmittance of the bottom surface of the inner tank.

Further, the object of the invention described in claim 2 is, in addition to the object of the invention described in claim 1, an ultrasonic cleaning apparatus in which a dead zone where ultrasonic energy is not transmitted in a cassette is reduced. To provide.

[0013]

The ultrasonic cleaning apparatus according to claim 1 of the present invention is an ultrasonic bath in which an ultrasonic transducer of 500 kHz to 1.5 MHZ is attached to the bottom surface, and ultrasonic waves in the external bath. Holds in medium liquid and plate thickness is half wavelength of ultrasonic frequency ±
2 for cleaning an object to be cleaned which is composed of an inner tank made of 10% quartz glass and is immersed in the cleaning liquid in the inner tank.
In the ultrasonic cleaning device having a heavy tank structure, the inner tank has a bottom surface having an inclination angle of 3 ° to 20 ° with respect to the horizontal, and the outer tank has a bottom surface to which the ultrasonic transducer is attached. It is characterized in that it is formed so as to be substantially parallel to the bottom surface of the inner tank according to the inclination of the bottom surface of the inner tank.

Further, in the ultrasonic cleaning apparatus according to the second aspect of the present invention, an ultrasonic bath having an ultrasonic transducer of 500 kHz to 1.5 MHZ is attached to the bottom surface, and an ultrasonic medium liquid in the external bath. It is composed of a quartz glass inner tank having a plate thickness of a half wavelength of ultrasonic frequency ± 10%, and has a double tank structure for cleaning an object to be cleaned which is immersed in a cleaning liquid in the inner tank. In the sonic cleaning device, the bottom surface of the inner tank has a V-shaped cross section and each surface has an inclination angle of 3 ° to 20 ° with respect to the horizontal, and the bottom surface of the outer tank is the bottom surface of the inner tank. It is characterized in that it is formed so as to have a V-shaped cross section substantially parallel to the bottom surface of the inner tank according to the inclination, and ultrasonic vibrators are attached to both the inclined bottom surfaces.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing an embodiment of the invention according to claim 1 of the present invention. In the figure, 1 is an outer tank, 2 is an ultrasonic medium liquid, 3 is an ultrasonic vibrator, 4 is an inner tank (beaker), and 5 is a cleaning liquid. The bottom surface of the beaker 4 is inclined with respect to the horizontal, and as soon as bubbles are generated, the buoyancy of the beaker ascends to the upper right, so that it does not stay on the bottom surface of the beaker 4. Therefore, the reflection of ultrasonic energy by the bubbles does not occur. Furthermore, since the bottom surface of the outer tank 1 to which the vibrator 3 is attached is formed to be parallel to the inclined bottom surface of the inner tank 4, the ultrasonic vibration radiated from the vibrator 3 is the bottom surface of the beaker 4. It is irradiated at a right angle to. Therefore, the transmittance of ultrasonic vibrations on the bottom surface of the beaker 4 is almost 100%, and the cleaning effect is extremely good.

FIG. 2 is a sectional view showing an embodiment of the invention described in claim 2 of the present invention. In the figure, 6 is an outer tank, 7
Reference numerals a and 7b are ultrasonic transducers, 8 is an inner tank (beaker), and 9 is a cassette. In this embodiment, since the bottom surface of the beaker 8 and the bottom surface of the outer tank 6 are both provided with a slope having a V-shaped cross section, bubbles do not adhere and ultrasonic energy is almost 100% transmitted. The dead zones in the cassette are reduced because the vibrations are transmitted to the beaker 8 at a high rate and the operating ranges of the two vibrators 7a and 7b intersect as shown in the drawing.

[0017]

【Example】

1) In the experiment according to the embodiment of FIG. 1, the bottom surface of the beaker 4 having a plate thickness of 4 mm is constituted by one surface having an inclination of 10 °, and pure water having a temperature of 70 ° C. is used as the cleaning liquid 5 in the beaker 4. Also, pure water having a temperature of 70 ° C. is also used as the ultrasonic medium liquid 2 in the outer tank 1, and the ultrasonic wave generation surface is inclined by 10 ° so as to be parallel to the bottom surface of the beaker. Sound wave frequency of 730 kHz, ultrasonic wave intensity of 4 W / cm
^When the ultrasonic waves of 2 are applied, the bubbles generated in the ultrasonic medium liquid 2 in the outer tub 1 do not reach the bottom of the beaker 4 due to the buoyancy in sequence, and the outer tub in the beaker 4 does not reach the bottom. It was confirmed by a sound pressure meter that almost the same ultrasonic energy as in the ultrasonic medium liquid 2 in 1 was transmitted. It was confirmed that the inclination angle of the bottom surface is effective in the range of 3 ° to 20 ° with respect to the horizontal.

2) In the experiment according to the embodiment shown in FIG. 2, the bottom surfaces of the beaker 8 and the outer tub 6 having a V-shaped cross section were provided with the ultrasonic irradiation surfaces with the inclinations of 10 ° with respect to the horizontal in opposite directions. When the wafer carrier 9 was placed in the beaker 8 so as to be parallel to the bottom surface of the beaker, and the ultrasonic wave was applied under substantially the same conditions as described above, the carrier 9 was filled with ultrasonic energy. There was no energy dead zone, and the same ultrasonic intensity as in the ultrasonic medium liquid 2 in the outer tank 6 was obtained.

[0019]

As described in detail above, the present invention has the following effects. 1) High-frequency ultrasonic energy generated from the vibrator mounting plate can be transmitted to the beaker with almost no attenuation or reflection, and the cleaning effect of the object to be cleaned such as a wafer can be improved. 2) The dead zone of ultrasonic wave transmission in the wafer holding portion of the carrier can be eliminated, and the entire wafer can be uniformly cleaned.

[Brief description of drawings]

FIG. 1 is a sectional view showing a first embodiment of the present invention.

FIG. 2 is a sectional view showing a second embodiment of the present invention.

FIG. 3 is a cross-sectional view of a conventional device.

FIG. 4 is a cross-sectional view showing another structural example of the conventional device.

FIG. 5 is a diagram showing an example of sound transmittance characteristics with respect to the angle of the bottom surface of the beaker.

FIG. 6 is an explanatory diagram of a dead zone of a conventional device.

[Explanation of symbols]

 1 Outer tank 2 Ultrasonic medium liquid 3 Ultrasonic vibrator 4 Inner tank 5 Cleaning liquid 6 Outer tank 7 Ultrasonic vibrator 8 Inner tank 9 Cassette 10 Outer tank 11 Inner tank 12 Bubble 13 Dead zone

Claims (2)

[Claims] 1. An outer tank having an ultrasonic vibrator of 500 kHz to 1.5 MHZ attached to the bottom surface, and a plate thickness held in an ultrasonic medium liquid in the outer tank and having a plate thickness of a half wavelength ± 10 of the ultrasonic frequency.
% Of the quartz glass inner tank, and a double tank structure ultrasonic cleaning device for cleaning an object to be immersed in the cleaning liquid in the inner tank, wherein the inner tank has a horizontal bottom surface. The outer tank has a tilt angle of 3 ° to 20 °, and the bottom surface of the outer tank to which the ultrasonic transducers are attached is substantially parallel to the bottom surface of the inner tank in accordance with the tilt of the bottom surface of the inner tank. An ultrasonic cleaning device characterized by being formed as follows. 2. An outer tank having an ultrasonic vibrator of 500 kHz to 1.5 MHZ attached to the bottom surface, and a plate thickness held in an ultrasonic medium liquid in the outer tank and having a plate thickness of a half wavelength ± 10 of the ultrasonic frequency.
% Of the quartz glass inner tank, and a double tank structure ultrasonic cleaning apparatus for cleaning an object to be immersed in the cleaning liquid in the inner tank, wherein the inner tank has a bottom surface of V Each of the surfaces has a V-shaped cross-section and has an inclination angle of 3 ° to 20 ° with respect to the horizontal, and the bottom surface of the outer tank is substantially parallel to the bottom surface of the inner tank according to the inclination of the bottom surface of the inner tank. An ultrasonic cleaning device, wherein the ultrasonic cleaning device is formed to have a V-shaped cross section, and ultrasonic vibrators are attached to both inclined bottom surfaces of the ultrasonic vibrator.