JPH03222419A - Supersonic cleaning device - Google Patents

Abstract

PURPOSE:To improve cleaning efficiency by allowing supersonic vibration which travels in a medium liquid to enter a wave receiving surface arranged at a slanting angle with a face of slope of the wave receiving surface in an inner tank. CONSTITUTION:An attempt is made to install a partial piece 7, which is a part of an outer tank 1, a supersonic vibrator 3 and a wave receiving surface and receives vibration energy V1 from the vibrator 3, using liquid 8 as a medium. When an attempt is made to have the wave receiving surface 7 postured as indicated by 7 at the angle of theta compared with the prior art position 7' of the wave receiving surface, the transmittivity in the case of theta 28 deg. will be 100% compared with about 26%, which is the prior art transmittivity in the case of theta=0. This construction makes it possible to transmit drive energy V of the vibrator 3 mounted with the outer tank to cleaned articles effectively, thereby exerting more drastic cleaning capacity compared with the prior art cleaning capacity.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical field to which the invention pertains) The present invention relates to an ultrasonic cleaning device, and in particular to an ultrasonic cleaning device with a dual tank structure using ultrasonic waves of 500 kHz or more used in semiconductor manufacturing processes. be.

(Prior art and its problems) Ultrasonic cleaning equipment used for ultra-precision cleaning of semiconductor wafers, glass masks, liquid crystals, etc. in the semiconductor manufacturing process removes fine particles (foreign objects) of about 0.1 μm. Because of the necessity, the wavelength is short and the ultrasonic frequency near IMH2 is used to avoid damage due to gearvitation.

Furthermore, if metal ions are present in the cleaning tank, they will adhere to the items to be cleaned due to ionic bonds and have a negative effect, so be sure to use bead force, etc., made of materials that do not elute metal ions or impurities, such as quartz glass or Pyrescu, from the inner tank. A cleaning device with a double tank structure is used.

FIG. 1 is a partial cross-sectional view of a conventional ultrasonic cleaning device with a double tank structure. In the figure, 1 is an outer tank, 2 is an inner tank, 3 is an ultrasonic vibrator, 4 is a liquid medium such as water, 5 is a cleaning liquid, and 6 is an object to be cleaned. The inner tank 2 is fixed by fitting Teflon feet attached to the four corners of the bottom surface into Teflon guides attached to the bottom surface of the outer tank (not shown). The outer tank l is made of stainless steel or the like like a general cleaning device, and an ultrasonic vibrator 3 is attached to the outside of the bottom.
The bottom surface of the inner tank 2 is vibrated by longitudinal waves of ultrasonic waves generated by a vibrator 3 using a medium liquid 4 (for example, water) as a transmission medium for ultrasonic waves. This vibration of the bottom surface of the inner tank 2 causes the cleaning liquid 5 in the inner tank 2 to vibrate as shown by the arrow, thereby cleaning the object 6 to be cleaned. The inner tank 2 has a mechanical strength that is not damaged during handling and has a thickness of 3 to 5 mm.

A major problem with such conventional cleaning devices is that the ultrasonic energy transmitted to the bottom surface of the inner tank 2 by the medium liquid 4 of the outer tank 1 is reflected by the bottom wave receiving surface of the inner tank 2, and the inside of the inner tank 2 is The vibration energy transmitted to the vibrator 3 is 20 to 30%, and the vibration energy transmission rate, in other words, the transmittance, is extremely poor, and the cleaning efficiency with respect to the driving power of the vibrator 3 is extremely low.

As a countermeasure to this problem, attempts have been made to attach an ultrasonic transducer directly to the bottom of the inner tank 2, or because the inner tank 2 is made of quartz glass or Nokuirex as described above, Not only is there a difficulty in manufacturing and processing technology to improve the flatness and plane precision of the surface to which the child is attached with adhesive, but also the inner tank (beam force) is difficult to clean.
(If a vibrator is not attached, the material can be recycled, but if a vibrator is attached, the purity of the material may be poor due to adhesive residue.) Moreover, it has the disadvantage of being expensive and causing a large economic loss.

(Object of the Invention) The object of the present invention is to solve such problems, and to eliminate the need to attach a vibrator to the inner tank, and to reduce the vibration energy of approximately 90 to 100% of the ultrasonic energy from the outer tank to the internal tank. An object of the present invention is to provide an ultrasonic cleaning device having a structure in which ultrasonic waves are transmitted to the inside of a tank and the cleaning efficiency is greatly improved.

(Structure of the Invention) The ultrasonic cleaning device of the present invention includes an outer tank equipped with a vibrator that generates ultrasonic vibrations of 500 kHz or more, and an inner tank for storing cleaning liquid and objects to be cleaned. and an inner tank disposed with a space for intervening a medium liquid for transmitting the ultrasonic vibration, and the ultrasonic vibration propagating in the medium liquid is transmitted along the normal line of the wave receiving surface of the inner tank. The present invention is characterized in that the transmittance of the vibration energy of the ultrasonic vibration transmitted through the wave receiving surface is significantly improved by making the ultrasonic vibration enter the wave receiving surface at an inclination angle relative to the wave receiving surface.

The present invention will be explained in detail below with reference to the drawings.

FIG. 2 is a partial structural sectional view for explaining the present invention in detail. In the figure, l is an outer tank, 3 is an ultrasonic transducer, and 7
is a part of the wave receiving surface of the inner tank, which receives the vibration energy v1 from the vibrator 3 using the liquid 8 as a medium. 7° indicated by a broken line indicates the position of the surface of the inner tank in the conventional device. If the vibration energy transmitted through the wave receiving surface 7 or 7 of the inner tank and transmitted to the liquid corresponding to the cleaning liquid inside the inner tank is V2, the vibration energy transmittance is V2/V.
It can be expressed as IX100 (%). In the present invention, the wave-receiving surface of the inner tank is set at an angle of θ compared to the conventional 7" position, so that it has a posture of 7. This θ is perpendicular to the wave-receiving surface (normal direction). It is expressed as a reference (θ=0) when vibration energy is applied to , and this corresponds to the inclination angle between the surface of the outer tank and the surface of the interior facing the surface.

FIG. 3 is a characteristic diagram that supports the principle of the present invention, and shows actually measured values of the transmittance of the partial piece 7 of the inner tank with respect to the incident angle (angle of inclination) θ. In the figure, the transmittance on the vertical axis is defined as 100% of the sound pressure level, which is the value of V2 (=V,) measured with an underwater microphone or the like when the partial piece 7 of the inner tank is not present. The inner tank section 7 is made of Pyrex (borosilicate glass) with a thickness of 3 m and a vibration frequency of I MHz.

As is clear from the figure, while the conventional transmittance when θ=0 is about 26%, the transmittance when θ#28° is almost 100%.

The material of the inner tank may be, for example, stainless steel with a thickness of t=1 to 2M, Pyrex with a thickness of t-2 to 5 mm, or t of 3 to 5 mm.
Even when using quartz glass etc., the transmittance when the incident angle of the ultrasonic wave to the wave receiving surface of the inner tank is at right angle (θ = 0) is 10 to 30% as shown in Table 1, or In the case of these materials as well, when the incident angle θ was changed as shown in FIG. 2, the transmittance was significantly improved, and it was experimentally confirmed that there were angles at which the transmittance was approximately 100%.

table ! FIG. 4 is an explanatory diagram in which the incident angle θ at which the transmittance becomes maximum (95 to 100%) was determined by experiment using these materials and plate thicknesses as parameters. As shown in this figure, since the present invention is intended to clean semiconductor wafers, etc., the material of the inner tank is described as Pyrex or quartz glass, but in the case of other general objects to be cleaned, other materials may be used. It is clear that the same effect can be obtained even if the material is used.

The above phenomena will be described in more detail.

In a conventional general ultrasonic cleaning device with a double tank structure, the frequency of the ultrasonic vibrator is 20 to 40 kHz, and the velocity C of the longitudinal wave (compressional wave) transmitted in the medium liquid (for example, water) is 145 kHz.
6 m/see and the frequency f is 26 kHz, the wavelength λ of the longitudinal wave is expressed by the following equation and is approximately 56 mm.

λ=C/f=1456(m/5ec)/26(
kl (z) = 56 (mm) On the other hand, the wall thickness of the bottom plate of the inner tank of the washing machine is approximately 1 to 2IIIf if it is made of stainless steel.
fl degree, 3-5I for quartz glass or pyrex
nff1, which is so small that it can be ignored with respect to the wavelength λ=56 mm. Therefore, vertical waves (P waves) and transverse waves (S waves) are induced on the bottom of the inner tank by the sparse parts and dense parts where the vibration energy from the outer tank is distorted, and most of the vibration energy is transferred to the inner tank. is transmitted to the cleaning fluid inside.

However, when cleaning objects such as semiconductor wafers, it is necessary to remove micron-level dirt, so the frequency is increased to approximately 5.
It is necessary to set the frequency between 00kHz and 1MHz.

Therefore, the wavelength of longitudinal waves in the medium liquid is approximately 1.4 to 2.8 m.
m, which is about the same thickness as the bottom plate of the inner tank, so it is greatly influenced by the boundary surface of the bottom plate, and no vertical or horizontal wave vibrations are induced in the bottom plate. Therefore, the conventional I
M) In a cleaning device that uses Iz ultrasonic vibration, as determined in experiments, 70 to 8096 of the vibration energy is reflected, resulting in a significant decrease in transmittance and only about 20 to 30% of the vibration energy enters the inner tank. Not communicated.

FIG. 5 is an explanatory diagram of the estimation principle of the present invention, and is a partial sectional view of FIG. 2. The outer tank 1 and the inner tank partial piece 7 face each other at an angle θ. The medium was omitted. The arrow indicates the direction of the longitudinal wave transmitted from the driving surface of the outer tank 1 through the medium liquid. By tilting the partial piece 7 of the inner tank, the longitudinal wave transmitted from point A1 reaches point A2 of the partial piece 7 at distance a at an incident angle θ, and the longitudinal wave from point B1 reaches point A2 at distance a. Reach the point.

By adjusting the angle θ, as shown in the figure, (ba) becomes one wavelength λ of the longitudinal wave, and the wavelength λ2 of the vibration of the plate wave induced on the partial piece 7 becomes A, B! When the distance matches the distance, plate wave vibrations called Lamb waves are induced in the partial piece 7, and the vibration energy is efficiently transmitted to the inside of the inner tank. That is, it can be expressed as sin θ=λ1/λ.

By setting the inclination angle (angle of incidence) θ in this manner, the wave receiving surface of the inner tank can be efficiently vibrated.

This Lamb wave is a type of guided wave that is guided in the longitudinal direction by the existence of the plate boundary surface, and is called Lamb wave (plate wave), PocharIlm.
These are special waves depending on the cross section of the board, called er-Chree waves (rod waves), Love waves (surface layer waves), etc. Such guided waves propagating through a plate are collectively called plate waves.

- As an example, if the medium liquid is water (temperature 20°C), frequency = I Mllz, sound speed in water = 1456 m/
From see, the wavelength λ of the longitudinal wave in the medium liquid is given by the following equation.

On the other hand, when borosilicate glass with a thickness of 3 mm is used as the plate of the inner tank, the sound velocity of the plate wave is 3100 m/see, so the wavelength λ2 of the vibration of the plate wave is given by the following equation.

Therefore, when calculating θ from the above sinθ=λI/λ2, θ==sin-' (λ1/λ-) = sin-'(1
, 456/3.1) = sni-'0.47 = 28°, which agrees with the measured value in FIG.

Next, examples of the present invention will be described.

FIGS. 6 to 1θ are structural diagrams schematically showing embodiments of the present invention. In these figures, the structure for attaching the inner tank to the outer tank is omitted because it is the same as the conventional well-known structure described above.

Furthermore, the ultrasonic transducer 3 is actually provided with a plurality of transducers, but since this structure is the same as the conventional well-known structure, the details are omitted. Further, the oscillation source of the vibrator 3 and the wiring to the vibrator 3 are omitted. Further, 4 indicates a medium liquid, and 5 indicates a cleaning liquid.

FIG. 6 is a longitudinal sectional view showing the first embodiment of the present invention,
The outer tank 1 has a conventional shape, and the wave receiving surfaces of the inner tanks 10 and 11 are sloped. The receiving surface in FIG. 6(b) may have two surfaces, four surfaces, or a conical shape.

FIG. 7 is a longitudinal sectional view showing a second embodiment of the present invention,
This is an embodiment in which the inner tank 2 has a conventional shape, and the mounting surfaces of the vibrator 3 of the outer tanks 12 and 13 are sloped.

FIG. 8 is a plan view showing a third embodiment of the present invention, in which the inner tank 2 has a conventional shape and the outer tank 14 has an inclined side surface and a vibrator 3 is attached thereto.

FIG. 9 is a plan view showing a fourth embodiment of the present invention, and shows an inner tank! A configuration is shown in which the side surfaces of the antenna 5 are inclined into two planes to serve as wave receiving surfaces. The figure shows a case with two inclined sides, but it may also have three or four sides.

FIG. 10 is a plan view showing a fifth embodiment of the present invention,
Both the outer tank 1 and the inner tank 2 have a conventional shape, but the structure shows that the inner tank 2 is fixed at a position rotated by θ around a substantially central vertical axis. The feature of this embodiment is that it can have a semi-fixed structure so that the rotation angle θ of the inner tank 2 can be adjusted, and the shape of the outer tank and the inner tank 2 as in the first to fourth embodiments. There is no need to make it into a special shape; it is possible to use a conventional shape. In the figure, the vibrator 3 is attached to only one side of the outer tank 1, or two
It can also be mounted on three or four sides.

FIG. 1 is a partial structural sectional view showing an example of the support structure for the inner tank in the first embodiment of the present invention shown in FIG. 6(a). In the figure, reference numerals 20 and 21 indicate cross sections of Teflon support structures provided at the four corners of the bottom surface of the inner tank 11. Reference numeral 23 denotes a guide (receiver) made of Teflon, which is provided at the bottom of the outer tank 1 and into which the support structures 20 and 21 are fitted. Reference numeral 22 shows a cross section of a Teflon nut, which is screwed into a male thread provided at the lower end of the support structure 21. By rotating the nut 22, the height of support for the inner tank 11 supported by the support structure 21 can be adjusted, and therefore, the incident angle θ can be adjusted to increase the transmittance. can.

The transmittance can be adjusted by adjusting the driving frequency of the vibrator 3. Since there are also restrictions on the vibration efficiency of the vibrator 3, the incident angle θ can be adjusted by adjusting the support structure of the inner tank 11 as shown in the figure. It is also effective to adjust the

(Effects of the Invention) As explained in detail above, by implementing the present invention, the driving energy of the ultrasonic transducer attached to the outer tank is efficiently transmitted to the object to be cleaned inserted into the inner tank. Therefore, it not only exhibits a much higher cleaning ability than the conventional method, but also reduces power consumption, which has an extremely large economical effect.

Furthermore, conventionally, using a high frequency (several M) lz),
When trying to perform more fine and precise ultrasonic cleaning,
The attenuation of the ultrasonic waves by the inner tank would be large, making it difficult to implement. According to the present invention, since attenuation can be significantly reduced, ultrasonic cleaning at a higher frequency is possible.
The quality of cleaning can be dramatically improved.

[Brief explanation of drawings]

Fig. 1 is a partial cross-sectional view of a conventional device, Fig. 2 is a partial cross-sectional view explaining the present invention in detail, Fig. 3 is an actual measurement characteristic diagram showing the principle of the present invention, and Fig. 4 is a case of various materials. Fig. 5 is a partial sectional view explaining the present invention in detail, Figs. 6 to 7 are structural partial sectional views showing embodiments of the invention, and Figs. FIG. 1O is a plan view showing an embodiment of the present invention, and FIG. 11 is a partial sectional view showing an example of the support structure of the present invention. 1, 12L 13.14...Outer tank, 2.10.11.
15...Inner tank, 3...Ultrasonic vibrator, 4...Medium liquid, 5...Cleaning liquid, 6...Object to be cleaned, 7...Partial piece of inner tank, 8...・Liquid, 20, 21...Support structure, 2
2...Natsuto, 23...Guide. Fig. 3 θ (fake) Fig. 2 Fig. 4 Slight thickness (mm) Fig. 5 7 (75) (DJ Fig. 9 fig. 5 Fig. 10 octopus Fig. 10 (Q) (b) Fig. 4 Fig. 11 Fig. δ 3 Procedural amendments stamped) January 16, 1991

Claims (1)

[Scope of Claims] An outer tank equipped with a vibrator that generates ultrasonic vibrations of 500 kHz or more, and a container that transmits the ultrasonic vibrations to the inside of the outer tank to accommodate cleaning liquid and objects to be cleaned. an inner tank disposed with a space for intervening a medium liquid, and the ultrasonic vibration propagating in the medium liquid has an inclination angle with respect to a normal to a wave receiving surface of the inner tank. An ultrasonic cleaning device configured to significantly improve the transmittance of vibration energy of the ultrasonic vibrations transmitted through the wave receiving surface by making the ultrasonic vibrations incident on the wave receiving surface.