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DESCRIPTION JP2000350282

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DESCRIPTION JP2000350282
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
ultrasonic cleaning control device and an ultrasonic cleaning control method, and more
particularly to an ultrasonic cleaning control device and an ultrasonic cleaning control method
for preventing burn-in due to cavitation collapse.
[0002]
[0002] Ultrasonic cleaning is known as a cleaning method. Ultrasonic cleaning using the
cavitation effect increases the cleaning effect by strongly generating cavitation. Although the
theoretical basis for the cavitation effect has not been clarified, it is estimated that the impact
pressure, micro jet, etc. generated at the time of cavitation collapse greatly affect the effect.
[0003]
It is known that if the strength of such cavitation is increased too much, an oxidation called
"seizure" occurs partially on the surface to be cleaned. Such oxidation, while apparently
appearing, impairs the quality of the material to be cleaned and should not be generated
absolutely.
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[0004]
In order to cope with such a problem, a washing test using an actual washing material has been
carried out, and after the critical cavitation strength has been ascertained, the apparatus has
been tuned to meet such conditions. Cavitation strength is very sensitive to conditions such as
cleaning solution temperature, air solubility and flow velocity, and it is well known that the
conditions set at the beginning are not maintained and the conditions change dynamically at all
times There is. In the process of continuous cleaning, there are many cases where "seizure"
occurs suddenly, and in such a case, the conditions for not causing "seizure" are set again or the
cavitation strength is appropriately reduced. It is the present condition which copes with such
burn-in by letting it do.
[0005]
It is desirable to establish a technique that can observe the physical state of cavitation
occurrence that causes burn-in. Furthermore, it is desirable to constantly monitor the occurrence
of cavitation that may cause a sudden burn-in and actively suppress the cavitation occurrence.
[0006]
SUMMARY OF THE INVENTION It is an object of the present invention to provide an ultrasonic
cleaning control device and an ultrasonic cleaning control method capable of establishing a
technique capable of observing the physical state of cavitation generation that causes burn-in. To
provide. Another object of the present invention is to provide an ultrasonic cleaning control
device and an ultrasonic cleaning control method capable of constantly monitoring the
occurrence of cavitation where a burn-in occurs suddenly and actively suppressing the cavitation
generation. It is to do.
[0007]
[Means for Solving the Problems] The means for solving the problems are expressed as follows.
In the technical matters corresponding to the claims in the expression, numbers, symbols and the
like are attached with parentheses (). The numbers, symbols, etc. clarify the correspondence /
correspondence between the technical matter corresponding to the claim and the technical
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matter of at least one of the embodiments. However, the art corresponding to the claim It is not
intended to indicate that the specific matters are limited to the technical matters of the
embodiment.
[0008]
The ultrasonic cleaning control method according to the present invention comprises measuring
the light emission intensity in the vicinity of the cavitation bubble generated by the ultrasonic
wave and controlling the generated energy of the ultrasonic wave by an electrical signal
corresponding to the light emission intensity. Cavitation strength can be measured contactlessly.
[0009]
The cavitation field can be kept constant and stabilized by decreasing the generated energy if the
value of the electrical signal increases. Furthermore, by measuring the spatial distribution of the
light emission intensity, the condition of the cavitation field can be properly grasped. By
monitoring the cavitation site in the cleaning process online, burn-in and erosion can be
prevented in real time in various cleaning processes such as semiconductor manufacturing
processes.
[0010]
The ultrasonic cleaning control apparatus according to the present invention comprises an
ultrasonic generator (3) for generating ultrasonic waves in a liquid, and an optical system (5) for
measuring the intensity of luminescence generated from a site in the liquid. Furthermore, it
comprises a conversion device (6) for converting the intensity into an electric signal, and a
control device (4) for changing the energy of the ultrasonic wave in accordance with the electric
signal. The addition of such a device enables control of the cavitation field. In particular, uniform
fields can be generated. This makes it important to monitor changes in intensity in real time.
[0011]
It is preferable that the optical system be provided with a variable device in which the
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measurement site is variable. The variable device can be configured by movement of the optical
system, change in angle, change in focal length, and the like.
[0012]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT In accordance with the drawings,
an embodiment of the ultrasonic cleaning control device according to the invention is provided
with an ultrasonic cleaning device together with a monitoring device. The ultrasonic cleaning
apparatus includes a cleaning tank 1 as shown in FIG. 1, and a cleaning liquid 2 is placed in the
cleaning tank 1. An ultrasonic transducer group 3 is disposed in the portion of the tank wall of
the cleaning tank 1. The ultrasonic transducer group 3 can generate ultrasonic vibrations in the
cleaning liquid 2 by emitting ultrasonic waves driven and controlled by the high frequency power
source 4.
[0013]
The monitoring device includes a condensing optical system 5 and a photomultiplier 6. The
condensing optical system 5 includes a condensing lens 7. The condensing lens 7 preferably has
a condensing function to form a point light source image P on the imaging surface of the
photomultiplier 6 as a point real image.
[0014]
When the input to the ultrasonic transducer group 3 of the high frequency power supply 4 is
increased, the sound pressure of the sound wave generated in the cleaning solution 2 increases.
When the sound pressure exceeds a certain value, cavitation starts to occur in the cleaning
solution 2. When the cavitation strength becomes high and cavitation collapse starts, the surface
of the material to be cleaned 10 in the cleaning solution 2 is oxidized and corroded.
[0015]
When the cavitation intensity increases and cavitation collapse starts, light emission phenomena
appear at the collapse point. The intensity of the light emission is weak, and the light emission
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can not usually be confirmed with the naked eye. The cleaning tank 1 and the condensing optical
system 5 are disposed in a dark room. In a dark room, such weak radiation can be observed with
a little glare and even the naked eye, and its S / N ratio becomes an observable level.
[0016]
The light emitted and emitted at the collapse point P is collected by the condensing lens 7 and is
imaged on the imaging surface of the photomultiplier 6. The converted light intensity signal 8 of
light that is weak even if collected is amplified by the photomultiplier 6 and input to the high
frequency power supply 4 having a control function.
[0017]
The output of the high frequency power source 4 is controlled according to the magnitude of the
electric conversion intensity signal 8. The output is in particular intensity controlled. By such
control, in the cleaning liquid in the physical state where cavitation occurs, an electromagnetic
field with which the light emission intensity becomes constant is formed.
[0018]
2 and 3 show the relationship between the light emission intensity and the sound pressure in
both of these figures. In both figures, the horizontal axis is the distance from the end face of the
transducer. The vertical axis in FIG. 1 indicates the light emission intensity. The vertical axis in
FIG. 2 indicates the sound pressure. If the sound pressure is increased, the correlation in which
the light emission intensity is increased can be clearly read by comparing at the equidistant
position. When the sound pressure is below a certain level, light emission is hardly observed.
Where the sound pressure is higher, the emission intensity is also higher.
[0019]
On the other hand, the existence of the correlation between sound pressure and cavitation
intensity is well known from the prior art. Accordingly, there is also a correlation between the
light emission intensity and the cavitation intensity, and the observation of the light emission
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intensity makes it possible to observe the cavitation intensity. By using the light emission
intensity signal as a feedback signal, the cavitation intensity state can be controlled to be
constant.
[0020]
Physical estimation and experimental confirmation: The burn-in phenomenon of ultrasonic
cleaning was confirmed by the inventor's experiments to be a high temperature oxidation
phenomenon. It is known that when cavitation occurs, a light emission phenomenon called sono
luminescence (SL) occurs. Since many cavitations occur in a region where the sound pressure is
strong, it is considered that SL is also distributed in that region. Conventionally, only cavitation
distribution measuring devices such as hydrophones and contact types such as aluminum foil
erosion condition observation are known. The SL distribution can provide a contactless
observation device.
[0021]
Until 1980, the causes of SL were not well understood. This is because the occurrence of
cavitation is random, and it is difficult to observe the behavior of each bubble and the light
generated accordingly, which hinders physical understanding and explanation. In 1988, after
Pelipe Gaitan created one stable cavitation bubble and discovered that SL occurs with each cycle
of the sound wave, the occurrence of SL, which is still discussed, is not It is considered to be due
to a mechanism like.
[0022]
(1) Due to adiabatic compression at the time of bubble collapse, a high pressure / high
temperature state is formed, and light is emitted from the high temperature air by black body
radiation. (2) A shock wave is formed at the time of bubble compression and collapse, and a high
pressure / high temperature plasma is formed by shock compression. From the high temperature
air in that state, it emits light by black body radiation, or by bremsstrahlung of electrons in the
plasma. According to the measurement of the emission spectrum of SL, the temperature at the
center of the bubble is predicted to be 10 5 to 10 6 (K).
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[0023]
As a test apparatus for investigating the surface oxidation phenomenon at the time of ultrasonic
cleaning, an inner diameter of 70 mm and an outer diameter of 80 mm was made of acrylic, and
an ultrasonic transducer was installed on the bottom. The ultrasonic transducer is made of
stainless steel and has a cylindrical shape with an outer diameter of 60 mm, and has a natural
frequency of about 27 kHz. A piezoelectric element is attached to one of the terminals of the
ultrasonic transducer, and a high frequency power source is connected to generate an ultrasonic
wave. Since the speed of sound in water is 1500 m / s, the wavelength of the sound wave is 55.6
mm. The height from the transducer end face of the bottom of the water tank to the water
surface was 111 mm, which is twice the wavelength of the sound wave. The size of the nonwashed material sample was 10 mm · 10 mm, the thickness was 1 mm SPC steel plate, and the
surface was finished to a mirror surface. The sample was fixed to a steel wire of φ 0.8 mm, and
placed at a 10 mm cavitation generation portion from the end face of the ultrasonic transducer.
Ion exchange water was used as washing water. At the time of cleaning, the input power to the
ultrasonic transducer was 105 W, and the cleaning time was 2 minutes. The cavitation generated
by this device became a cavitation with many bubbles.
[0024]
The samples were immersed in the water bath of such an apparatus for 2 minutes. The electron
micrograph of the sample surface showed that bumps and holes of 1 to 1.5 μm were formed on
the surface. Such bumps and holes are considered to be generated by the high temperature, high
pressure, and micro jets that are formed when the cavitation bubbles generated near the
extremes of the sample collapse.
[0025]
As a result of creating an Auger spectrum and comparing it with the results of analysis of
samples in which the state of iron compounds is known in advance, a waveform peculiar to
triiron tetraoxide is shown, and therefore, triiron tetraoxide (FE3O4) has a high temperature
When it comes to, it is known that the substance identified in the compound formed by reacting
with oxygen and water is formed on the sample surface. Other comparative tests show that the
iron oxide formed by cavitation is caused by high temperature oxidation.
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[0026]
According to other experiments, the emission of foamy cavitation is pulsed and random. When
the cavitation occurrence status changes, the emission intensity of the observed SL is due to the
change in the number of pulses generated by MBSL (multi-bubble sono luminescence) or the
change in the peak value of the SL emission intensity generated individually. It is considered to
be a thing.
[0027]
According to an experiment examining the relationship between the input voltage of the
ultrasonic transducer and the intensity change of SL, when the input power to the ultrasonic
transducer is increased, the emission intensity of SL increases. Although it was difficult from the
obtained data to distinguish the change in the number of occurrence of SL from the change in the
intensity of each SL emission, according to visual observation, cavitation The main cause of the
emission intensity is considered to be the increase in the cavitation number, since the number of
occurrences and the region of occurrence have increased.
[0028]
According to one other experiment, the luminescence intensity differs depending on the amount
of gas (air in the experiment) dissolved in water. The larger the amount of air, the larger the
emission intensity. According to another experiment, the light emission intensity is attenuated
while repeating the maximum and minimum at the half wavelength period of the sound wave.
Therefore, if the sound pressure becomes strong, the number of cavitation increases.
[0029]
Cavitation erosion is a chemical reaction in a high temperature state, particularly a chemical
reaction with a gas dissolved in a liquid, and in a high temperature and high pressure condition
where the number of cavitation occurrence is large, the cavitation strength is strong and the
cavitation erosion is severe. Cavitation intensity corresponds to sound pressure and corresponds
to the degree of input energy. The signal of the MBSL intensity corresponding to the cavitation
intensity is an effective control signal for control of the cavitation intensity field.
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[0030]
According to the ultrasonic cleaning control device and the ultrasonic cleaning control method
according to the present invention, cavitation generation can be observed without contact, and
cavitation generation suppression conditions can be controlled.
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