JPS631951A - Apparatus for measuring fine particle in liquid - Google Patents

Abstract

PURPOSE:To measure even fine particles extremely difficult to measure by conventional technique on-line, in an apparatus for detecting or counting insoluble fine particles contained in a liquid, by detecting air bubbles generated using said particles as nuclei. CONSTITUTION:A liquid 30 to be measured is supplied into a transparent detection cell 10 made of glass at a constant flow speed through piping 20. The beam emitted from a relatively intensive exciting beam source 40 such as argon ion laser is converged to the center part of the cell 10 by a lens 50 to locally heat a liquid in a range not exceeding b.p. of the liquid and the saturation at the locally heated part rises to generate air bubbles 80 in the liquid. The emitted beam from the cell 10 is condensed by a lens 60 to be guided to a beam trap 70. The air bubbles generated are detected by detecting the probe beam emitted from a beam source system constituted of a semiconductive laser 90 and a beam condenser 100 in the downstream part and said probe beam is amplified and subjected to signal processing by an electric circuit 120 to be detected and counted as a pulse.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to the detection and counting of minute (approximately 1 μm) insoluble particles in a liquid, and in particular to the detection and counting of impurity solid particles in pure water used in semiconductor device manufacturing. The present invention relates to an in-liquid particle measuring device suitable for measuring.

[Conventional technology]

BACKGROUND ART Conventionally, as a method for counting microparticles (hereinafter simply referred to as particles) in a liquid, a method that utilizes absorption and scattering of light by particles has been widely used. -For example, JP-A-54-24
The method described in Japanese Patent No. 683 is cited as a method for identifying the size of particles by utilizing light absorption (light shielding by particles). Examples of methods that utilize scattering of light by particles include the method described in JP-A-53-1.7773.

[Problem that the invention seeks to solve]

” 2. Among the conventional techniques, in the method that utilizes light absorption by particles, when the particle size decreases to about 3 μm, the light absorption ability (power to block light) becomes dependent on the particle size, making the measurement reliable. In addition, although methods that utilize light scattering by particles can be applied to particles of 1 μm or less, the ratio of light scattered by the liquid itself to light scattered from the particles decreases as the particle size increases. 0.
When trying to detect particles of about 5 μm, there is still a problem in that reliability decreases.

An object of the present invention is to provide an in-liquid particle measuring device that has improved detection ability for particles of around 1 μm.

[Means for solving problems]

The above objective is achieved by increasing the apparent size of the particles by generating bubbles in the liquid using the particles as nuclei, and detecting and counting the bubbles using existing optical or acoustic methods. Ru.

Particles in a liquid must have a size larger than a certain radius (critical radius) in order to become a nucleus for bubble growth, but by pressurizing the liquid or adding a surfactant to the liquid, the critical radius can be increased. can be reduced. In other words, even the smallest particles can be turned into bubbles and made "visible".

[Operation] Bubbles grow and increase in size under appropriate conditions. Therefore, when detecting air bubbles using the light-shielding effect of air bubbles, it is best to grow the bubbles to a size sufficiently larger than the wavelength of the light being used before measurement to make particle detection easier. Measurement errors resulting from dependence can be removed.

Furthermore, when detecting bubbles by light scattering, by growing the bubbles and increasing their size, the background component caused by the scattered light of the liquid itself can be reduced relative to the light scattered by the bubbles. .

Additionally, when detecting particles using effects such as absorption and scattering of ultrasound waves, the difference in acoustic impedance is magnified when measuring the formation of air bubbles rather than measuring the solid particles themselves. Therefore, it is advantageous in terms of sensitivity.

Furthermore, if appropriate conditions are selected, particles of about 0.1 μm can also function as nuclei, generating bubbles, so conventional optical methods,
It is now possible to detect minute particles that were previously difficult to detect acoustically.

When considering the mechanism of bubble generation in a liquid, first of all, the liquid must be saturated with air (see [Ultrasonic Technology Handbook, Revised New Edition], Nikkan Kogyo Shimbun, 1966).
. When bubbles are generated in a liquid for some reason, if the liquid is unsaturated, the air within the bubbles dissolves into the bubble surface liquid again and the bubbles disappear. Conversely, if the liquid is supersaturated with air, excess air will precipitate and bubbles will grow. but,
If the bubbles are too small, the pressure inside the bubbles will increase due to interfacial tension, so the bubbles will disappear even if they are slightly oversaturated. Critical radius a at which bubbles neither grow nor disappear. is known to be given by the following equation.

Here, T is interfacial tension (dyne/cm), Pa'
is the static pressure of the liquid where the bubble is present ('clyne
/cxN), Pv is the liquid vapor pressure (dyne/
ri), S is the degree of saturation. S is expressed by the following formula under a certain temperature and pressure.

According to Herry's law, the saturated solubility is proportional to the partial pressure of air (the value obtained by subtracting the vapor pressure of the liquid from the total pressure).

Now, in general, bubbles cannot occur without the walls of the container or the surface of foreign matter in the liquid. Here, we will consider excluding the container wall for the time being. Assuming that there are no foreign substances, in order for a bubble to be generated, its radius must start from zero and grow to 80 or more, but bubbles with a radius of ac or less should disappear, so no bubbles are generated after all. On the other hand, if there is a foreign substance, air will precipitate on its surface, causing the bubble surface to become ac
It can grow without passing through the following radius states.

This situation is shown in FIG. Various shapes can be considered for the shape of the foreign object in the liquid, but if it is assumed that it is disk-shaped, it can be determined whether or not it can become the nucleus of a bubble based on its radius and ac. The specific size of ac is, if the liquid is pure water, Pv ~ 02 dyne) θ' = 1.013X 10Bdyne
/cJ (latm), T=73dyne/G,
Assuming S=1.3, nc=4.8pm.

To further reduce the critical radius, pressurize the liquid, increase the static pressure Po', and heat the liquid.

Decrease saturation solubility and increase saturation S.

Possible methods include adding a surfactant to the liquid to lower the interfacial tension T. - As an example, in the case of pure water, if the liquid is pressurized to 20°C + +30 aL m, saturated with air at the same time, and then heated to 80°C, the degree of saturation S will be approximately 2, so aC ~ 0 0.048 .mu.m, and bubbles are generated from particles whose long sides are approximately 0.096 .mu.m or larger.

The critical radius is related to the static pressure and degree of saturation of the liquid (which depends on the temperature of the liquid), so if you take measures to make the static pressure and liquid temperature vary from place to place, you can make the critical radius different from place to place. The size of the particles can be identified because they generate bubbles.

Although a heater may be used to partially raise the temperature of the liquid, it is more ideal to irradiate it with a focused laser beam. In this case, by keeping the degree of light condensation low near the wall of the container holding the liquid to be measured or the pipe, the rise in liquid temperature near the wall can be suppressed, and the generation of air bubbles on the wall surface can be suppressed. can be prevented.

In the above-described method, the liquid to be measured is not contaminated, so after the measurement is completed, if necessary, the liquid can be used for a predetermined purpose by degassing the liquid.

Measurement with fluid flowing is also possible, and oll-1i
Neil measurement can be performed.

If a portion of the liquid is allowed to be sampled and measured, the criticality of -. The static pressure in the liquid required to obtain the radius could be reduced, and the equipment could be simpler.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

a) Example 1 Figure 1 shows a detection cell, in which a liquid to be measured 30 is supplied at a constant flow rate into a transparent detection cell 10 made of glass through a pipe 20. Light emitted from a relatively powerful excitation light source 40, such as an argon ion laser, is focused by a lens 50 onto the center of the cell, heating the liquid locally within a range that does not exceed the boiling point of the liquid. By increasing the degree of saturation (the relationship between temperature and degree of saturation is schematically shown in FIG. 6, please also refer to equation (2)), bubbles 80 are generated in the liquid. cell 1
The light emitted from
It leads to 0. The generated bubbles transmit probe light emitted from a light source system consisting of a semiconductor laser 90 and a beam condenser 100 downstream to a photocell 110.
The pulses are detected and counted as pulses by being amplified and signal-processed by the electric circuit 120. In the figure, the flow of the liquid is drawn horizontally for convenience, but if the flow is set vertically, it is possible to prevent air bubbles from adhering to the cell walls and to reduce measurement errors.

b) Embodiment 2 FIG. 2 is a diagram showing an embodiment equipped with a liquid pressurizing mechanism, and is a block diagram of the entire device including a detection cell. The pure water to be measured is continuously supplied through the pipe 20, pressurized to 30 atmospheres by the pressurizing device 130, and saturated with air fed from the air pump 150 in the container 140.

After bubbling, the air is released and exhausted from the pressure reducer 1.60. The pure water saturated with air is guided to a bubble detector 170, and the presence or absence of bubbles is identified by an optical detection device consisting of a probe light source 180 (semiconductor laser and beam condenser) and a photocell 190. It is desirable that no air bubbles exist, and if air bubbles are detected, lower the pressure setting of the pressurizing device 130 to prevent the critical radius from becoming smaller than the maximum particle radius existing in pure water, and eliminate air bubbles. prevent the occurrence of , Ili water measures the water pressure in the pressure detection unit 200, and the controller 21-
The pressure is set and maintained at a constant value by controlling the pressurization measurement back to Fee 1 via 〇. Then the first
As shown in the figure, in the detection cell 10, an excitation light source 4
Bubbles generated by heating pure water at 0 are optically detected and counted by the probe light source system 240 and the photocell 110, and processed by the electrical processing circuit 1.20.
1 numeric value (]0) is displayed on the display section 230. The pure water is then led to a decompression/deaeration device 220, subjected to depressurization/deaeration treatment, and used for a predetermined purpose.

C) Example 3 In the above-described example, the particles in the detection cell 10 that are capable of generating air bubbles inside the heating volume are
All particles have a radius equal to or larger than the critical radius ac determined by (assumed to be constant for convenience).

Therefore, if the critical radius when the effective water temperature inside the heating volume is TI is acJ, and the critical radius when the water temperature is T2 (Tz < T2) is Re'', then the water temperature is changed from T1 to T.
By increasing it to 2 and measuring the number of bubbles, the radius is ac
The number of particles contained between 2- and ac"(ac"<ac") can be obtained. This example is shown in FIG. 3. In the example of FIG. The two detection cells shown are connected in series, and the two excitation light sources 40 have different emission intensities.

The outputs of the two photocells are processed in electrical processing circuit 120 to calculate the difference in the number of pulses from each photocell.

Once bubbles are generated using particles as nuclei, they grow over time. This situation is shown in FIG. Therefore, even if bubbles are difficult to detect optically due to their small diameter and low light blocking ability at the point where they are generated, it is necessary to set the detection area sufficiently in front of the heating area (by setting Ql and Q2 sufficiently large in Figure 3). For example, it can have a large light blocking ability.

d) Embodiment 4 In the embodiment shown in FIG. 5, a plurality of probe beams are used and the outputs of the photodiode flares are electrically added together in order to be able to detect the total number of generated bubbles. In the figure, a laser beam emitted from a probe light source 240 is transmitted through an optical fiber 250 and a cylindrical lens 26.
0, it becomes parallel light with a minute thickness and passes through the detection cell 1.
incident on 0. The laser light transmitted through the cell is detected by a photodiode array 270, and the outputs of each photodiode are added by an adder circuit 120. When this detection system is used, information regarding the particle size distribution of bubbles can be obtained by measuring the output of each photodiode individually.

e) Example 5 In the example shown in FIG. 6, a temperature distribution is created inside the liquid by the excitation light 290, and the critical radius at each point within the excitation light transmission region is set to have a different value depending on the location. has been done. Bubbles 8 generated within the excitation light transmission region
0 in the same manner as shown in FIG. is sufficiently low that the probe light does not affect the temperature distribution), and the signal for each photodiode is sent to the electrical processing circuit 120. The number of pulses counted in one channel of the photodiode statistically has the following relationship, assuming that the probe light incident on the channel passes through a region where the liquid temperature is T°C. Here, ΔV (T) is the total volume of the part where the liquid temperature is T'C inside the light passage region, N(r) is the number density of particles with radius r, ac(T) is the critical radius, and the liquid temperature T
is a function of Particle size distribution N(r) can be obtained by applying appropriate differential processing to equation (3).

f) Example 6 In the example shown in FIG. 7, a focused ultrasonic generator 310 is used as a heat source for generating bubbles, and the ultrasonic waves transmitted through the piping are incident on the sound absorbing material 320.

In this case, as in the case of FIG. 1, since heating occurs intensively near the focal point of the ultrasonic waves, the adhesion of air bubbles to the pipe wall can be reduced. The generated bubbles are detected and counted downstream by a probe ultrasonic generator 330 and an ultrasonic detector 340 using the absorption and scattering effects of ultrasonic waves by the bubbles. The advantage of this embodiment is that since an optically transparent detection cell is not required, the piping can be used as it is as a detection cell.

g) Example 7 In another example whose illustration is omitted, a surfactant mixing container is installed upstream of the pressurizing device 130 shown in FIG. 2 to reduce the interfacial tension of the liquid. By reducing the critical radius at-, even smaller particles can be turned into bubbles and detected.

〔Effect of the invention〕

As described in 1-1 above, according to the present invention, the apparent size of fine particles in a liquid can be increased by making them bubbles, thereby improving the measurement accuracy of existing optical and acoustic particle detection methods. In addition, depending on how conditions are set, it is possible to measure on-one microparticles of 0.1 μm or less, which is extremely difficult with conventional techniques.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a detection cell according to an embodiment of the present invention, and FIG.
Figure 3 is a block diagram showing the entire device of one embodiment, Figure 3 is a diagram showing a detection cell of one embodiment, Figure 4 is a diagram showing changes in bubble radius over time, and Figure 5 is a detection diagram of one embodiment. Diagram showing cells,
FIG. 6 is a diagram showing a detection cell of one embodiment, FIG. 7 is a diagram of one embodiment, FIG. 8 is a diagram showing the relationship between temperature and saturated solubility, and FIG. 9 is a diagram of bubbles with fine particles as the core. It is a figure showing growth. DESCRIPTION OF SYMBOLS 10...Detection cell, 20...Piping, 3(>...Measurement liquid, 40...Excitation light source, 50...Condensing lens, C'
) 0 Condensing lens, 70... Optical trap, 80... Bubbles, 90... Semiconductor laser, 100... Beam condenser, 110... F1~Cell, 120... Electrical calculation/processing Circuit, 130... Pressure device, 140...
Mixing container, 150...Air pump, 160...Reducing pressure
Exhaust device. 170... Air bubble detector, 180... Probe light source,
190...F first to cell, 200...Pressure detection section,
210... Controller, 220 - Depressurization/deaeration device. 230...Display unit, 240・Probe light source, 250・
...Optical fiber, 260...Cylindrical lens,
270... First hediode array, 280... Microparticle, 290... Excitation light beam, 300... Probe light beam, 3]-〇... Focused ultrasound generator, 320...
・Sound absorbing material, 330...Ultrasonic generator for probe, 34
0... Ultrasonic detector.

Claims (1)

[Claims] 1. A device for detecting or counting minute insoluble particles contained in a liquid, which is characterized by detecting bubbles generated using the particles as nuclei. Device. 2. The in-liquid particle measuring device according to claim 1 is characterized in that the particle size of microparticles that can contribute to bubble growth is reduced by pressurizing the liquid to be measured. Liquid particulate measurement device. 3. In the in-liquid particle measuring device according to claim 1, by adding a surfactant to the liquid to be measured,
An in-liquid particle measuring device characterized by reducing the particle size of microparticles that can contribute to bubble growth.