JPH04109141A - Particle counting method and device - Google Patents

Abstract

PURPOSE:To improve the grain size measurement precision by irradiating multiple pulse rays with different intensity, and guiding the grain size distribution from the count values corresponding to each pulse. CONSTITUTION:The pulse light from a pulse laser 1 is divided into multiple pulse rays with different intensity by multiple beam splitters 11, and they are guided to optical fibers 9 through lenses 10. The pulse rays are integrated by beam splitters 11 and collected into a sample cell 2 in a black box 5. The plasma emission due to laser breakdown is detected by a light detector 3 through a filter 4. Particles with the grain size range (a) inducing laser breakdown via the first pulse are detected if they exist in the region A. Particles with the grain size range (b) or (c) inducing laser breakdown via the second or third pulse are detected if they exist in the region B or C. The counting corresponding to each pulse is performed by a signal processor 7 by utilizing the synchronization signal by a power monitor 8.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method optimal for particle size discrimination counting of particulate matter contained in liquids such as ultrapure water used in semiconductor manufacturing processes and the like.

[Conventional technology]

In Japanese Patent Application Laid-Open No. 60-38345, pulsed laser light is focused and the energy density of the light is set higher than the laser breakdown threshold of the particles and lower than the threshold of the medium to make the particles sensitive. Laser breakdown is generated only when particles are present in the particle, and the accompanying acoustic waves are detected and counted. Furthermore, since the intensity of the generated acoustic waves tends to be proportional to the particle size, the possibility of application to particle size measurement has been suggested.

However, with this method, the energy density of light is non-uniform in the light condensing region, so the amount of light absorbed by the breakdown plasma differs depending on the position of the particle, and even particles of the same size can receive acoustic waves. The strength was not the same. For this reason, the accuracy of particle size measurement using acoustic wave intensity has not always been high.

Furthermore, according to the specification of Japanese Patent Application No. 62-277110, particle size can be measured from the atomic spectrum intensity during plasma emission, but the atomic spectrum intensity in white plasma light is very weak and is not necessarily suitable for measuring minute particle sizes. It wasn't suitable.

[Problem to be solved by the invention]

The above conventional technology does not take into account the fact that the amount of light absorbed by the plasma differs depending on the position where laser breakdown occurs (position of particles), and the resulting acoustic wave intensity also varies accordingly. There was a problem in that the accuracy of particle size measurement was not necessarily high.

An object of the present invention is to provide a method for counting particles in a liquid with improved particle size measurement accuracy.

[Means to solve the problem]

In order to achieve the above object, the present invention irradiates a plurality of pulsed lights with different intensities, and makes it possible to derive the particle size distribution from the count value corresponding to each pulse.

[Effect]

The pulsed laser beam causes laser breakdown of particles whose laser breakdown threshold is smaller than the power density in the pulsed laser beam. If the threshold value of particles in the condensing region of the pulsed laser beam is higher than the i-th pulsed laser beam and lower than the i+1th pulsed laser beam, breakdown occurs at the i+1th pulse. Therefore, by determining at which pulse the breakdown occurs, it becomes possible to perform counting with particle size discrimination. Even if multiple particles with different diameters exist simultaneously within the light focusing area (during the irradiation time of multiple pulse trains), they are counted in descending order of particle size and disappear due to breakdown, so one particle size There is no effect on discrimination.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG.

In this example, a pulse laser 1, a sample cell 2. Photodetector 3
．． Filter 4. Dark box 5. Beam stopper 6, signal processing device 7. Pulsed light monitor8. Optical fiber9. Lens 10.
It consists of a beam splitter 11.

The pulsed light from the pulsed laser 1 is split into a plurality of pulsed lights with different intensities by a plurality of beam splitters, and guided to the optical fiber 9 through the lens 10. The length of the optical fiber is set so that the pulses with lower intensity are shorter and the pulsed light reaches the exit of the optical fiber in descending order of intensity. Pulsed light emitted from the optical fiber 9 is integrated by a beam splitter 11 and focused by a lens 10 into a sample cell 2 in a dark box 8 . Plasma emission due to laser breakdown is detected by a photodetector 3 through a filter 4 that cuts off the excitation pulsed light. At this time, the temporal and spatial profiles of the pulsed light are as shown in FIG. Particle size range a that can induce laser breakdown with the first pulse
If the particles exist in area A, they will be detected. Similarly, two (
or 3) Particles in the particle size range b (or C) that can induce laser breakdown for the first time in the third pulse are detected if they exist in region B (or C). If the movement of particles due to the flow of liquid in the sample cell 2 can be ignored within the irradiation time of the pulse train, particle size discrimination can be performed instantaneously with this procedure. That is, if a particle with a particle size range a exists within the region A of the first pulse, it will undergo laser breakdown in the first pulse, so it will disappear as soon as it is detected, and there will be no effect on the second pulse or later. If particles in the particle size range a exist within the region A of the second pulse, laser breakdown will not occur in the first pulse, but will occur in the second pulse.

A lakedown will occur. In this case, if particles within the particle size range are present in region B, discrimination can be made from the plasma emission intensity. Since the plasma emission intensity depends on the energy absorbed by the plasma after reaching the breakdown threshold, as shown in Figure 3, the particle size increases in the second pulse region A where the power density of the pulsed light is relatively low. Since the plasma emission intensity induced by the particles in the range a is smaller than that caused by the particles in the particle size range A in the region B of the second pulse, it is possible to distinguish between the two. Counting corresponding to each pulse is performed by the signal processing device 7 using a synchronization signal from the power monitor 8.

According to this embodiment, particles can be sequentially counted and annihilated in descending order of particle size using a plurality of pulsed lights of different intensities, and at the same time, when particles with different particle sizes are present in the same pulse, they can be discriminated based on the emission intensity. Therefore, there is an advantage that particle size measurement accuracy can be improved.

In this embodiment, a photodetector is used as a means for detecting laser breakdown, but an acoustic wave detector can be used as well.

The device configuration of this embodiment can also be incorporated into an ultrapure water production device and used as a means for determining the presence or absence of an abnormality in ultrapure water by measuring particle size distribution and number density. In this case, the sampling pipe from the ultrapure water can be connected to the sample cell, the cell outlet can be connected to the drain pipe, or the output signal from the signal processing device can be used to return the ultrapure water to the ultrapure water production equipment. The presence or absence of an abnormality is transmitted to a display device and/or a control device.

These systems can be applied to manufacturing devices for chemical liquids other than ultrapure water, and manufacturing processes for industrial products such as semiconductors that use these liquids.

〔Effect of the invention〕

According to the present invention, by irradiating pulsed light of different intensities in descending order of intensity and counting and extinguishing particles in the condensed region in descending order of particle size by laser breakdown, fine particles can be measured with high particle size measurement accuracy. can be counted.

[Brief explanation of drawings]

FIG. 1 is a system diagram of an embodiment of the present invention, FIG. 2 is a temporal and spatial profile diagram of a plurality of pulsed lights, and FIG.
FIG. 3 is an explanatory diagram showing the amount of energy absorbed by laser breakdown. DESCRIPTION OF SYMBOLS 1... Pulse laser, 2... Sample cell, 3... Photodetector, 7... Signal processing device, 9... Optical fiber. Figure 3 Time →

Claims (1)

[Claims] 1. A pulsed laser that irradiates a sample with pulsed light, a breakdown signal detector that detects laser breakdown occurring in the sample, and signal processing that processes the signal from the breakdown signal detector. A breakdown analyzer comprising a pulse control means for irradiating a plurality of pulsed lights having different intensities in descending order of intensity, and a particle size detection device that detects the breakdown signals corresponding to the plurality of pulsed lights. A particle counting device characterized in that it includes means for discriminating. 2. In claim 1, the particle size range serving as the measurement sub-elephant is divided into N particle size ranges, and the i-th pulse light intensity causes only particles in the i-th or smaller particle size range to induce laser breakdown. Set it as follows, and irradiate the pulsed light in the order of numbers 1 to N.
In addition, the i+1th pulse is applied after the breakdown plasma caused by the i-th pulse has sufficiently attenuated. 3. The particle counting method according to claim 2, wherein the optical axes of the N pulsed lights coincide. 4. In claim 2, a threshold value is set when measuring the breakdown signal due to the i-th pulse, and particle counts corresponding to the i-1th particle size range are excluded, or A particle counting method that discriminates that a signal corresponding to is based on multiple particle counts. 5. A particle counting method and apparatus according to claim 2, which utilizes transmission time differences through optical fibers to create pulse trains numbered 1 to N. 6. Incorporate into an ultrapure water or chemical solution manufacturing device or the manufacturing process of an industrial product using these, and perform particle size discrimination counting of particulate impurities contained in the ultrapure water or chemical solution. A particle counting method that determines and displays the presence or absence of abnormalities in the manufacturing process.