JPH0737935B2 - Particle detector by light scattering method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a fine particle detection device used in a clean room of a semiconductor manufacturing factory or the like for optically detecting fine particles, and particularly to improvement of an optical system portion thereof. is there.

[Prior art]

A fine particle counting device used in a clean room of a semiconductor factory, etc., extracts aerosol in the factory, ejects it from a nozzle into a predetermined measurement area, irradiates it with laser light, etc., and determines the number of particles based on the presence or absence of scattered light. A particle counting device for measuring is known. Further, as disclosed in JP-A-57-42839, there is also known a fine particle detecting device in which fine particles are used as nuclei to condense and grow vapor such as alcohol to optically detect the fine particles. In such a particle detection device, a light source such as a laser beam is focused to irradiate the measurement area, and an aerosol containing particles is passed through the measurement area to collect the scattered light, which is converted into an electric signal and The signals are discriminated at a predetermined threshold level to detect the presence or absence of fine particles. A condenser lens has been used to efficiently collect the scattered light.

[Problems to be solved by the invention]

However, such a conventional light scattering type particle detection device has a problem in that only a part of the scattered light is detected and the detection efficiency is not very good.

The present invention has been made in view of the above-mentioned problems of the conventional light scattering type particle detection device, and it is possible to detect particles with high efficiency and eliminate malfunctions due to noise or the like. Is a technical issue.

[Means for solving problems]

The first invention of the present application is, as shown in FIGS. 1 and 2, a suction means for sucking an aerosol containing fine particles through a duct and ejecting it to a measurement region, and a light beam irradiation means for irradiating a light beam to the measurement region. And a particle detection device using a light scattering method for detecting particles based on scattered light accompanying passage of particles, the measurement area being surrounded, and the same point of the measurement area is set as one focal point, respectively, and is opposed to each other. And a pair of concave mirrors having spheroidal surfaces, which are provided on the mirror surfaces of the concave mirrors, respectively, are arranged at the focal positions of the other spheroids facing each other, and receive scattered light reflected by the facing concave surfaces to generate electricity. It is characterized by comprising a pair of photoelectric converters for converting into signals and an adder circuit for adding outputs of the pair of photoelectric converters to obtain a scattering detection signal.

The second invention of the present application is, in addition to these, provided with a coincidence discriminating means for intermittently summing the outputs by discriminating the coincidence of outputs of the pair of photoelectric converters as shown in FIG. In addition to the first invention, a third invention is characterized by comprising an integrating circuit for integrating the output of the adding circuit with a predetermined time constant.

[Action]

According to the first invention of the present application having such a feature, two concave mirrors having a spheroidal surface are opposed to each other, and their focal points are made to coincide with each other, and they are arranged in the measurement region. Since the photoelectric converters are arranged at the other focal positions of the concave mirrors having the respective spheroids, even if scattered light is scattered in any direction, it is reflected by any concave mirror and is reflected by the other photoelectric converter. Be guided. Then, the outputs of the two photoelectric converters are added and output as a scattering detection signal. Further, in the second invention of the present application, when a signal is obtained from only one of the photoelectric converters, the output at that time is prohibited as noise. Further, in the third invention of the present application, the outputs of the photoelectric converters are added, and the output is further given to an integrating circuit having a predetermined time constant so as to reduce the change in signal intensity due to the position of the particles passing through the duct. ing.

[Explanation of Examples]

FIG. 1 is a sectional view showing an optical system portion of a particle detecting device according to an embodiment of the present invention, and FIG. 2 is a sectional view taken along the line AA. In these drawings, a duct 1 is a duct through which an aerosol is guided from one end, and the other end is opened to a light measurement chamber 3 as a tapered nozzle 2. A duct 5 is provided so as to face the tip of the nozzle 2 and to sandwich the optical path 4 of the laser beam as will be described later. The duct 5 sucks the aerosol containing fine particles from the nozzle 2 in the light detection chamber 3 at a predetermined flow rate, and its end is connected to the flow meter 6 and the pump 7. The pump 7 is a suction means for sucking the aerosol through the duct 1, and the sucked aerosol is discharged to the outside through the filter 8.

On the other hand, a laser light source such as a laser diode 11 is arranged in the light source chamber 10 as shown in FIGS. 1 and 2, and a collimator lens 12 and a condenser lens 13 for expanding the light diameter in parallel are provided on the optical axis thereof. To be An opening 10a for irradiating a laser beam is formed at the tip of the light source chamber 10. An optical trap 14 is provided facing the opening 10a of the light source chamber 10 to absorb the laser beam without reflecting it, with the optical path 4 passing through the gap between the duct 1 and the duct 5 being interposed. The laser beam and the aerosol of the ducts 1 and 5 constitute a measurement area 15 for generating scattered light. Here, the light source chamber 10 constitutes a light beam irradiation means for irradiating the measurement region 15 with a light beam.

The light detection chamber 3 is composed of a pair of concave mirrors 16 and 17 having a spheroidal surface as shown in the figure. FIG. 3 (a) shows a concave mirror 1
It is sectional drawing which shows the spheroidal surface of 6,17. If the focal points of the ellipse are F1 and F2, as shown in this figure, the light emitted from one of the focal points is reflected in the spheroidal surface and is all given to the other focal point. Therefore, there are two focal points between focal points F1 and F2 and long axes A and B.
The photoelectric converters 21 and 22 such as PIN diodes are provided at the positions of the major axes A and B, respectively, using ellipses that are nearly spherical so that the distances between F1 and F2 are both a, and FIG. As shown in b), the portion between the focal points F1 and F2 is removed to form a pair of concave mirrors 16 and 17. Then, the focal points F of the two ellipses coincide with each other, and the focal point position F coincides with the optical path 4 of the laser beam to the measurement area 15 where the nozzle 2 and the opening of the duct 5 face each other. That is, the ellipse forming the mirror surface of the concave mirror 16 is the measurement area.
15 and the photoelectric converter 21 form a spheroidal surface having a pair of focal points, respectively. Similarly, the concave mirror 17 also forms a spheroidal surface with the measurement area 15 and the photoelectric converter 22 as the focal points. Then, when the light scattered from the focal point F, that is, the measurement region 15 is applied to one concave mirror 16, it is applied to the photoelectric converter 21 arranged at the center of the other concave mirror 17. Of the light scattered from the focal point, the light reflected by the other concave mirror 17 is applied to the photoelectric converter 22 arranged at the center of the concave mirror 16.
Therefore, the scattered light reflected at all solid angles can be given to one of the photoelectric converters 21 and 22. Photoelectric converter 21,22
Respectively converts the scattered light reflected from the other spheroid to an electric signal.

Next, the configuration of the signal processing unit of this embodiment will be described with reference to FIG. The outputs of the pair of photoelectric converters 21 and 22 are given to amplifiers 23 and 24, respectively. The amplifiers 23 and 24 amplify the signals given at the same amplification rate, and their outputs are given to the adder 25 and the multiplier 26. The multiplier 26 multiplies these signals, and its output is given to the comparator 27. The comparator 27 is set with a predetermined threshold value, discriminates the signal at the threshold level, and gives an output to the analog switch 28 when the signal is a predetermined value or more. The analog switch 28 gives an addition output to the integration circuit 29 when a signal is given from the comparator 27. The integrator circuit 29 is an integrator circuit having a time constant centered on the time when the fine particles passing through the center of the nozzle 2 pass through the light beam, as will be described later, and the output thereof is given to the second comparator 30. If this device is used as a particle number counting device, the comparator 30 is set to a predetermined threshold level and discriminates a signal exceeding that level, and its output is given to the counter 31. counter
31 counts the number of particles based on the comparison output.
Further, as shown by the broken line in FIG. 4, if the present embodiment is used as a detection device for detecting the particle size based on the scattered light level, the integrated output is passed through the comparators 31, 32 having different threshold levels, the counter 31, Shall be given to 33. Where multiplier 26, comparator
The analog switch 27 and the analog switch 28 constitute the coincidence determining means of the second invention of the present application.

Next, the operation of this embodiment will be described. First, the pump 7 is driven to suck the aerosol from the duct 5 to guide the aerosol to the duct 1. Then, the aerosol containing fine particles is ejected from the tip of the nozzle 2 and is sucked into the duct 5. At this time, the laser light source 11 such as a laser diode is driven to drive the collimator lens 12 and the condenser lens 1.
A parallel laser beam is emitted toward the optical trap 14 side via 3. Then, as shown in FIG. 1, the light beam will pass through the measurement region 15 where the nozzle 2 and the duct 5 face each other. Therefore, if fine particles pass through this period, scattered light is generated. As shown in Fig. 2, the scattered light is generated by two concave mirrors 16,1.
Although the light is scattered on the surface of the concave mirror 16 almost uniformly, the scattered light applied to the spherical surface of the concave mirror 16 is applied to the other focus different from the measurement area 15, that is, the photoelectric converter 21. Further, the light scattered on each surface of the concave mirror 17 is applied to the other focus different from the measurement area 15, that is, the center of the photoelectric converter 22. Therefore, almost the same received light signals are obtained from the photoelectric converters 21 and 22, and the respective outputs are amplified through the amplifiers 23 and 24. Therefore, the addition output from the adder 25 is an analog switch.
Added to 28. The outputs of the amplifiers 23 and 24 are multiplied by the multiplier 26 and transmitted to the comparator 27. Therefore, if a signal exceeding the threshold level of the comparator 27 is given, the analog switch
28 is closed, and the addition signal is transmitted to the integrating circuit 29.

Here, FIG. 5 is a diagram showing a change in scattered light intensity with respect to particles passing through different positions of the laser beam when the time constant of the integrating circuit 29 is changed. As shown in this figure, the time constant d is the time when the particles passing through the center of the fastest nozzle 2 cross the laser beam in the measurement region 15, and the curve A shows the time constant d = 0, That is, in the case where the integrating circuit 29 is not provided, it is a diagram showing changes in signal intensity when the curves B to D are changed to have time constants d = 0.5, 1, and 1.5, respectively. As shown in the figure, the integration circuit 29 can reduce the change in the signal intensity of particles passing through all positions of the laser beam. When the time constant is selected to be 1, the change can be minimized. The output of the integration circuit 29 is discriminated by the comparator 30 and the counter
Since it is counted at 31, it is possible to measure the number of fine particles passing through the measurement region 15. Also, in the case of measuring the particle diameter according to the peak value level, by providing a large number of comparators 30, 32 ... Having different threshold levels, it is possible to count the fine particles having the peak value based on the level.

Now, noise is weighted to one of the photoelectric converters, for example, the photoelectric converter 21 and a signal is given to the adder 25 and the multiplier 26 via the amplifier 23, and no signal is obtained to the other photoelectric converter 22. In that case, the output of multiplier 26 will be at a low level.
If the level is below the threshold level of the comparator 27, no signal is transmitted to the analog switch 28 and the addition output is not given to the comparator 29. Therefore, the noise removing effect can be improved by not only simply adding the outputs of the photoelectric converters 21 and 22 but also by determining whether or not the signals can be obtained at the same time by the coincidence determining means.

In this embodiment, the laser beam is a thin parallel laser beam, but it may be focused in the measurement area. Also in this case, the time constant of the integrating circuit is calculated with reference to the time required for passing the converged laser beam.

Further, the coincidence discriminating means of this embodiment multiplies two signals in the state of analog signals to discriminate the coincidence, but the outputs of the amplifiers 23 and 24 are given to the comparators and converted into a square wave. It is also possible to determine the coincidence based on the logical product signal. Alternatively, the outputs of the two amplifiers 23 and 24 may be given to the differential image amplifier, and the coincidence may be determined when the differential output is below a predetermined level.

〔The invention's effect〕

As described above, according to the first invention of the present application, since the photodetection chamber is covered by the pair of concave mirrors having spheroidal surfaces facing each other with one focus of each as the measurement region, all the scattered light is prevented. It can be reflected by one of the concave mirrors and guided to the photoelectric converter. Therefore, it is possible to significantly improve the efficiency of collecting scattered light passing through the measurement region.

Further, according to the second invention of the present application, when noise is heavy in one of the photoelectric converters, a signal can be obtained from only one photoelectric converter, and therefore the added signal is stopped based on the mismatch. I am trying. In this way, even if the noise is heavy, there is no possibility of outputting an erroneous detection signal.

Further, according to the third invention of the present application, since this output is guided to the integrating circuit, it is possible to obtain an effect that a substantially uniform crest value can be obtained in the entire area of the opening of the nozzle for ejecting the aerosol. .

[Brief description of drawings]

FIG. 1 is a view showing an optical system portion of a particle detecting device according to an embodiment of the present invention, FIG. 2 is a sectional view taken along the line AA, and FIG. 3 (a) shows a spherical surface of a concave mirror of this embodiment. FIG. 3 (b) is a schematic diagram showing a state in which the central portion is deleted to configure an optical measurement chamber consisting of a pair of concave mirrors, and FIG. 4 is a block diagram showing the configuration of the signal processing unit of this embodiment. FIG. 5 is a diagram showing a change in signal intensity with respect to a passage position of fine particles when the integration time constant of the integrating circuit according to the present embodiment is changed. 1,5 ... Duct, 2 ... Nozzle, 3 ... Optical measurement room, 4 ...
… Light path, 7 …… Pump, 10 …… Light source room, 11 …… Laser diode, 15 …… Measuring area, 16,17 …… Concave mirror, 21,22
...... Photoelectric converter, 23,24 ...... Amplifier, 25 …… Adder, 26
…… Multiplier, 27,30,32 …… Comparator, 28 …… Analog switch, 29 …… Integrator circuit, 31,33 …… Counter

Claims (3)

[Claims] 1. Scattering accompanying the passage of fine particles, comprising suction means for sucking an aerosol containing fine particles through a duct and ejecting it to a measurement region, and light beam irradiation means for irradiating the measurement region with a light beam. In a light scattering type fine particle detection device for detecting fine particles based on light, a pair of concave mirrors having a spheroidal surface that surrounds the measurement region and has the same point of the measurement region opposed to each other as one focus, A pair of photoelectric converters provided on the mirror surfaces of the concave mirrors respectively, which are arranged at the focal positions of the other spheroids facing each other and receive scattered light reflected by the facing concave surfaces to convert the scattered light into an electric signal, A particle detection device using a light scattering method, comprising: an adder circuit that adds outputs of a pair of photoelectric converters to obtain a scattering detection signal. 2. Scattering accompanying the passage of fine particles, comprising suction means for sucking an aerosol containing fine particles through a duct and ejecting it to a measurement area, and light beam irradiation means for irradiating the measurement area with a light beam. In a light scattering type fine particle detection device for detecting fine particles based on light, a pair of concave mirrors having a spheroidal surface that surrounds the measurement region and has the same point of the measurement region opposed to each other as one focus, A pair of photoelectric converters provided on the mirror surfaces of the concave mirrors respectively, which are arranged at the focal positions of the other spheroids facing each other and receive scattered light reflected by the facing concave surfaces to convert the scattered light into an electric signal, An adder circuit for adding the outputs of the pair of photoelectric converters to obtain a scattering detection signal; and a match determining unit for intermittently adding the outputs by determining the match of the outputs of the pair of photoelectric converters. Particle detecting apparatus according to a light scattering method, wherein Rukoto. 3. Scattering accompanying the passage of fine particles, comprising suction means for sucking an aerosol containing fine particles through a duct and ejecting it to a measurement region, and light beam irradiation means for irradiating the measurement region with a light beam. In a light scattering type fine particle detection device for detecting fine particles based on light, a pair of concave mirrors having a spheroidal surface surrounding the light measurement region and facing each other with the measurement region as one focus, and a mirror surface of the concave mirror A pair of photoelectric converters, which are provided at respective focal positions of the other spheroids facing each other and receive scattered light reflected by the concave surfaces facing each other, and convert the scattered light into an electric signal, and the pair of photoelectric converters. A light scattering type fine particle characterized by comprising: an adding circuit for adding the output of the converter to obtain a scattering detection signal; and an integrating circuit for integrating the output of the adding circuit with a predetermined time constant. Detection device.