JP2012189509A - Particle counter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a particle counter capable of more exactly performing count of particles.SOLUTION: In a particle counter which counts particles P which pass through a measurement target area 140 toward the fixed direction, it is provided with: light irradiation means 129 for irradiating the measurement target area with light; scattered light detection means 132 for detecting scattered light to be generated when the measurement target area 140 is irradiated with the light: and particle counting means 211 for comparing detection signals to be sequentially output from the scattered light detection means 132 with a predetermined threshold, and determining that until detection signals become less than the threshold again after the detection signals exceed the threshold as signals derived from one particle to count the particles.

Description

  The present invention relates to a particle counter that detects particles such as dust contained in exhaust gas from a semiconductor processing apparatus or the like.

  Particles such as dust generated in the semiconductor processing process and floating in the processing chamber cause the performance of the product to deteriorate. Therefore, a semiconductor processing apparatus is provided with a particle counter that detects particles floating in the processing chamber in real time (see, for example, Patent Document 1). The particle counter is disposed in, for example, an exhaust duct from a processing chamber. When light from a light source is irradiated on a measurement target area in the exhaust duct, the particle counting apparatus scatters when particles pass through the measurement target area. Emits light. Particles are counted by detecting the scattered light with a detector and comparing the detection signal of the detector with a preset threshold value.

  Further, since the intensity of the scattered light by the particle depends on the particle size of the particle, the particle size of the particle can be estimated from the height of the peak derived from each particle appearing in the detection signal. Furthermore, the time required for the particles to pass through the measurement target region can be obtained from the width of the peak appearing in the detection signal, and the passing speed of each particle (ie, the length of the measurement target region (ie, the length of the measurement target region) Particle flow velocity).

  However, in the particle counting apparatus as described above, when a particle having a large particle diameter passes through the measurement target region, a peak crack may occur on the detection signal due to light interference. Therefore, in the conventional particle counter, as shown in FIG. 5, a plurality of peaks (threshold values) are detected after a predetermined time (“particle determination time” in the figure) elapses after the intensity of the detection signal exceeds the threshold value. Even when a portion exceeding (1) appears, these were determined to be peaks derived from one particle, and particles were counted.

At this time, the maximum signal intensity (S _max in the figure) within the particle determination time is set as the signal intensity corresponding to the one particle, and the particle size of the particle is calculated based on the signal intensity. Further, the time from the time when the first peak of the plurality of peaks exceeds the threshold to the time when the last peak falls below the threshold is defined as the time required for the one particle to pass through the measurement target region. The passing speed of particles was calculated.

Japanese Patent Laid-Open No. 6-26833

  However, in the conventional particle counter, even when a plurality of particles actually pass through the measurement target region during the particle determination time, one particle is treated as having passed. Therefore, the particle counting result, the particle size calculation result, and the passing speed calculation result may be inaccurate.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a particle counter capable of more accurately counting particles and estimating the particle size and passing speed of particles. There is to do.

A particle counting device that counts particles passing through a measurement target region in a certain direction,
a) a light irradiation means for irradiating the measurement target region with light;
b) scattered light detection means for detecting scattered light generated when light is irradiated onto the measurement target region;
c) The detection signals sequentially output from the scattered light detection means are compared with a predetermined threshold value, and the detection signal from the time when the detection signal exceeds the threshold value and again falls below the threshold value is determined as a signal derived from one particle. Particle counting means for counting particles;
It is characterized by having.

Moreover, the particle counter according to the present invention further includes:
d) Particle size calculation means for calculating the particle size of the particles based on the maximum value of the detection signal from when the detection signal exceeds the threshold value to again below the threshold value,
It is desirable to have.

Moreover, the particle counter according to the present invention further includes:
e) Passing speed calculation means for calculating the passing speed of particles based on the time from when the detection signal exceeds the threshold value until it falls below the threshold value again, and the length of the measurement target region along the particle passing direction. ,
It is desirable to have.

  According to the particle counter according to the present invention having the above-described configuration, since the detection signal from the scattered light detector exceeds the threshold value and again falls below the threshold value as a signal derived from one particle, Even when a plurality of particles pass through the measurement target region in a short time, it is possible to accurately calculate the particle count and the particle size and passage speed of the particles.

Schematic which shows the whole structure of the particle counter which concerns on one Embodiment of this invention. The figure which shows the measurement object area | region in an exhaust pipe. FIG. 3 is a schematic diagram for explaining a particle counting method, a particle diameter calculating method, and a passing speed calculating method in the embodiment. The schematic diagram explaining another example of the counting method of the particle | grains in the embodiment. The schematic diagram explaining the counting method of the particle in the conventional particle counter, the calculation method of a particle size, and the calculation method of passage speed. The graph which shows the counting result of the particle by the conventional method. The graph which shows the count result of the particle | grains by the method of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic configuration diagram of a particle counter according to an embodiment of the present invention. The particle counting device is roughly composed of a detection unit 100 and a control / processing unit 200. As shown in FIGS. 1 and 2, the detection unit 100 is provided in the middle of an exhaust pipe 122 of a semiconductor manufacturing apparatus, for example. The inside of the exhaust pipe 122 is in a vacuum state or a state close to a vacuum, and in FIG. 2, particles P flow in a direction perpendicular to the paper surface (for example, from the front side to the back side of the paper surface).

  The detection unit 100 includes a light incident window 124 and a light emission window 126 that are arranged to face the wall surface of the exhaust pipe 122, a light irradiation unit 128 that irradiates laser light from the light incident window 124 toward the light emission window 126, and the laser. A detection window 130 provided on the wall surface of the exhaust pipe 122 in a direction substantially orthogonal to the light irradiation direction, a light shielding plate 136 having a slit 137 extending in the laser light irradiation direction, and the scattering that has passed through the detection window 130 and the slit 137 There are provided a scattered light detector 132 for detecting light, a condenser lens 134 disposed between the detection window 130 and the scattered light detector 132, and the like.

  The light irradiation unit 128 includes a light source 129 such as a semiconductor laser element and a lens (not shown) that converts laser light emitted from the light source 129 into sheet-like light. The sheet-like light irradiated from the light irradiation unit 128 enters the exhaust pipe 122 from the light incident window 124 and passes through the exhaust pipe 122 (vacuum region). As a result, the rectangular sheet-shaped measurement target region 140 in the exhaust pipe 122 is irradiated with light, and scattered light is generated by particles passing through the region 140. Of the scattered light generated in the measurement target region 140, the scattered light that has passed through the detection window 130 and the slit 137 is condensed on the scattered light detector 132 by the condenser lens 134.

  The scattered light detected by the scattered light detector 132 is converted into an electrical signal there, and this electrical signal is input to the signal processing unit 210 provided in the control / processing unit 200. The signal processing unit 210 performs predetermined processing based on the detection signal from the scattered light detector 132, and includes a counting unit 211 that counts particles, a particle size calculation unit 212 that calculates particle size of particles, and the like. And a passage speed calculation unit 213 for calculating the passage speed of the particles. The control / processing unit 200 further includes a control unit 220 that controls operations of the detection unit 100 and the signal processing unit 210, an input unit 230 including operation buttons and a keyboard, a display unit 240 including a monitor, and a signal processing unit. And a storage unit 250 that stores processing results in the unit 210, measurement conditions set using the input unit 230, and the like. The control / processing unit 200 may be configured by dedicated hardware, or may be configured by a personal computer on which predetermined control / processing software is installed. Further, it may be a combination of dedicated hardware and a personal computer.

  Next, the operation of the particle counter of this embodiment will be described. First, when the user sets parameters (sampling frequency, threshold voltage, measurement time, etc.) necessary for measurement from the input unit 230 and instructs the start of measurement, collection of detection signals by the signal processing unit 210 is started. That is, the scattered light generated by the light irradiation by the light source 129 is detected by the scattered light detector 132, and the detection signal (analog voltage) is sequentially sent to the signal processing unit 210.

  The detection signal sent to the signal processing unit 210 is compared with a threshold voltage by the counting unit 211. The detection signal is usually lower than the threshold voltage, and exceeds the threshold voltage when scattered light from particles is detected. The counting unit 211 determines that one particle has passed when the detection signal once exceeds the threshold voltage and then falls below the threshold voltage again. Therefore, for example, as shown in FIG. 3, when a plurality of time zones (A, B, C in the figure) exceeding the threshold voltage appear in a short time, conventionally, these are combined into one particle. In the particle counting device of the present embodiment, the counted number is counted as three particles. At this time, depending on the setting of the threshold value, there is a possibility that the peak cracking due to the large particle size is counted as a plurality of particles. Since the ratio of such large-sized particles to be generated is small, the accuracy of particle detection can be improved as a whole.

  The counting unit 211 may convert the detection signal from the scattered light detector 132 into a digital signal and count particles based on the digital signal. In this case, the detection signal in FIG. 3 is binarized as high (H) if it is greater than or equal to the threshold, and low (L) if it is less than the threshold, resulting in a signal as shown in FIG. Then, one pulse on the signal (a region from when the signal goes to a high state until it goes back to a low state) is counted as one particle.

The detection signal from the scattered light detector 132 is also sent to the particle size calculator 212, where the particle size of the particle is calculated from the intensity of the detection signal corresponding to each particle. At this time, in the particle measuring apparatus according to the present embodiment, as in the case of the above-described particle counting, the time range (A, B, C in the figure) from when the signal intensity exceeds the threshold value to below the threshold value again. Each is treated as a time region in which scattered light derived from one particle is detected, and the maximum value of signal intensity in each time region (A _max , B _max , C _max in the figure) is a detection signal corresponding to each particle. Determine as the intensity.

Note that the scattered light intensity I _scatt generated when the incident light I ₀ is applied to the particles is expressed by the following equation.

Here, a is the particle radius, λ is the wavelength of the incident light, n is the refractive index of the particle, θ is the angle between the traveling direction of the incident light and the observation direction of the scattered light, and r is the distance from the particle to the detector.
From equation (1), it can be seen that the scattered light intensity is proportional to the sixth power of the particle radius a and inversely proportional to the fourth power of the wavelength λ of the light. Since the scattered light intensity corresponds to the intensity of the detection signal in the detection unit 100, if the intensity of the detection signal by each particle is known, the radius of the particle can be obtained based on the intensity.

  Specifically, for example, a conversion formula or a correspondence table representing the relationship between the intensity of the detection signal from the scattered light detector 132 and the particle size of the particles is stored in the storage unit 250 in advance, and the particle size calculation unit 212 The particle size of the particle is determined from the signal intensity corresponding to each particle with reference to the conversion formula or the correspondence table.

  Furthermore, the detection signal from the scattered light detector 132 is also sent to the passage speed calculation unit 213, where the passage speed of each particle when passing through the measurement target region 140 is calculated. At this time, in the particle measuring apparatus according to the present embodiment, as described above, each particle measures between the time when the signal intensity exceeds the threshold value and again falls below the threshold value (A, B, and C in the figure). The measurement target region 140 is determined to be a time region passing through the target region 140, and the width of each time region (that is, the time required for each particle to pass through the measurement target region 140) along the flow direction of the particles. Is divided by the length (namely, the thickness w1 of the sheet-like light or the opening width w2 of the slit 137) to calculate the passing speed of each particle.

  During the measurement and signal processing as described above, the display unit 240 provides real-time information on the passage state of particles (for example, the number of particles that have passed during a certain period of time, the particle size, the passage speed, etc.). Is displayed. When the measurement is completed, a series of measurement results (the number of passing particles at each time point during the measurement, the total number of particles passed during the measurement, the distribution of the particle size and the passing speed, etc.) are stored as a particle measurement file. 250. In each file, header information is recorded, and data obtained by detection is sequentially stored under the header information. In addition, parameter data set before data acquisition is also stored in the storage unit 250. The file stored in the storage unit 250 can be appropriately read and displayed on the display unit 240.

  As mentioned above, although the form for implementing this invention was demonstrated, this invention is not limited to said embodiment, A change is accept | permitted suitably in the range of the meaning of this invention. For example, as a scattered light detector in the particle counter of the present invention, a detector comprising a plurality of detection elements as described in JP 2010-190814 (for example, a 32-channel photomultiplier tube) is used. It is also possible to obtain accurate information on the distribution of particles passing through the exhaust pipe by individually processing these signals. In addition, the particle counting device of the present invention includes the particle counting, particle size calculation, and passage speed calculation according to the method of the present invention (described with reference to FIGS. 3 to 5) and the conventional method (FIG. 5). Both particle counting, particle size calculation, and passage speed calculation can be performed, and the user can appropriately select which method to apply when performing measurement. May be.

  Next, the results of experiments conducted to confirm the effects of the particle counter according to the present invention will be described. FIG. 6 and FIG. 7 show the result (FIG. 6) of particle counting by the conventional method using the same signal (corresponding to the detection signal from the scattered light detector 132) and the particle by the method of the present invention. The result (FIG. 7) which performed the count is shown. In each graph, the horizontal axis represents the signal intensity, and the vertical axis represents the cumulative number of particles. Since the signal intensity corresponds to the particle size of the particle, the particle size increases as the horizontal axis moves to the right. Comparing these graphs, it can be seen that the number of detected particles is increased in the circled portion in FIG. 7, and the particle counting sensitivity is improved by the method of the present invention.

DESCRIPTION OF SYMBOLS 100 ... Detection part 122 ... Exhaust pipe 128 ... Light irradiation part 129 ... Light source 132 ... Scattered light detector 137 ... Slit 140 ... Measurement object area 200 ... Control / processing part 210 ... Signal processing part 211 ... Counting part 212 ... Particle size calculation Unit 213 ... Passing speed calculation unit 220 ... Control unit 230 ... Input unit 240 ... Display unit 250 ... Storage unit

Claims (3)

A particle counting device that counts particles passing through a measurement target region in a certain direction,
a) a light irradiation means for irradiating the measurement target region with light;
b) scattered light detection means for detecting scattered light generated when light is irradiated onto the measurement target region;
c) The detection signals sequentially output from the scattered light detection means are compared with a predetermined threshold value, and the detection signal from the time when the detection signal exceeds the threshold value and again falls below the threshold value is determined as a signal derived from one particle. Particle counting means for counting particles;
A particle counting device comprising: Furthermore,
d) Particle size calculation means for calculating the particle size of the particles based on the maximum value of the detection signal from when the detection signal exceeds the threshold value to again below the threshold value,
The particle counter according to claim 1, wherein Furthermore,
e) Passing speed calculation means for calculating the passing speed of particles based on the time from when the detection signal exceeds the threshold value until it falls below the threshold value again, and the length of the measurement target region along the particle passing direction. ,
The particle counter according to claim 1, wherein:

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