JPH047952B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a particle counting device that is used in clean rooms of semiconductor manufacturing plants and the like and counts the number of minute particles contained in the air.

[Summary of the invention]

The particle counting device according to the present invention optically detects the number of particles by condensing high-temperature saturated steam using particles contained in an aerosol as nuclei, expanding the particle size, and using propylene glycol as a solvent for the vapor. It was there. By using propylene glycol, a particulate counting device that is odorless, harmless, consumes less, and is easy to maintain can be obtained.

[Prior art and its problems]

A particle counting device used in clean rooms of semiconductor factories, etc. extracts aerosol in the factory and ejects it into a predetermined measurement area from a nozzle.
A particle counting device is known that irradiates a particle with a laser beam or the like and measures the number of particles based on the presence or absence of scattered light. With such conventional particle counting devices, it is difficult to measure ultrafine particles in the submicron order region, and the problem is that the particle size that can be measured is limited by the speed at which the particles are ejected into the measurement area. It was hot.

For example, as shown in Japanese Patent Application Laid-Open No. 57-42839, a particle detection device is known in which vapor is condensed using particles as nuclei, and the particles are allowed to grow and optically detected. As the vapor produced by such a nuclear condensation method, a vapor of butyl alcohol, hexanol, or the like is usually used. Since these solvents have low heat of vaporization, low specific heat, and low surface tension, they can easily generate saturated steam and can easily form condensation nuclei with large particle sizes using fine particles as nuclei. However, these solvents are harmful, and there is a problem that harmful vapors may leak into the air after the nuclei are condensed and the number of fine particles is measured, and an unpleasant odor may be generated.
Furthermore, in the conventional particulate counting device, a solvent is supplied to the evaporation column to generate steam, but there is a problem in that a large amount of solvent is consumed and it takes time and effort to replenish the solvent.

[Purpose of the invention]

The present invention has been made in view of the problems of conventional particulate counting devices, and provides a particulate counting device that is odorless, harmless, and capable of easily counting the number of particulates using a solvent that consumes a small amount. The purpose is to provide

[Structure and effects of the invention]

The present invention includes a laser light source that generates a laser beam, an optical means that focuses the laser beam, and a particle size enlarging means that enlarges the particle size of the particles, and includes This is a particle counting device that counts the number of particles based on scattering holes, and the particle size expansion means mixes high-temperature propylene glycol saturated vapor with an aerosol containing the particles to be measured, and condenses the vapor using the particles as nuclei to form particles. It is characterized by expanding the diameter.

According to the present invention having such characteristics, the particle size is expanded by generating high-temperature saturated steam using propylene glycol as a solvent for the particle size expanding means and mixing it with an aerosol. By using propylene glycol, it is possible to significantly reduce the consumption amount to, for example, about 1/10 compared to conventional hexanol and the like. Furthermore, even if propylene glycol vapor leaks into the air, it is odorless and harmless to the human body, making it possible to construct a safe particle counting device.

[Explanation of Examples]

(Configuration of Example) FIG. 1 is an overall configuration diagram showing an example of a particle counting device according to the present invention. In this figure, a laser light source such as a laser diode 2 is arranged in a light source chamber 1, and a collimating lens 3 and a cylindrical lens 4 for expanding the diameter of light into parallel light are arranged on its optical axis.
The cylindrical lens 4 has a flat front surface and an arcuate back surface, and focuses the laser beam only in the X-axis direction without focusing it in the axial direction perpendicular to the plane of the paper. . Light source room 1
A glass plate 5 to which a heater is attached is attached to the front surface of the glass plate 5 except for the central portion through which the laser beam passes. A measurement chamber 6 is formed along the optical path via the glass plate 5. The measurement chamber 6 is a region where aerosol is ejected at a predetermined speed into the optical path of the laser beam to scatter light, and has a closed structure in order to maintain the expanded particle size and reduce dark noise due to stray light. A photodetection chamber 7 is further arranged on the right side of the measurement chamber 6 along the optical path. The photodetection chamber 7 is a part that collects scattered light and converts it into an electrical signal,
Condensing lenses 8 and 9 condensing scattered light on the front surface thereof
is provided. A photoelectric converter 10 such as a PIN diode is provided at the focal point of the condensing lens 9, and converts the scattered light into an electrical signal corresponding to the scattered light. Here, a beam trap 11 is provided at the center of the condensing lens 8 to block the laser beam directly applied from the cylindrical lens 4, and a heater is provided on the surface of the condensing lens 8, covering almost the entire surface of the lens at predetermined intervals. is provided.

Next, a means for enlarging the aerosol particle size will be explained. As shown in FIG. 2, air within the clean room is taken into a flow meter 21 via a valve 20. A filter 22 is connected to the flow meter 21, and dust is removed by the filter 22, and the air is supplied as clean air to the high temperature saturated steam chamber 23. In the high-temperature saturated steam chamber 23, propylene glycol serving as a solvent is heated by a heater 24, and the supplied air is transmitted as high-temperature saturated steam to the mixing chamber 26 via a duct 25. Mixing chamber 26
Further, an aerosol containing particles to be measured from within a clean room or the like is provided through a duct 27. The mixing chamber 26 is a region where room temperature aerosol and clean high temperature saturated steam are mixed, and the steam is condensed using fine particles of the aerosol as nuclei to expand the particle size, and is formed integrally with the nozzle 28. The tip of the nozzle 28 has a double structure of a central jet nozzle 28a and a peripheral jet nozzle 28b, and the nozzle 28 faces the discharge duct 31 via the optical path of the laser beam. The discharge duct 31 sucks in the aerosol ejected from the nozzle 28, and a flow meter 33 is connected to one end of the discharge duct 31 via a valve 32, and a pump 34 is connected to the outlet side of the flow meter 33. The pump 34 sucks in the exhaust gas from the exhaust duct 31 and discharges it into the air through the filter 35, thereby ejecting an aerosol for measurement from the nozzle 28 side.

Next, FIG. 2 is a sectional view showing one embodiment of the mixing chamber 26 formed integrally with the nozzle 28. As shown in the figure, a duct 40 below the mixing chamber 26 is connected to the high-temperature saturated steam chamber 23 via a duct 25, and the aerosol in the measurement area is guided through the duct 41 from the right side of the figure. The tip of the duct 41 communicates with an air chamber 42a provided in an annular holding member 42 and temporarily holding the aerosol. A duct 40 is located at the left end of the air chamber 42a.
A mixing nozzle 43 is formed to penetrate through the. A cylindrical fixing ring 44 is further provided on the outside of the holding member 42 in which the air chamber 42a is formed. Near the duct 41 of the fixed ring 44,
As shown in the figure, air cooling fins 44a are formed to suppress the rise in temperature of the duct 41 and the holding member 42.
Furthermore, a nozzle 42b and a chamber 42c are formed in the holding member 42 at a position facing the mixing nozzle 43, and a drain duct 45 is provided for discharging unnecessary propylene glycol in the form of droplets. The upper end of this duct 40 communicates with a diffusion tube 46 having a tapered inner circumference. The diffusion tube 46 is a part that condenses propylene glycol vapor using fine particles as a nucleus, and is made of a poor thermal conductor, such as synthetic resin, to provide a heat insulating effect, and its end is connected to the cooling tube 47. be done. The cooling cylinder 47 is made of a material such as metal having good thermal conductivity, and air cooling fins 47a are provided at regular intervals on its outer periphery as shown in the figure. The cooling cylinder 47 is a region for cooling the passing propylene glycol vapor, and serves to remove excess vapor and promote the growth of condensation nuclei. The cooling cylinder 47 has a depression and a drain hole 4 communicating with the depression as shown in the figure.
7b is provided to discharge unnecessary liquefied propylene glycol vapor from the mixing chamber 26. A constricted portion 48 made of a synthetic resin material or the like is formed in communication with the cooling cylinder 47, and its tip serves as the central spout 28a of the nozzle 28 and faces the measurement chamber 6. As described above, the nozzle 28 has a double structure, and clean air is introduced from the upper side of the paper between the constricted portion 48 of the cylindrical member 49 and communicates with the peripheral jet port 28b of the nozzle 28.

(Characteristics of Particle Size Enlargement Part) Next, the characteristics of the particle size enlargement means using propylene glycol according to the present invention will be explained. The particle size expansion in the mixing chamber 26 is determined based on the overall heat balance and mass balance, with the flow rate and temperature of the high temperature saturated steam and the flow rate and temperature of the aerosol being important factors. FIG. 3 illustrates these relationships on a temperature-vapor amount diagram. Now, the temperature of the high temperature saturated steam given from the high temperature saturated steam chamber 23 is T _sh , and the steam amount is
Assuming that H _sh is the temperature of the aerosol given to the mixing chamber 26, and the amount of steam _{is H sl ,} the high temperature saturated steam given from the high temperature saturated steam chamber 23 is on the saturation curve A, as shown in FIG. , aerosols are located below this curve. Immediately after these are mixed in the mixing chamber 26, they become supersaturated and reach point i, where the temperature is T _i and the amount of steam is H _i as shown in the figure. If there are sufficient condensation nuclei in the supersaturated air, point i changes adiabatically due to the condensation process, and reaches point f on the saturation curve A after a predetermined time due to the Kelvin effect. The temperature at that time is T _sf and the amount of steam is H _sf . Now, at this time, the difference ΔH (= H _i - H _sf ) between the steam amount at point i and point f is taken as the amount of steam condensation, and the ratio of the saturated vapor pressures at T _i and T _sf is the supersaturation degree S (= P _i /P _sf ), the degree of supersaturation S and the amount of condensed vapor ΔH are determined. And the flow rate of high temperature saturated steam is
If Q _sh and the aerosol flow rate are Q _sl , then the mixing ratio R _h
(=Q _sh / (Q _sh + Q _sl )) is determined, but when hexanol, propylene glycol, water and butanol are selected as the medium, the degree of supersaturation S and the amount of condensed vapor ΔH with respect to the mixing ratio Rh are determined by the amount of high temperature saturated steam. The respective temperatures can be determined as shown in Figures 4 to 7 a and b, respectively.

In these figures, if the degree of supersaturation S is large, the particle size can be expanded even for small particles, and the value of the amount of condensed vapor ΔH indicates the amount of vapor adhering to the particles at that time. Therefore, in order to optically detect fine particles, it is preferable that the degree of supersaturation S is large. Further, if the condensed vapor amount ΔH is large, optical detection becomes easier, but the consumption of the medium increases, so it is preferable to select a medium that has a small value within the optically detectable range. For example, for hexanol and propylene glycol, if the temperature T _sh of high temperature saturated steam is 70°C, the temperature T _sl of the aerosol is 25°C, and the mixing ratio R _h is 0.3, the supersaturation degree is as shown in Figures 4a and 5a. S
are both 2.3, which is almost the same value.
At this time, the amount of condensed vapor ΔH is 0.01 for hexanol, as shown in FIGS. 4b and 5b, and 0.0025, which is about 1/4 of the amount for propylene glycol.
In the optical system using the laser light source described above, it is possible to sufficiently detect fine particles even when propylene glycol is used as a solvent. Therefore, if propylene glycol is selected as the solvent, microparticles can be sufficiently expanded in the same manner as hexanol, and the amount of solvent consumed can be significantly reduced. Furthermore, as shown in FIGS. 6 and 7, water and butanol have a low degree of supersaturation S, making it difficult to sufficiently enlarge microparticles.

(Operation of the Embodiment) Laser light oscillated by the laser diode 2 in the light source chamber 1 is collimated by the lens 3, and focused only in the X-axis direction by the cylindrical lens 4. This laser beam is applied to the measurement chamber 6 and focused just in front of the nozzle 28. Then, by operating the pump 34, the discharge duct 31
The air inside the mixing chamber 26 is sucked out. Therefore, the air in the clean room is controlled by the valve 20 and the flow meter 21.
The air is then guided as clean air to the high temperature saturated steam chamber 23 via the filter 22, and the clean high temperature saturated steam is conveyed to the mixing chamber 26 through the ducts 25 and 40. Furthermore, the aerosol containing the particles to be measured in the clean room flows through the ducts 27 and 41 to the mixing chamber 2.
6 can be conveyed. Here, the temperature of the duct 41 increases due to heat conduction from the duct 40 to which high-temperature saturated steam is supplied, but air cooling fins 44a are formed in the fixed ring 44 that connects the duct 41 to the mixing chamber 26 as shown in the figure. Therefore, the temperature of the duct 41 can be lowered, and the temperature of the aerosol can be maintained at approximately the room temperature of the clean room. Therefore, the temperature difference between the high-temperature saturated steam and the aerosol is ensured to be above a certain level, and the saturated steam tends to condense around the fine particles with the fine particles as the nucleus. When the fine particles and high-temperature saturated steam mixed in the duct 40 pass through the diffusion tube 46, the saturated steam condenses and grows with the fine particles as nuclei, and is supplied to the cooling section 47. In the cooling cylinder 47, the saturated steam is cooled by air cooling fins 47a to condense excess saturated steam, and liquefied propylene glycol is discharged from the drain 47b. Furthermore, by suppressing the temperature rise caused by absorbing the latent heat of liquefaction, the degree of supersaturation is kept constant and the growth of condensation nuclei grown using fine particles as nuclei is promoted. The condensation nuclei thus formed are passed through the constriction section 48 to the nozzle 28.
It is ejected from the central ejection port 28a through the measurement chamber 6 into the exhaust duct 31. Also, the air in the clean room is sucked through the duct 30 and passed through the filter 2.
9 and is ejected as clean air from the peripheral ejection port 28b of the nozzle 28. Therefore, condensation nuclei with enlarged particle size are ejected at the focus of the laser beam,
Clean air will be blown out at the same speed around it. When this condensation nucleus passes through the focal point of the laser beam, the laser light is scattered, and the scattered light is focused by the condenser lens 8. Even if the floating condensation nuclei in the measurement chamber 6 pass through the laser beam, almost no scattered light is transmitted to the condenser lens 8 because the energy density is low in the area where the laser beam is not focused. In addition, near the measurement area where the laser beam is focused, clean air is ejected from the peripheral ejection port 28b of the nozzle 28, so the influence of scattering by floating condensation nuclei can be removed, and the air is ejected from the central ejection port 28a. It is possible to collect only the light scattered by the particles. The scattered light thus obtained is collected by condensing lenses 8 and 9, transmitted to a photoelectric converter 10, and converted into an electrical signal.

Although a semiconductor laser is used as a light source in this embodiment, it goes without saying that a He--Ne laser, a white light source, etc. can also be used. Furthermore, it is also possible to introduce the exhaust gas from the filter 35 into the mixing chamber again and configure the particle size enlarging means in a circulating manner. Further, if the liquefied propylene glycol obtained from the drains 45 and 47b is refluxed to the high temperature saturated steam chamber 23, the amount of solvent consumed can be further reduced.

[Brief explanation of drawings]

FIG. 1 is an overall configuration diagram showing an embodiment of a particle counting device according to the present invention, FIG. 2 is a sectional view showing an embodiment of a mixing chamber 26, and FIG. 3 is a temperature-vapor amount diagram in the mixing chamber 26. , Figures 4a and 4b are graphs showing the degree of supersaturation and amount of condensed vapor with respect to the mixing ratio for hexanol, and Figures 5a and b are graphs showing the degree of supersaturation and amount of condensed vapor for propylene glycol.
6A and 6B are graphs showing the degree of supersaturation and the amount of condensed vapor for water, and FIGS. 7A and 7B are graphs showing the degree of supersaturation and the amount of condensed vapor for butanol, respectively. 1...Light source chamber, 2...Laser diode, 3...
...Collimating lens, 4...Cylindrical lens, 6...
...Measurement chamber, 7...Photodetection chamber, 10...Photoelectric converter, 11...Beam trap, 21, 33...Flowmeter, 22, 29, 35...Filter, 23...
High temperature saturated steam chamber, 26...Mixing chamber, 27, 30,
40, 41...Duct, 28...Nozzle, 31...
...Discharge duct, 34...Pump, 42...Holding member, 43...Mixing nozzle, 44...Fixing ring, 46...Diffusion tube, 47...Cooling tube, 44
a, 47a... air cooling fin, 48... constriction part.

Claims (1)

[Scope of Claims] 1. A laser light source that generates a laser beam, an optical means that focuses the laser beam, and a particle size enlarging means that enlarges the particle size of fine particles, and the focal position of the laser beam is In a particle counting device that counts the number of particles based on scattered light of passing particles, the particle size enlarging means mixes high-temperature propylene glycol saturated vapor and an aerosol containing the particles to be measured, and generates steam using the particles as nuclei. A particle counting device characterized by condensing particles and expanding particle size. 2. The particle size enlarging means is provided at a first cooling means provided at a connection portion of the duct containing the aerosol with a duct that guides high temperature saturated steam, and in a flow path for the mixed measurement target particles and high temperature saturated steam. A claim characterized in that the invention comprises a second cooling means, and a jetting means for spouting particles having an enlarged particle size to a focal position of a laser beam through a flow path having the second cooling means. The particulate counting device according to item 1. 3. The particle counting device according to claim 2, wherein the second cooling means is a cooling cylinder having air cooling fins formed around the periphery.