JPS6093944A - Light-scattering particle measuring apparatus - Google Patents

Abstract

PURPOSE:To make it possible to reduce a min. measurable particle size without using a lens in a light condensing system, by crossing a specimen stream and laser beam at right angles at the focus of a first parabolic surface mirror and condensing laser beam to a photoelectric converter provided at the focus position of a second parabolic surface mirror. CONSTITUTION:Specimen gas containing an aerosol passes the inside 17 of a short double pipe and passed the focus of a first rotary parabolic surface mirror 11 as a minute diameter gas stream. Laser beam passes a passage 15 and crosses the specimen stream at right angles at the focus 13 and beams scattered by fine particles are reflected by the parabolic surface mirror 11 and enter a second parabolic surface mirror 21 as parallel beams. The beams reflected by the parabolic surface mirror 21 are condensed to the photodiode 23 at the focus position and converted to a photoelectric signal and the particle size distribution of the aerosol is measured. Therefore, there is no noise based on the scattering on the surface of a lens because no lens is used and a min. measurable particle size becomes small.

Description

Detailed Description of the Invention In an aerosol particle measuring device using a light scattering method, a sampling aerosol flow is intersected with a light flux, and the light scattered by the aerosol particles is focused by a condensing optical system.
It is common to detect light using a photoelectric conversion means such as a photomultiplier (photomultiplier tube) or a photodiode, convert it into an electrical signal, and measure the particle distribution.

In this photoelectric conversion system, one pulse signal with a peak value corresponding to the particle size is obtained from the light scattered by one aerosol particle, and the signal processing circuit classifies the particle size according to the peak value and counts the number of particles. By counting, the particle size distribution of the aerosol can be analyzed.

Recently, in semiconductor factories, etc., as the degree of integration of LSI (Large-Scale Integrated Circuit) and ■LSI (Large-Scale Integrated Circuit) has increased, there has been a demand for improved air cleanliness in the manufacturing room (clean room). The target was particles of 0.8 μm, but recently, ultrafine particles of 0.8 μm or less, 0.2 μm, or even 0.1 μm have become a problem. Also, as a light source, a powerful laser beam, such as a He--He beam, has been used in place of the conventional white light, and improvements in measurement volume have been attempted.

Generally, in the optical system of a light scattering particle measuring instrument, a spherical lens or an aspherical lens is currently used in the condensing system. However, the light is scattered on the surface of the lens, especially when the finishing dust is poor, resulting in considerable stray light, which causes noise and reduces measurement accuracy, making the measurement results inaccurate. There is a drawback. Also, as light passes through the lens, it is absorbed, reducing the amount of light.
There is a drawback that the minimum measurable particle size cannot be reduced.

The particle measuring device of the present invention does not use any lenses in the condensing system and uses only two parabolic mirrors for RI, thereby providing a new high-precision measuring device that completely eliminates the above-mentioned drawbacks. do. In addition, the need to use a condensing lens is eliminated, the number of parts is reduced, the structure is simplified, and the laser optical axis can be easily adjusted, and the overall size is reduced, resulting in lower manufacturing costs. It was possible to obtain advantages such as a reduction in the amount of Furthermore, since the first parabolic mirror can be made larger and the light scattering part can be placed inside the parabolic mirror, the scattered light collection angle can be greatly improved compared to the case of a lens. The advantage was that the minimum measurable particle size could be made very small.

The present invention will be explained in detail with reference to Examples below.

Figure 1 shows Example 1 of the present invention, Figure 2 shows Example 2,
Furthermore, FIG. 8 shows Example δ. In these drawings,
The sampled sample gas containing aerosol passes through the inner side 17 of the short double tube, becomes an aerodynamic airflow with a small radius, and passes through the outer side 18 of the clean air sheath 70.
- passes through the focal point 1& of the first parabolic mirror 11 of revolution. At this position, the airflow intersects with a laser beam (for example, Hs-lie laser wavelength 682.8 mm) passing through a laser beam path arranged at right angles to the direction of the airflow. Here, FIG. 1 shows that the laser beam path 15 is the rotation axis of the first parabolic mirror and the second parabolic mirror.
The figure shows an embodiment in which the aerosol flow path is aligned with its rotation axis, and FIG. 8 shows an embodiment in which the aerosol flow path and laser beam are arranged perpendicular to the rotation axis of the first parabolic mirror. , and the aerosol flow path and laser beam! This is the case when they are arranged to intersect at right angles. The laser beam scattered by the particles in the airflow is reflected by the first parabolic mirror, becomes a parallel beam, and enters the second parabolic mirror 21 of revolution.

The light reflected by the second parabolic mirror is automatically focused at its focal point. The focused light is converted into a photocurrent signal by a photomultiple or photodiode 28 placed at the focal point. Then, a pulse signal having a peak value corresponding to the particle size of each aerosol particle is generated, and the pulse signal is measured and used as an argument in the signal processing section, and the particle size distribution of the aerosol can be obtained.

Regarding the relationship between the first and second parabolic mirrors, the second parabolic mirror is a part of a larger parabolic mirror, and its axis of rotation (A) is It is preferable that the rotation axis of the parabolic mirror is substantially parallel to the rotation axis of the parabolic mirror.

As is clear from the above description, the present invention provides a light scattering particle measuring device based on a novel technique that overcomes the drawbacks of the conventional technology and has the advantages described above.

[Brief explanation of the drawing]

FIGS. 1, 2, and 8 show embodiments of the present invention. In the figure, 11 is the first parabolic mirror 18, the focal position 15 of the first parabolic mirror 1 is the laser beam 1, the aerosol flow path 18 is the outer tube 19 of the double tube, and the exhaust port 21 is The second parabolic mirror 28 is a photoelectric conversion means placed at the focal point of the second parabolic mirror.

Claims (1)

[Claims] (1) Aerosol flow and luminous flux! In an aerosol/particle measurement device using a light scattering method, the light scattered by aerosol particles is collected at right angles by a condensing optical system and detected by a photoelectric conversion means. Using an object mirror, the aerosol flow and laser beam intersect at right angles at the focal point of the first parabolic mirror, and the second parabolic mirror crosses the laser beam at a right angle. This light is characterized by having a mechanism that collects the parallel laser beam reflected from the plane mirror and focuses it on a photoelectric conversion means placed at the focal point of the second parabolic mirror. Aerosol particle measurement device using scattering method. (2. In the aerosol particle wax measurement device using a light scattering method according to claim 1, the laser beam path is provided to coincide with the rotation axis of the first parabolic mirror of revolution, and the aerosol flow path is This aerosol particle measuring device using a light scattering method is characterized in that it is installed to intersect at right angles to the rotation axis. (3) In the aerosol particle measuring device using a light scattering method according to claim 1, the This aerosol particle measuring device using a light scattering method, characterized in that the path is provided to coincide with the rotation axis of the first parabolic mirror of revolution, and the laser beam path is provided to intersect the rotation axis at right angles. (4) In the aerosol particle measuring device using a light scattering method according to claim 1, the aerosol flow path and the laser beam are provided perpendicular to the rotation axis of the first parabolic mirror,
Is it an aerosol flow path or a laser beam? This aerosol particle measuring device using a light scattering method is characterized in that it is installed so as to intersect at right angles.