JPH04167087A - Measuring instrument for number of particulates in liquid - Google Patents

Abstract

PURPOSE:To accurately measure the number of particulates in liquid even if air bubbles are formed in the liquid by providing two lasers which are installed at an equal distance to a detected part in the liquid and two photodetectors which are installed at an equal distance to the detected part and lasers. CONSTITUTION:The two lasers 1 and 2 which have the same intensity are installed at the equal distance to a particulate or air bubble 5 so as to irradiate the particulate or air bubble 5 with their laser light beams at right angles; and the photodetectors 3 and 4 which detect scattered light are installed at symmetrical positions at a constant angle to the lasers in the plane containing the laser light beams and detect scattered light from the particulate or air bubble 5. Consequently, even if the air bubble is present in the liquid, the number of particulates in the liquid can be measured distinctively from the air bubble.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a device for measuring the number of fine particles in a liquid.

<Conventional technology> With the increasing integration of LSIs, wafer cleaning technology to remove foreign matter adhering to wafers in the LSI manufacturing process has improved.
This is important for ensuring high wafer yield. However, foreign matter is suspended in the form of fine particles in the chemical solution used to clean the wafer, and these fine particles conversely adhere to the wafer, causing problems such as poor conduction of LSIs and short circuit conduction. Therefore, it is necessary to reduce the number of particles in chemicals and pure water used for cleaning wafers, and for this purpose, technology for accurately calculating the number of particles in chemicals and pure water is important.

A laser light scattering method is usually used to measure the number of particles suspended in a liquid. In this method, when microparticles suspended in a liquid are irradiated with l laser light, part of the laser light is scattered by the particles, and a photodetector detects this scattered light. This measures the number of fine particles inside.

<Problems to be Solved by the Invention> When measuring the number of particles in a liquid using the laser light scattering method described above, if bubbles are generated in the liquid, the bubbles will also scatter the laser light, so the bubbles will also be treated as particles. False detection occurs. Therefore, with chemicals that tend to generate bubbles, such as hydrogen peroxide, which is widely used as a cleaning chemical for semiconductor wafers, it is difficult to accurately detect the number of particles in the chemicals.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an apparatus that accurately measures the number of particles in a liquid even if bubbles are generated in the liquid.

Means for Solving the Problem> The particle number measuring device of the present invention includes two lasers installed at positions equidistant from a detection part in a liquid that detects particles, and a combination of the detection part and the laser. It is characterized by having two photodetectors installed equidistant from each other.

Effect> When using the above-mentioned present invention, when a bubble is irradiated with a laser beam, since the bubble is spherical in a liquid, the directional distribution of the scattered light of the two lasers will be different from the incident direction of each laser beam. are exactly the same, and the scattered light intensities detected by the two photodetectors are the same. On the other hand, since actual fine particles have a complicated shape, the scattered light direction distribution of the two laser beams differs with respect to the incident direction of each laser beam. Therefore, the difference in the intensity of scattered light detected by a photodetector is 0 in the case of scattering by bubbles, but not 0 in the case of scattering by actual particles, and only the actual number of particles is calculated. It is possible to measure.

Embodiment> Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

As shown in FIG. 1, two lasers l of equal intensity are used.

2 to the fine particles or bubbles 5 so that they are equidistant,
Moreover, each laser beam is directed at right angles to the fine particles or bubbles 5.
and photodetectors 3 and 4 for detecting the scattered light are installed at symmetrical positions at an angle of 45° with respect to each laser within the plane formed by the laser beam, and
Consider the case where scattered light from particulates or bubbles 5 is detected.

In Fig. 2, 6 is the center of the light-shielding tube 11, 7 is the window into which the laser beam enters, 8 is the window through which the laser beam is emitted, 9 is the condenser lens, 10 is the slit, 11 is the light-shielding tube, and 12 is the measuring device. A liquid supply port 18 is a liquid drain port 14 for the liquid to be measured.
indicates a signal processing section.

Next, the measurement procedure will be described. First, the liquid to be measured is injected at a constant flow rate into the light-shielding cylinder 1 from the liquid supply port 12 and discharged from the liquid drain port 13. Next, the two laser beams from the lasers 1 and 2 are irradiated onto the light-shielding tube 11 through the window 7, intersect at the center 6 of the light-shielding tube, and exit from the light-shielding tube 11 through the window 8. At the center 6 of the light-shielding cylinder, a laser beam irradiates the particles or bubbles 5, and the scattered light passes through a condenser lens 9 and is detected by photodetectors 3 and 4, and the detected signal is is processed by the signal processing unit 14 to distinguish between particles and bubbles based on the difference in intensity, and the number of particles in the liquid is measured based on the flow rate and the number of particles present at the center 6 of the light-shielding tube measured in the above procedure. .

As the laser 1.2, for example, a He-Ne laser can be used, and as the photodetectors 3, 4, for example, photomultiplier tubes can be used. Furthermore, the arrangement of the laser 1.2 and the photodetectors 3 and 4 is not limited to the values of 90° and 45° in this example, but can be arranged at any angle as long as symmetry is maintained. be.

<Effects of the Invention> As explained in detail above, by using the present invention, even when air bubbles are generated in the liquid, fine particles in the liquid can be distinguished from air bubbles, and the fine particles can be accurately identified in the liquid. It becomes possible to measure numbers.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are diagrams showing an embodiment of the present invention. Explanation of symbols 1, 2: Laser, 3.4: Photodetector, 5: Fine particles or bubbles, 6: Center position of light-shielding tube. 7.8: window, 9: condensing lens, lO: slit,
11: Light-shielding tube, 12: Liquid supply port, 13: Liquid drain port, 14: Signal processing section.

Claims (1)

[Claims] 1. In a device that measures the number of particles in a liquid using laser light, two lasers are installed at positions equidistant from a detection section in the liquid that detects particles, and the detection section and A device for measuring the number of particles in a liquid, comprising two photodetectors installed equidistantly from the laser.