JPS6319535A - Evaluating instrument for fine particle in liquid - Google Patents

Abstract

PURPOSE:To accurately evaluate fine particles in a liquid by flowing a sample liquid in a transparent narrow tube to form a certain flow passage and projecting a laser light to the narrow tube in the vertical direction and detecting the diffracted light and the scattered light due to fine particles in the liquid by a Fourier transform optical system. CONSTITUTION:The light from a laser oscillator 2 is not only expanded but also converted to parallel rays of a luminous flux by a beam expanding system 3. A Fourier transform lens 5 is arranged on the opposite side of a narrow tube 4, and a scattered pattern evaluating semiconductor detector 6 is set on the focal surface of the lens 5. Washing water including fine particles 9 flows from the upper flow passage and traverses the laser light at right angles. A diffracted and scattered pattern 7, which is generated when fine particles 9 pass the center part of the wide projected light, is received by a photodetector 6. The photodetector 6 consists of light receiving areas having concentricity and directivity, and an address code is given to each light receiving area, and the output condition from an optional element is unequivocally determined. Consequently, signals from concentric light receiving areas are analyzed to obtain an extreme value of the intensity distribution expressed with the Bessel function, and the particle size is determined.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for counting extremely small objects, and particularly to an apparatus for simply and rapidly counting microparticles present as insoluble matter in a liquid.

[Conventional technology]

If heavy metal substances, dust, etc. are mixed into various types of cleaning water, including water used in the semiconductor device manufacturing process, it will have an adverse effect on the final product, and in some cases, produce defective products.

Such effects have long been a problem, but in recent years, as the degree of integration has increased, urgent measures have become necessary. Methods for dealing with this include the Coulter counter method, light scattering method, ultrasonic scattering method, and image forming method.

Among these, image forming methods are relatively adopted. Since the present invention is closest to the image forming method, a related device will be described as a conventional device.

As described in Japanese Unexamined Patent Publication No. 54-24683, the conventional device has a structure in which a laser beam is directly irradiated onto the thin tube portion, and an enlarged projection system is provided in front of the irradiated light to image the fine particles in the thin tube. A screen and a phototransistor are placed in the area (monitor section) where six images are formed. The role of the screen here is to confirm the positional relationship between the inside of the capillary through which the sample liquid passes and the enlarged projection optical system, and to visually determine the shape of the particles on the screen.

Particles are detected using a phototransistor array (hereinafter abbreviated as phototransistor) arranged above the screen. An enlarged image of the fine particles is formed on the photodetector, and the existence and size of the fine particles can be determined by evaluating the output signals from the individual elements. Furthermore, since moiré caused by light interference in the thin tube section results in an intermittent changing signal, a Schmitt circuit and a one-shot multi-circuit are installed together to solve this problem.

[Problem to be Solved by the Invention 3] In the conventional device described above, since the arrays are arranged one-dimensionally, the dimensions at a position parallel to the arrays are only clear. Therefore, it is difficult to fix the size of the fine particles using this method. According to the patent publication, 50μm
It is written that it is possible to detect the above particles.

Furthermore, since it is necessary to use a lens similar to a microscope objective lens for image magnification (magnification of 100 in the conventional device), the field of view inside the tubule is limited. The diameter of the cross section of the internal channel is also limited, and the flow rate of the sample liquid that can be delivered to the channel is also small.

In the conventional device, 5 cc of water is stored in the solution container, and the inner diameter of the tube is 0.
．． 8rrn was measured by flowing the sample solution at a flow rate of 9/sac.

Since a large amount of various cleaning liquids are handled during the semiconductor manufacturing process, it can be said that it is difficult to evaluate the cleaning liquids in-line using the above-mentioned apparatus.

SUMMARY OF THE INVENTION An object of the present invention is to provide an evaluation apparatus for fine particles in liquid, which can determine the size and shape of fine particles in liquid and can perform in-process measurement as much as possible during a semiconductor process.

[Means for solving problems]

In order to overcome such problems, instead of image evaluation using an enlarged projection system, which is the measurement principle in conventional devices, the present invention deals with diffraction and scattering phenomena due to fine particles in sample liquid.The 0 diffraction phenomenon is well known. When light is irradiated onto an object such as a circle or a slit, a pattern unique to the object is generated in three-dimensional space.

Diffraction phenomena can be roughly divided into two types: Presnel diffraction and Fraunhofer diffraction, but since the latter is easier to analyze, the optical system is often arranged in accordance with this. Needless to say, there is no need to be persistent.

Since there is a correlation between the shape of the diffraction pattern and the shape of the object, it is possible to evaluate this and solve the problem 1 of conventional devices.
can be solved. The second problem of the measured flow rate can be solved by expanding the laser beam using a beam expansion system and converting it into a parallel beam. The beam expansion system uses a combination of a microscope objective lens and a single lens.

The inner diameter of the thin tube can be increased along with the beam expansion diameter, and a diameter much larger than the 0.8-diameter of the conventional device can be secured. As a result, the flow rate increases by about two fingers, creating the possibility of in-line measurement during the process.

[Effect]

Since the size of dust or undissolved substances contained in cleaning liquids used in semiconductor manufacturing processes is about 0.1 to 3 μm, their shape can be considered to be approximately spherical. Therefore, in explaining the present invention,
For ease of understanding, it is first assumed that the particles in the liquid are spherical in shape.

Since the cross section of each spherical particle is circular, the diffraction pattern generated when a spherical particle is irradiated with a laser beam has an intensity distribution expressed by a Bessel function in a plane perpendicular to the laser beam transmission direction. The position of the extreme value of this Bessel function changes depending on the particle size. By determining the position of each extreme value, it becomes possible to identify the particle size. Furthermore, by evaluating the directionality of the diffraction pattern intensity, it is possible to estimate a state where the pattern deviates from a circular pattern.

〔Example〕

The configuration and operation of the embodiment will be explained below with reference to FIG.

This will be explained according to FIG.

FIG. 1 shows the configuration forming the core of the measurement principle.

In the conventional device, light from a laser oscillator 2 directly irradiates a thin tube 4, and a magnifying lens such as a microscope objective lens is placed on the opposite side of the thin tube 4, and an image magnified at a magnification of 100 is formed on the image plane. The configuration is as follows. Further, on the image plane, phototracers for determining the size of the submerged particles 9 in the capillary tube 4 are arranged one-dimensionally.

In the present invention, the light from the laser oscillator 2 is transferred to the beam expansion system 3.
At the same time, the beam is made thicker, and at the same time, it is made into a parallel light beam and irradiated to the thin tube 4 (which can be made about 10 times thicker than the conventional device). A Fourier transform lens 5 is placed on the opposite side of the thin tube 4, and the diffraction beam shown in FIG.
The semiconductor detector 6 for scattering pattern evaluation is set. Cleaning water (indicated as sample liquid 1 here) containing fine particles 9 during the semiconductor manufacturing process flows from the upper channel and crosses the laser beam at right angles. A photodetector 6 receives the diffraction and scattering pattern 7 generated at the point where the fine particles 9 pass through the center of the thick irradiation light. The surface shape of the photodetector 6 is as shown in FIG. 2, and consists of a light-receiving area that is both concentric and directional. An address code is given to each light-receiving area, and the output status from any element can be uniquely determined. Therefore,
Signals from concentric light receiving areas, for example 8Art.

8A21. By analyzing the 8A, the extreme value of the intensity distribution expressed by the Bessel function can be found, and the particle size can be determined.

In addition, directional light receiving elements 8A1z, 8A21. ...
...Intensity variations can be detected from 8AIJ. As a result, it is possible to estimate the state in which the fine particles 9 have an extremely flat elliptical or rectangular shape. for example.

If it is a rectangular fine particle, the directional light receiving element is 6Azt.

The intensity increases with the right angle component of 6A11S, but 6Ata
.

It happens that 6A17 becomes weaker.

When measuring microparticles 9 in a liquid with the configuration shown in FIG. 1, even when there are no microparticles 9 in the sample liquid 1, reflections and scattered light by the capillary tube 4 or Rayleigh scattering by the sample liquid 1 are constantly present. As a result, noise components consisting of DC components are superimposed on the originally intended signal components, making it difficult to detect particles. In order to overcome such drawbacks, the apparatus of the present invention stores the output values of each element in the diffraction/scattering pattern evaluation detector in a state where no particulates 9 are included (clean water supply state) as a pre-measurement step.

FIG. 3 shows a signal processing system diagram in the present invention.

Signal 8A1118A without the above-mentioned particulates
IJ and 8B are all stored in the signal conversion storage circuit 10.10' in the form of signal strength corresponding to the address. Next, the sample liquid 1 containing the fine particles 9 is poured into the signal conversion storage circuit 1.
When a signal with properties different from those previously stored at 0' appears, signal conversion is performed and the signal intensity and pulse width are stored. A differential amplifier circuit 11 takes the difference between the signals from the signal storage circuits 10 and 10', and eliminates the DC component caused by the thin tube 4 and the clean sample liquid 1 described above. The address signal obtained here is sent to the pattern determination circuit 12 in the form of one strength and pulse width.

The shape and size, such as a sphere or an ellipsoid, are determined from the intensity generation state, pulse width, etc. The signal after the judgment is
It is visually represented on the display device 13.

The arrangement of the measuring device during the cleaning process targets the liquid that is branched from the main stream of cleaning water. As shown in FIG. 4, clean water is prepared in a part of the measurement system for the purpose of measuring background noise components.

〔Effect of the invention〕

According to the present invention, the generation state of diffracted light unique to the measurement object can be analytically evaluated using a photodetector having both radial and concentric shapes. can be facilitated. Furthermore, since the detection principle deals with spatial frequencies, an increase in resolution can be expected compared to evaluation by image formation. This is because the image forming method is limited in magnification.

Further, in the present invention, since the Fourier transform method is used, the diameter of the thin tube can be increased, and the measured flow rate can also be increased by about two orders of magnitude. Therefore, semi-in-process measurements branched from the mainstream can be performed, and in-liquid particle evaluation can be performed relatively accurately.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view showing the main measurement part of the present invention, Fig. 2 is a front view of the photodetector of Fig. 1, Fig. 3 is an electronic circuit diagram for signal processing, and Fig. 4 is the invention of the present invention. FIG. 2 is a cross-sectional view showing the entire implantation of an example.

Claims (1)

[Claims] 1. A sample liquid is made to flow in a transparent capillary to form a certain flow path, and when the capillary is irradiated with a laser beam from the perpendicular direction, the diffraction and scattered light generated by fine particles in the liquid is detected using a Fouri transform optical system. An evaluation device for fine particles in liquid that is characterized by fixing the size and shape of fine particles through detection.