JPH0886738A - Method and device for measuring particulate - Google Patents

Abstract

PURPOSE: To provide a method and a device capable of measuring not only the diameters and concentrations of particles but also the refractive indexes or the like of the particulates. CONSTITUTION: In this particulate measuring device, a space S to be measured is illuminated with a laser beam from a laser beam source 1 via a depolarizing plate 2. Two light receiving systems 10, 20 are placed to the right and left of the space S to be measured. In one light receiving system 10, an aperture 11, a lens system 12, an aperture 13, a polarizing filter 14, a wavelength selecting filter 15, and a photoelectric conversion element 16 are aligned; in the other light receiving system 20, an aperture 21, a lens system 22, an aperture 23, a condensing lens 24 and a polarizing prism 25 are aligned. Further, waveform selecting filters 26, 27 and photoelectric conversion elements 28, 29 are so arranged to diverge from the polarizing prism 25.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention irradiates particles in a measurement target space with a laser beam, and based on the intensity of scattered light of each polarization component, representative particle sizes of particles in the measurement target space, two-dimensional particles The present invention relates to a fine particle measuring method and apparatus capable of knowing the concentration and the refractive index of particles.

[0002]

2. Description of the Related Art In the process of manufacturing a semiconductor integrated circuit, fine particles adhere to the surface to cause defects in the circuit and reduce the yield of products. Therefore, it is necessary to detect the particle size of fine particles and the number (concentration) of fine particles in a predetermined system such as a processing chamber. Further, knowing the composition of the particles is effective in inferring the cause of the generation of the particles.

The Mie theoretical formula is applied to the measurement of such fine particles, and as a prior art to which the Mie theoretical formula is applied, Japanese Patent Publication No. 5-75975 and a magazine (Plas
ma Sources Science and Technology 1993 Vol.2, pp.35-39). FIG. 4 shows a schematic configuration of the above-mentioned paper, in which a single-wavelength laser beam generated by a laser light source 100 is made into unpolarized laser beam by a depolarizing plate 101, and this laser beam is irradiated to a measurement target space S. Further, two optical systems are arranged on the left and right of the measurement target space S so as to have the same optical axis crossing angle with respect to the irradiation optical axis, and each optical system is sequentially arranged from the side closer to the measurement target space S in the aperture 102a. , 102b, polarization filter 103a,
103b, apertures 104a and 104b, lens 10
5a, 105b, wavelength selection filters 106a, 106b
Further, the photoelectric conversion elements 107a and 107b are arranged, and among the scattered light from the measurement target space S, a polarization component having a polarization angle of 0 ° with respect to the observation plane is provided to the photoelectric conversion element 107a and a polarization component having a polarization angle of 90 ° is provided. The size of a representative particle is obtained from the ratio of the light amounts of these two polarization components by making the light incident on the photoelectric conversion element 107b, and the particle concentration is obtained by comparison with the known data created in advance. In addition, magazines (Jpn.J.Appl.Phys. 33, 1994 L476 pages-L4
There is a paper described on page 78). In this paper, the polarization component of the scattered light from the particle group is temporally separated using a rotating analyzer and a quarter-wave plate, and the particle is measured using one light receiving element.

[0004]

In order to improve the product yield in the manufacturing process of semiconductor integrated circuits, etc., it is important to know the particle size and number of fine particles, but to know what the fine particles are. Thus, it becomes an important clue as to which process the mixing was carried out, and can be used as a guideline for improving the equipment and line. However, in the method shown in the conventional example, since only a part of the information (dipolarized component) of scattered light is used, only the typical size and concentration of suspended particles can be measured, and the particles related to the composition of particles can be measured. It was not possible to obtain information about the refractive index of.

Further, according to the conventional method, the measurable particle diameter and the number of particles are limited to one point in the system, and it is impossible to accurately measure the entire particle distribution or the average number of particles in the system.
However, in the latter paper, the polarization component of the scattered light from the particle group is used. However, since the polarization plane is temporally rotated and received by one photoelectric conversion element (Photomul), each polarization component There was no simultaneity of measurement. In addition, since signals having different light intensities are converted into electric signals by one photoelectric conversion element, the dynamic range is narrowed and it is difficult to measure small particles.

[0006]

In order to solve the above-mentioned problems, a method for measuring fine particles according to the present invention irradiates laser light containing three different polarization components as irradiation light onto a space to be measured, and measures the space from the space to be measured. The scattered light is separated for each of the three different polarization components, the scattered light for each polarization component is incident on the photoelectric conversion element, the scattered light intensity for each polarization component is obtained, and the polarization is calculated from these three scattered light intensity values. The parameters were determined, and the time series change of the polarization parameter was compared with the time series change of the polarization parameter of the known substance that was theoretically obtained in advance, so that the fine particles in the measurement target space were measured.

Another method for measuring fine particles according to the present invention is: a first laser beam composed of a polarized component having a predetermined angle; and a second laser beam having a polarization angle and a wavelength different from those of the first laser beam. The measurement target space is irradiated with a third laser beam having a polarization angle and a wavelength different from the first and second laser beams from the same direction, and scattered from a predetermined planar area in the measurement target space. The light is taken out, the scattered light is separated into scattered light for each polarization component and is made incident on the image sensor, the scattered light intensity for each polarized light component is obtained, and the polarization parameter is obtained from these three scattered light intensity values. By comparing the time series change of the polarization parameter with the time series change of the polarization parameter of a known substance that was theoretically obtained in advance, the fine particles in the measurement target space were specified.

On the other hand, the fine particle measuring apparatus according to the present invention comprises a laser light source for generating a laser beam of a single wavelength, and a depolarizing plate for irradiating the laser light from the laser light source into the space to be measured as non-polarized light. An aperture and a lens system that extracts scattered light from the measurement target space, and a polarization element that separates the scattered light that has passed through the aperture and the lens system into three polarization components, such as a polarization filter or a polarization prism, and three separated light components. The first, on which each of the polarization components is incident,
A fine particle measuring device was constituted by the second and third photoelectric conversion elements.

Further, another particle measuring apparatus according to the present invention is such that a first laser light source for generating a first laser light having a polarization component of a predetermined angle and a polarization angle and a wavelength of the first laser light are A second laser light source for generating a different second laser light; a third laser light source for generating a third laser light having a polarization angle and a wavelength different from those of the first and second laser lights; A lens system that synthesizes the second and third laser beams and irradiates the measurement target space as irradiation light, a lens system that extracts scattered light from a predetermined planar area in the measurement target space, and this lens system A wavelength selection unit that separates the scattered light extracted through the wavelength division unit into three polarization components using the wavelength, and the first, the second, and the third that the scattered light of each polarization component separated by the wavelength selection unit enters. Particle measuring device with image sensor Configuration was.

In the above description, one light receiving system including a lens system for taking out scattered light from the measurement object space can be arranged on one side of the measurement object space or can be arranged on both sides of the measurement object space. .

[0011]

[Operation] The scattered light is separated into three different polarization components, and the particle size that changes with the passage of time and the polarization parameter that also changes with the passage of time are obtained from the intensity of the scattered light of each polarization component, and a graph is created. By comparing this with a graph prepared for a known substance and selecting the same, it is possible to know what the substance is in the system.

[0012]

Embodiments of the present invention will be described below with reference to the accompanying drawings. Here, FIG. 1 is an overall configuration diagram of a fine particle measuring apparatus according to the present invention. In this fine particle measuring apparatus, laser light generated by a laser light source 1 is converted into unpolarized laser light by a depolarizing plate 2, and this laser is used. The measurement target space S is irradiated with light as irradiation light.

Further, two light receiving systems 1 are arranged on the left and right sides of the space S to be measured so that they have the same optical axis intersection angle (γ) with respect to the irradiation optical axis.
0 and 20 are arranged. The optical axis intersection angles (γ) are preferably equal to each other, and the angle is preferably 90 °. However, if the optical axis intersection angle (γ) is known in advance, the optical axis intersection angle (γ) is It can be different.

In one light receiving system 10, the aperture 11, the lens system 12, the aperture 13, the polarization filter 14, and the wavelength selection filter 15 are arranged in this order from the side closer to the space S to be measured.
Further, the photoelectric conversion element 16 is arranged, and among the scattered light from the measurement target space S, only the scattered light having a polarization angle of 45 ° with respect to the observation surface is selected by the polarization filter 14 and the photoelectric conversion element 16 is selected.
It is designed to be incident on. The wavelength selection filter 15 cuts light having a wavelength other than the emitted laser light,
It is for improving / N.

In the other light receiving system 20, the aperture 21 and the lens system 2 are arranged in this order from the side closer to the space S to be measured.
2, an aperture 23, a condenser lens 24, and a polarization prism (Glan-Thompson prism) 25 are arranged, and further branched from this polarization prism 25, the wavelength selection filters 26, 2
7 and photoelectric conversion elements 28 and 29 are arranged.

The scattered light that has entered the light receiving system 20 is condensed again by the condenser lens 24 and further separated by the polarizing prism 25 into scattered light having polarization angles of 0 ° and 90 °, and further the wavelength selection filter. After passing through 26, the scattered light having a polarization angle of 0 ° is incident on the photoelectric conversion element 28 and the polarization angle of 9 °
The scattered light of 0 ° passes through the wavelength selection filter 27 and then enters the photoelectric conversion element 29.

FIG. 2 is an overall configuration diagram showing another example of the fine particle measuring apparatus according to the present invention. This fine particle measuring apparatus produces laser beams of different wavelengths (λ ₁ , λ ₂ , λ ₃ ). The light sources 31, 32 and 33 are provided. Laser light source 3
The laser light λ ₁ generated at ₁ is composed of a polarized light component having an angle of 90 ° with respect to the observation plane, and the laser light source 32 has 1
/ 2 wavelength plate 34 is attached, the polarization component of the laser beam λ ₂ is set to an angle of 45 ° with respect to the observation plane, and the laser light source 33 is also attached with a 1/2 wavelength plate 35 to polarize the laser beam λ ₃ . The component has an angle of 0 ° with respect to the observation plane.

Further, the laser beam λ ₁ is reflected by the mirror 36, transmitted through the dielectric mirrors 37 and 38, and the laser beam λ 1
₂ is reflected by the dielectric mirror 37, is transmitted through the dielectric mirror 38, and the laser light λ ₃ is reflected by the dielectric mirror 38 and is combined into one laser light. This laser light is a lens such as a cylindrical lens. Irradiation light L having a sheet-like width is formed by the system 39, and this irradiation light L is the measurement target space S.
Is irradiated.

On one side of the space S to be measured, 1
Two light receiving systems 40 are arranged. The light receiving system 40 includes a lens system 41, dielectric mirrors 42 and 43, a mirror 44, wavelength selection filters 45, 46 and 47, and a CCD image pickup device 4.
It is composed of 8, 49 and 50.

The light receiving system is preferably arranged in the same observation direction as described above. That is, it is preferable that they are arranged so as to have the same optical axis intersection angle with respect to the irradiation optical axis. In the present embodiment, as shown in FIG. 2, since the light receiving systems are collectively arranged on one side of the measurement target space S, the optical axis crossing angle with respect to the irradiation optical axis is naturally equal to each other. This is convenient because it is not necessary to make the optical axis intersection angles equal to each other as compared with the example.

Thus, the scattered light from the space S to be measured is taken out by the lens system 41 in a predetermined planar area, and the scattered light having the wavelength λ ₁ out of the scattered light transmitted through the lens system 41 (polarization angle = Only 90 °) is reflected by the dielectric mirror 42, is incident on the CCD image pickup device 48 through the wavelength selection filter 45 for improving the S / N, and the wavelength of the scattered light transmitted through the dielectric mirror 42 is λ. ₂ scattered light (polarization angle = 45
Scattered light having a wavelength of λ ₃ (polarization angle = 0 °) after being reflected by the dielectric mirror 43, incident on the CCD image pickup device 49 via the wavelength selection filter 46, and transmitted through the dielectric mirror 43. Is reflected by the mirror 44 and is incident on the CCD image pickup device 50 via the wavelength selection filter 47. Incidentally, as shown in FIG. 1, the same applies to the embodiment, but the combination of polarization angles is most preferably 0 °, 45 °, 90 °. However, the combination of polarization angles is not limited to this combination, and other combinations may be used. Since the scattered light of the same particle group is incident on the image elements of the image pickup devices 48, 49, and 50 that image the same position in the measurement target space S, the scattered light intensity (I _{0 for} each polarization component) is obtained. , I ₄₅ , I ₉₀ ) are detected and sent to the arithmetic processing unit as electrical signals.

As described above, the photoelectric conversion elements 16 and 2
8, 29 or scattered light intensity (I ₀ , I ₄₅ , I ₉₀ ) for each polarization component detected by the CCD imagers 48, 49, 50
A method for measuring the fine particles detected based on the above will be described below.

Generally, when the intensity of the irradiation light is I, the intensity of the scattered light is expressed by the following (Equation 1) using the polarization angle (x) as a parameter.

[Equation 1] In the above (Equation 1), if the polarization angle (x) is known, there are three unknowns I, a, and b. Therefore, if the time transition of the scattered light intensity is measured for at least three polarization angles (x), the time transitions of I, a, and b can be obtained, and the polarization parameters (Δ, Ψ) can be calculated using these a and b. You can ask. That is, from (Equation 1), x = 0 °, 45 °, 9
When the scattered light at 0 ° is obtained, the following (Equation 2), (Equation 3) and (Equation 4) are obtained.

[Equation 2]

(Equation 3)

[Equation 4] In (Equation 2) and (Equation 4), S ₁ and S ₂ are vibration functions that are guided by Mie's theoretical formula, and represent the vertical component and the horizontal component of the vibration plane of the incident light. The parameters are the diameter, the refractive index of the particles, and the wavelength of incident light (known value here). Therefore, the following (Equation 5)
And (Equation 6) are derived.

(Equation 5)

(Equation 6) From these, the polarization parameters (△, Ψ) are
And (Equation 8).

(Equation 7)

[Equation 8] On the other hand, when the Mie theoretical formula is used, the polarization parameter (Δ, Ψ) is represented by the following (Equation 9), and the typical size of the particle, the spread of the particle size distribution, the refractive index of the particle Can be expressed as a function of

[Equation 9]

Therefore, it was measured by comparing the time series change of the polarization parameter (Δ, Ψ) obtained by the actual measurement with the time series change of the polarization parameter (Δ, Ψ) obtained from the Mie theoretical formula. By detecting the refractive index of the particles, it is possible to know what kind of substance the particles are made of.

Explaining with a concrete example, particles grow in the treatment process using plasma, and FIG. 3 is a graph showing the change of the polarization parameter with the growth of the particles. On the other hand, for many known substances, the relationship between the time series change of the polarization parameter (Δ, Ψ) obtained from Mie's theoretical formula and the particle diameter is created in the same graph as in FIG. Then, if the graph as shown in FIG. 3 is completed by actual measurement, it is possible to know what the particles are made of by comparing the graph of the known substance already created and selecting the same graph. .

[0026]

According to the present invention as described above,
The scattered light from the space to be measured is separated into three different polarized light components, the scattered light is incident on the image sensor for each polarized light component, and the scattered light intensity for each polarized light component is obtained. The polarization parameter is obtained from the value, and the time series change of this polarization parameter is compared with the time series change of the polarization parameter of the known substance that has been theoretically obtained in advance, so that the particles in the measurement target space can be specified. Because I did
It can be an important clue as to which process the fine particles were mixed in, or in which place the fine particles were generated, and can be used as a guideline for improving the apparatus or line.

Further, since the refractive index of the fine particles in the system can be measured in real time, when the composition of the particles changes in multiple layers, the change time can be measured. Effective for management and development.

Further, by irradiating the measuring object space with a certain spread, the scattered light is made to enter the image pickup element for each polarization component from a predetermined planar area in the measuring object space. The effect can be measured with a planar spread instead of one point in space.

In particular, when the scattered light is made to enter the image pickup element for each polarization component from a predetermined planar area, if the wavelengths of the two laser lights having different polarization angles are made different, instead of the polarization filter. A wavelength selection filter that is not so sensitive to the incident angle can be used, and since a member that requires highly accurate alignment such as an aperture is not used, a highly accurate measurement result can be obtained.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of a particle measuring device according to the present invention.

FIG. 2 is an overall configuration diagram showing another example of a particle measuring apparatus according to the present invention.

FIG. 3 is a graph showing changes in polarization parameters with growth of particle size.

FIG. 4 is a block diagram of a conventional particle measuring device.

[Explanation of symbols]

1, 31, 32, 33 ... Laser light source 10, 20, 40
... Light receiving system, 11, 13, 21, 23 ... Aperture, 1
4, 24 ... Polarizing filter, 15, 26, 27, 45, 4
6, 47 ... Wavelength selection filter, 16, 28, 29 ... Photoelectric conversion element, 25 ... Polarizing prism, 37, 38, 42, 4
3 ... Dielectric mirror, 48, 49, 50 ... CCD image pickup device, L ... Irradiation light with width, S ... Measurement target space.

Claims (8)

[Claims] 1. A laser beam containing three different polarization components is irradiated as irradiation light onto a measurement target space, and scattered light from the measurement target space is separated for each of the three different polarization components.
The scattered light is made to enter the photoelectric conversion element for each polarization component, the scattered light intensity for each polarization component is obtained, the polarization parameter is obtained from the values of these three scattered light intensities, and the time series change of this polarization parameter and the theoretical A method for measuring fine particles, characterized in that the fine particles in the measurement target space are measured by comparing the time-series change of the polarization parameter of a known substance that has been obtained in advance. 2. A first laser beam having a polarization component of a predetermined angle, a second laser beam having a polarization angle and a wavelength different from those of the first laser beam, and a polarization angle and a wavelength having the first and second laser beams. The third laser light and the third laser light different from the above are irradiated to the measurement target space as irradiation light from the same direction, the scattered light is taken out from a predetermined planar area in the measurement target space, and the scattered light is wavelength-dependent. By separating the scattered light into scattered light for each polarization component and making it enter the image sensor, the scattered light intensity for each polarization component is obtained, and the polarization parameter is obtained from these three scattered light intensity values. A method for measuring fine particles, characterized in that fine particles in a measurement target space are specified by comparing time-series changes in parameters with time-series changes in polarization parameters of known substances that have been theoretically obtained in advance. . 3. The fine particle measuring method according to claim 1 or 2, wherein different polarization components have angles of 0 °, 45 ° and 90 ° with respect to the observation surface. 4. A laser light source that generates a laser beam of a single wavelength, a depolarizing plate that irradiates the measurement target space with the laser light from the laser light source as unpolarized light, and takes out scattered light from the measurement target space. An aperture and a lens system, a polarizing element that separates scattered light that has passed through the aperture and the lens system into three polarization components, and first, second, and third polarization components into which the three separated polarization components are incident. A fine particle measuring device comprising a photoelectric conversion element. 5. A first laser light source for generating a first laser light having a polarization component of a predetermined angle, and a second laser light for generating a second laser light having a polarization angle and a wavelength different from those of the first laser light. Laser light source, a third laser light source that generates a third laser light beam having a polarization angle and a wavelength different from those of the first and second laser light beams, and the first, second, and third laser light beams are combined. The lens system that irradiates the measurement target space as irradiation light with this, the lens system that extracts scattered light from a predetermined planar area in the measurement target space, and the wavelength from the scattered light extracted through this lens system as an index A fine particle measuring apparatus comprising: a wavelength selecting means for separating into three polarized light components; and first, second and third image pickup elements on which scattered light for each polarized light component separated by the wavelength selecting means is incident. 6. The particle measuring apparatus according to claim 4 or 5, wherein one light receiving system including a lens system for taking out scattered light from the measurement target space is arranged on one side of the measurement target space. A particle measuring device characterized in that 7. The particle measuring apparatus according to claim 4 or 5, wherein one light receiving system including a lens system for extracting scattered light from the measurement target space is arranged on each of the left and right sides of the measurement target space. A particle measuring device characterized by the above. 8. The fine particle measuring device according to claim 5, wherein the wavelength selecting means is a dielectric mirror.