JP3046504B2 - Particle measuring method and particle measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention irradiates particles in a measurement object space with laser light, and calculates a two-dimensional distribution of typical particle size and particle concentration from the scattered light based on Mie's theoretical formula. The present invention relates to a method and an apparatus for measuring.

[0002]

2. Description of the Related Art In the process of manufacturing a semiconductor integrated circuit, fine particles adhere to the surface of the semiconductor integrated circuit, thereby causing defects in the circuit and reducing the product yield. Therefore, it is necessary to detect the particle diameter and the number (concentration) of the fine particles in a predetermined system such as a processing chamber.

Incidentally, Mie's theoretical formula is applied to the measurement of particles. As a prior art to which the Mie's theoretical formula is applied, Japanese Patent Application Laid-Open No. Hei 6-82358 and a magazine (Plasma Sou
rcesScience and Technology 1993 Volume 2 3
Pp. 5-39).

The method disclosed in Japanese Patent Application Laid-Open No. 6-82358 discloses a method of irradiating particles with an Ar-Kr continuous wave laser (white laser light), measuring the scattered light from the particles with a video camera,
This is a method of detecting a change over time in particle diameter by a change in color of scattered light.

On the other hand, in the method described in the above-mentioned article, as shown in FIG. 4, a laser beam of a single wavelength generated by a laser light source 100 is converted into a non-polarized laser beam by a depolarizing plate 101,
The laser light is applied to the measurement target space S, and two optical systems are arranged on the left and right sides of the measurement target space S so as to have the same optical axis intersection angle with respect to the irradiation optical axis. The apertures 102 are arranged in order from the one closer to the measurement target space S.
a, 102b, polarizing filters 103a, 103b, apertures 104a, 104b, lenses 105a, 105
b, the wavelength selection filters 106a and 106b and the photoelectric conversion elements 107a and 107b are arranged, and a polarization component of the scattered light from the measurement target space S whose polarization direction is 0 ° with respect to the observation plane is polarized by the photoelectric conversion element 107a. A polarization component having a direction of 90 ° is made incident on the photoelectric conversion element 107b, a typical particle size is determined from the ratio of the light intensity of each polarization component, and a comparison is made with known data prepared in advance. The particle concentration is determined.

[0006]

Among the above-mentioned prior arts, in the method disclosed in Japanese Patent Application Laid-Open No. Hei 6-82358, it is possible to observe the change in the particle size of the particles in the system by the change in color. However, the diameter of the particles in the system cannot be directly known.
The practical limit of measurable particles is about 0.2 μm.

On the other hand, according to the method shown in FIG. 4, the particle diameter and the number of particles (concentration) in the system can be known in real time without disturbing the system. It is limited to one point in the system, and the entire particle distribution and the average number of particles in the system cannot be measured accurately.
It is sufficient to move the entire apparatus with respect to the measurement target space S, but the entire apparatus becomes large-sized, and such a situation cannot be practically performed.

In the method shown in FIG. 4, the size of the aperture determines the observation solid angle, and the value determines the limit of the detectable scattered polarization ratio, and determines the measurable particle size. . Therefore, high-precision positioning must be performed in order to measure particles having a determined particle size.

[0009]

In order to solve the above-mentioned problems, a method for measuring fine particles according to the present invention comprises a first laser beam composed of a polarization component having a predetermined angle, and the first laser beam having a polarization angle and wavelength. By irradiating a different second laser beam to the measurement target space as irradiation light from the same direction, extracting scattered light from a predetermined planar area in the measurement target space, and separating the scattered light for each wavelength. The scattered light is separated into scattered light for each polarization component and made incident on the image sensor, and a typical particle size and particle concentration of the fine particles present in the measurement target space are determined from the scattered light intensity ratio for each polarization component. I asked for it.

The particle measuring apparatus according to the present invention further comprises a first laser light source for generating a first laser beam having a polarization component at a predetermined angle, and a first laser beam having a polarization angle and a wavelength different from those of the first laser beam. A second laser light source for generating the second laser light, a lens system for irradiating the first and second laser lights as irradiation light to the measurement target space, and scattering from a predetermined planar area in the measurement target space. A lens system for extracting light, wavelength selecting means for separating the scattered light extracted through this lens system into two polarized light components using the wavelength as an index, and scattered light of one polarized light component separated by the wavelength selecting means is incident. to a first image sensor, constituted by a second image sensor which is the other of the scattered light of the polarization component incident the said first image sensor
Ratio of voltage according to scattered light intensity output from the second image sensor
Representative particles of the particle group existing in the space to be measured from
And the particle concentration were determined .

Here, the different polarization components may be those having angles of 0 ° and 90 ° with respect to the observation surface, and the irradiation light may be sheet light. Alternatively, one laser light source may generate two wavelengths of laser light.

[0012]

[Function] By using two types of laser beams having different polarization angles and making the wavelengths of the respective laser beams different, it is possible to use a polarization filter which is extremely sensitive to the incident angle (the incident angle accuracy is strict) without using a polarizing filter. With a dielectric mirror or the like that is not sensitive to angle, it becomes possible to separate scattered light for each polarization angle using wavelength as an index for discrimination. Therefore, it is possible to make the scattered light enter the image pickup device while having a two-dimensional spread to some extent.

[0013]

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 particle measuring apparatus according to the present invention.
Laser light sources 1 and 2 that generate laser beams of different wavelengths (λ ₁ , λ ₂ ) are provided. The laser light λ ₁ generated by the laser light source 1 is composed of a polarized light component having an angle of 90 ° with respect to the observation surface, and the laser light source 2 is provided with a half-wave plate 3 to observe the polarized light component of the laser light λ _2. The angle to the plane is 0
° things. In order to make the polarization planes of the laser beams λ ₁ and λ ₂ orthogonal, the laser light source may simply be rotated.

The laser beam λ ₁ is reflected by the mirror 4 and passes through the dielectric mirror 5, and the laser beam λ ₂ is reflected by the dielectric mirror 5, and the two are combined to form a lens system 6 composed of a cylindrical lens or the like. The irradiation light L having a width such as a sheet shape is applied to the measurement target space S.

On one side of the measurement target space S, 1
One light receiving system 10 is arranged. This light receiving system is a lens system 11 for extracting scattered light from a predetermined planar area in the measurement target space S. Of the scattered light transmitted through the lens system 11, scattered light having a wavelength of λ ₁ or λ ₂ , in other words Polarization angle 9
The dielectric mirror 12 reflects only one scattered light of 0 ° or 0 °, the wavelength selection filter 13 transmits only the light of the wavelength of one scattered light reflected by the dielectric mirror 12, and the dielectric mirror 12 is transmitted. The dielectric mirror 14 that reflects the other scattered light, the wavelength selection filter 15 that transmits only the light of the wavelength of the other scattered light reflected by the dielectric mirror 14, and the scattered light that has passed through these wavelength selection filters 13 Incident first and second CCD imaging elements 16,
17.

Here, the wavelength selection filters 13, 15
Not only separates scattered light but also cuts light of a wavelength other than the irradiated laser light to improve S / N.

Thus, of the scattered light from the measurement target space S, the scattered light having a polarization direction of 90 ° with respect to the observation surface enters the first CCD image pickup device 16 and is polarized with respect to the observation surface. The scattered light having an angle of 0 ° is incident on the second CCD imaging device 17. Here, since the scattered light of the same particle group is incident on the image elements of the CCD image sensors 16 and 17 which image the same position in the measurement target space S, the Mie value is obtained from the ratio of the light intensity of each polarization component. Based on the theoretical formula, a representative size of the fine particles floating in the measurement target space S is obtained. In addition, the particle concentration is determined by comparing with data of known fine particles prepared in advance.

Preferably, the light receiving systems are installed in the same observation direction. That is, it is preferable to arrange the optical axes so as to have the same optical axis intersection angle with the irradiation optical axis. In the present embodiment, as shown in FIG. 1, the light receiving systems are collectively arranged on one side of the measurement target space S, so that the optical axis intersection angle with respect to the irradiation optical axis is naturally equal, in other words, the light The axis intersection angle is no longer restricted to a specific angle, and alignment is facilitated.

FIG. 2 is a block diagram showing another example of the particle measuring apparatus according to the present invention. In this particle measuring apparatus, unlike the particle measuring apparatus shown in FIG. Two light receiving systems are arranged so as to have the same optical axis intersection angle (γ) with respect to the irradiation optical axis. Note that the same members as those of the particle measuring apparatus shown in FIG. 2 are denoted by the same reference numerals, and description thereof will be omitted.

With such a configuration, it is necessary to provide the same optical axis crossing angle (γ), but it is sufficient to provide only one of the wavelength filter and the dielectric mirror as the wavelength selecting means. . Although the optical axis intersection angle (γ) is preferably 90 °, both optical axis intersection angles (γ) may be different as long as both optical axis intersection angles (γ) are known in advance.

In each of the above-described embodiments, the laser light source is two.
However, since it is only necessary that two types of wavelengths having different polarization planes exist, one laser light source may be used that oscillates at two wavelengths.

FIG. 3 shows an example in which laser light of two wavelengths is generated by one laser light source 21. As shown in FIG.
It is also possible to use two laser light sources 21, a dielectric mirror 22, a half-wave plate 23 and a mirror 24.

In the examples, different polarization components having 0 ° and 90 ° are shown in order to increase the detection sensitivity, but the present invention is not limited to these.

[0024]

According to the present invention as described above,
Two laser beams having different polarization directions and wavelengths with respect to the observation surface are irradiated to the measurement target space as irradiation light having a certain spread, and scattered light is imaged for each polarization component from a predetermined planar area in the measurement target space. Scanning the device because it was made to enter the element and the typical particle size and two-dimensional particle concentration of the particle group existing in the measurement target space were obtained from the scattered light intensity ratio for each polarization component. The particle diameter and the number of particles in a predetermined region can be obtained without any problem.

In addition, the conventional measurement method using no polarization characteristic can measure only a two-dimensional spatial distribution.
By measuring the scattered light intensity of two types of polarized light components based on the polarization characteristics of the scattered light and using the wavelength as a medium as in the present invention, it is possible to simultaneously measure the particle size and the two-dimensional spatial distribution. .

In the case where scattered light having a certain spread in a plane is separated by a polarizing filter, the angle of incidence on the filter sensitively affects the polarization separation, making separation difficult.
If the wavelengths of the two laser beams having different polarization angles are different, a wavelength selection filter that is not so sensitive to the incident angle can be used instead of the polarization filter, and a high-precision alignment such as an aperture can be achieved. Since a required member is not used, a highly accurate two-dimensional distribution can be measured as a result.

Furthermore, if only one light receiving system is provided for extracting scattered light from a predetermined planar area in the space to be measured, alignment can be performed very easily. On the other hand, if a pair of light receiving systems for extracting scattered light from a predetermined planar area in the measurement target space are arranged on the left and right sides, parts can be omitted.

[Brief description of the drawings]

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

FIG. 2 is an overall configuration diagram showing another example of the particle measurement device according to the present invention.

FIG. 3 is a diagram showing one laser light source that generates laser light of two wavelengths;

FIG. 4 is a configuration diagram of a conventional particle measuring apparatus.

[Explanation of symbols]

Reference numerals 1, 2, laser light source, 6: a lens system for providing divergent irradiation light, 10: a light receiving system, 11: a lens system for extracting scattered light from a predetermined planar area, 12, 14, a dielectric mirror , 13, 15 ... wavelength selection filter, 16, 17
... CCD imaging device, L ... Sheet irradiation light, S ... Measurement target space.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-185336 (JP, A), Plasma Sources Science and Technology, 2, (1993) p. 35-39 (58) Field surveyed (Int. Cl. ⁷ , DB name) G01N 15/00-15/14 JICST file (JOIS)

Claims (9)

(57) [Claims] 1. A measurement target space is irradiated with a first laser beam having a polarization component at a predetermined angle and a second laser beam having a different polarization angle and wavelength from the first laser beam as irradiation light from the same direction. Then, the scattered light from the measurement target space is taken out from a predetermined planar area, and the scattered light is separated for each wavelength by separating the scattered light for each wavelength, and the scattered light is incident on the imaging device. A method for measuring fine particles, wherein a typical particle size and particle concentration of a group of fine particles present in a measurement target space are determined from a scattered light intensity ratio of each polarized light component. 2. The method for measuring fine particles according to claim 1, wherein the different polarization components have an angle of 0 ° with respect to the observation plane.
And a 90 ° angle, and the irradiation light is a sheet-like light having a certain width when viewed from the observation direction. 3. A first laser light source for generating a first laser light composed of a polarization component having 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. A lens system for irradiating the measurement target space with the first and second laser lights as irradiation light, a lens system for extracting scattered light from a predetermined planar area in the measurement target space, and a lens system Wavelength selecting means for separating the scattered light extracted through the system into two polarized light components using the wavelength as an index, a first image pickup device on which scattered light of one polarized light component separated by the wavelength selecting means is incident, and A second image pickup device on which scattered light having a polarization component of
The intensity of the scattered light output by the image sensor and the second image sensor.
Particles present in the measurement target space from the corresponding voltage ratio
To determine the typical particle size and particle concentration of
Fine particle measuring device. 4. The fine particle measuring apparatus according to claim 3, wherein the light receiving system including a lens system for extracting scattered light from a predetermined planar area in the measurement target space is provided on one side of the measurement target space. A fine particle measuring device, comprising: 5. The particle measuring apparatus according to claim 3, wherein one light receiving system including a lens system for extracting scattered light from a predetermined planar area in the measurement target space is provided on each of the left and right sides of the measurement target space. A fine particle measuring device, which is arranged. 6. The particle measuring apparatus according to claim 5, wherein each of the light receiving systems has an optical axis intersection angle of 90 ° with an irradiation optical axis.
A particle measuring device, characterized in that: 7. The particle measuring apparatus according to claim 3, wherein said wavelength selecting means is a dielectric mirror. 8. The particle measuring apparatus according to claim 3, wherein the first and second laser light sources are one laser light source. 9. The fine particle measuring apparatus according to claim 3, wherein the different polarization components have an angle of 0 ° and 90 ° with respect to the observation surface, and the irradiation light has a sheet-like shape having a constant width. A fine particle measuring device characterized by light.