KR100978397B1 - System for analyzing plasma density - Google Patents

Abstract

The present invention provides a plasma density analysis system. The plasma density analysis system reflects or transmits a light source unit, a beam amplifying unit that sequentially amplifies the emitted laser beam in a plasma formation space, and a laser beam having plasma density information through the plasma formation space. And a plasma density distribution analyzer for acquiring the interference information of the reflected laser beam and the beam intensity information of the transmitted laser beam to calculate the plasma density distribution. Therefore, the present invention can analyze the density distribution of the plasma by passing the laser beam through the plasma and deriving an interference fringe from the laser beam.

Description

 [0001] SYSTEM FOR ANALYZING PLASMA DENSITY [0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma density analyzing system, and more particularly, to a plasma density analyzing system capable of analyzing a plasma density distribution by passing a laser beam through a plasma and deriving an interference pattern from the laser beam.

Typically, a laminar interferometer is used as a device for measuring and evaluating the precision or optical aberration of optical or mechanical parts such as optical lenses or glass.

The layer-milling interferometer is a device that evaluates the characteristics and performance of a part to be inspected by making an interference pattern by using a plate or a diffraction grating to transmit or reflect the light to be inspected or measured.

Since the layer-based interferometer does not need a light source for making an interference pattern by combining with the light transmitted or reflected through the part, and has a strong mechanical strength against vibration, the light passing through the part to be separated is separated from each other. It is used as a device to inspect the optical aberration or plan of parts by analyzing the interference fringes in the X direction and the Y direction made from the interference.

1, a conventional layer-milling interferometer has a structure in which light rays having passed through the inspected component 100 are reflected from the front surface 105a and the rear surface 105b of the flat plate 105, respectively, (II), and the light beams of these different paths are interfered with each other to constitute the interference fringes 110 in the solid-state image pickup device. The layer indicated by m in the interference fringe 110 represents the amount of layer milling.

Here, as the thickness of the flat plate 105 is thinner, inspection of a smaller optical component is possible. However, it is difficult to make the flat plate 105 thinner, and accordingly, the thin flat plate causes a phenomenon that the accuracy of the flat plate 105 is lowered.

On the other hand, if the thickness of the flat plate is large, it is impossible to obtain interference fringes with a light ray passing through a small component smaller than the thickness of the flat plate. Therefore, measuring the characteristics of the parts using the interference fringes by the flat plate 105 is not suitable for miniaturization and high-precision trend of the parts.

In addition, although the layer-milling interferometer of FIG. 1 has an advantage that it can simultaneously measure a large area, it is difficult to obtain accurate information on the optical path difference from the interference fringes. In the case of plasma, Unlike the components, since the refractive index changes in the medium, it is more difficult to analyze.

The present invention provides a plasma density analysis system capable of analyzing a density distribution of a plasma having a variable refractive index in a medium through a horizontal layer milling interference pattern, have.

The plasma density analysis system of the present invention includes a light source unit for emitting a laser beam, a beam amplification unit for sequentially amplifying the emitted laser beam so as to be included in the plasma forming space, And a plasma density distribution analyzing unit for obtaining the interference information of the reflected laser beam and the beam intensity information of the transmitted laser beam to calculate the plasma density distribution.

The beam amplifying unit may include a first beam amplifying unit configured to amplify a laser beam emitted from the light source unit to a first width, which is a width suitable for processing by an optical path guide unit, and a laser beam amplified by the first width in a plasma formation space. It is preferable to include a second beam amplifying unit for amplifying a second width which is amplified by a predetermined width rather than the first width to be included.

The optical path guide includes a beam splitter for reflecting or transmitting the laser beam having the plasma density information, and the beam splitter is preferably a high-interference beam splitter capable of more accurately measuring interference information.

In addition, the system may further include a 50% beam splitter between the first beam amplification unit and the second beam amplification unit.

The system may further include a mirror for reflecting the laser beam having the plasma density information and guiding the laser beam to the 50% beam splitter.

In addition, the laser beam having the plasma density information reflected from the mirror is reduced to a predetermined width in the second beam amplifier before being guided to the 50% beam splitter.

The 50% beam splitter transmits the laser beam to the mirror side and guides the laser beam reflected by the mirror to the optical path guide.

Further, the plasma generating space is located between the second beam amplifying part and the mirror.

In addition, the plasma density distribution analyzer may include a reference meter, a first meter, a second meter, and a controller, wherein the reference meter measures reference beam intensity information of the laser beam emitted from the light source, Wherein the measuring unit measures interference information having a light path difference of the laser beam having the reflected plasma density information and the second measuring unit measures the measurement beam intensity information of the laser beam having the transmitted plasma density information, It is preferable to analyze the plasma density distribution using the reference beam intensity information, the interference information, and the measurement beam intensity information.

In addition, the controller may be configured such that a calculation formula of a plasma refractive index N, a light path L (x, y) and a light path difference DELTA L (x, y) are predefined and a ratio of the reference beam intensity information and a measurement beam intensity information Is defined such that the ratio of the plasma is not variable, and the density of the plasma is defined as being radially symmetrical.

이고, 상기

이고, 상기

이고, 상기 ΔL(x,y)을 각 y에 대하여 x축 방향으로 유한차분하여 상기 L(x,y)을 구하고, 상기 구해진 L(x,y)을 사용하여 각 y에 대하여 x축 방향으로 아벨 인버전 방법으로 상기 플라즈마 밀도를 구하는 것이 바람직하다.Where

And

And

L (x, y) is obtained by finite difference of ΔL (x, y) in the x-axis direction with respect to y, and in the x-axis direction with respect to each y using the obtained L (x, y). It is preferable to obtain the plasma density by the Abel inversion method.

The present invention has the effect of analyzing the density distribution of the plasma whose refractive index is variable in the medium through the interlayer interference fringe.

Hereinafter, a plasma density analysis system according to the present invention will be described with reference to the accompanying drawings.

2 shows a plasma density analysis system of the present invention. Figure 3 compares the magnitudes of the reflected beams of a 50% beam splitter and a high interference beam splitter according to the invention. 4 is a view showing the optical path of a measurement beam having plasma density information according to the present invention. 5 is a view showing a process of generating an interference fringe for a density distribution of a plasma according to the present invention.

Referring to FIG. 2, the plasma density analyzing system of the present invention includes a light source 100 for emitting a laser beam, a beam amplifier (not shown) for sequentially amplifying the emitted laser beam so as to be included in a plasma forming space An optical path guide unit 300 that reflects or transmits a laser beam having a plasma density information through the plasma forming space, and an optical path guide unit 300 for measuring interference intensity of the reflected laser beam and beam intensity information And a plasma density distribution analyzing unit 500 for calculating the plasma density distribution.

More specifically, the light source unit 100 is a laser generator capable of irradiating a laser beam. The laser beam emitted from the light source unit 100 is emitted along the first optical path.

The beam amplifying unit 200 is disposed on the first optical path.

The beam amplification unit 200 includes a first beam amplification unit 210 for amplifying the laser beam emitted from the light source unit 100 to a first width suitable for processing in the optical path guide unit, And a second beam amplifying unit 220 amplifying the laser beam to a second width amplified by a constant width than the first width so as to be included in the plasma forming space.

In addition, a plasma, which is a test piece, is placed on the side of the beam amplification part 200 on the first optical path.

A mirror 250 is disposed on the first optical path so as to be spaced a predetermined distance from the side of the plasma.

On the other hand, a 50% beam splitter 400 is installed on the first optical path between the first beam amplification part 210 and the second beam amplification part 220.

The 50% beam splitter 400 transmits the laser beam emitted from the light source unit 100 toward the mirror 250, and reflects the laser beam reflected by the mirror 250 along the second light movement path.

Here, the laser beam emitted from the light source unit 100 is sequentially amplified while passing through the first and second beam amplification units 210 and 220. That is, after being amplified to a first width to be processed in the optical path guide unit, the amplified light is amplified to a second width so as to include a predetermined width of the plasma, and is moved to the mirror 250.

In this case, the laser beam passing through the plasma may include density information of the plasma.

Thus, a beam that includes density information of the plasma, is reflected through the mirror 250, reflected by the 50% beam splitter 400, and travels along the second optical path is referred to as a "measurement beam ".

On the other hand, the optical path guide unit 300 is disposed on the second optical path. The optical path guide unit 300 is a high-interference beam splitter that reflects or transmits a laser beam having the plasma density information.

The high-interference beam splitter reflects or transmits a measurement beam having density information of the plasma. When the high-interference beam splitter is reflected, the high-interference beam splitter moves along the third optical path, Move along the path of travel.

The plasma density distribution analyzer 500 includes a reference meter (not shown), a first meter 510, a second meter 520, and a controller 530.

The reference measuring unit 510 may measure reference beam intensity or intensity information of the laser beam emitted from the light source unit 100.

The first measuring unit 510 may measure interference information having an optical path difference of a laser beam having the reflected plasma density information disposed in the third optical movement path.

The second measuring device 520 may be disposed on the second optical path to measure a measurement beam intensity or intensity information of the laser beam having the transmitted plasma density information.

The controller 530 may analyze the plasma density distribution using the reference beam intensity information, the interference information, and the measurement beam intensity information.

Next, the operation of the plasma density analysis system of the present invention constructed as described above will be described.

Referring to FIG. 2, the laser beam emitted from the light source unit 100 is moved along the first optical path and amplified to a first width to be processed by the optical path guide unit in the first beam amplification unit 210.

Subsequently, the laser beam amplified to the first width is transmitted through the 50% beam splitter 400, and the transmitted laser beam may include a predetermined width of the plasma while passing through the second beam amplifier 220. Is amplified.

The laser beam amplified by the second width may pass through the plasma, and thus the laser beam passing through the plasma may acquire the density information of the plasma.

The laser beam obtained from the density information of the plasma is reflected by the mirror 250 and then travels along the first optical path to be reduced in width by the second beam amplifier 220.

As such, the laser beam having the density information of the plasma and reduced in a predetermined width may be reflected by the 50% beam splitter 400 and moved along the second light movement path.

Therefore, the laser beam having the density information of the plasma and reduced to a predetermined width can be transmitted through the high-interference splitter as the optical path guide portion and can be reflected along the second optical path or along the third optical path .

Then, the first measuring device 510 measures intensity information of the laser beam transmitted from the high-interference splitter, and the second measuring device 520 measures interference information or interference pattern of the laser beam reflected from the high-interference splitter Can be.

Here, referring to FIG. 3, the optical path guide unit 300 according to the present invention uses a high interference splitter.

When dividing the measurement beam into two by using a general 50% beam splitter 400 coating, as shown in FIG. 3, in addition to the two necessary beams, multiple beams reflected in multiple stages are simultaneously generated.

Therefore, it is necessary to minimize the intensity of beams other than the primary and secondary reflected beams because such beams cause errors in the measurement.

Accordingly, it is possible to adjust the reflectance of both sides of the beam splitter to reduce the size of the third and higher order beams while matching the sizes of the primary and secondary beams to be interfered.

The application of the specially coated high-interference beam splitter can generate more accurate interference fringes, and it is possible to analyze the density distribution of the plasma using the interference fringe.

At this time, when a high-interference beam splitter is used, a transmission beam is generated on the opposite side of the beam reflected by the beam splitter, and the size of the beams other than the primary transmission beam is very small. Therefore, On the other hand, intensity information of the measurement beam is mainly transmitted to the transmission beam.

Therefore, by analyzing these two beams together, the phase information of the measurement beam can be more accurately analyzed.

Therefore, the plasma density distribution analyzing unit 500 according to the present invention can obtain the plasma density distribution by acquiring the interference information of the laser beam reflected by the high interference splitter and the beam intensity information of the transmitted laser beam.

That is, the reference measuring unit measures the reference beam intensity information of the laser beam emitted from the light source unit 100, and the first measuring unit 510 measures interference information having the optical path difference of the laser beam having the reflected plasma density information The second measuring instrument 520 measures the measurement beam intensity information of the laser beam having the transmitted plasma density information, and the controller 530 measures the reference beam intensity information, the interference information, The intensity information is used to analyze the plasma smear distribution.

The controller 530 may be configured to determine a calculation formula of the plasma refractive index N, the optical path L (x, y) and the optical path difference DELTA L (x, y), and the ratio of the reference beam intensity information and the measurement beam intensity The proportion of information is defined not to vary, and the density of the plasma is defined to be symmetric in the radial direction.

이고, 상기

이고, 상기

이고, 상기 ΔL(x,y)을 각 y에 대하여 x축 방향으로 유한 차분하여 상기 L(x,y)을 구하고, 상기 구해진 L(x,y)을 사용하여 각 y에 대하여 x축 방향으로 아벨 인버전 방법으로 상기 플라즈마 밀도를 구할 수 있다.Where

And

And

Finite difference of ΔL (x, y) in the x-axis direction with respect to y, and obtain L (x, y) in the x-axis direction with respect to each y using the obtained L (x, y) The plasma density can be obtained by the Abel inversion method.

은 다음과 같이 정의할 수 있다.More specifically, assuming that the plasma is circular as shown in FIG. 4 and the density of the plasma is radially symmetric, the refractive index of the plasma

Can be defined as:

............................................(1)

............................................(One)

은,Therefore, light path

silver,

........................................(2)

........................................(2)

 And the interference fringes are finally generated by the difference of these values.

Since the refractive index of the plasma is determined by the density of the plasma and the wavelength of the measuring beam, the inverse calculation from this can inversely deduce the plasma density distribution from the final interference pattern.

5 shows a process in which the final interference fringe is generated by the density distribution of the plasma.

If the refractive index N of the plasma and the optical path L are defined as described above in the controller 530, the optical path difference? L finally calculated by the controller 530 is expressed by?

.......................................(3)

....................... (3)

Is calculated. At this time, the intensities of the beams measured by the first measuring device 510, which is an interference CCD, and the second measuring device 520, which is an intensity CCD, are as follows.

............(4)

............(4)

Where I ₁ = reference beam intensity, I ₂ = measurement beam intensity, R ₁ = intensity ratio of the first reflected beam in the high interference beam splitter, R ₂ = intensity ratio of the second reflected beam in the high interference beam splitter, T ₁ = intensity ratio of the first transmitted beam in the high interference beam splitter, and T ₂ = intensity ratio of the second transmitted beam in the high interference beam splitter.

Assuming that the intensity ratio of the reference beam and the measurement beam does not change during the measurement,

.............................................................(5)

........................................ ........... (5)

The optical path difference? L can be inversely calculated from the measured data using the above-described (4) and (5).

............(6)

............ (6)

From the thus obtained DELTA L, L is obtained by using a finite difference method or the like in the x-axis direction with respect to each y in the above-mentioned relation (3). Assuming the axisymmetricity of the plasma density, N can be obtained by a method such as abel inversion.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a diagram illustrating a conventional transverse stripline interferometer system.

2 shows a plasma density analysis system of the present invention.

Figure 3 is a view comparing the size of the reflected beam of the 50% beam splitter and the high interference beam splitter according to the present invention.

4 is a view showing the optical path of a measurement beam having plasma density information according to the present invention.

5 is a view showing a process of generating an interference fringe for a density distribution of a plasma according to the present invention.

* Description of Signs of Main Parts of Drawings *

100: light source

200: beam amplifier

250 mirror

300: light path guide

400: 50% beam splitter

500: plasma density analysis unit

510: first measuring instrument

520: second measuring instrument

530: third measuring instrument

Claims (10)

A light source unit emitting a laser beam; A beam amplifier for sequentially amplifying the emitted laser beam so as to be included in the plasma forming space; An optical path guide unit that reflects or transmits the laser beam having the plasma density information through the plasma forming space; And a plasma density distribution analyzer configured to acquire the interference information of the reflected laser beam and the beam intensity information of the transmitted laser beam to calculate the plasma density distribution. The beam amplification unit includes a first beam amplification unit for amplifying the laser beam emitted from the light source unit to a first width so as to be processed by the optical path guide unit, and a second beam amplification unit for amplifying the laser beam amplified by the first width, And a second beam amplifying unit configured to amplify a second width which is amplified by a predetermined width rather than the first width. delete The method of claim 1, The optical path guide portion Wherein the plasma density analyzer is a high-interference beam splitter that reflects or transmits a laser beam having the plasma density information. The method of claim 3, wherein The system And a 50% beam splitter is provided between the first beam amplification unit and the second beam amplification unit. The method of claim 4, wherein The system And a mirror that reflects the laser beam having the plasma density information and directs it to the 50% beam splitter. The method of claim 5, Wherein the laser beam having the plasma density information reflected from the mirror is reduced to a constant width in the second beam amplifying part before being guided to the 50% beam splitter. The method of claim 6, Wherein the 50% beam splitter transmits the emitted laser beam to the mirror side and guides the laser beam reflected on the mirror to the optical path guide. The method of claim 7, wherein The plasma formation space is And the second beam amplifying unit is located between the second beam amplifying unit and the mirror. The method of claim 3, wherein Wherein the plasma density distribution analyzer comprises a reference meter, a first meter, a second meter, and a controller, The reference meter measures reference beam intensity information of the laser beam emitted from the light source unit, Wherein the first measuring unit measures interference information having a light path difference of the laser beam having the reflected plasma density information, Wherein the second measuring device measures the measurement beam intensity information of the laser beam having the transmitted plasma density information, And the controller analyzes the plasma density control distribution using the reference beam intensity information, the interference information, and the measured beam intensity information. The method of claim 9, (X, y), which is a refractive index of the plasma, L (x, y), and L (x, y) of the optical path are defined in advance, and the ratio of the ratio of the reference beam intensity information to the ratio Wherein the density of the plasma is defined as being radially symmetrical, remind

ego, remind

ego, remind

ego, The L (x, y) is obtained by finely differencing the DELTA L (x, y) in the x-axis direction with respect to each y, And the plasma density is obtained by using the obtained L (x, y) as an abelian version method in the x-axis direction for each y.

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