KR100867632B1 - System for Measuring Density of Fine Particles Using Multi-pass Laser Light Extinction - Google Patents

Abstract

The present invention relates to a density measurement system of fine particles using a multi-pass laser light extinction, which is a laser beam generating mechanism for generating a laser beam to be incident into a chamber in which fine particles to be measured are present. ; A beam splitter for separating the laser beam radiated from the laser beam generating device into two laser beams that have different paths so as to separately measure the intensity of the incident light and the transmitted light; A multiple optical path generating mechanism for generating multiple optical paths while transmitting the particles of particles in the chamber so that a laser beam of one path separated from the beam splitter is incident to measure the intensity of transmitted light; A first detector for detecting an electrical signal from the laser beam separated by the beam splitter; A second detector for detecting an electrical signal from the laser beam emitted from the multiple optical path generation mechanism; Amplification means for amplifying the electrical signals from the first and second detectors; And a controller for comparing the applied electric signals to detect a difference between the two amplified signals and calculating the density of the fine particles based on the difference.

Microparticles, Density, Deposition, Semiconductors, Multiple Light Paths, Lambert-Beered, Spherical Mirrors

Description

System for Measuring Density of Fine Particles Using Multi-pass Laser Light Extinction}

1 is a schematic diagram schematically showing a system for measuring the density of microparticles using a multiple optical path laser light attenuation method according to the present invention;

2 is a view showing a multiple light path generating means used in the present invention,

3 (a), (b) is a photograph showing a multiple light path implemented according to the present invention,

4 is a graph showing the light attenuation signal, the number of optical paths, and the attenuation rate obtained in the plasma including the particle particles, (a) shows a single optical path, and (b) shows a nine optical path.

<Explanation of symbols for the main parts of the drawings>

5: Iris 6: Pinhole aperture

10: laser generating mechanism 20: filter

30: Mirror 40: Beam splitter

50: detector 60: plasma chamber

70: first amplifying means 80: second amplifying means

90: optical modulator 100: control unit

200: multiple light path generating mechanism 210, 220: spherical mirror

215: laser beam entrance 225: laser beam exit

230: laser beam path

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical diagnostic system for diagnosing the density of particles present in various process plasmas using plasma, and more particularly, in a process plasma using multi-pass laser light extinction. The present invention relates to a system for measuring the density of fine particles using a multiple optical path laser light attenuation which can diagnose in real time the density of particles having various sizes ranging from nm to μm and minimize the defect rate.

Currently, the cleanliness of the external environment required for semiconductor processing is class-10 (10 particles of 0.5 μm per 1 ft ³ ). However, even if the cleanliness of the external environment is ensured, particles of various sizes ranging from several nm to hundreds of micrometers, which occur during various processes such as etching, deposition, etc., not only reduce the cleanliness in the process vessel, but the fine particles have almost the same size during the process. Sticking on a circuit with a line width of the circuit damages the circuit and causes a serious yield drop. Therefore, monitoring of these fine particles is essential in the process.

In addition, the production of fine particles of less than 10nm and research using them are also in progress. Research results have been reported to change the optical properties of the film or to impart optical stability by depositing the first 10nm or less of the fine particles generated during a-Si: H photovoltaics or thin film transistor process on the film. In addition, the possibility of using Si particles of 10 nm or less as a material to replace polysilicon, which is currently used as a floating gate (FG) in a next generation flash memory process, is emerging. In order to control these particles, measurement of the size and density of the particles must first be carried out.

In general semiconductor equipment, various types of filters are used to block particles that may enter the semiconductor equipment. Particle diagnosis is a method of measuring particles using bare wafers and wafer surface scanning equipment or sampling and inspecting wafers that are actually produced. In general, since particles tend to increase in density at a certain point (sputtering of the chamber wall, leaving of the polymer, etc.) and tend to be maintained continuously afterwards, the conventional method has failed after the last particle inspection. There is a problem that the occurrence of defects in the manufactured wafers between the inspection time points when they are exceeded) can not be prevented. These particles eventually act as a major factor in drastically lowering the productivity of semiconductor devices.

Therefore, a diagnostic method for diagnosing particles after such a process is limited, and a diagnostic system for diagnosing particles in real time is required. Optical diagnostic methods are suitable for such real-time monitoring, and the laser light attenuation method proposed in the present invention is particularly suitable for diagnosing the density of particles. In practice, the single optical path light attenuation method has been mainly considered in the implementation of this measurement due to the simple configuration of the device. The most important point in determining the density of a particle is to lower its measurement limits. The simplest method of laser light attenuation is a single optical path in which a laser is incident on a plasma containing particle particles in a single optical path. The main advantage of this device is that the hardware configuration is relatively simple and the alignment of the optical system is not very demanding, but the measurement sensitivity is not so high that for 20-100 nm particles, the density is measurable more than 10 ¹⁰ cm ^-3 . High side. However, in the conventional single optical path light attenuation method, the measurement limit of the particle density measurement is not good because the number of optical paths is small, and the measurement limit of the particle density is relatively high, so that it cannot be usefully used when the density is small.

Therefore, the present inventors have improved sensitivity in proportion to the number of paths of the laser beam in the case of the multiple optical path system in which the optical path number is multiple, so that the multiple optical path attenuation method satisfies the requirements for the particle size and density of the region of interest. It can be realized that if it can be implemented to have a very useful particle diagnostic method.

The present invention has been made to improve the disadvantages of the prior art as described above, the object of the present invention is to provide a density measurement system of the particle particle applying a multi-path laser light attenuation method to increase the measurement sensitivity to greatly increase the minimum measurable density. .

In addition, another object of the present invention is to provide a system for measuring the density of microparticles capable of monitoring the particles of particles over time from the initial plasma in a situation where particles of particles occur in the plasma chamber.

Density measurement system of the microparticles using the multi-path optical attenuation according to the present invention for achieving the above object, the laser beam generating mechanism for generating a laser beam to be incident to the chamber in which the fine particles to be measured density;

A beam splitter for separating the laser beam radiated from the laser beam generating device into two laser beams that have different paths so as to separately measure the intensity of the incident light and the transmitted light;

A multiple optical path generating mechanism generating multiple optical paths while transmitting dust particles inside the chamber so that the laser beam of one path separated from the beam splitter is incident to measure the intensity of transmitted light;

A first detector for detecting an electrical signal from the laser beam separated by the beam splitter;

A second detector for detecting an electrical signal from the laser beam emitted from the multiple optical path generation mechanism;

Amplification means for amplifying the electrical signals from the first and second detectors; And

Comprising a control unit for comparing the electrical signal applied from the amplifying means detects the difference between the two amplified signal and calculates the density of the fine particles based on this.

The above objects, features and advantages of the present invention will be more readily understood from the following detailed description taken in conjunction with the accompanying drawings which illustrate preferred embodiments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a density measurement system of microparticles using multipath laser light attenuation according to the present invention will be described with reference to the accompanying drawings showing preferred embodiments.

First of all, the principle of laser light attenuation is to quantitatively determine the density of scatterers included in a medium by measuring how much the light intensity decreases while the light incident on the medium passes through the medium. It is a way. If the intensity of the incident light is I ₀ and the intensity of the transmitted light is I ₁ , the intensity of the lost light can be expressed by Equation 1 according to Lambert-Beer's law.

[Equation 1]

ΔI = I ₀ -I ₁ = I ₀ [1-exp (-nσ _ex ℓ)]

Where s _ex is the attenuation cross-sectional area, n is the particle density, and l is the total optical path length. Normally, nσ _ex ℓ is much smaller than 1, so the damping ratio can be simply expressed as ΔI / I ₀ = nσ _ex ℓ. [sigma _ex] can be theoretically obtained from the particle size, and [l] is the total optical path length through which the laser can pass through the naked eye or observation using a detector such as a CCD. The density (n) of the particles can be obtained by measuring the intensity reduction ratio of the laser beam passing through the particles after the amount is obtained.

Single-path attenuation is a method of measuring the amount of attenuation of the laser intensity after the laser passes through the particle once. Using Lambda-Beer's equation, it is possible to reduce the limit of measurement of density in proportion to the number of paths, i.e., to measure lower particle density, compared to a single optical path. You can easily expect it.

In the present invention, multiple light paths are implemented using two spherical mirrors. Spherical mirrors can be designed to optimize the number of optical paths to best fit the chamber structure and maintain the size of the laser beam.

1 illustrates a fine particle density measurement system using multipath laser light attenuation according to the present invention.

Referring to FIG. 1, first, a laser beam emitted from the laser generator 10 is passed through basic optical components such as the filter 20a, the mirrors 30a and 30b, and the filter 20a is a neutral concentration filter. density filter, which reduces the transmission to about the same amount for each wavelength within a specific wavelength range so as not to affect the color balance. The laser may be a low power laser such as a diode laser or a HeNe laser.

The laser beam passing through this basic optical component is then divided into two laser beams that cross the path in a beam splitter (also called a beam sampler) 40. One of the laser beams separated from the beam splitter 40 directly enters a detector 50a such as a photoelectric diode, and the other laser beam passes through the plasma chamber 60 in which the microparticles are generated and another detector 50b. Is configured to enter As the detectors 50a and 50b, a photodiode, a photomultiplier tube, a charge coupled device (CCD), or the like can be used.

As such, after directly entering the detector 50a or passing through the multiple optical path realization mechanism 200, after entering the detector 50b, the current signals from each of the detectors 50a and 50b are first amplified first. The gain is adjusted as it is converted into a voltage signal while passing through the means 70, wherein the amplification means mainly used is an operational amplifier (Op-Amp).

The amplified voltage signal from the first amplifying means 70 is then input to the second amplifying means 80 to recover the signal from noise and to obtain only the desired signal. As the second amplifying means, LIA (Lock-In-) Amplifier is mainly used.

Next, the amplified signals from the second amplifying means 80 are input to the control unit 100 to measure the difference between the two amplified signals and convert them therefrom into the density of the fine particles. Therefore, the control unit 100 has a program built in so as to detect the density of the fine particles in terms of data on the intensity of incident light and transmitted light.

In Fig. 1, the irises 5a and 5b installed between the mirror 30b and the beam splitter 40 and on the optical path on the exit side of the plasma chamber 60 are elements for controlling the amount of beams to be transmitted. The pinhole aperture 6 provided between the iris 5b and the detector 50b is an element for limiting the out-of-focus beam, and the reference numeral 90 denotes a beam splitter as an optical chopper. It is branched from the rear beam path and installed between the second amplifying means 80, which is an auxiliary element for synchronization of the second amplifying means 80 which is LIA.

As shown in the schematic diagram of FIG. 2, the multiple optical paths are implemented using a pair of facing concave spherical mirrors 210 and 220 arranged at a predetermined distance as the multiple optical path realization mechanism 200 installed in the plasma chamber 60 of the semiconductor process. Implement The spherical mirror 210 forms the laser beam inlet 215 through the hole at the end of the mirror, and the spherical mirror 220 is formed with the laser beam outlet 225 through the other hole at the end of the mirror. The laser beam entering the spherical mirror 210 through the laser beam inlet 215 is repeatedly reflected on a single plane by the spherical mirror 220 to form a plurality of optical paths 230 and then a spherical mirror ( It exits through the laser beam outlet 225 formed at 220 and passes through the plasma chamber 60 to enter the detector 50b.

The reason for using the spherical mirrors 210 and 220 in this embodiment is to maintain the beam size because the size of the laser beam increases as the number of reflections of the beam increases. If the radius of curvature of the spherical mirror 210 is too small, the number of reflections of the laser beam is significantly reduced even if the beam size is maintained. Therefore, a spherical mirror having a large radius of curvature should be used.

As an example, in an optical system having two mirrors having a reflectance of 99% and a radius of curvature of 8 m at intervals of 390 mm, the total number of optical paths can be obtained 32 times while maintaining the size of the laser beam. The distance between the radius of curvature of the spherical mirror and the spherical mirror can be changed according to the purpose of the present measurement method, Figure 3 (a) (b) shows an example of the multiple light path implemented.

Therefore, the density measurement system of the microparticles using the multiple optical path light attenuation according to the present invention configured as described above operates as follows.

That is, as can be seen from FIG. 1, for example, a HeNe laser beam of 632.8 nm emitted from the laser beam generator 10 is incident to the first mirror 30a via the first filter 20a and here The direction is changed and is incident on the second mirror 30b, and the reflected laser beam is incident on the beam splitter 40 through the iris 5a.

At this time, a part of the laser beam is branched to enter the light modulator 90.

Subsequently, the laser beam of the first path separated from the beam splitter 40 enters the first detector 50a through the second filter 20b to detect an electrical signal at the intensity of the incident light. It is input to the first amplification means 70.

On the other hand, the laser beam of the second path separated from the beam splitter 40 enters into the chamber 60 for plasma deposition of the semiconductor wafer and passes through the built-in spherical mirrors 210 and 220 in this embodiment. The intensity of the laser beam is reduced to generate an optical path of the light beam and to measure the intensity of the transmitted light, and then enters the second detector 50b via the iris 5b and the pinhole aperture 6, where An electrical signal indicating strength is detected.

Next, the electrical signal representing the intensity of the transmitted light from the second detector 50b is amplified and input to the controller 100 through the amplifying means 70 and 80, and the electrical signal representing the intensity of the incident light is output from the controller 100. Compared to the signal to detect the difference and based on this it is possible to measure the density of the particle particles through the calculation process according to equation (1) to measure the density of the microparticles in the chamber.

Table 1 below summarizes the minimum measurable value of particle density according to the number of optical paths, and shows the advantages of multiple optical paths. Multi-path laser attenuation will enable the diagnosis and measurement of small density or small size microparticles in semiconductor deposition or etching processes.

Fine particle density n _d (cm ^-3 ) Measurable density 20 nm (cm ^-3 ) Measurable density 50nm (cm ^-3 ) Measurable density 100nm (cm ^-3 ) Single light 4.3 x 10 ¹² 8.7 x 10 ¹⁰ 1.9 x 10 ¹⁰ 9 light path 4.8 x 10 ¹¹ 9.6 x 10 ⁹ 2.1 x 10 ⁹ 17 light path 2.5 x 10 ¹¹ 5.1 x 10 ⁹ 1.1 x 10 ⁹ 35 light path 1.2 x 10 ¹¹ 2.4 x 10 ⁹ 5.5 x 10 ⁸ 140 Medium Light Path 3.0 x 10 ¹⁰ 6.0 x 10 ⁸ 1.4 x 10 ⁸

In addition, when the multi-optical optical system proposed in the present invention is applied to the reactive plasma, it can be represented as shown in FIG. 4, where (a) represents a single optical path and (b) represents a nine-light optical path, the same from Lambert-Beer's law. In the case of conditions, as the number of light paths increases, the light attenuation rate can be expected to increase proportionally. In FIG. 4, the light attenuation rate is 2.4%, and in the case of the ninth light path, the light attenuation is generally proportional to the number of optical paths, and it can be seen that density measurement can be performed about 10 times lower than that of the single light path.

Therefore, when the number of optical paths increases, it is possible to measure an optical attenuation signal that is difficult to measure when the number of optical paths is small, thereby making it easy to measure the density even when the particle density is low.

In the multiple optical path light attenuation method described in the present invention, the measurement limit is improved in proportion to the number of optical paths, so that low density measurement can be performed. Therefore, applying the subject matter of the present invention, it is also possible to monitor the particle particles with time from the initial plasma in the situation where the particles are generated in the plasma chamber.

In addition, dust particles are composed of various sizes ranging from several nm to hundreds of micrometers generated during etching or deposition, causing serious yield reduction during the process, and the semiconductor industry is highly profitable depending on production yield. In consideration of this, the plasma diagnostic technology associated with such particles is expected to increase the industrial requirements, and the density measurement method of the particles shown in the present invention is a diagnostic system capable of real-time diagnosis of the density of particles generated in the process It has great meaning as development.

As described above, in the present invention, the optical system is added but relatively simple compared to the case of the single optical path light attenuation method, and the density measurement of the low particle is possible because the limit of density measurement is improved in proportion to the longer optical path.

As described above, the present invention has been described in detail with reference to specific embodiments, but the present invention is not limited to the above embodiments and various modifications can be made by those skilled in the art within the scope of the technical idea of the present invention. Of course it is. That is, in the above embodiment, the density measurement system of the fine particles and the measurement method according to the present invention, for example, the plasma chamber in which the deposition process is performed, but the measurement method according to the present invention is applied to the sputtering equipment or the etching equipment in addition to the deposition process equipment. Of course, it can be applied.

Claims (8)

A laser beam generating mechanism (10) for generating a laser beam to be incident into a chamber in which fine particles to be measured are present; A beam splitter (40) for separating the laser beam emitted from the laser beam generating mechanism into two laser beams having different paths so that the intensity of incident light and transmitted light can be measured separately; The laser beam of one path separated from the beam splitter is incident to the plasma chamber 60 to transmit multiple dust particles inside the chamber to measure the intensity of the transmitted light and to generate multiple optical paths, respectively. A multiple optical path generating mechanism (200) having spherical mirrors (210, 220) formed at inlet and outlet holes and spaced apart from each other to face each other; A first detector (50a) for detecting an electrical signal from the laser beam separated by the beam splitter; A second detector (50b) for detecting an electrical signal from the laser beam emitted from the multiple optical path generating mechanism (200); First amplifying means (70) which is an operational amplifier whose gain is adjusted while converting the current signal from the detectors (50a, 50b) into a voltage signal; Second amplifying means (80) which is an LIA recovering the voltage signal from the first amplifying means (70) and obtaining only a desired signal; And Comparing the electric signal applied from the amplifying means to detect the difference between the two signals and based on the control unit 100 for calculating the density of the fine particles, characterized in that the micro-particles using the multiple optical path laser light attenuation Density measurement system. delete delete delete 2. The system of claim 1, wherein the laser beam generator (10) generates a low power laser comprising a HeNe laser. The system of claim 1, wherein a photodiode, a photomultiplier tube, or a CCD is used as the detector. delete delete

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