KR20180133151A - Low-pressure plasma reactor for the increase in abatement efficiency of pollutions - Google Patents

Abstract

Disclosed is a low-pressure plasma reactor for improving a contaminant removal rate. The low pressure plasma reactor includes an insulator, a first ground electrode, a high voltage electrode, a second ground electrode, and a magnetic field generator. The insulator has a tubular shape through which the process gas passes, and the first ground electrode has a tubular shape connecting the insulator and the vacuum pump. The high voltage electrode is located on the outer surface of the insulator at a distance from the first ground electrode, and is connected to an AC power source to receive the driving voltage. The second ground electrode is located inside the first ground electrode, and a magnetic field generating unit is installed outside the first ground electrode to apply a magnetic field around the second ground electrode.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a low-pressure plasma reactor for improving a pollutant removal rate,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-pressure plasma reactor, and more particularly, to a low-pressure plasma reactor for improving pollutant removal rate using capacitively coupled plasma (CCP).

In the manufacturing line of semiconductors, displays, and solar cells, a process chamber in which etching, deposition, and cleaning are performed is installed, and the process chamber is connected to a vacuum pump to discharge the process gas. There are various pollutants in the process gas. For example, in the etching process, greenhouse gases such as CF ₄ , CHF ₃ , C ₂ F ₆ and C ₄ F ₈ are discharged. In the deposition process, the undecomposed precursor is discharged. In the process, greenhouse gases such as NF ₃ and SF ₆ and particles by-products are discharged.

GHGs are substances that cause global warming, and emission regulations are getting worse, and particulate by-products accumulate inside the vacuum pump, which lowers the durability of the vacuum pump. Undegraded precursors that are not used for deposition accumulate inside the vacuum pump or between the vacuum pump and the scrubber, which can cause an explosion when over-expanded and can cause a fire if exposed to the atmosphere.

The present invention provides a low-pressure plasma reactor capable of generating a high-density plasma and raising a decomposition rate of contaminants by 100% in a stabilization treatment technique for decomposing and removing contaminants using plasma at the front end of the vacuum pump.

A low pressure plasma reactor according to an embodiment of the present invention includes an insulator, a first ground electrode, a high voltage electrode, a second ground electrode, and a magnetic field generator. The insulator is tubular through which the process gas passes. The first ground electrode is of a tubular shape connecting the insulator and the vacuum pump. The high voltage electrode is located on the outer surface of the insulator at a distance from the first ground electrode, and is connected to the AC power source to receive the driving voltage. The second grounding electrode is located within the first grounding electrode and includes an opposing portion that faces the inner center of the insulator along the transfer direction of the process gas. The magnetic field generator is installed outside the first ground electrode to apply a magnetic field around the second ground electrode.

The first ground electrode may include a first portion connected to the rear end of the insulator and a second portion connected to the rear end of the first portion. The diameter of the first portion may be greater than the diameter of the insulator and the diameter of the second portion.

The opposing portion may be located within the first portion at a distance from the inner wall of the first portion and at least two supports may be located between the opposing portion and the inner wall of the first portion. The magnetic field generating part may be installed so as to surround the second part on the outer side of the second part.

According to the present invention, the magnetic field generating section applies a strong magnetic field inside the ground electrode, and the magnetic field increases the density of the plasma in the positive pulse section which is disadvantageous to the pollutant decomposition. Therefore, the low-pressure plasma reactor can obtain a high-density plasma in the positive pulse section by the magnetic field applied to the ground electrode, and can increase the decomposition rate of contaminants.

1 is a configuration diagram of a process facility including a low-pressure plasma reactor according to an embodiment of the present invention.
2 is a cross-sectional view of a low pressure plasma reactor according to one embodiment of the present invention.
FIG. 3 is a left side view of a second ground electrode of the low-pressure plasma reactor shown in FIG. 2. FIG.
FIG. 4 is a schematic view showing an operating state of the low-pressure plasma reactor shown in FIG. 2. FIG.
FIG. 5 is a graph showing current-voltage characteristics of the low-pressure plasma reactor shown in FIG. 2. FIG.
6 is a view showing a discharge image obtained in the negative pulse section shown in FIG.
7 is a diagram showing a discharge image obtained in the positive pulse section shown in Fig.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings, which will be readily apparent to those skilled in the art to which the present invention pertains. The present invention may be embodied in many different forms and is not limited to the embodiments described herein.

1 is a configuration diagram of a process facility including a low-pressure plasma reactor according to an embodiment of the present invention. The process equipment of FIG. 1 may be a low-pressure process equipment such as semiconductor, display, and solar cell.

1, the process facility 100 includes a process chamber 11 in which operations such as etching, deposition, or cleaning are performed, and a process gas 11 connected to the process chamber 11 to process the process gas used in the process chamber 11 And a low pressure plasma reactor 210 provided between the process chamber 11 and the vacuum pump 12.

The low pressure plasma reactor 210 is a piping connecting the process chamber 11 and the vacuum pump 12 and is an eco-friendly device for removing contaminants in the process gas. The low pressure plasma reactor 210 is located in front of the vacuum pump 12 and maintains a low pressure state, such as the process chamber 11. Here, the low pressure means a pressure falling within a range of about 0.1 Torr to 10 Torr, but is not limited to the above range.

A reaction gas inlet 13 may be connected to a pipe between the process chamber 11 and the low pressure plasma reactor 210. The reaction gas may include at least one of O ₂ and H ₂ O and may be injected into the pipe together with a carrier gas such as argon (Ar), helium (He), nitrogen (N ₂ ) have.

The low-pressure plasma reactor 210 generates a plasma therein to decompose various pollutants (greenhouse gases, non-decomposed precursors, particle by-products, etc.) contained in the process gas. The decomposed components chemically bond with the reaction gas and become harmless elements. Because the plasma enriches the reactive species and the high energy electrons, it accelerates the chemical reaction between the decomposed components of the contaminants and the reactive gas.

The low pressure plasma generator 210 described below has the characteristic of generating a capacitively coupled plasma (CCP) and increasing the decomposition rate of contaminants by generating a high density plasma in the positive pulse section using a magnetic field.

FIG. 2 is a cross-sectional view of a low-pressure plasma reactor according to an embodiment of the present invention, and FIG. 3 is a left side view of a second ground electrode of the low-pressure plasma reactor shown in FIG.

2 and 3, the low-pressure plasma reactor 210 includes a tubular insulator 20 through which a process gas flows, a tubular first ground electrode 31 connecting the insulator 20 and the vacuum pump 12, A high voltage electrode 40 located on the outer surface of the insulator 20, a plate-shaped second ground electrode 32 located inside the first ground electrode 31, And a magnetic field generator 50 provided in the magnetic field generator 50.

The insulator 20 may be formed into a cylindrical shape having a predetermined diameter, and may be made of alumina, glass, quartz, or the like. One end of the insulator 20 may be sealed with a transparent plate 21 and a gas injection port 22 may be positioned at a front end of the high voltage electrode 40 in the body of the insulator 20. [ The process gas mixed with the reaction gas is injected into the insulator 20 through the gas inlet 22.

An ICCD (Intensified Charged Coupled Device) 60 (see FIG. 1) for photographing a discharge image inside the insulator 20 is provided on the outer side of the transparent plate 21 Can be located.

The first ground electrode 31 is a grounded metal pipe connecting the insulator 20 and the vacuum pump 12 and may include at least two portions having different diameters. For example, the first ground electrode 31 may include a first portion 31a, a second portion 31b, and a third portion 31c that are successively arranged along the flow direction of the process gas.

The diameter of the first portion 31a may be larger than the diameter of the insulator 20 and the diameter of the second portion 31b and the diameter of the second portion 31b may be equal to the diameter of the insulator 20. [ The second portion 31b may be formed longer than the first portion 31a. The process gas can be deflected at a right angle in the flow direction while passing through the third portion 31c.

The high voltage electrode 40 is a cylindrical electrode that surrounds the insulator 20 one turn and is connected to the AC power source unit 45 to receive a driving voltage. The high voltage electrode 40 is formed to have a length smaller than that of the insulator 20 and is spaced apart from the gas inlet 22 and the first ground electrode 31a by a predetermined distance.

The driving voltage Vs applied to the high voltage electrode 40 may have a magnitude of several kV and a frequency of several kHz to several hundreds of kHz and the operation voltage may have a positive value of 1/2 Vs and a negative value of -1 / 2Vs) may be implemented in a periodically varying pulse form. The driving voltage Vs may have a pulse waveform of any one of a triangular waveform, a sine waveform, and a square waveform.

The second ground electrode 32 is located within the first ground electrode 31 and includes an opposing portion 32a that faces the inner center of the insulator 20 along the direction of feed of the process gas. Specifically, the second grounding electrode 32 includes a disc-like counter portion 32a located inside the first portion 31a, and at least a second ground electrode 32a connecting the counter portion 32a and the inner wall of the first portion 31a. And includes two support portions 32b.

The opposing portion 32a is installed across the discharge path of the process gas and is fixed to the inner wall of the first portion 31a by the support portion 32b and is energized with the first ground electrode 31 while maintaining the predetermined position . The opposing portion 32a is spaced from the end portion of the insulator 20 and the second portion 31b and is formed with a diameter larger than the diameter of the insulator 20. [ The process gas impinging on the opposed portion 32a is discharged to the second portion 31b through the space between the opposed portion 32a and the first portion 31a.

The first portion 31a surrounding the opposing portion 32a is the portion having the largest diameter among the first ground electrodes 31 while contacting the end portion of the insulator 20 and therefore the opposing portion 32a has the first portion 31a The diameter of the insulator 20 may be larger than the diameter of the insulator 20. [

The magnetic field generating unit 50 is provided outside the first ground electrode 31 and applies a magnetic field around the second ground electrode 32. The magnetic field generating unit 50 may be installed in a manner to surround the second portion 31b of the first ground electrode 31 by one turn and may be composed of a solenoid or a permanent magnet connected to a power source.

FIG. 4 is a schematic view showing an operating state of the low-pressure plasma reactor shown in FIG. 2. FIG.

4, when an AC driving voltage is applied to the high voltage electrode 40, a voltage difference between the high voltage electrode 40 and the first and second ground electrodes 31, A sintered plasma (CCP) discharge is induced. The plasma repeats the generation, maintenance, and extinction processes while the applied voltage is maintained, and remains in the glow region without being transferred to the arc, thereby removing contaminants discharged from the process chamber.

In this process, the opposing portion 32a of the second grounding electrode 32 faces the inner center of the insulator 20 along the transfer direction of the process gas. Therefore, the high-voltage electrode 40 and the opposing portion 32a Plasma is generated. That is, strong plasma is generated on one side of the facing portion 32a facing the insulator 20.

Within the low pressure plasma reactor 210, the plasma includes a sheath region A10 and a positive column region A20. The sheath region A10 is located between the positive photoresist region A20 and the inner surface of the low pressure plasma reactor 210. [ Since most of the power is consumed in the sheath area A10, the decomposition rate of contaminants in the sheath area A10 is higher than that in the positive light area A20.

As the internal pressure of the low-pressure plasma reactor 210 increases, the sheath area A10 becomes smaller and the light-incident area A20 expands. In the structure of the low-pressure plasma reactor without the opposed portion, the higher photoresist region A20 may be enlarged and the decomposition rate of the contaminant may be lowered. In this case, contaminants passing through the center of the low-pressure plasma reactor can be directly introduced into the vacuum pump without decomposition.

However, in the low-pressure plasma reactor 210 of the first embodiment, the sheath region A10 is formed at one side of the opposing portion 32a facing the insulator 20. Accordingly, contaminants that have not completely decomposed while passing through the center of the low-pressure plasma reactor 210 are completely decomposed while passing through the sheath region A10 on one side of the opposing portion 32a.

As a result, the low-pressure plasma reactor 210 of the first embodiment can increase the decomposition rate of contaminants at high pressure and can exhibit high decomposition performance over a wider pressure range by lowering the pressure dependency of the contaminant decomposition rate.

Further, the magnetic field generating section 50 applies a strong magnetic field to the rear of the opposing section 32a. When a strong magnetic field is applied from the outside to the inside of the first ground electrode 31, the electrons rotate about the magnetic field. As a result, the electron loss to the inner wall of the first ground electrode 31 is reduced, and the number of collision with the neutral gas increases, and a high-density plasma can be obtained.

FIG. 5 is a graph showing current-voltage characteristics of the low-pressure plasma reactor shown in FIG. 2. FIG. In Fig. 5, the frequency of the driving voltage applied to the high voltage electrode is 80 kHz (period of 12.5 mu s).

Referring to FIG. 5, the discharge current shows the characteristic of a typical capacitive coupled plasma (CCP) followed by a predetermined phase difference relative to the applied voltage.

The discharge that occurs when the high voltage electrode has a positive polarity is referred to as a positive pulse and the discharge that occurs when the high voltage electrode has a negative polarity is referred to as a negative pulse. In the positive pulse, the high voltage electrode becomes an anode, and in the negative pulse, the high voltage electrode 40 becomes a cathode.

FIG. 6 is a view showing a discharge image obtained in the negative pulse section shown in FIG. 5, and FIG. 7 is a view showing a discharge image obtained in the positive pulse section shown in FIG.

The internal pressure of the low pressure plasma reactor used in the experiment was 0.5 Torr, and the discharge image was measured using ICCD installed outside the transparent plate. Specifically, the discharge image was measured by synchronizing the trigger pulse and the applied voltage at a time interval of 0.2 μs.

Referring to FIGS. 6 and 7, it can be seen that as the applied voltage increases in both the negative and positive pulses, the discharge intensity becomes stronger and weaker again. In the negative pulse, the plasma intensity shows the maximum value at 1.6 μs, and the plasma intensity at the positive pulse shows the maximum value at 7.6 μs.

As shown in Figs. 6 and 7, the discharge intensity of the negative pulse is higher than the discharge intensity of the positive pulse, and the discharge sustaining period (approximately 5.0 mu s) of the negative pulse is longer than the discharge sustaining period of the positive pulse (approximately 3.0 mu s). This result is due to the DC self-bias voltage being formed on the high voltage electrode.

The thickness of the sheath region in capacitively coupled plasma (CCP) is inversely proportional to plasma density and operating pressure. And, when two electrodes (high voltage electrode and ground electrode) causing plasma discharge have different areas, a DC bias voltage occurs across the sheath region, which is referred to as a DC self-bias voltage.

The area of the high-voltage electrode 40 in the low-pressure plasma reactor 210 of the first embodiment is smaller than the area of the first grounding electrode 31 functioning as a pipe. The DC self-bias voltage is higher in the high-voltage electrode 40 having a small area, so that the discharge strength is strong and the discharge is sustained when the high-voltage electrode 40 is a cathode.

The magnetic field generator 50 applies a strong magnetic field inside the first ground electrode 31, not around the high voltage electrode 40, and the magnetic field increases the density of the plasma in the positive pulse section which is disadvantageous to the pollutant decomposition. That is, the high-density plasma can be obtained in the positive pulse section by the magnetic field applied to the first ground electrode 31, and the decomposition rate of the pollutant can be increased.

On the other hand, the improvement of the degradation rate of the pollutant by the magnetic field generator 50 can be effective in a pressure range of about 0.3 Torr or more. At pressures below about 0.3 Torr, the residence time of the process gas passing through the plasma is reduced and the plasma tends to be shortened in the longitudinal direction, so that the effect of applying the magnetic field may be limited.

Table 1 below shows the decomposition rates of nitrogen dioxide (N ₂ O) measured in the low pressure plasma reactor of the comparative example without the magnetic field generator and the low pressure plasma reactor of the embodiment. The comparative example has the same configuration as the low-pressure plasma reactor of the embodiment except that there is no magnetic field generator.

The flow rate of N ₂ O used in the experiment is 500 sccm, the plasma output is 1.4 kW, and the output of the solenoid constituting the magnetic field generating portion is 225 W (15 A, 17 V).

0.2 Torr 0.3 Torr 0.4 Torr 0.5 Torr Comparative Example 98.08 98.12 98.13 98.10 Example 98.06 99.15 99.46 99.65

As shown in Table 1, it can be seen that the N ₂ O decomposition rate of the low pressure plasma reactor according to the embodiment having the magnetic field generator is higher than the N ₂ O decomposition rate of the comparative example in the pressure range of 0.3 Torr or more.

In addition, the decomposition ratios of carbon tetrafluoride (CF ₄ ) measured in the low pressure plasma reactor of the comparative example and the low pressure plasma reactor of the embodiment are shown in Table 2 below. The comparative example has the same configuration as the low-pressure plasma reactor of the embodiment except that there is no magnetic field generator.

The flow rate of CF ₄ used in the experiment was 50 sccm, and the flow rate of H ₂ O added as the reaction gas was 100 sccm. The plasma output is 1.4 kW, and the output of the solenoid constituting the magnetic field generator is 225 W (15 A, 17 V).

0.2 Torr 0.3 Torr 0.4 Torr 0.5 Torr Comparative Example 95.12 95.80 96.12 96.10 Example 95.06 97.43 98.62 99.14

As shown in Table 2, the decomposition rate of CF ₄ in the low pressure plasma reactor according to one embodiment includes a magnetic field generating section is higher than the comparative example confirmed that CF ₄ at a pressure range above 0.3Torr decomposition rate.

As the internal pressure of the low pressure plasma reactor increases, both the gas density and the plasma density increase. Magnetic field generation increases the plasma density without increasing the gas density because it helps the rotation of electrons and ions. Therefore, in Table 1 and Table 2, the improvement of the degradation rate of pollutants by magnetic field generation becomes more apparent as the plasma density increases, that is, as the pressure increases.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, Of course.

100: Process equipment 11: Process chamber
12: Vacuum pump 210: Low pressure plasma reactor
20: insulator 30: ground electrode
31: first ground electrode 32: second ground electrode
32a: opposing portion 40: high voltage electrode
45: AC power supply unit 50:

Claims (4)

A low pressure plasma reactor installed in a discharge path of a process gas from a process chamber toward a vacuum pump to remove contaminants contained in the process gas,
A tubular insulator through which the process gas passes;
A tubular first ground electrode connecting the insulator and the vacuum pump;
A high voltage electrode located on an outer surface of the insulator at a distance from the first ground electrode, the high voltage electrode being connected to the AC power source and receiving a driving voltage;
A second ground electrode located inside the first ground electrode and having a facing portion facing the inner center of the insulator along the transfer direction of the process gas; And
And a magnetic field generating unit installed outside the first ground electrode and applying a magnetic field around the second ground electrode,
Lt; / RTI > The method according to claim 1,
The first ground electrode includes a first portion connected to a rear end of the insulator and a second portion connected to a rear end of the first portion,
Wherein the diameter of the first portion is greater than the diameter of the insulator and the diameter of the second portion. 3. The method of claim 2,
Wherein the opposing portion is located inside the first portion at a distance from the inner wall of the first portion,
Wherein at least two support portions are positioned between the opposing portion and the inner wall of the first portion. The method of claim 3,
Wherein the magnetic field generating unit is installed so as to surround the second part on the outer side of the second part.

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