A system and method for etching SiO2 using SF6 waste gas plasma

Abstract

The present invention discloses a system and method for etching SiO2 using SF6 waste gas plasma. The gas washing chamber and dilution gas compression chamber in the system are connected to the gas mixing chamber through a flow meter and a solenoid valve, and are also connected to the discharge chamber. The discharge chamber is respectively connected to the S deposition chamber and the buffer gas chamber. The buffer gas chamber is connected to the absorption chamber, the collection gas cylinder (SiF4) and the Ar dilution gas compression chamber. The present invention can first perform a preliminary washing on the SF6 waste gas, and then form an SF6 / H2 / diluent gas mixture according to the degradation requirements. A reductive degradation reaction occurs in the discharge chamber and etching occurs with SiO2 to generate S element and SiF4 gas. The impurity gas, SiF4 and Ar are separated through the buffer gas chamber, and the S element and SiF4 high-purity gas are collected, as well as the dilution gas carrier gas is recycled, ensuring the efficient and irreversible degradation process of the SF6 waste gas and the secondary utilization after the F element is separated.

Description

Technical Field

[0001] The present invention belongs to the field of environmentally friendly treatment of sulfur hexafluoride waste gas, and in particular relates to a system and method for etching SiO2 using SF6 waste gas plasma based on low-temperature plasma. Background Art

[0002] Sulfur hexafluoride (SF6) is a chemically stable synthetic gas. Due to its excellent insulation properties, it is widely used in the power industry as one of the most important insulating gases for medium and high voltage power equipment. However, SF6 gas has a high thermal conductivity at 915-950 cm -1 The spectral absorption characteristics of this band lead to a significant greenhouse effect. It has been estimated that the greenhouse gas potential of SF6 is 23,500 times that of CO2, making it the most potent of the six restricted gases under the Kyoto Protocol. Since 2015, my country has ranked first in the world in installed power equipment capacity. The urgent need to build a new power system in my country necessitates the development of SF6 harmless degradation and conversion technology.

[0003] In my country, SF6 emissions from the power industry account for over 80% of total emissions. Recovery, purification, and reuse, as well as harmless SF6 degradation, are the two mainstream SF6 waste gas emission reduction technologies. SF6 waste gas recovery and reuse is currently the mainstream operation and maintenance technology for power grids, but this technology is still in its developmental stages. Most recovery equipment is bulky and relies on provincial power companies for operation, making it difficult to cover remote areas at the prefecture and city levels and their subordinate areas. Furthermore, the proportion of recovered and purified SF6 gas reused is relatively low, failing to meet the diverse treatment needs of SF6 waste gas in various regions, volumes, and types. Currently, commercially available SF6 degradation technologies include thermal degradation, thermal catalysis, and low-temperature plasma (NTP) degradation. Thermal degradation, which uses alkaline materials at temperatures of 1100°C to achieve combustion decomposition of SF6, suffers from low energy efficiency and high CO2 emissions. Thermal catalysis reduces the reaction temperature by adding catalysts, but this also reduces the processing rate. NTP degradation, which uses discharge plasma to decompose SF6 molecules at atmospheric pressure, has high industrial potential, but suffers from issues such as uncontrollable reaction pathways and difficult to handle toxic products.

[0004] Regarding SF6 degradation treatment, the published academic paper "Disposal methods, health effects and emission regulations for sulfur hexafluoride and its by-products" states that NTP degradation technology is the most effective degradation technology for treating SF6 waste gas in the power industry. The Chinese invention patent "A sulfur hexafluoride degradation treatment device and method based on sliding arc discharge (CN113082952B)" and the Chinese invention patent "A SF6 cyclic degradation device and method based on low-temperature plasma (CN114931848A)" both propose the use of low-temperature plasma to degrade SF6 waste gas. These proposals include degradation treatment methods using different discharge methods and gas circulation schemes. However, these inventions still have the following problems:

[0005] (1) In order to promote the irreversible decomposition of SF6, a large amount of catalyst needs to be added. Its replacement and pretreatment will increase the material, operation and maintenance and labor costs. In addition, due to the generation of a large amount of acidic and toxic products such as SO and SOF, multiple steps of tail gas washing are required, which poses a hidden danger to personnel safety.

[0006] (2) It is inevitable that there are gaseous products such as SFx (x<6) and SOF in the degradation exhaust gas. The separation of S and F elements is not complete, and the complex product mixture is difficult to be effectively classified and reused after the exhaust gas washing treatment, which is not conducive to the economic recovery of the products after SF6 degradation. Summary of the Invention

[0007] The present invention aims to improve and address the issues of imperfect SF separation and difficulty in reusing degradation products in existing NTP technology for SF6 waste gas degradation. By combining efficient NTP SF6 waste gas degradation with SiO2 etching, the method uses H2 to reduce SF6. While simultaneously depositing elemental sulfur, HF is formed, which reacts with SiO2, fixing the F element as SiF4. This provides feed gas for high-crystalline silicon production and enables the secondary use of degradation products. This method boasts high degradation efficiency, good stability, minimal carrier gas consumption, complete SF6 separation, and efficient product secondary use.

[0008] In order to achieve the above-mentioned purpose of the invention, the present invention provides a low-temperature plasma-based SF6 waste gas degradation and SiO2 etching reaction system, which includes a gas washing chamber, a gas mixing chamber, a discharge chamber, a buffer gas chamber, a collection gas cylinder, an S deposition chamber, an absorption chamber, an Ar compression chamber, a flow meter, a solenoid valve, and SF6 waste gas, H2 pure gas, dilution gas and other components. Figure 1 shown.

[0009] The scrubbing chamber, mixing chamber, discharge chamber, buffer gas chamber and gas collection cylinder are connected in sequence, and reducing gas H2 and dilution gas are introduced into the mixing chamber. Flow meters and solenoid valves are provided on the pipes between the scrubbing chamber and the mixing chamber, and on the pipes between the mixing chamber and the discharge chamber. The scrubbing chamber is used to pre-treat SF6 waste gas, the discharge chamber is provided with a grounding electrode, a high-voltage driving power supply and a low-temperature plasma reactor, and the low-temperature plasma reactor is filled with SiO2 particles. The buffer gas chamber is used to separate the dilution gas, SiF4 and other impurity gases.

[0010] The S deposition chamber is connected to the discharge chamber to deposit S elemental solid powder produced by the reductive degradation of SF6 / H2 in the discharge chamber;

[0011] The absorption chamber is connected to the buffer gas chamber, and the absorption chamber is used to process impurity gases generated by the discharge process.

[0012] Furthermore, an SF6 waste gas source is provided. The scrubbing chamber includes an inlet and an outlet. The inlet is connected to the SF6 waste gas source, and the outlet is connected to a mixing chamber. A first flowmeter and a first solenoid valve are installed on the pipeline between the outlet and the mixing chamber. The scrubbing chamber is equipped with solid and liquid adsorbent materials required for scrubbing and purifying the SF6 waste gas. Depending on the type and composition of the SF6 waste gas, the treatment materials include but are not limited to alkaline solutions / solid particles (such as NaOH, KOH, Ca(OH)2, and NaHCO3) and adsorbent particles (such as activated carbon, activated alumina, and KDHF-03). These materials are used to initially filter out major impurities such as CO, SO2, SOF, and H2S from the SF6 waste gas.

[0013] Furthermore, it also includes a dilution gas compression chamber for introducing dilution gas into the gas mixing chamber, wherein both ends of the dilution gas compression chamber are respectively connected to the gas mixing chamber and the buffer gas chamber to realize the recycling of the dilution gas.

[0014] An air pump is also provided between the dilution gas compression chamber and the buffer gas chamber.

[0015] Furthermore, the dilution gas may be any one of Ar, He and N2.

[0016] Furthermore, an air mixing fan is provided in the air mixing chamber.

[0017] Furthermore, the system also includes an H2 standard gas cylinder connected to a mixing chamber. A third pressure reducing valve, a fifth flowmeter, and a fifth solenoid valve are installed on the pipeline between the two chambers. The mixing chamber is also connected to a dilution gas compression chamber, with a third flowmeter and a third solenoid valve installed on the pipeline between the two chambers. The mixing chamber receives SF6 waste gas after scrubbing in the scrubber and mixes it with H2 and a carrier gas (diluent). The evenly mixed SF6 / H2 / diluent gas enters the discharge chamber via a second flowmeter and a second solenoid valve. The SF6 / H2 ratio is controlled between 1:3 and 1:4 based on processing requirements. The dilution gas serves as a background gas, used to dilute the SF6 and promote NTP discharge. It does not participate in the SF6 discharge decomposition reaction, and the dilution ratio is generally no less than 50%.

[0018] The discharge chamber is where NTPs are generated. The low-temperature plasma reactor utilizes dielectric barrier discharge, sliding arc discharge, or microwave discharge. It includes a discharge reactor, a ground electrode, and a high-voltage drive power supply. The reactor is recommended to be a vertically positioned coaxial cylindrical structure, with an upper air inlet connected to a second solenoid valve and a lower air outlet connected to a buffer gas chamber. The NTP region formed within the discharge chamber promotes a reduction reaction between SF6 and H2, forming elemental sulfur and HF gas. A slight excess of H2 (SF6:H2 > 1:3) is added to ensure sufficient SF6 reduction. The bottom of the reactor is directly connected to an sulfur deposition chamber, which is cooled by a water bath or fan. Any sulfur that falls from the reactor bottom is deposited in the deposition chamber. The reactor is filled with SiO2 particles, with a quartz sand diameter not exceeding 70 mm. Based on the SF6 treatment rate requirement, dielectric barrier discharge (DBD) is used to generate NTPs for temperatures below 50 g / h (ideal SF6 mass). For rates exceeding this, sliding arc discharge or microwave discharge is used. In these cases, the discharge chamber requires a cooling fan or other scattering device.

[0019] Furthermore, a first distillation tower and a second distillation tower connected in sequence are arranged in the buffer gas chamber, which are temperature-controlled separation tanks, respectively connected to the discharge chamber, the collecting gas cylinder, the absorption chamber and the dilution gas compression chamber. The dilution gas is Ar. According to the obvious difference in boiling points, Ar (-185.8 °C), SiF4 (-86 °C), SO2 (-10 °C), SOF2 (-43.8 °C), SO2F2 (-55.4 °C), a cooling separation method is adopted to achieve reliable separation of carrier gas Ar, SiF4 and impurity gas, wherein Ar is diverted to the dilution gas compression chamber, SiF4 is diverted to the collecting gas cylinder, and other impurity gases are diverted to the absorption chamber for adsorption and reaction.

[0020] Furthermore, a saturated alkaline solution is provided in the absorption chamber to wash and absorb a small amount of SOF and SO-type acidic waste gas generated by degradation, and finally form metal sulfide salts.

[0021] The dilution gas compression chamber is a closed gas container containing a compressed gas pump, which is used to collect Ar gas separated from the first distillation tower. After compression, the gas is input into the gas mixing chamber through the third flow meter and the third solenoid valve to achieve the recycling of Ar.

[0022] The present invention also provides a method for etching SiO2 using SF6 waste gas plasma, the method comprising the steps of:

[0023] S1. SF6 waste gas pretreatment: The scrubbing chamber is filled with SF6 waste gas, and an alkaline material or adsorbent is built in to scrub and adsorb the SF6 waste gas to remove impurities carried by the waste gas;

[0024] S2, SF6 dilution mixing and discharge treatment: SF6 exhaust gas, H2, and dilution gas are introduced into the mixing chamber. The flow rates of the three gases are adjusted to achieve mixing according to the ratio. The SF6:H2 ratio is controlled between 1:3 and 1:4, and the dilution ratio of the dilution gas is not less than 50%. The mixed gas is introduced into the discharge chamber, and the high-voltage power supply is driven to form NTP discharge to discharge the mixed gas.

[0025] S3. Product separation and collection after discharge: The S elemental powder produced by SF6 reduction falls into the S deposition chamber for collection; the buffer gas chamber separates the impurity gas into the absorption chamber, SiF4 into the collection gas cylinder, and the dilution gas into the dilution gas compression chamber according to the boiling point of the mixed gas, thereby achieving alkaline absorption of the impurity gas, closed storage of SiF4, and compressed collection of the dilution gas;

[0026] S4. The dilution gas enters the gas recycling: the dilution gas in the buffer gas chamber is recovered and stored in the dilution gas compression chamber, and the dilution gas in the dilution gas compression chamber can be passed into the gas mixing chamber for recycling.

[0027] Compared with the prior art, the present invention can at least achieve the following beneficial effects:

[0028] (1) The present invention can pre-treat SF6 waste gas, remove common impurities such as CO, SO2, SOF gases, and effectively inhibit the products of impurity gases during the reductive degradation of SF6.

[0029] (2) The present invention can realize the reductive degradation of SF6, realize the irreversible separation of SF, form S element and HF gas, and realize the complete degradation process of SF6.

[0030] (3) The present invention can realize the process of efficient HF etching of SiO2. Due to the high reactivity of NTP, HF and active F radicals formed by SF6 degradation can effectively react with SiO2 to form SiF4 gas, thereby realizing the directional conversion and fixation of F element.

[0031] (4) The present invention can achieve efficient purification and collection of SiF4 based on the difference in boiling points among Ar, SiF4 and a small amount of impurity gases.

[0032] (5) The present invention provides a system and method for reliable reductive degradation of SF6 waste gas and secondary utilization of its products. By means of NTP technology, it is possible to achieve irreversible separation of SF while simultaneously performing SiO2 etching, thereby fixing SF in the form of elemental S and SiF4. No additional catalyst is required, and the material used is low-cost quartz sand, which has good economic efficiency and industrial prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A flow chart of a system for etching SiO2 using SF6 waste gas plasma is provided in an embodiment of the present invention.

[0034] Figure 2 This is a schematic diagram of the device principle of Example 2 of the present invention using DBD as the NTP discharge form.

[0035] Figure 3 Schematic diagram of the processing flow in an embodiment of the present invention.

[0036] In the figure: 1. Gas washing chamber; 2. First flowmeter; 3. First solenoid valve; 4. Gas mixing chamber; 5. Second flowmeter; 6. Second solenoid valve; 7. Discharge chamber; 8. First distillation tower; 9. Second distillation tower; 10. Gas collecting cylinder; 11. S deposition chamber; 12. Absorption chamber; 13. Dilution gas compression chamber; 14. Third flowmeter; 15. Third solenoid valve; 16. SF6 waste gas source; 17. Dilution gas standard cylinder; 18. H2 standard cylinder; 19. Fourth flowmeter; 20. Second pressure reducing valve; 21. Fourth solenoid valve; 22. First pressure reducing valve; 23. DBD discharge reactor; 24. Third pressure reducing valve; 25. Fifth flowmeter; 26. Fifth solenoid valve; 27. High-voltage power supply; 28. Air pump. DETAILED DESCRIPTION

[0037] The technical solution of the present invention will be further specifically described below through embodiments and in conjunction with the accompanying drawings.

[0038] Example 1

[0039] An embodiment of the present invention provides a processing device for etching SiO2 using SF6 waste gas plasma, including a gas washing chamber 1, a gas mixing chamber 4, a discharge chamber 7, a buffer gas chamber, a collection gas bottle 10, an S deposition chamber 11, an absorption chamber 12, a dilution gas compression chamber 13, and gas path control devices such as solenoid valves and flow meters.

[0040] One end of the scrubbing chamber 1 is used to be connected to the SF6 waste gas source. The scrubbing chamber 1 contains one or more materials such as alkaline solution / solid particles, adsorbent, etc. for pre-treating the SF6 waste gas. The other end of the scrubbing chamber 1 is connected to the first flowmeter 2 and is connected to the gas mixing chamber 4 through the first solenoid valve 3.

[0041] The gas mixing chamber 4 is connected to the first solenoid valve 3, the H2 gas source, and the third solenoid valve 15 respectively to receive and mix the SF6 exhaust gas, H2, and dilution gas. The outlet end of the gas mixing chamber 4 is connected to the second flowmeter 5 to pass the proportionally configured SF6 / H2 / Ar mixed gas into the discharge chamber 7 through the second solenoid valve 6 at a specified flow rate.

[0042] A grounding electrode, a high-voltage driving power supply and a low-temperature plasma (NTP) reactor are provided in the discharge chamber 7. The low-temperature plasma (NTP) reactor is filled with quartz sand particles SiO2, and the outlet end of the discharge chamber 7 is connected to the S deposition chamber 11 and the first distillation tower 8 respectively. The discharge chamber 7 is physically above the S deposition chamber 11 and is used to deposit the S elemental solid powder produced by the reductive degradation of SF6 / H2.

[0043] Among them, the buffer gas chamber includes a first distillation tower 8 and a second distillation tower 9. The first distillation tower 8 and the second distillation tower 9 are separation tanks that can be temperature-controlled. The first distillation tower 8 includes an inlet end, a first gas outlet end and a second gas outlet end. The inlet end of the first distillation tower 8 is connected to the discharge chamber 7, the first gas outlet end is connected to the dilution gas compression chamber 13, and the second gas outlet end is connected to the second distillation tower 9. The second distillation tower 9 includes a third gas outlet end and a fourth gas outlet end. The third gas outlet end is connected to the collecting gas bottle 10, and the fourth gas outlet end is connected to the absorption chamber 12. The dilution gas in this embodiment is Ar. Based on the obvious differences in boiling points, Ar (-185.8 °C), SiF4 (-86 °C), SO2 (-10 °C), SOF2 (-43.8 °C), and SO2F2 (-55.4 °C), a cooling separation method is adopted to achieve reliable separation of carrier gas Ar, SiF4 and impurity gas, wherein Ar is diverted to the dilution gas compression chamber 13, SiF4 is diverted to the collection gas bottle 10, and other impurity gases are diverted to the absorption chamber 12 for adsorption and reaction. In detail, a condensing and cooling device is provided in the first distillation tower 8, which separates the discharge treatment gas input from the discharge chamber 7 by controlling the temperature. Ar is in a gaseous state at the top of the first distillation tower 8 due to its low boiling point. After separation, it is introduced into the dilution gas compression chamber 13. The remaining gas is collected in liquid form, heated and restored to gaseous state, and then introduced into the second distillation tower 9. Based on the characteristic that the boiling point of SiF4 is significantly lower than that of acidic impurity gases such as SO2, SO2F2, and H2S, the temperature is reduced in the second distillation tower 9 to achieve gas-liquid separation. SiF4 gathers in gaseous form at the top of the tower and is introduced into the collection gas cylinder 10 after collection. The remaining impurity gas is collected in liquid form, heated and restored to gaseous state, and introduced into the absorption chamber 12. The absorption chamber contains a saturated alkaline solution for treating the impurity gas by-products generated after the discharge treatment, mainly acidic gases such as SO2, SO2F2, and H2S. The dilution gas compression chamber 13 has a built-in air pump, which can pump the dilution gas separated by the first distillation tower 8 into it for compressed storage. The compressed gas pressure is between 1 and 3 atm. Once it exceeds 1.5 atm, it can be recycled and used. It is controlled by the third flow meter 14 and the third solenoid valve 15 in sequence and input into the gas mixing chamber 4. At this time, the dilution gas source may be reduced or shut down according to the dilution gas content and flow rate in the dilution gas compression chamber 13.

[0044] The NTP discharge method is determined by the SF6 processing rate. When the required SF6 mass is less than 50 g / h (ideal SF6 mass), dielectric barrier discharge (DBD) is used to generate NTP. Above this processing rate, sliding arc discharge or microwave discharge is used. In this case, the discharge chamber 7 can be equipped with a cooling fan or other scattering device. The reactor is filled with SiO2 particles, with a quartz sand diameter not exceeding 70 mm.

[0045] Example 2

[0046] The present invention proposes to drive SF6 / H2 discharge decomposition by NTP and realize SiO2 etching process, as shown in the schematic diagram. Figure 1 The specific processing process is as follows:

[0047] (1) SF6 waste gas purification: SF6 waste gas is introduced into the scrubbing chamber 1. According to the type and content of SF6 waste gas, different materials such as alkaline material absorption and adsorbent adsorption are set in the scrubbing chamber 1 to wash the SF6 waste gas and filter out common impurity gases in the SF6 waste gas, including CO, CO2, SO2, SO2F2, H2S, etc. The washed SF6 waste gas is controlled by the first flow meter 2 and the first solenoid valve 3 and input into the mixing chamber 4 at a set flow rate. The flow rate is determined according to the SF6 treatment rate requirement and the volume of the degradation equipment.

[0048] (2) SF6 dilution and gas mixing: In the mixing chamber 4, SF6, H2, and diluent gas are mixed to form a fixed ratio of SF6 / H2 / diluent gas mixed gas. H2 can be provided by a standard gas source. The volume of the mixing chamber 4 is not less than 10L, and a mixing fan can be installed inside to ensure uniform mixing. The ratio of SF6 to H2 is controlled between 1:3 and 1:4 to ensure that H2 is sufficient to reduce the sulfur element in SF6 to zero valence state, but not excessively to H2S. The dilution rate of the diluent gas is not less than 50%.

[0049] In this embodiment, the interior of the gas mixing chamber 4 may be equipped with a flow uniforming device such as a fan to ensure uniform mixing of SF6 / H2 / Ar.

[0050] In this embodiment, the dilution gas is Ar, which serves as a dilution gas (carrier gas). The Ar gas source includes both Ar standard gas and recycled dilution gas. It is understood that in other embodiments, other types of dilution gases, such as He or N2, may be used.

[0051] (3) Discharge degradation and etching: In the discharge chamber 7, a low-temperature plasma reactor is driven by a high-voltage power supply to form a low-temperature plasma discharge. The NTP reactor is filled with quartz sand particles (SiO2). The NTP reactor should be placed vertically. The gas to be treated generated by the mixing chamber 4 enters from the upper end of the NTP reactor and is discharged from the bottom end into the buffer gas chamber after passing through the discharge area. The bottom of the discharge chamber 7 is connected to the top of the S deposition chamber 11 and is physically above it, so that the reducing S generated by the SF6 / H2 / Ar discharge can fall into the S deposition chamber 11 to achieve solid collection. It should be noted that in actual applications, exhaust gas sampling can be performed at the end of the discharge chamber 7 to ensure that the SF6 degradation rate exceeds 99% to prevent the discharge of the remaining undecomposed SF6 from affecting the gas separation in the buffer gas chamber, and its discharge will also cause a greenhouse effect.

[0052] (4) SiF4 separation: In the buffer gas chamber, according to the difference in boiling points of the mixed gas components after treatment, the dilution gases Ar (-185.8 °C), SiF4 (-86 °C), SO2 (-10 °C), SOF2 (-43.8 °C), and SO2F2 (-55.4 °C) are cooled by a condensation cooling device to achieve the separation of carrier gas Ar, SiF4, and other impurity gases. Ar is introduced into the dilution gas compression chamber 13, SiF4 is introduced into the collection gas cylinder 10, and the remaining impurity gases are introduced into the absorption chamber 12. The absorption chamber 12 contains alkaline solution or solid particles to absorb the impurity gases and recover them in the form of metal sulfides.

[0053] (5) Dilution gas circulation: The dilution gas acts as a background gas to dilute the SF6 concentration and promote NTP discharge. It does not react in the discharge chamber 7. After separation in the buffer gas chamber, it is introduced into the dilution gas compression chamber 13 for compression and collection. It is then controlled by the third flow meter 14 and the third solenoid valve 15 and replenished into the mixing chamber 4 at a preset flow rate for recycling.

[0054] Example 3

[0055] In order to refine the application scenarios of the present invention, dielectric barrier discharge (DBD) is used as a typical NTP generation method to explain the specific application of the present invention in detail. The structural diagram is shown in FIG. Figure 2 shown.

[0056] The specific system includes a gas source, a gas distribution system, a DBD discharge system, and a gas separation and circulation system, wherein the gas sources include an SF6 waste gas source 16, a dilution gas standard cylinder 17, and an H2 standard gas cylinder 18; the gas distribution system includes a gas washing chamber 1, a gas mixing chamber 4, and related gas path facilities, and the related gas path facilities include a first pressure reducing valve 22, a first flowmeter 2, a second flowmeter 5, a second solenoid valve 6, a second pressure reducing valve 20, a third pressure reducing valve 24, a fifth flowmeter 25, and a fifth solenoid valve 26. The SF6 waste gas source 16 is connected to the gas washing chamber 1 through an exhaust gas pipe, and a fourth flowmeter 19, a fourth solenoid valve 21, and a first pressure reducing valve 22 are provided on the exhaust gas pipe; the dilution gas standard cylinder 17 is connected to the gas mixing chamber 4 through a gas pipe, and a second pressure reducing valve 20 is provided on the gas pipe; the H2 standard gas cylinder 18 is connected to the gas mixing chamber 4 through a hydrogen pipe, and the third pressure reducing valve 24, the fifth flowmeter 25, and the fifth solenoid valve 26 are provided on the hydrogen pipe.

[0057] The discharge chamber 7 is a DBD discharge system, housing a low-temperature plasma reactor. The low-temperature plasma reactor utilizes dielectric barrier discharge (DBD). The discharge chamber 7 comprises a DBD discharge reactor 23 and a high-voltage power supply 27. The DBD reactor is a coaxial, double-layer cylindrical reactor. The inner electrode of the copper rod is connected to the high-voltage power supply 27, while the outer electrode is wrapped with stainless steel mesh, serving as the positive electrode and providing a solid ground connection. In this embodiment, due to the characteristics of the DBD reactor, the discharge chamber and the S deposition chamber are integrated. Specifically, the lower air gap of the DBD serves as the S deposition zone, while the upper portion serves as the SiO2 reaction zone, i.e., the DBD plasma discharge region. Quartz wool / glass wool is used to support the SiO2. The high-voltage power supply 27 is controlled by an AC power supply (typical parameters: discharge voltage 10 kV, discharge frequency 10 kHz, input power 100-150 W / reactor).

[0058] Specifically, the DBD discharge reactor is a coaxial, double-layer cylindrical reactor with a central copper rod inner electrode surrounded by an inner ceramic dielectric tube (inner dielectric), and an outer ceramic dielectric tube (outer dielectric). A 6mm air gap exists between the inner and outer dielectric tubes. Quartz sand is filled between the inner and outer dielectric tubes, and a stainless steel mesh is wrapped around the outer side of the outer ceramic dielectric tube as the positive electrode, which is then properly grounded. Specifically, the DBD discharge reactor is vertically positioned, with a total length of 30 cm and a 20 cm discharge zone. 2.5 cm buffer zones are provided above and below the discharge zone, filled with quartz wool / glass wool as support material. The bottom 5 cm area serves as a sulfur deposition zone. The discharge chamber and sulfur deposition chamber are directly integrated into the DBD discharge reactor. The sulfur elemental reduction that occurs after DBD discharge can be deposited directly at the bottom of the reactor, eliminating the need for a separate sulfur deposition chamber.

[0059] If sliding arc discharge or microwave discharge is used in the discharge chamber, the low-temperature plasma discharge reactor is semi-open. Ignition is driven by a high-voltage power supply from one side of the reactor, and the generated plasma is ejected with the airflow. In this case, the ignition end is located at the top of the tube, and the airflow is ejected downwards accompanied by the plasma discharge process. Quartz sand is filled to the middle of the reactor. The S deposition chamber 11 is located physically below the reactor to collect the purged S element. That is, after the plasma airflow is generated, it is blown out of the reactor pipeline into an open environment. Therefore, the low-temperature plasma discharge reactor and the S deposition chamber 11 are configured as two separate devices / components, wherein the S deposition chamber 11 is located physically behind / below the sliding arc or microwave discharge reactor to receive the S element generated by the NTP discharge reduction and purged by the airflow.

[0060] The gas classification and circulation system includes a first distillation tower 8, a second distillation tower 9, a gas collection cylinder 10, an absorption chamber 12, an air pump 28, a dilution gas compression chamber 13, a third flowmeter 14, and a third solenoid valve 15. The gas collection cylinder 10 is used to collect SiF4, and the absorption chamber 12 is an alkaline solution absorption tank.

[0061] Before starting the discharge point treatment, first open the SF6 waste gas source 16, pressurize the gas cylinder outlet to about 1 atmosphere through the first pressure reducing valve 22, and then control the set flow rate of SF6 waste gas into the scrubbing chamber 1 through the fourth flowmeter 19 and the fourth solenoid valve 21. Saturated Ca(OH)2 solution and KDHF-03 adsorbent particles are introduced into the scrubbing chamber 1 in turn for preliminary washing. The SF6 waste gas enters the solution and passes through the adsorbent in turn to realize the scrubbing process. The washed gas is controlled by the first flowmeter 2 and the first solenoid valve 3 to enter the mixing chamber 4 and wait for mixing.

[0062] Separately, open the H2 standard gas cylinder 18 and the diluent (Ar) standard gas cylinder 17. The H2 gas flow rate is controlled via the third pressure-reducing valve 24 and the fifth flowmeter 25, while the Ar gas flow rate is controlled via the second pressure-reducing valve 20, the third flowmeter 14, and the third solenoid valve 15. Both streams flow into the mixing chamber 4, with the SF6 / H2 / Ar flow rate ratio controlled at 1:3:4 and the SF6 concentration at 12.5%. A built-in fan in the mixing chamber 4 purges the gas mixture, accelerating its uniform mixing.

[0063] Before the DBD discharge reactor 23 is operational, an appropriate amount of SiO2 quartz sand is filled between the double-layer dielectric tube, and quartz wool is added to the top and bottom for securement. The discharge region of the DBD discharge reactor 23 is 20 cm long, with a 10 cm long S deposition zone at the bottom, serving as the S deposition chamber 11. Before powering on, ensure that the external electrodes of the DBD discharge reactor and the HV high-voltage power supply 27 are reliably grounded. While mixing and distributing gases in the gas mixing chamber 4, pre-discharge is initiated in the DBD discharge reactor 23 for 3-5 minutes to ensure that the DBD discharge is in a normal state (voltage and current do not fluctuate significantly, with amplitude variations of less than 10%). The second flowmeter 5 and second solenoid valve 6 are then controlled to allow the gas in the gas mixing chamber 4 to enter the DBD discharge reactor 23 for discharge treatment. During the discharge process, observe the collection of elemental S in the S deposition zone. It is generally recommended to shut down the reactor for cleaning and collection every 3-5 hours. The specific timeframe depends on parameters such as the SF6 treatment rate and reactor power.

[0064] The first and second distillation towers 8 and 9 are 40L gas tanks with built-in condensation and cooling devices, which can condense and extract the waste gas after the discharge treatment. The diluent gas is Ar. Ar gas is extracted in the first distillation tower 8 using its low boiling point. The gas is pumped into the dilution gas compression chamber 13 by the air pump 28 for compression and storage. SiF4 gas is extracted in the second distillation tower 9 using its low boiling point. The SiF4 gas is passed into the collection cylinder 10 for storage. The remaining impurity gas is liquefied and collected, then heated to a gaseous state and enters the alkaline solution absorption tank 16 for absorption reaction.

[0065] A built-in pressure gauge in dilution gas compression chamber 13 monitors the dilution gas (Ar) storage status. Before initial use, dilution gas compression chamber 13 must be evacuated or filled with high-purity dilution gas (Ar). The dilution gas (Ar) separated by first distillation tower 8 is pumped into dilution gas compression chamber 13, causing the internal pressure to rise, typically operating between 1 and 3 atm. Once the internal pressure of dilution gas compression chamber 13 exceeds 1.5 atm, it can be used to replenish gas to mixing chamber 4. The third flowmeter 14 and third solenoid valve 15 are controlled to pass the positive-pressure dilution gas (Ar) in dilution gas compression chamber 13 into mixing chamber 4 at a set flow rate (determined by the SF6 dilution ratio) for the next discharge cycle.

[0066] The specific embodiments described herein are merely illustrative of the principles and methods of the present invention. Persons skilled in the art may make various modifications, additions, or substitutions to the described embodiments, such as by changing the low-temperature plasma discharge configuration, reactor geometry, tail gas absorption medium type and absorption treatment sequence, sample introduction method, and mixing ratio, without departing from the spirit of the present invention or exceeding the scope of the appended claims.

Claims

1. A system for etching SiO2 using SF6 waste gas plasma, characterized in that: It includes a gas washing chamber (1), a gas mixing chamber (4), a discharge chamber (7), a buffer gas chamber, a gas collecting bottle (10), an S deposition chamber (11) and an absorption chamber (12). The scrubbing chamber (1), the mixing chamber (4), the discharge chamber (7), the buffer gas chamber and the gas collecting cylinder (10) are connected in sequence, and the reducing gas H2 and the diluting gas are introduced into the mixing chamber (4), and the pipes between the scrubbing chamber (1) and the mixing chamber (4) and the pipes between the mixing chamber (4) and the discharge chamber (7) are provided with flow meters and solenoid valves, wherein the scrubbing chamber (1) is used for pre-treating the SF6 waste gas, the discharge chamber (7) is provided with a grounding electrode, a high-voltage driving power supply and a low-temperature plasma reactor, and the low-temperature plasma reactor is filled with SiO2 particles, and the SF6 / H2 discharge decomposition is driven by the low-temperature plasma to realize the SiO2 etching process, and the buffer gas chamber is used for separating the diluting gas, SiF4 and other impurity gases; The S deposition chamber (11) is connected to the discharge chamber (7) to deposit S elemental solid powder generated by the reductive degradation of SF6 / H2 in the discharge chamber (7); The absorption chamber (12) is connected to the buffer gas chamber, and the absorption chamber (12) is used to process impurity gases generated by the discharge process; It also includes a dilution gas compression chamber (13) for introducing dilution gas into the gas mixing chamber (4), wherein both ends of the dilution gas compression chamber (13) are respectively connected to the gas mixing chamber (4) and the buffer gas chamber to achieve recycling of the dilution gas; A first distillation tower (8) and a second distillation tower (9) are arranged in the buffer gas chamber and are connected in sequence. The input end of the first distillation tower (8) is connected to the discharge chamber (7), and the output end is connected to both the dilution gas compression chamber (13) and the second distillation tower (9). The output end of the second distillation tower (9) is connected to both the collecting gas cylinder (10) and the absorption chamber (12).

2. The system for etching SiO2 using SF6 waste gas plasma according to claim 1, characterized in that: Any one or more materials selected from the group consisting of alkaline solution, alkaline solid particles and adsorbent are placed in the scrubbing chamber (1).

3. The system for etching SiO2 using SF6 waste gas plasma according to claim 2, characterized in that: The choice of alkaline solution and alkaline solid particles includes but is not limited to any one of NaOH, KOH, Ca(OH)2 and Na2CO3, and the choice of adsorbent includes but is not limited to any one of KDHF-03, activated carbon and activated alumina.

4. The system for etching SiO2 using SF6 waste gas plasma according to claim 1, characterized in that: The dilution gas is any one of Ar, He and N2.

5. The system for etching SiO2 using SF6 waste gas plasma according to claim 1, characterized in that: An air mixing fan is provided in the air mixing chamber (4).

6. A system for etching SiO2 using SF6 waste gas plasma according to any one of claims 1 to 5, characterized in that: The low-temperature plasma reactor of the discharge chamber (7) adopts dielectric barrier discharge, sliding arc discharge or microwave discharge.

7. The system for etching SiO2 using SF6 waste gas plasma according to claim 6, characterized in that: When the low-temperature plasma reactor adopts dielectric barrier discharge, the low-temperature plasma reactor at this time is defined as a DBD discharge reactor. The DBD discharge reactor includes a discharge area and a deposition area located below the discharge area. The discharge area includes an inner electrode, an inner ceramic dielectric tube surrounded by the inner electrode, an outer ceramic dielectric tube surrounded by the inner ceramic dielectric tube, quartz sand filled between the inner ceramic dielectric tube and the outer ceramic dielectric tube, and a metal mesh positive electrode wrapped around the outside of the outer ceramic dielectric tube, and a gap is left between the inner ceramic dielectric tube and the outer ceramic dielectric tube.

8. A method for etching SiO2 using SF6 waste gas plasma, characterized in that: Using the system according to any one of claims 1 to 7, the method comprises the steps of: S1. SF6 waste gas pretreatment: the gas washing chamber (1) is filled with SF6 waste gas, and an alkaline material or adsorbent is built in to wash and adsorb the SF6 waste gas to remove impurities carried by the waste gas; S2, SF6 dilution mixing and discharge treatment: SF6 waste gas, H2, and dilution gas are introduced into the mixing chamber (4), and the flow rates of the three gases are adjusted to achieve mixing according to the ratio, wherein SF6:H2 is controlled between 1:3 and 1:4, and the dilution ratio of the dilution gas is not less than 50%; the mixed gas is introduced into the discharge chamber (7), and the high-voltage power supply is driven to form a discharge, and the mixed gas is subjected to discharge treatment; S3. Product separation and collection after discharge: The S elemental powder generated by SF6 reduction falls into the S deposition chamber (11) for collection; the buffer gas chamber separates the impurity gas into the absorption chamber (12), the SiF4 into the collection gas cylinder (10), and the dilution gas into the dilution gas compression chamber (13) in accordance with the boiling point of the mixed gas, thereby achieving alkaline absorption of the impurity gas, closed storage of SiF4, and compressed collection of the dilution gas; S4. Circulation of dilution gas: The dilution gas in the buffer gas chamber is recovered and stored in the dilution gas compression chamber (13), and the dilution gas in the dilution gas compression chamber (13) can be passed into the gas mixing chamber (4) for circulation.

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