Method for processing graphite boat through plasma

Abstract

The invention discloses a method for treating a graphite boat by plasma. The method comprises the following steps: S1, transferring the graphite boat subjected to dry cleaning to a PECVD (Plasma Enhanced Chemical Vapor Deposition) boat plating machine; s2, putting the graphite boat into a PECVD furnace tube, and inserting an electrode into the graphite boat; s3, the PECVD furnace tube is vacuumized and heated; s4, when the pressure and the temperature in the PECVD furnace tube reach preset values, introducing process gas; s5, applying a radio frequency power supply to the graphite boat, ionizing the process gas to form plasmas, and carrying out chemical reaction on the plasmas and the fluorocarbon film on the surface of the graphite boat; and S6, a product formed by reaction in the PECVD furnace tube is pumped out, and cleaning of the graphite boat is completed. The graphite boat cleaning device has the advantages of being simple in principle, convenient to operate, high in cleaning efficiency and the like, online graphite boat treatment can be achieved, the graphite boat treatment efficiency is greatly improved, and timeliness is improved.

Description

Technical Field

[0001] The invention relates to the technical field of graphite boat cleaning, and in particular to a method for treating a graphite boat with plasma. Background Art

[0002] With the continuous advancement of photovoltaic technology, tunnel oxide passivated contact (TOPCon) solar cell technology has become the current mainstream battery technology. The mass production efficiency has reached more than 25%, and the production capacity of TOPCon solar cells is still expanding.

[0003] In the TOPCon solar cell preparation process, plasma enhanced chemical vapor deposition (PECVD) technology has been widely used. Among them, PECVD equipment is required for the preparation of passivation contact film (tunnel silicon oxide + doped polysilicon film) and anti-reflection passivation film (silicon nitride). The PECVD equipment on the photovoltaic production line uses a graphite boat carrier to carry the battery cells. After multiple thin film deposition processes, the surface of the graphite boat carrier will become rougher, and parameters such as resistivity will change, resulting in continued thin film deposition. The uniformity and electrical properties of the film will deteriorate. At this time, the graphite boat carrier needs to be cleaned.

[0004] At present, the most advanced cleaning method for solar cell production lines is to use plasma dry cleaning technology, because this technology has the advantages of simple cleaning, short cleaning time, convenient exhaust gas treatment, no need for boat cleaning room and special boat cleaning personnel, etc., which greatly increases the timeliness of graphite boats. Plasma dry cleaning technology includes capacitive coupled plasma (CCP) cleaning technology, remote plasma (RPS) cleaning technology, etc., but no matter which plasma dry cleaning technology is used, the fluorinated gas is ionized to generate active fluorine free radicals and fluorine plasma, which react with the thin film on the surface of the graphite boat to form gaseous products to achieve the purpose of cleaning the graphite boat.

[0005] However, during the reaction between active fluorine free radicals and fluorine plasma and the surface film, some of the gaseous products (such as SiF4, F2, NF2, etc.) will be adsorbed by the pores in the graphite boat. In addition, some solid byproducts will be formed, which will react with the carbon element on the graphite boat to form a fluorocarbon film attached to the surface of the graphite boat. These adsorbed gaseous products and fluorocarbon films will continue to be released during the subsequent plating boat and film deposition process of the graphite boat, resulting in an excessive leakage rate alarm during the plating boat or film deposition process, which seriously affects the operating efficiency of the graphite boat and thus affects the production capacity of the solar cell. In addition, if the adsorbed gaseous products and attached fluorocarbon film are not disposed of, the formed film will also be contaminated, thereby reducing the performance of the solar cell.

[0006] In the past, the etching process in the semiconductor manufacturing field also required the use of fluorinated gases to etch thin films such as polysilicon and silicon nitride, and problems such as residues after cleaning would also be encountered. Currently, a variety of wet and dry methods have been proposed to remove residues during the plasma dry etching cleaning process.

[0007] Wet treatment methods include RCA cleaning, HF immersion cleaning, H2SO4 / H2O2 cleaning, and UV ozone treatment methods. However, it is found that the above methods all have obvious disadvantages: 1) The above wet treatment processes all take a long time, which will greatly reduce the timeliness of plasma dry cleaning of graphite boats, thereby reducing its cleaning capacity and increasing production costs; 2) The need to add new wet treatment equipment and increase the use of chemical agents will also increase production costs; 3) The wet chemical cleaning method is incompatible with the low-budget in-situ cleaning needs.

[0008] High temperature treatment is also a method for treating residues in the dry cleaning process. Its advantage is that it does not require additional chemical reagents and can reduce costs. However, its disadvantages are also obvious: 1) Additional high temperature treatment equipment is required, which reduces timeliness; 2) High temperature process can easily damage the graphite boat, resulting in a shortened life of the graphite boat.

[0009] In addition, the prior art also mentions the use of NH3 plasma to treat the residual fluorocarbon film on the surface of the graphite boat and the gaseous residue inside the graphite boat. Although NH3 plasma can remove the residue, NH3 plasma will react with the fluorocarbon film and the gaseous residue inside the graphite boat to form solid powders such as ammonium hexafluorosilicate, which can easily cause problems such as blockage of vacuum pipes and vacuum pumps. Summary of the invention

[0010] The technical problem to be solved by the present invention is to provide a method for plasma processing a graphite boat with simple principle, convenient operation and high cleaning efficiency in view of the deficiencies in the prior art.

[0011] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0012] A method for plasma treating a graphite boat comprises the following steps:

[0013] Step S1, transferring the graphite boat after dry cleaning to a PECVD boat plating machine;

[0014] Step S2, placing a graphite boat into a PECVD furnace tube, and inserting electrodes into the graphite boat;

[0015] Step S3, evacuating the PECVD furnace tube and heating it;

[0016] Step S4: When the pressure and temperature in the PECVD furnace tube reach preset values, introducing process gas;

[0017] Step S5, applying radio frequency power to the graphite boat to ionize the process gas to form plasma, and the plasma reacts chemically with the fluorocarbon film on the surface of the graphite boat;

[0018] Step S6, extracting the product formed by the reaction in the PECVD furnace tube to complete the cleaning of the graphite boat.

[0019] As a further improvement of the present invention, the following steps are also included:

[0020] Step S7, after the graphite boat is cleaned, the RF power supply is turned off and ventilation is stopped, the process gas pipeline is cleaned, and the process gas pipeline and the furnace tube are evacuated and then leak tested;

[0021] Step S8: After the leak detection is passed, the boat plating process is performed;

[0022] Step S9, after the plating boat is completed, evacuate the boat, clean the process gas pipeline, fill it with nitrogen to normal pressure, open the furnace door, and take out the graphite boat.

[0023] As a further improvement of the present invention, in step S4, when the pressure in the PECVD furnace tube is pumped below 5 Pa and the temperature is 400-500° C., process gas is introduced to keep the pressure in the PECVD furnace tube at 100-300 Pa.

[0024] As a further improvement of the present invention, the process gas is H2 or N2 or a mixed gas of H2 and N2.

[0025] As a further improvement of the present invention, the total flow rate of the process gas is 2000-15000 sccm.

[0026] As a further improvement of the present invention, in step S5, the frequency of the radio frequency power supply is 40kHz to 200kHz, and the power of the radio frequency power supply is 5000 to 10000W.

[0027] As a further improvement of the present invention, the power of the radio frequency power supply is increased to 5000-10000W in stages.

[0028] As a further improvement of the present invention, the radio frequency power supply discharges for a time period of 10 to 60 minutes.

[0029] Compared with the prior art, the advantages of the present invention are:

[0030] 1. The method for plasma treating a graphite boat of the present invention utilizes plasma technology to treat a graphite boat after dry cleaning, and reacts adsorbed gaseous products and attached fluorocarbon films through plasma technology without affecting the boat plating process and the thin film deposition process, thereby solving the problem of excessive leakage rate alarm and the problem of decreased performance of solar cells during the boat plating process and the thin film deposition process.

[0031] 2. In view of the shortcomings of wet processing, the present invention adopts dry plasma processing technology. By using capacitive coupled plasma generation technology in the PECVD plating boat equipment, H2 or N2 or a mixture of the two gases is ionized to obtain hydrogen plasma or nitrogen plasma, which reacts with the gaseous and film residues on the graphite boat at a certain temperature to obtain volatile gaseous substances, thereby solving the problem of alarm due to excessive leakage rate of the graphite boat. At the same time, the method of the present invention does not require the addition of additional equipment, and can achieve online processing of the graphite boat, thereby greatly improving the processing efficiency of the graphite boat and improving timeliness. In addition, the method of the present invention does not require high temperature and can reduce damage to the graphite boat. Finally, the hydrogen plasma and nitrogen plasma in the present invention will not form solid powder when reacting with the residue, but will form gaseous substances such as HF or NF3, which will not cause blockage to the vacuum pipeline and improve the running stability of the PECVD plating boat equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of the process of plasma treatment of a graphite boat in a specific embodiment of the present invention. DETAILED DESCRIPTION

[0033] The present invention is further described below in conjunction with the accompanying drawings and specific preferred embodiments, but the protection scope of the present invention is not limited thereby.

[0034] In the description of the present invention, it should be understood that the terms "side", "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0035] In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or suggesting relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "multiple" means two or more, unless otherwise clearly and specifically defined.

[0036] like Figure 1 As shown, the method for plasma treating a graphite boat of the present invention comprises the following steps:

[0037] Step S1, transferring the graphite boat after dry cleaning to a PECVD boat plating machine;

[0038] Step S2, placing a graphite boat into a PECVD furnace tube, and inserting electrodes into the graphite boat;

[0039] Step S3, evacuating the PECVD furnace tube and heating it;

[0040] Step S4: When the pressure and temperature in the PECVD furnace tube reach preset values, introducing process gas;

[0041] Step S5, applying radio frequency power to the graphite boat to ionize the process gas to form plasma, and the plasma reacts chemically with the fluorocarbon film on the surface of the graphite boat;

[0042] Step S6, extracting the product formed by the reaction in the PECVD furnace tube to complete the cleaning of the graphite boat;

[0043] Step S7: After the graphite boat is cleaned, turn off the RF power supply and stop ventilation, clean the process gas pipeline, and vacuumize the pipeline and furnace tube for leak detection;

[0044] Step S8: After the leak detection is passed, the boat plating process is performed;

[0045] Step S9, after the plating boat is completed, evacuate the boat, clean the process gas pipeline, fill it with nitrogen to normal pressure, open the furnace door, and take out the graphite boat.

[0046] The method of plasma treatment of graphite boat in this embodiment can remove the fluorinated gas adsorbed inside the graphite boat and the fluorocarbon film formed on the surface during the dry cleaning of the graphite boat, thereby solving the problem of excessive leakage rate alarm during the graphite boat plating process or thin film deposition process. Since the graphite boat is directly treated online, there is no need to put the graphite boat into other equipment for treatment. It only needs to be put into the PECVD plating boat machine for treatment. After the treatment is completed, there is no need to take out the tube, and the plating boat process can be directly carried out.

[0047] In step S4 of this embodiment, when the pressure in the PECVD furnace tube is pumped to below 5Pa and the temperature is 400-500°C, process gas is introduced to keep the pressure in the PECVD furnace tube at 100-300Pa. The process gas is H2 or N2 or a mixture of H2 and N2, and the total flow rate of the process gas is 2000-15000sccm. In this embodiment, H2 or N2 is used as the process gas, and plasma discharge is directly performed on the graphite boat. The formed hydrogen plasma or nitrogen plasma bombards and reacts with the fluorocarbon film on the surface of the graphite boat, and the generated gaseous substances are directly pumped away by the vacuum pump. Since high-temperature processes are not required, the damage to the graphite boat caused by high temperature is reduced, and the production cost is reduced.

[0048] In step S5 of this embodiment, the frequency of the RF power supply is 40kHz to 200kHz, the power of the RF power supply is 5000 to 10000W, and the discharge time of the RF power supply is 10 to 60min. It can be understood that the specific cleaning time is determined by the amount of fluorine gas in the graphite boat and the thickness of the fluorocarbon film on the surface. In order to obtain a better treatment effect, it is necessary to obtain a stable plasma, and the power of the RF power supply is slowly or staged to the preferred power, which is conducive to the stable and uniform generation of plasma. In the vacuum furnace tube, the process gas will be ionized under the action of the RF power supply to produce high-energy hydrogen plasma or nitrogen plasma. The hydrogen plasma or nitrogen plasma generated between the graphite boat sheets reacts chemically with the fluorocarbon film on the surface of the graphite boat to form HF or NF3 and other volatile by-products, or the high-energy ions caused by the electric field bombard the surface of the graphite boat, while accelerating the chemical reaction rate; in addition, in the heating environment, the fluorinated gas substances adsorbed inside the graphite boat are also forced out.

[0049] In this embodiment, gaseous substances adsorbed inside the graphite boat and the fluorocarbon film on the surface are removed by capacitively coupled hydrogen plasma or nitrogen plasma, H2 or N2 or a mixture of the two is used as the process gas, the graphite boat is inserted between the upper and lower electrodes on the PECVD plating boat equipment, and an RF power supply is used to discharge to generate an electric field between the graphite boat sheets, thereby ionizing the process gas such as H2 or N2 into hydrogen plasma or nitrogen plasma. At a certain temperature, the hydrogen plasma or nitrogen plasma reacts with the gaseous products adsorbed by the graphite boat and the fluorocarbon film on the surface to obtain volatile gases such as HF and NF3, which are then pumped away by a vacuum pump, thereby achieving the removal of the gaseous products adsorbed by the graphite boat and the fluorocarbon film on the surface, solving the problem of alarming excessive leakage rate of the graphite boat.

[0050] The advantages of the present invention are: 1) there is no need to remove the fluorocarbon film by high-temperature decomposition, thereby reducing the damage of high temperature to the graphite boat. In addition, plasma bombardment is directly performed at the plating boat process temperature, without the temperature rise and fall process, thereby reducing the graphite boat processing time and improving the production capacity; 2) solid powders such as ammonium hexafluorosilicate will not be formed to cause the problem of vacuum pipe blockage and vacuum pump blockage; 3) only a small amount of processing time and special gas need to be added on the basis of the conventional plating boat process, thereby reducing the production cost; 4) online processing can be realized, and no improvement is required to the existing PECVD equipment. The cleaned graphite boat is directly placed in the plating boat equipment for plasma treatment, and then the plating boat process is performed.

[0051] Example 1

[0052] The method for plasma treating a graphite boat in this embodiment comprises the following steps:

[0053] Step S1, the graphite boat of the battery production line is transferred to the PECVD boat plating machine after being dry plasma cleaned;

[0054] Step S2, opening the furnace door, placing the graphite boat into the PECVD furnace tube, and inserting electrodes into the graphite boat;

[0055] Step S3, closing the furnace door, evacuating the PECVD furnace tube and heating it;

[0056] Step S4: When the pressure in the PECVD furnace tube is pumped down to below 5 Pa and the temperature is stabilized at about 480° C., H2 is introduced as a process gas with a total gas flow rate of 10,000 sccm, so that the pressure in the quartz tube is maintained at 215 Pa;

[0057] Step S5, applying a radio frequency power supply to the graphite boat, the power supply frequency is 40kHz, the power supply power is 8000W, and the radio frequency discharge time is 30min. The H2 process gas is ionized under the action of the radio frequency power supply to generate high-energy hydrogen plasma; in the vacuum furnace tube, the hydrogen plasma generated between the graphite boat sheets reacts chemically with the fluorocarbon film on the surface of the graphite boat to form HF and other volatile by-products, or the high-energy ions caused by the electric field bombard the surface of the graphite boat, while accelerating the chemical reaction rate; in addition, under the heating environment, the fluorinated gas substances adsorbed inside the graphite boat are also forced out;

[0058] Step S6, extracting HF and other volatile by-products formed by the reaction in the PECVD furnace tube, and completing the cleaning of the graphite boat;

[0059] Step S7, after the graphite boat is cleaned, the RF power supply is turned off and ventilation is stopped, the process gas pipeline is cleaned, and the process gas pipeline and the furnace tube are evacuated and then leak tested;

[0060] Step S8: After the leak detection is passed, the boat plating process is performed;

[0061] Step S9, after the plating boat is completed, evacuate the boat, clean the process gas pipeline, fill it with nitrogen to normal pressure, open the furnace door, and take out the graphite boat.

[0062] Table 1. Changes in leakage rate after hydrogen plasma treatment of graphite boat

[0063]

[0064] As can be seen from Table 1, as a reference group, without hydrogen plasma treatment, after only heating in the furnace tube for 30 minutes, the leak rate dropped from 50.5Pa / min to 35.4Pa / min, and the leak rate was still very large and could not meet the requirements of the plating boat process. After a short period of hydrogen plasma treatment, the leak rate of the graphite boat was significantly improved, and as the treatment time increased, the leak rate decreased more. After 30 minutes of hydrogen plasma treatment, the leak rate dropped to below 8Pa / min, which can meet the requirements of the plating boat leak rate, and there will be no alarm problem of excessive leak rate.

[0065] Example 2

[0066] The method for plasma treating a graphite boat in this embodiment comprises the following steps:

[0067] Step S1, the graphite boat of the battery production line is transferred to the PECVD boat plating machine after being dry plasma cleaned;

[0068] Step S2, opening the furnace door, placing the graphite boat into the PECVD furnace tube, and inserting electrodes into the graphite boat;

[0069] Step S3, closing the furnace door, evacuating the PECVD furnace tube and heating it;

[0070] Step S4: When the pressure in the PECVD furnace tube is pumped down to below 5 Pa and the temperature is stabilized at about 480° C., N2 is introduced as a process gas with a total gas flow rate of 10,000 sccm, so that the pressure in the quartz tube is maintained at 215 Pa;

[0071] Step S5, applying a radio frequency power supply to the graphite boat, the power supply frequency is 40kHz, the power supply power is 8000W, and the radio frequency discharge time is 30min. The N2 process gas is ionized under the action of the radio frequency power supply to generate high-energy nitrogen plasma; in the vacuum furnace tube, the nitrogen plasma generated between the graphite boat sheets reacts chemically with the fluorocarbon film on the surface of the graphite boat to form NF3 and other volatile by-products, or the high-energy ions caused by the electric field bombard the surface of the graphite boat, while accelerating the chemical reaction rate; in addition, under the heating environment, the fluorinated gas substances adsorbed inside the graphite boat are also forced out;

[0072] Step S6, extracting NF3 and other volatile by-products formed by the reaction in the PECVD furnace tube to complete the cleaning of the graphite boat.

[0073] Step S7, after the graphite boat is cleaned, the RF power supply is turned off and ventilation is stopped, the process gas pipeline is cleaned, and the process gas pipeline and the furnace tube are evacuated and then leak tested;

[0074] Step S8: After the leak detection is passed, the boat plating process is performed;

[0075] Step S9, after the plating boat is completed, evacuate the boat, clean the process gas pipeline, fill it with nitrogen to normal pressure, open the furnace door, and take out the graphite boat.

[0076] Table 2. Changes in leakage rate after nitrogen plasma treatment of graphite boat

[0077]

[0078] It can be seen from Table 2 that after a short period of nitrogen plasma treatment, the leak rate of the graphite boat can be significantly improved, and the longer the treatment time, the more the leak rate is reduced. After 30 minutes of hydrogen plasma treatment, the leak rate is reduced to below 8Pa / min, which can meet the leakage rate requirements of the plating boat, and there will be no excessive leak rate alarm problem.

[0079] The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A method for plasma treatment of a graphite boat, characterized in that: The following steps are involved: Step S1, transferring the graphite boat after dry cleaning to a PECVD boat plating machine; Step S2, placing a graphite boat into a PECVD furnace tube, and inserting electrodes into the graphite boat; Step S3, evacuating the PECVD furnace tube and heating it; Step S4: When the pressure and temperature in the PECVD furnace tube reach preset values, introducing process gas; Step S5, applying radio frequency power to the graphite boat to ionize the process gas to form plasma, and the plasma reacts chemically with the fluorocarbon film on the surface of the graphite boat; Step S6, extracting the product formed by the reaction in the PECVD furnace tube to complete the cleaning of the graphite boat.

2. The method for plasma treating a graphite boat according to claim 1, characterized in that: The following steps are also included: Step S7, after the graphite boat is cleaned, the RF power supply is turned off and ventilation is stopped, the process gas pipeline is cleaned, and the process gas pipeline and the furnace tube are evacuated and then leak tested; Step S8: After the leak detection is passed, the boat plating process is performed; Step S9, after the plating boat is completed, evacuate the boat, clean the process gas pipeline, fill it with nitrogen to normal pressure, open the furnace door, and take out the graphite boat.

3. The method for plasma treatment of a graphite boat according to claim 2, characterized in that: In the step S4, when the pressure in the PECVD furnace tube is pumped to below 5 Pa and the temperature is 400-500° C., process gas is introduced to keep the pressure in the PECVD furnace tube at 100-300 Pa.

4. The method for plasma treatment of a graphite boat according to claim 3, characterized in that: The process gas is H2 or N2 or a mixed gas of H2 and N2.

5. The method for plasma treating a graphite boat according to claim 4, characterized in that: The total flow rate of the process gas is 2000-15000 sccm.

6. The method for plasma treating a graphite boat according to claim 2, characterized in that: In step S5, the frequency of the radio frequency power source is 40kHz to 200kHz, and the power of the radio frequency power source is 5000 to 10000W.

7. The method for plasma treatment of a graphite boat according to claim 6, characterized in that: The power of the radio frequency power supply is increased in stages to 5000-10000W.

8. The method for plasma treating a graphite boat according to claim 6, characterized in that: The radio frequency power supply discharges for 10 to 60 minutes.

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