Coating equipment and coating method for quartz tube of chemical vapor deposition tube furnace and quartz tube

Abstract

The invention belongs to the technical field of plasma coating, and relates to coating equipment and a coating method for a quartz tube of a chemical vapor deposition tube furnace and the quartz tube. The coating equipment comprises a coating furnace body, an outer electrode arranged on the inner wall of the coating furnace body, an inner electrode arranged in an inner cavity of the coating furnace body, a radio frequency power supply electrically connected with the inner electrode and the outer electrode, and a heating structure for providing heat for the inner cavity of the coating furnace body, the supporting structure is arranged in an inner cavity of the coating furnace body and used for supporting a quartz tube to be coated, the air inlet structure and the air outlet structure are arranged at the end of the coating furnace body, a reaction area is formed between the outer electrode and the inner electrode, and during coating, the quartz tube to be coated is arranged outside the inner electrode in a sleeving mode and located in the reaction area. The thin film formed on the inner surface of the quartz tube is good in compactness and thickness uniformity, and the quartz tube can be effectively prevented from being broken in the chemical vapor deposition process.

Description

Technical Field

[0001] The invention belongs to the technical field of plasma coating, and relates to a coating device, a coating method and a quartz tube used for a chemical vapor deposition tube furnace. Background Art

[0002] Improving efficiency and reducing costs is an eternal topic in the development of photovoltaics. With the development of solar cell technology, the efficiency limit of PERC solar cells due to their structure can no longer meet the development needs of photovoltaic technology. TOPCon (Tunnel Oxide Passivated Contacts) cells have a theoretical limit efficiency of 28.7% (double-sided passivated contact structure) due to their excellent structure and have become the next generation of crystalline silicon solar cell structures to replace mass-produced PERC (Passivated Emitter and Rear Cell) solar cells. The preparation process of TOPCon cells is inseparable from chemical vapor deposition technology, which requires a high temperature environment. At present, in order to smoothly carry out the reaction, most of them use quartz tubes as the reaction chamber of the chemical vapor deposition tube furnace.

[0003] Quartz tubes are widely used in the field of photovoltaic equipment due to their excellent high temperature resistance. However, the production process of solar cells requires a vacuum environment, a high temperature environment, and the introduction of corresponding reaction gases. During the low-pressure chemical vapor deposition reaction, monosilane gas needs to be introduced. The single crystal silicon produced during the monosilane reaction will adhere to the wall of the quartz tube, causing the performance of the quartz tube to deteriorate. When a certain amount of impurities are attached, the quartz tube may break during the vacuum extraction process, causing the quartz tube to explode, damage the silicon wafer, and other problems, affecting production.

[0004] Quartz tube coating is a common method, which can reduce the impact of impurities on quartz tubes by isolating the direct contact between quartz tubes and impurities, and can improve the high temperature resistance of quartz tubes. At present, the quartz tube coating method is not mature, so it is particularly important to study a convenient, fast and effective coating equipment and process. Summary of the invention

[0005] The purpose of the present invention is to provide a coating device, a coating method and a quartz tube for a quartz tube used in a chemical vapor deposition tube furnace. A protective film is formed on the inner surface of the quartz tube by a plasma chemical vapor deposition method. The film is dense and has a uniform thickness, and can effectively avoid cracking during the chemical vapor deposition process.

[0006] The present invention adopts the following technical solution: In the first aspect, the present invention provides a coating device for a quartz tube of a chemical vapor deposition tube furnace, comprising a coating furnace body, an outer electrode arranged on the inner wall of the coating furnace body, an inner electrode arranged in the inner cavity of the coating furnace body, a radio frequency power supply electrically connected to the inner electrode and the outer electrode, a heating structure for providing heat to the inner cavity of the coating furnace body, a supporting structure arranged in the inner cavity of the coating furnace body for supporting the quartz tube to be coated, and an air inlet structure and an air outlet structure arranged at the end of the coating furnace body, a reaction area is formed between the outer electrode and the inner electrode, and during coating, the quartz tube to be coated is sleeved outside the inner electrode and is located in the reaction area.

[0007] In the above scheme, for the coating of the inner surface of the cylindrical quartz tube, the inner wall of the coating furnace is used as the outer electrode, and the inner electrode is arranged in the cavity. During coating, the quartz tube to be coated is sleeved outside the inner electrode, and the air intake structure introduces working gas between the quartz tube and the inner electrode. The working gas is electrolyzed into plasma under the action of power supply of the inner and outer electrodes, and then reacts to generate gas deposited on the inner wall of the quartz tube, thereby achieving coating of the inner wall of the quartz tube.

[0008] For coating on the inner surface of a cylindrical quartz tube, the inner electrode and the outer electrode can be arranged at the two ends of the quartz tube in the coating equipment, and gas can be introduced into the quartz tube. However, tests have shown that the film obtained by the coating equipment of this structure has poor density. When used in the chemical vapor deposition process, the surface film will still be destroyed, thereby failing to protect the quartz tube.

[0009] Preferably, the coating device further comprises a sealing structure, which is in contact with the outer electrode and the outer wall of the quartz tube and is close to the end of the quartz tube. The sealing structure is provided to prevent the working gas from entering between the quartz tube and the inner wall of the coating furnace body. This can not only prevent the coating of a thin film on the outer wall of the quartz tube, but also help to concentrate the working gas inside the quartz tube, which is conducive to the coating of the inner wall of the quartz tube.

[0010] Preferably, the coating furnace body adopts a multi-section type, and each section of the coating furnace body corresponds to an independent heating structure. Generally speaking, if the furnace body is controlled at a fixed temperature, the temperature of the middle section will usually be higher than the temperature at both ends, resulting in uneven temperature distribution in the furnace body. This solution adopts a multi-section furnace body and controls the temperature of the coating furnace body in sections, which is more conducive to maintaining the uniformity of the temperature distribution in the furnace body cavity. The more uniform the temperature distribution, the more conducive it is to forming a dense film with consistent thickness.

[0011] Preferably, the inner electrode is installed at the end of the coating furnace body through a rotating base, and the inner electrode rotates under the drive of the rotating base. The present invention is aimed at the coating of quartz tubes. Since the inner cavity of the quartz tube is cylindrical, it is difficult to evenly distribute the working gas after it is introduced, resulting in uneven thickness of the formed film. Therefore, in this solution, by rotating the inner electrode, the inner electrode can not only be used as a power generation electrode, but also as a tool to make the working gas and plasma distribution more uniform. In the process, properly rotating the inner electrode is conducive to significantly improving the uniformity of the film thickness.

[0012] Preferably, the reaction area includes a front area close to the opening and a rear area away from the opening. During film coating, the quartz tube to be coated is located in the rear area of ​​the reaction area. The front area is set, and the working gas begins to be decomposed into active groups in the front area. The active groups move forward to the rear area under the action of the airflow. In this area, although part of the working gas continues to be decomposed into active groups, the concentration of the active groups is relatively large due to the existence of the front area. In the rear area, the active groups react on the surface of the quartz tube to generate a silicon carbide film, which is more conducive to forming a denser film and accelerating the efficiency of film formation.

[0013] Preferably, the length of the pre-zone is 1 / 2 or more of the length of the post-zone.

[0014] Preferably, the lengths of the inner electrode and the outer electrode are equal, and equal to or greater than the length of the quartz tube.

[0015] In a second aspect, the present invention provides a coating method for a quartz tube of a chemical vapor deposition tube furnace, based on the above-mentioned coating equipment, comprising at least the following steps: S-1. The quartz tube to be coated is sent into the inner cavity of the coating furnace, and the quartz tube to be coated is sleeved outside the inner electrode; S-2. Evacuate the inner cavity of the coating furnace to maintain the inner cavity vacuum; S-3. Raise the temperature of the coating furnace cavity to T and adjust the pressure to P; S-4. Introduce working gas into the area between the inner electrode and the quartz tube to be coated, turn on the RF power supply to generate plasma, and deposit a thin film on the inner surface of the quartz tube to be coated.

[0016] Preferably, in step S-4, the inner electrode is rotated at a rotation speed of 5 rpm to 25 rpm, in particular 10 rpm to 25 rpm.

[0017] Preferably, in step S-3, T is 400°C to 600°C, and P is 1000mtorr to 2500mtorr.

[0018] Preferably, in step S-2, the vacuum degree is less than or equal to 15 mtorr.

[0019] Preferably, in step S-4, the working gases are methane and monosilane, the flow rate of methane is 1000-5000 sccm, and the flow rate of monosilane is 1000-2500 sccm.

[0020] Preferably, the power of the radio frequency power supply is 20 kW to 40 kW and the frequency is greater than 20 KHz.

[0021] Preferably, after the deposition is completed in step S-4, a low-temperature inert gas is introduced into the inner cavity of the coating furnace to quickly reduce the inner cavity temperature, which is beneficial to improving the adhesion of the film.

[0022] In a third aspect, the present invention provides a quartz tube for a chemical vapor deposition tube furnace, wherein a silicon carbide film is formed on the inner surface of the quartz tube by the above-mentioned coating method.

[0023] By implementing the above technical solution, the present invention has the following beneficial effects: 1. The present invention can coat the inner wall of a quartz tube by improving the internal structure of a coating furnace body.

[0024] 2. The present invention can make the thickness of the silicon carbide film formed on the inner wall of the quartz tube more uniform and the film more dense by further optimizing the internal structure of the coating furnace body. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the planar structure of the coating device shown in Example 1 of the present invention; Figure 2 Schematic diagram of the planar structure of the coating device shown in Example 2 of the present invention Figure 3 Schematic diagram of position selection for measuring film thickness on the surface of a quartz tube. DETAILED DESCRIPTION

[0026] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0027] This specific embodiment is merely an explanation of the present invention and is not a limitation of the present invention. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed. However, as long as they are within the scope of the claims of the present invention, they are protected by the patent law.

[0028] Example 1 This embodiment provides a coating device for coating the inner surface of a quartz tube. The coated quartz tube is used in a chemical vapor deposition tube furnace. By forming a protective film on the inner surface of the quartz tube, it is helpful to reduce the breakage of the quartz tube during the chemical vapor deposition process.

[0029] See also Figure 1 and Figure 2 The coating device provided in this embodiment includes a coating furnace body 200, which has an opening on the side, which is sealed by a cover, and the inside is an inner cavity 201. The wall of the coating furnace body 200 has two layers, and a heating structure 300, such as a thermocouple, is arranged between the two layers to provide a thermal environment for the reaction in the inner cavity. In the inner cavity of the coating furnace body 200, a support structure 400 for supporting the quartz tube 100 is installed. The support structure 400 is installed by a track and can be freely moved in and out of the opening to facilitate the placement and removal of the quartz tube 100.

[0030] In this embodiment, the coating furnace body 200 is divided into three sections in the length direction. The walls of the three sections are the same. The difference is that a heating structure 300 is provided for each section so that the temperature can be controlled separately. Generally speaking, if the same heating structure is shared, the temperature in the middle area of ​​the coating furnace body 200 will be higher, while the temperature at the two end areas will be lower. Dividing the coating furnace body 200 into sections and controlling the area of ​​the middle section to be slightly lower than the two end sections is beneficial to maintaining the uniformity of the temperature in the inner cavity 201.

[0031] An outer electrode 501 is installed on the inner wall of the coating furnace body 200, and an inner electrode 502 extending into the middle of the inner cavity 201 is installed at the end (the end opposite to the opening) of the coating furnace body 200. The inner electrode 502 is fixed to the coating furnace body 200 by an insulating base 600. A reaction area is formed between the outer electrode 501 and the inner electrode 502, and the length of the reaction area is equal to the length of the quartz tube to be coated. When coating, the quartz tube to be coated is sheathed outside the inner electrode 502 and is located in the reaction area.

[0032] In this embodiment, the outer electrode is equal to the inner electrode in length and is equal to the length of the quartz tube.

[0033] A sealing structure 700 is also provided on the inner wall of the coating furnace body 200. The sealing structure is a high temperature resistant sealing ring which is sleeved on the quartz tube and is located close to the end of the quartz tube.

[0034] An air inlet structure 10 and an air outlet structure 20 are installed on the opening side of the coating furnace body 200. The air inlet structure 10 is an air inlet pipeline, and the outlet of the air inlet pipeline is located at the opening end of the coating furnace body 200, flush with the end of the inner electrode 502. The air outlet structure 20 is an air outlet pipeline, and the inlet of the air outlet pipeline is close to the end of the coating furnace body 200 (the end opposite to the opening).

[0035] Example 2 This embodiment provides a coating device, see Figure 2 On the basis of Example 1, further structural improvements are made. Specifically, the inner electrode 502 is rotatably mounted on the coating furnace body 200 by an insulating base, the insulating base includes a chassis, a clamp rotatably mounted on the chassis, and a driving motor driving the clamp to rotate, and the inner electrode 502 is clamped on the clamp.

[0036] Example 3 This embodiment provides a coating device, see Figure 2 On the basis of Example 2, further structural improvements are made. Specifically, the length of the reaction area is greater than the length of the quartz tube to be coated, the reaction area includes a front area 201a and a rear area 201b, and the length of the front area must be guaranteed to be 1 / 2 or more of the length of the rear area, and the length of the rear area is greater than or equal to the length of the quartz tube. When coating, the quartz tube to be coated is located in the rear area of ​​the reaction area.

[0037] Example 4 This embodiment provides a coating device, which is modified on the basis of Embodiment 2. The difference from Embodiment 2 is that the outer electrode is equal to the inner electrode in length, which is smaller than the length of the quartz tube and is only half the length of the quartz tube.

[0038] Example 5 This embodiment provides a quartz tube coating method, which uses the coating equipment of embodiment 1, embodiment 2, embodiment 3, and embodiment 4 to coat a layer of silicon carbide film on the inner surface of the quartz tube.

[0039] The coating method comprises the following steps: S-1. The quartz tube to be coated is sent into the inner cavity of the coating furnace, and the quartz tube to be coated is sleeved outside the inner electrode to ensure that the quartz tube is completely placed in the reaction area; S-2. Evacuate the inner cavity of the coating furnace to maintain the inner cavity vacuum less than 15mtorr; S-3. Raise the inner temperature of the coating furnace to 500°C and adjust the pressure to 1500mtorr; S-4. Introduce methane and monosilane gas into the reaction area between the inner electrode and the quartz tube to be coated. Among them, methane is introduced at a flow rate of 2000sccm, and monosilane is introduced at a flow rate of 1000sccm. The radio frequency power supply is turned on, and the power is adjusted to 25kW and the frequency is 25KHz to generate plasma, and a thin film is deposited on the inner surface of the quartz tube to be coated. The reaction time is 10min.

[0040] Example 6 This embodiment provides a quartz tube coating method, using the coating equipment of embodiment 2 and embodiment 3 to coat a layer of silicon carbide film on the inner surface of the quartz tube. The coating method includes the following steps: S-1. The quartz tube to be coated is sent into the inner cavity of the coating furnace, and the quartz tube to be coated is sleeved outside the inner electrode to ensure that the quartz tube is completely placed in the rear area of ​​the reaction area; S-2. Evacuate the inner cavity of the coating furnace to maintain the inner cavity vacuum less than 15mtorr; S-3. Raise the inner temperature of the coating furnace to 500°C and adjust the pressure to 1500mtorr; S-4. Introduce methane and monosilane gas into the reaction area between the inner electrode and the quartz tube to be coated. Among them, methane is introduced at a flow rate of 2000sccm, and monosilane is introduced at a flow rate of 1000sccm. The RF power supply is turned on, and the power is adjusted to 25kW and the frequency is 25KHz to generate plasma, and a thin film is deposited on the inner surface of the quartz tube to be coated. The reaction time is 10min, during which the inner electrode rotates at a speed of 10rpm.

[0041] Example 6 This embodiment provides a quartz tube coating method, using the coating equipment of embodiment 2 and embodiment 3 to coat a layer of silicon carbide film on the inner surface of the quartz tube. The coating method includes the following steps: S-1. The quartz tube to be coated is sent into the inner cavity of the coating furnace, and the quartz tube to be coated is sleeved outside the inner electrode to ensure that the quartz tube is completely placed in the rear area of ​​the reaction area; S-2. Evacuate the inner cavity of the coating furnace to maintain the inner cavity vacuum less than 15mtorr; S-3. Raise the inner temperature of the coating furnace to 450°C and adjust the pressure to 2000mtorr; S-4. Introduce methane and monosilane gas into the reaction area between the inner electrode and the quartz tube to be coated. Among them, methane is introduced at a flow rate of 3500sccm, and monosilane is introduced at a flow rate of 2000sccm. The RF power supply is turned on, and the power is adjusted to 35kW and the frequency is 25KHz to generate plasma, and a thin film is deposited on the inner surface of the quartz tube to be coated. The reaction time is 10min, during which the inner electrode rotates at a speed of 10rpm.

[0042] The thickness uniformity of the thin film formed on the inner surface of the quartz tube using the methods of Examples 5 to 7 was tested.

[0043] Detection method: Select 5 points on the inner wall of the quartz tube (see the selection positions of the 5 points Figure 3In the middle, three points are evenly selected in the circumferential direction of the quartz tube. In addition, one point is randomly selected at the front of the quartz tube and one point is randomly selected at the back of the quartz tube (respectively marked as point 1, point 2, point 3, point 4, and point 5). The film thickness is measured using an ellipsometer.

[0044] The uniformity calculation formula is as follows: Thickness uniformity = [(maximum film thickness - minimum film thickness) / (2*average film thickness)]*100%.

[0045] Test results: See Table 1.

[0046] Table 1 Thickness of silicon carbide films formed in various embodiments It can be seen from Table 1 that the silicon carbide film formed on the inner surface of the quartz tube by using the coating equipment and method of the present invention has good thickness uniformity.

[0047] Specifically, the coating method of Example 5 was implemented using the coating equipment of Example 1-2. Although the structure of the inner electrode in Example 2 can rotate, the rotating inner electrode was not turned on during the coating process, and the uniformity of the obtained thin film was equivalent. The coating method of Example 5 was implemented using the coating equipment of Example 3. Due to the setting of the pre-zone and the post-zone, the uniformity of the obtained thin film was better than that of the coating equipment of Example 1-2 without the pre-zone, indicating that the setting of the pre-zone is beneficial to improve the thickness uniformity of the silicon carbide film formed on the inner surface of the quartz tube to a certain extent.

[0048] Using the coating equipment of Examples 2-3, the coating method of Example 6 is implemented. Compared with the method of Example 5, in the reaction stage (i.e., step S-4), the inner electrode rotates at a fixed speed. The obtained film uniformity is better, indicating that the transfer of the inner electrode is beneficial to improving the thickness uniformity of the silicon carbide film formed on the inner surface of the quartz tube to a certain extent. Compared with the coating equipment of Example 2, the coating equipment of Example 3 is provided with a pre-zone, and the obtained film uniformity is better, indicating that the provision of the pre-zone is beneficial to improving the thickness uniformity of the silicon carbide film formed on the inner surface of the quartz tube to a certain extent. Similarly, using the coating equipment of Examples 2-3 to implement the coating method of Example 7 can also illustrate the above effect.

[0049] In order to study the effect of the rotation speed of the inner electrode on the film performance, the present invention also uses the coating equipment of Example 2, adjusts the rotation speed of the inner electrode at different speeds, and coats the quartz tube using the method of Example 7. The results are shown in Table 2 (the rotation speed is different, and other conditions are the same as in Example 7).

[0050] Table 2 Thickness of silicon carbide films formed under different rotation speeds of the inner electrode It can be seen from Table 2 that when the internal electrode rotation speed is controlled within the range of 5rpm to 25rpm, the thickness uniformity of the silicon carbide film formed on the inner surface of the quartz tube is good. When the internal electrode rotation speed exceeds 30rpm, due to excessive disturbance, the thickness uniformity of the silicon carbide film deteriorates, and even brings negative effects, which is worse than the effect of fixing the internal electrode without rotating.

Claims

1. A coating device for a quartz tube of a chemical vapor deposition tube furnace, characterized in that: The invention comprises a coating furnace body, an outer electrode arranged on the inner wall of the coating furnace body, an inner electrode arranged in the inner cavity of the coating furnace body, a radio frequency power supply electrically connected to the inner electrode and the outer electrode, a heating structure for providing heat to the inner cavity of the coating furnace body, a supporting structure arranged in the inner cavity of the coating furnace body for supporting a quartz tube to be coated, and an air inlet structure and an air outlet structure arranged at the end of the coating furnace body. A reaction area is formed between the outer electrode and the inner electrode. During coating, the quartz tube to be coated is sleeved outside the inner electrode and is located in the reaction area. The air inlet structure introduces working gas between the quartz tube to be coated and the inner electrode. The working gas is electrolyzed into plasma under the action of electricity supplied to the inner electrode and the outer electrode.

2. A quartz tube coating device according to claim 1, characterized in that: The coating furnace body adopts a multi-section type, and each section of the coating furnace body corresponds to an independent heating structure.

3. The quartz tube coating device according to claim 1, characterized in that: The inner electrode is installed at the end of the coating furnace body through a rotating base, and the inner electrode rotates under the drive of the rotating base.

4. The quartz tube coating device according to claim 3, characterized in that: The reaction area includes a front area close to the opening and a rear area far from the opening. During coating, the quartz tube to be coated is located in the rear area of ​​the reaction area. In the front area, the working gas begins to be decomposed into active groups, and the active groups move forward to the rear area under the action of the airflow.

5. The quartz tube coating device according to claim 4, characterized in that: The length of the pre-zone is 1 / 2 or more of the length of the post-zone.

6. A coating method using the coating device according to any one of claims 1 to 5, characterized in that: At least the following steps are included: S-1. The quartz tube to be coated is sent into the inner cavity of the coating furnace, and the quartz tube to be coated is sleeved outside the inner electrode; S-2. Evacuate the inner cavity of the coating furnace to maintain the inner cavity vacuum; S-3. Raise the temperature of the coating furnace cavity to T and adjust the pressure to P; S-4. Introduce working gas into the area between the inner electrode and the quartz tube to be coated, turn on the RF power supply to generate plasma, and deposit a thin film on the inner surface of the quartz tube to be coated.

7. The coating method according to claim 6, characterized in that: In step S-4, the inner electrode is rotated at a rotation speed of 10 rpm to 25 rpm.

8. The coating method according to claim 6, characterized in that: In step S-4, the working gases are methane and monosilane, the flow rate of methane is 1000-5000 sccm, and the flow rate of monosilane is 1000-2500 sccm.

9. The coating method according to claim 6, characterized in that: After the deposition is completed in step S-4, a low-temperature inert gas is introduced into the inner cavity of the coating furnace.

10. A quartz tube, characterized in that: By the coating method described in any one of claims 6 to 9, a silicon carbide film is formed on the inner surface of a quartz tube for use in a chemical vapor deposition tube furnace.

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