Method for prolonging service life of graphite boat

Abstract

The invention relates to the technical field of graphite boats, in particular to a method for prolonging the service life of a graphite boat, which comprises the following steps: S1, cleaning and drying the graphite boat and a silicon wafer to be coated with a film by using a pickling solution and a cleaning solution, and S2, cleaning the silicon wafer to be coated with the film by using a tubular PECVD (Plasma Enhanced Chemical Vapor Deposition) device under the conditions that the furnace temperature is 430-480 DEG C, the radio frequency current is 8-12A, the voltage is 400-420V and the power is 1.5-2.7 kW. And sequentially plating three layers of silicon films on the silicon wafer by adopting a plasma enhanced chemical vapor deposition method. When the graphite boat is cleaned, dried and coated, hydrofluoric acid is used as a pickling solution, low radio-frequency current is realized, the graphite boat adopts a round sticking point shape with a large contact area with a silicon wafer, and three layers of silicon films are sequentially coated on the silicon wafer by using a plasma enhanced chemical vapor deposition method; the problems that the coating color uniformity is poor, and the thickness of the surface film of the silicon wafer is not uniform are solved, the silicon wafer coating quality is remarkably improved, and the service life of the graphite boat is prolonged.

Description

Technical Field

[0001] The invention relates to the technical field of graphite boats, and in particular to a method for extending the service life of a graphite boat. Background Art

[0002] Graphite boat is a special boat with graphite as the base material. With the continuous development of new material technology, the application of graphite boat in many fields has gradually attracted attention. Plasma chemical vapor deposition (PECVD) is one of the most commonly used coating processes and is widely used in the production process of semiconductors and solar cells. In the preparation of solar cells, the use of plasma enhanced chemical vapor deposition process to coat the back of silicon wafers is one of the important processes, and the graphite boat that carries a large number of silicon wafers is the key core component of the tubular PECVD equipment.

[0003] The existing graphite boat has been used for a certain number of times or for a certain period of time. Due to the serious corrosion damage of the graphite boat sheets, it is necessary to use tubular PECVD equipment to coat the graphite boat. Although PECVD technology has a fast film forming speed, slight winding plating, and in-situ doping, the color uniformity of the PECVD coating is poor, and due to the void structure of graphite, it has a certain adsorption capacity for silicon nitride gas. During the PECVD coating process, the film thickness on the surface of the silicon wafer is uneven, and the silicon wafers at the stuck points of the graphite boat often have defects after coating, which in turn affects the service life of the graphite boat.

[0004] In summary, developing a method for extending the service life of a graphite boat is still a key issue that needs to be urgently addressed in the field of graphite boat technology. Summary of the invention

[0005] In view of the problems existing in the prior art, the object of the present invention is to provide a method for extending the service life of a graphite boat.

[0006] To achieve the above object, the present invention provides the following technical solutions: A method for extending the service life of a graphite boat comprises the following steps: S1. Clean and dry the graphite boat and the silicon wafer to be coated using pickling liquid and cleaning liquid; S2. Using a tubular PECVD device, three layers of silicon film are sequentially deposited on the silicon wafer using plasma enhanced chemical vapor deposition method under the conditions of furnace temperature of 430℃~480℃, RF current of 8A~12A, voltage of 400V~420V, and power of 1.5~2.7kW.

[0007] The present invention is further configured as follows: in step S1, the following steps are included: S11, preparing a pickling solution, wherein the raw materials of the pickling solution are 35% to 90% hydrofluoric acid, 0% to 20% hydrochloric acid, 15% surfactant and 60% to 85% cleaning solution in a volume ratio; S12, bubbling water washing: Use cleaning liquid to clean the graphite boat and silicon wafer for 2-3 hours, change the water every 0.5 hours, and keep bubbling during cleaning until the graphite boat is rinsed until there is no dust on the surface; S13, bubbling pickling: soak the cleaned graphite boat and silicon wafer in pickling solution for 1-3 hours, use pickling solution to clean the graphite boat and silicon wafer to be coated at a temperature of 30°C-50°C, and use N2 to set bubbling for 15-25 minutes every 20-50 minutes; S14, bubbling water washing: put the acid-washed graphite boat and silicon wafer into the cleaning solution and soak them for 3-5 hours, change the water every 0.5 hours, and keep bubbling during the cleaning process. Test the pH value of the graphite boat surface before each pure water washing until the pH value of the graphite boat surface is neutral. S15. Exhaust drying: Place the cleaned graphite boat in a nitrogen cabinet and exhaust dry it at a temperature of 300℃~320℃ for 9~16h.

[0008] The present invention is further configured as follows: in step S11, the surfactant is selected from any one of lignin sulfonate, alkylphenol polyoxyethylene ether and sulfobetaine, and the cleaning liquid is pure water.

[0009] The present invention is further configured as follows: in step S2, the following steps are included: S21, placing the cleaned and dried silicon wafer into the silicon wafer mounting groove of the graphite boat, and clamping the silicon wafer into the silicon wafer mounting groove through the circular clamping point of the graphite boat, so that the silicon wafer is completely mounted on the graphite boat; S22, placing the graphite boat on a push boat, and the push boat carries the graphite boat and sends it into the reaction chamber of the tubular PECVD device; S23, closing the coating furnace door of the reaction chamber, checking the sealing of the coating furnace, and after confirming that the sealing is good, extracting the air in the coating furnace; S24, introducing nitrogen into the coating furnace, checking the sealing of the coating furnace again, and after confirming that the sealing is good, introducing silane and inert gas ammonia into the coating furnace, and maintaining the temperature in the coating furnace at 430° C. to 480° C., reacting under the conditions of radio frequency current 8A to 12A, voltage 400V to 420V, and power 1.5 to 2.7kW, silane and ammonia react to generate silicon nitride, and the generated silicon nitride is deposited on the silicon wafer, and a first layer of silicon film is plated on the silicon wafer by a plasma enhanced chemical vapor deposition method; S25, after purging the coated silicon wafers, the push boat pushes the graphite boat out of the tubular PECVD device, performs quality inspection on the coated silicon wafers, and removes unqualified products; S26, repeating steps S24 and S25 twice, and coating a second silicon film and a third silicon film on the silicon wafer by plasma enhanced chemical vapor deposition; S27, under the protection of inert gas, slowly raising the temperature in the coating furnace to 900° C. to 960° C., crystallizing the amorphous silicon film on the silicon wafer to obtain a crystalline silicon film; S28. Under the protection of inert gas, wait for the graphite boat to cool to room temperature, and then use a push boat to push the graphite boat out of the tubular PECVD device.

[0010] The present invention is further configured as follows: the tubular PECVD device includes a furnace body, a furnace door, a furnace tail, an internal thermocouple, a graphite boat assembly, a support, a quartz tube and an insulation layer, one end of the inner wall of the furnace body is fixedly installed with one end of the internal thermocouple, and the outer wall of the furnace body is fixedly connected with multiple external thermocouples, and the inner wall of the furnace body is symmetrically fixedly installed with multiple auxiliary heating components.

[0011] The present invention is further configured as follows: the quartz tube is sleeved on the outer wall of the furnace body, and a resistance heating wire is fixedly installed on the outer wall of the quartz tube, and the thermal insulation layer is sleeved on the outer side of the resistance heating wire.

[0012] The present invention is further configured as follows: the inner wall of the furnace body is fixedly mounted on both ends of the support member, and support flanges are symmetrically welded to the outer sides of both ends of the furnace body.

[0013] The present invention is further configured as follows: one end of the furnace body is fixedly installed with one end of the furnace door, and the other end of the furnace body is fixedly installed with one end of the furnace tail, one end of the furnace door is fixedly installed with a sealing and water-cooling flange, and one end of the furnace tail is fixedly connected with an air intake flange. Beneficial Effects

[0014] Compared with the known public technology, the technical solution provided by the present invention has the following beneficial effects: (1) In the present invention, when the graphite boat is cleaned and coated by the method, the graphite boat and the silicon wafer to be coated are cleaned and dried by using an acid wash liquid and a cleaning liquid. The graphite boat cleaning liquid is pure water and the acid wash liquid is a simple hydrofluoric acid solution. During the cleaning process of the graphite boat, a large amount of plasma will not be generated, which avoids the tip discharge at the contact position between the circular card point of the graphite boat and the silicon wafer, reduces the temperature at the circular card point of the graphite boat, avoids affecting the coating quality at the circular card point, thereby ensuring the overall coating quality of the graphite boat, solving the problem that the silicon wafer at the card point of the graphite boat often has defects after coating, and prolongs the service life of the graphite boat.

[0015] (2) In the present invention, a tubular PECVD device is used and under the conditions of a furnace temperature of 430°C, a radio frequency current of 8A, a voltage of 400V, and a power of 1.5kW, a plasma enhanced chemical vapor deposition method is used to sequentially coat three layers of silicon film on a silicon wafer to obtain a final graphite boat. A low radio frequency current is used and the graphite boat adopts a circular card point shape with a large contact area with the silicon wafer, which effectively solves the problem of silicon wafer defects and burning at the circular card points of the graphite boat, significantly improves the quality of silicon wafers when coated with the device, and extends the service life of the graphite boat. The film thickness and refractive index uniformity of the obtained silicon wafers on the graphite boat are greatly improved, which solves the problems of poor color uniformity and uneven film thickness on the surface of the silicon wafers in the prior art using the PECVD technology for coating.

[0016] (3) In the present invention, a tubular PECVD device is provided, and two sets of upper and lower auxiliary heating components are added to the furnace body. The heating rod adopts infrared radiation heating. In a low-pressure environment, this heating method has high efficiency, small mass and low heat capacity. After the auxiliary heating is turned off, the impact on the temperature in the furnace is small, which promotes the uniform distribution of the temperature in the furnace. The auxiliary heating components can not only shorten the heating time in the furnace body and improve the equipment production capacity, but also obtain better silicon nitride film uniformity indicators, especially have a more obvious improvement effect on the uniformity between wafers, thereby improving the heating effect, improving the uniformity and thickness of the silicon film on the silicon wafer, and improving the coating quality of the graphite boat. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A process flow chart of a method for extending the service life of a graphite boat; Figure 2 A front cross-sectional view of a tubular PECVD device for extending the service life of a graphite boat; Figure 3 A side view of a method for extending the service life of a graphite boat.

[0018] In the figure: 1. furnace body; 2. furnace door; 3. furnace tail; 4. internal thermocouple; 5. graphite boat assembly; 6. support; 7. sealing and water cooling flange; 8. external thermocouple; 9. quartz tube; 10. resistance heating wire; 11. insulation layer; 12. auxiliary heating assembly; 13. support flange; 14. air inlet flange. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] The present invention will be further described below in conjunction with the embodiments. Example 1

[0021] Please refer to Figure 1 As shown, a method for extending the service life of a graphite boat comprises the following steps: Step 1: using pickling liquid and cleaning liquid to clean and dry the graphite boat and the silicon wafer to be coated, including the following steps: S11, preparing a pickling solution, wherein the raw materials of the pickling solution are 90% hydrofluoric acid, 15% surfactant and 85% cleaning solution in a volume ratio; Among them, the surfactant is lignin sulfonate, and the cleaning liquid is pure water; S12, bubbling water washing: use cleaning liquid to clean the graphite boat and silicon wafer for 2 hours, change the water every 0.5 hours, and keep bubbling during cleaning until the graphite boat is rinsed until there is no dust on the surface; S13, bubbling pickling: soak the cleaned graphite boat and silicon wafer in pickling solution for 1 hour, use the pickling solution to clean the graphite boat and the silicon wafer to be coated at a temperature of 30°C, and use N2 to set bubbling for 15 minutes every 20 minutes; S14, bubbling water washing: the graphite boat and silicon wafer after acid washing are then placed in the cleaning solution for immersion and cleaning for 3 hours, and the water is changed every 0.5 hours. Bubbling is continued during cleaning, and the pH value of the graphite boat surface is tested before each pure water washing until the pH value of the graphite boat surface is neutral; S15. Drying by exhaust: Place the cleaned graphite boat in a nitrogen cabinet and dry it by exhaust at 300°C for 9 hours.

[0022] Step 2: Using a tubular PECVD device, under the conditions of a furnace temperature of 430°C, a radio frequency current of 8A, a voltage of 400V, and a power of 1.5kW, three layers of silicon film are sequentially plated on the silicon wafer using a plasma enhanced chemical vapor deposition method, comprising the following steps: S21, placing the cleaned and dried silicon wafer into the silicon wafer mounting groove of the graphite boat, and clamping the silicon wafer into the silicon wafer mounting groove through the circular clamping point of the graphite boat, so that the silicon wafer is completely mounted on the graphite boat; S22, placing the graphite boat on a push boat, and the push boat carries the graphite boat and sends it into the reaction chamber of the tubular PECVD device; S23, closing the coating furnace door of the reaction chamber, checking the sealing of the coating furnace, and after confirming that the sealing is good, extracting the air in the coating furnace; S24, introducing nitrogen into the coating furnace, checking the sealing of the coating furnace again, and after confirming that the sealing is good, introducing silane and inert gas ammonia into the coating furnace, and maintaining the temperature in the coating furnace at 430° C., reacting under the conditions of radio frequency current 8A, voltage 400V, and power 1.5kW, silane and ammonia react to generate silicon nitride, and the generated silicon nitride is deposited on the silicon wafer, and a first layer of silicon film is plated on the silicon wafer by a plasma enhanced chemical vapor deposition method; S25, after purging the coated silicon wafers, the push boat pushes the graphite boat out of the tubular PECVD device, performs quality inspection on the coated silicon wafers, and removes unqualified products; S26, repeating steps S24 and S25 twice, and coating a second silicon film and a third silicon film on the silicon wafer by plasma enhanced chemical vapor deposition; S27, under the protection of inert gas, slowly raising the temperature in the coating furnace to 900° C. to crystallize the amorphous silicon film on the silicon wafer to obtain a crystalline silicon film; S28. Under the protection of inert gas, wait for the graphite boat to cool to room temperature, and then use a push boat to push the graphite boat out of the tubular PECVD device. Example 2

[0023] Please refer to Figure 1 As shown, a method for extending the service life of a graphite boat comprises the following steps: Step 1: using pickling liquid and cleaning liquid to clean and dry the graphite boat and the silicon wafer to be coated, including the following steps: S11, preparing a pickling solution, wherein the raw materials of the pickling solution are 50% hydrofluoric acid, 10% hydrochloric acid, 15% surfactant and 75% cleaning solution in a volume ratio; Among them, the surfactant is alkylphenol polyoxyethylene ether, and the cleaning liquid is pure water; S12, bubbling water washing: use cleaning liquid to clean the graphite boat and silicon wafer for 3 hours, change the water every 0.5 hours, and keep bubbling during cleaning until the graphite boat is rinsed until there is no dust on the surface; S13, bubbling pickling: soak the cleaned graphite boat and silicon wafer in pickling solution for 2 hours, use the pickling solution to clean the graphite boat and the silicon wafer to be coated at a temperature of 40°C, and use N2 to bubble for 20 minutes every 30 minutes; S14, bubbling water washing: the graphite boat and silicon wafer after acid washing are then placed in the cleaning solution for immersion and cleaning for 4 hours, and the water is changed every 0.5 hours. Bubbling is continuous during cleaning, and the pH of the graphite boat surface is tested before each pure water washing until the pH of the graphite boat surface is neutral; S15. Vacuum drying: Place the cleaned graphite boat in a nitrogen cabinet and vacuum dry it at 310°C for 12 hours.

[0024] Step 2: Using a tubular PECVD device, under the conditions of a furnace temperature of 450°C, a radio frequency current of 10A, a voltage of 410V, and a power of 2kW, three layers of silicon film are sequentially plated on the silicon wafer using a plasma enhanced chemical vapor deposition method, comprising the following steps: S21, placing the cleaned and dried silicon wafer into the silicon wafer mounting groove of the graphite boat, and clamping the silicon wafer into the silicon wafer mounting groove through the circular clamping point of the graphite boat, so that the silicon wafer is completely mounted on the graphite boat; S22, placing the graphite boat on a push boat, and the push boat carries the graphite boat and sends it into the reaction chamber of the tubular PECVD device; S23, closing the coating furnace door of the reaction chamber, checking the sealing of the coating furnace, and after confirming that the sealing is good, extracting the air in the coating furnace; S24, introducing nitrogen into the coating furnace, checking the sealing of the coating furnace again, and after confirming that the sealing is good, introducing silane and inert gas ammonia into the coating furnace, and maintaining the temperature in the coating furnace at 450° C., reacting under the conditions of radio frequency current 10A, voltage 410V, and power 2kW, silane and ammonia react to generate silicon nitride, and the generated silicon nitride is deposited on the silicon wafer, and a first layer of silicon film is plated on the silicon wafer by a plasma enhanced chemical vapor deposition method; S25, after purging the coated silicon wafers, the push boat pushes the graphite boat out of the tubular PECVD device, performs quality inspection on the coated silicon wafers, and removes unqualified products; S26, repeating steps S24 and S25 twice, and coating a second silicon film and a third silicon film on the silicon wafer by plasma enhanced chemical vapor deposition; S27, under the protection of inert gas, slowly raising the temperature in the coating furnace to 930° C. to crystallize the amorphous silicon film on the silicon wafer to obtain a crystalline silicon film; S28. Under the protection of inert gas, wait for the graphite boat to cool to room temperature, and then use a push boat to push the graphite boat out of the tubular PECVD device. Example 3

[0025] Please refer to Figure 1 As shown, a method for extending the service life of a graphite boat comprises the following steps: Step 1: using pickling liquid and cleaning liquid to clean and dry the graphite boat and the silicon wafer to be coated, including the following steps: S11, preparing a pickling solution, wherein the raw materials of the pickling solution are 35% hydrofluoric acid, 20% hydrochloric acid, 15% surfactant and 85% cleaning solution in a volume ratio; Among them, the surfactant is sulfobetaine, and the cleaning liquid is pure water; S12, bubbling water washing: use cleaning liquid to clean the graphite boat and silicon wafer for 3 hours, change the water every 0.5 hours, and keep bubbling during cleaning until the graphite boat is rinsed until there is no dust on the surface; S13, bubbling pickling: soak the cleaned graphite boat and silicon wafer in pickling solution for 3 hours, use the pickling solution to clean the graphite boat and the silicon wafer to be coated at a temperature of 50°C, and use N2 to set bubbling for 25 minutes every 50 minutes; S14, bubbling water washing: the graphite boat and silicon wafer after acid washing are then placed in the cleaning solution for 5 hours, and the water is changed every 0.5 hours. Bubbling is continued during the cleaning process, and the pH value of the graphite boat surface is tested before each pure water washing until the pH value of the graphite boat surface is neutral; S15. Exhaust drying: Place the cleaned graphite boat in a nitrogen cabinet and exhaust dry it at 320°C for 16 hours.

[0026] Step 2: Using a tubular PECVD device, under the conditions of a furnace temperature of 480°C, a radio frequency current of 12A, a voltage of 420V, and a power of 2.7kW, three layers of silicon film are sequentially plated on the silicon wafer using a plasma enhanced chemical vapor deposition method, comprising the following steps: S21, placing the cleaned and dried silicon wafer into the silicon wafer mounting groove of the graphite boat, and clamping the silicon wafer into the silicon wafer mounting groove through the circular clamping point of the graphite boat, so that the silicon wafer is completely mounted on the graphite boat; S22, placing the graphite boat on a push boat, and the push boat carries the graphite boat and sends it into the reaction chamber of the tubular PECVD device; S23, closing the coating furnace door of the reaction chamber, checking the sealing of the coating furnace, and after confirming that the sealing is good, extracting the air in the coating furnace; S24, introducing nitrogen into the coating furnace, checking the sealing of the coating furnace again, and after confirming that the sealing is good, introducing silane and inert gas ammonia into the coating furnace, and maintaining the temperature in the coating furnace at 480° C., reacting under the conditions of radio frequency current 12A, voltage 420V, and power 2.7kW, silane and ammonia react to generate silicon nitride, and the generated silicon nitride is deposited on the silicon wafer, and a first layer of silicon film is plated on the silicon wafer by a plasma enhanced chemical vapor deposition method; S25, after purging the coated silicon wafers, the push boat pushes the graphite boat out of the tubular PECVD device, performs quality inspection on the coated silicon wafers, and removes unqualified products; S26, repeating steps S24 and S25 twice, and coating a second silicon film and a third silicon film on the silicon wafer by plasma enhanced chemical vapor deposition; S27, under the protection of inert gas, slowly raising the temperature in the coating furnace to 960° C. to crystallize the amorphous silicon film on the silicon wafer to obtain a crystalline silicon film; S28. Under the protection of inert gas, wait for the graphite boat to cool to room temperature, and then use a push boat to push the graphite boat out of the tubular PECVD device. Example 4

[0027] Reference Figure 2 and Figure 3 As shown, the present embodiment provides a tubular PECVD device, which includes a furnace body 1, a furnace door 2, a furnace tail 3, an internal thermocouple 4, a graphite boat assembly 5, a support 6, a quartz tube 9 and a thermal insulation layer 11. One end of the inner wall of the furnace body 1 is fixedly installed with one end of the internal thermocouple 4, and the outer wall of the furnace body 1 is fixedly connected with a plurality of external thermocouples 8, and the inner wall of the furnace body 1 is symmetrically fixedly installed with a plurality of auxiliary heating components 12, the quartz tube 9 is sleeved on the outer wall of the furnace body 1, and the outer wall of the quartz tube 9 is fixedly installed with a resistance heating wire 10, the thermal insulation layer 11 is sleeved on the outer side of the resistance heating wire 10, the inner wall of the furnace body 1 is fixedly installed with both ends of the support 6, and support flanges 13 are symmetrically welded on the outer sides of both ends of the furnace body 1, one end of the furnace body 1 is fixedly installed with one end of the furnace door 2, and the other end of the furnace body 1 is fixedly installed with one end of the furnace tail 3, one end of the furnace door 2 is fixedly installed with a sealing and water-cooling flange 7, and one end of the furnace tail 3 is fixedly connected with an air intake flange 14.

[0028] The working principle of this embodiment is as follows: Figure 2 and Figure 3As shown, when the tubular PECVD device is in use, the staff puts the cleaned and dried silicon wafer into the silicon wafer mounting groove of the graphite boat assembly 5, and clamps the silicon wafer into the silicon wafer mounting groove through the circular clamping point of the graphite boat, so that all the silicon wafers are installed on the graphite boat, and puts the graphite boat assembly 5 on the push boat, which carries the graphite boat assembly 5 and sends it into the reaction chamber (furnace body 1) of the tubular PECVD device, closes the coating furnace door 2 of the furnace body 1, checks the sealing of the coating furnace body 1, and after confirming that the sealing is good, the air in the coating furnace body 1 is The gas is extracted, and nitrogen is introduced into the coating furnace body 1 through the air inlet flange 14. The sealing of the coating furnace body 1 is checked again. After confirming that the sealing is good, silane and inert gas ammonia are introduced into the coating furnace body 1, and the temperature in the coating furnace body 1 is maintained at 480°C through the resistance heating wire 10 and the auxiliary heating component 12 (which can be a heating rod). The internal thermocouple 4 and the external thermocouple 8 can monitor the temperature inside and outside the furnace body 1 in real time and accurately, ensuring the safe and stable operation of the resistance heating wire 10 and the auxiliary heating component 12; because the graphite boat component 5 is Before entering the reaction chamber for thin film deposition, it is necessary to heat up under low pressure. If the furnace is heated by the resistance heating wire 10 alone, the heating effect of thermal radiation becomes poor, the heating time is long, and the temperature uniformity of the graphite boat component 5 is not good, resulting in reduced production capacity and film quality. The reaction chamber of the existing furnace body 1 heating method is difficult to meet the production needs of increasing silicon wafer size and increasing wafer loading requirements. By adding two sets of upper and lower auxiliary heating components 12 (heating rods) in the furnace body 1, the heating rods use infrared radiation heating. In a low-pressure environment, this heating method has high efficiency, small mass and low heat capacity. After turning off the auxiliary heating, the temperature in the furnace is less affected, which promotes the uniform distribution of the temperature in the furnace. The auxiliary heating component 12 can not only shorten the heating time in the furnace body 1 and improve the equipment production capacity, but also obtain better silicon nitride film uniformity indicators, especially the uniformity between wafers has a more obvious improvement effect, thereby improving the heating effect and improving the temperature uniformity of the graphite boat; at the same time, when the RF current is 12A, the voltage is 420V, and the power is 2.7kW conditions, silane and ammonia react to generate silicon nitride, the generated silicon nitride is deposited on the silicon wafer, a first layer of silicon film is plated on the silicon wafer by a plasma enhanced chemical vapor deposition method, the plated silicon wafer is purged, and the graphite boat assembly 5 is pushed out of the tubular PECVD device by a boat pusher, the plated silicon wafer is quality inspected, and unqualified products are removed. Similarly, the above steps are repeated, and a second layer of silicon film and a third layer of silicon film are plated on the silicon wafer by a plasma enhanced chemical vapor deposition method. Under the protection of an inert gas, the temperature in the coating furnace body 1 is slowly raised to 960°C, the amorphous silicon film on the silicon wafer is crystallized to obtain a crystalline silicon film, and under the protection of an inert gas, the graphite boat assembly 5 is cooled to room temperature, and the graphite boat assembly 5 is pushed out of the tubular PECVD device by a boat pusher; after the above three coatings, a uniform silicon film with a film thickness of 6-22 μm is formed on the silicon wafer, the uniformity and thickness of the silicon film on the silicon wafer are improved, thereby improving the coating quality of the graphite boat. .

[0029] Please refer to Figure 1 As shown, this embodiment provides a method for extending the service life of a graphite boat, and the method is substantially the same as that of Embodiment 1, with the main difference being that in step 1, bubbling pickling is not performed.

[0030] Please refer to Figure 1 As shown, this embodiment provides a method for extending the service life of a graphite boat, and the method is substantially the same as that of Embodiment 1, with the main difference being that in step 2, a second layer of silicon film is not deposited.

[0031] Please refer to Figure 1 As shown, this embodiment provides a method for extending the service life of a graphite boat, and the method is substantially the same as that of Embodiment 1, with the main difference being that in step 2, the third silicon film is not deposited.

[0032] The graphite boats coated by the methods of Examples 1 to 3 are recorded as Example Groups 1 to 3, and the graphite boats coated by the methods of Comparative Examples 1 to 3 are recorded as Comparative Groups 1 to 3. According to the GOST 18262.12-1988 standard, the coated graphite boats of the experimental groups 1 to 3 and the comparative groups 1 to 3 are respectively subjected to coating uniformity and refractive index uniformity analysis, wherein the film thickness and refractive index of the silicon wafer after coating are tested by a sendech laser ellipsometer, and the color of the silicon wafer after coating is tested by a GP COl-Q color inspection device; the coating uniformity includes intra-wafer uniformity and inter-wafer uniformity, and the intra-wafer uniformity is characterized by: the film thickness and refractive index of the silicon wafer after coating are tested by a laser ellipsometer, and the 5 silicon wafers used for testing are all taken from the same position, and each silicon wafer is tested at 5 fixed points, namely, 1 center and 4 corners, and the standard deviation is used to characterize the intra-wafer uniformity according to the test data; the inter-wafer uniformity is characterized by: using a GP The COl-Q color inspection equipment tests the color of the silicon wafer after coating. The standard deviation is used to characterize the uniformity between wafers based on the test data. The relevant data are recorded in Table 1.

[0033] Table 1: Test data record table Group In-chip uniformity (%) Uniformity between sheets (%) Refractive index uniformity (%) Example 1 Group 0.71 2.02 0.64 Example 2 Group 0.79 2.15 0.69 Example 3 Group 0.82 2.04 0.72 Comparison group 1 1.11 2.21 0.82 Comparison of 2 groups 1.28 2.13 0.85 Comparison of 3 groups 1.22 2.10 0.94 It can be seen from Table 1 that, compared with the comparison groups 1 to 3, the graphite boat prepared by the examples 1 to 3 groups can reduce its intra-sheet uniformity and inter-sheet uniformity, and the smaller the inter-sheet uniformity value is, the better the uniformity of the graphite boat after coating, and the smaller the intra-sheet uniformity value is, the trend of improvement of its uniformity is. When the graphite boat is cleaned and coated by the method of Example 1, the film thickness uniformity and refractive index uniformity of the obtained graphite boat silicon wafer are the smallest, thereby concluding that the film thickness and refractive index uniformity of the graphite boat silicon wafer obtained by this method are greatly improved.

[0034] In the present invention, when the graphite boat is cleaned and coated by the method, the graphite boat and the silicon wafer to be coated are cleaned and dried by using an acid wash liquid and a cleaning liquid (the raw materials of the acid wash liquid are 90% hydrofluoric acid, 15% surfactant and 85% cleaning liquid by volume, and the steps are bubbling water washing for 2 hours, bubbling acid washing for 1 hour, bubbling water washing for 3 hours, and exhaust drying), and then a tubular PECVD device is used to perform plasma enhanced evaporation at a furnace temperature of 430°C, a radio frequency current of 8A, a voltage of 400V, and a power of 1.5kW. The chemical vapor deposition method sequentially deposits three layers of silicon film on the silicon wafer, and each time a layer of film is deposited, the coated silicon wafer is purged, and the coated silicon wafer is quality inspected to remove unqualified products, thereby obtaining the final graphite boat. The film thickness uniformity and refractive index uniformity of the obtained graphite boat silicon wafer are both minimized, so it is concluded that the film thickness and refractive index uniformity of the graphite boat silicon wafer obtained by this method are greatly improved, which solves the problems of poor color uniformity and high film thickness on the surface of the silicon wafer in the prior art using PECVD technology for coating. The problem of unevenness; at the same time, in the process of cleaning and drying the graphite boat and the silicon wafer, hydrofluoric acid is used as the pickling liquid and pure water is used as the cleaning liquid. In the process of coating using a tubular PECVD device, under the conditions of a furnace temperature of 430°C, a radio frequency current of 8A, a voltage of 400V, and a power of 1.5kW, a plasma enhanced chemical vapor deposition method is used to sequentially coat three layers of silicon film on the silicon wafer; a lower radio frequency current is used during coating to reduce the probability of silicon wafer burning at the circular card point of the graphite boat; the binding force between hydrogen and fluorine atoms in hydrofluoric acid is relatively strong, and there are hydrogen bonds between hydrogen fluoride molecules in water, so that hydrofluoric acid is not easy to ionize in water. During the cleaning process of the graphite boat, a large amount of plasma will not be generated, which avoids the tip discharge at the contact position between the circular card point of the graphite boat and the silicon wafer, reduces the temperature at the circular card point of the graphite boat, and avoids affecting the coating quality at the circular card point, thereby ensuring the overall coating quality of the graphite boat, solving the problem that the silicon wafer at the card point of the graphite boat often has defects after coating, and extending the service life of the graphite boat; In summary, when using a tubular PECVD device to coat silicon wafers, a low RF current is used, the graphite boat adopts a circular card point shape with a large contact area with the silicon wafer, pure water is used as the graphite boat cleaning liquid, and a pure hydrofluoric acid solution is used as the graphite boat pickling liquid. This effectively solves the problem of silicon wafer defects and burning at the circular card points of the graphite boat, significantly improves the quality of silicon wafers when coated using the device, and extends the service life of the graphite boat.

[0035] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for extending the service life of a graphite boat, It is characterized in that The following steps are involved: S1. Clean and dry the graphite boat and the silicon wafer to be coated using pickling liquid and cleaning liquid; S2. Using a tubular PECVD device, three layers of silicon film are sequentially deposited on the silicon wafer using plasma enhanced chemical vapor deposition method under the conditions of furnace temperature of 430℃~480℃, RF current of 8A~12A, voltage of 400V~420V, and power of 1.5~2.7kW.

2. A method for extending the service life of a graphite boat according to claim 1, It is characterized in that In step S1, the following steps are included: S11, preparing a pickling solution, wherein the raw materials of the pickling solution are 35% to 90% hydrofluoric acid, 0% to 20% hydrochloric acid, 15% surfactant and 60% to 85% cleaning solution in a volume ratio; S12, bubbling water washing: Use cleaning liquid to clean the graphite boat and silicon wafer for 2-3 hours, change the water every 0.5 hours, and keep bubbling during cleaning until the graphite boat is rinsed until there is no dust on the surface; S13, Bubble pickling: Soak the cleaned graphite boat and silicon wafer in the pickling solution for 1~3 hours, and use the pickling solution to clean the graphite boat and the silicon wafer to be coated at a temperature of 30℃~50℃. 2 Set the bubbling time to 15-25 minutes; S14, bubbling water washing: put the acid-washed graphite boat and silicon wafer into the cleaning solution and soak them for 3-5 hours, change the water every 0.5 hours, and keep bubbling during the cleaning process. Test the pH value of the graphite boat surface before each pure water washing until the pH value of the graphite boat surface is neutral. S15. Exhaust drying: Place the cleaned graphite boat in a nitrogen cabinet and exhaust dry it at a temperature of 300℃~320℃ for 9~16h.

3. A method for extending the service life of a graphite boat according to claim 2, It is characterized in that In step S11, the surfactant is selected from any one of lignin sulfonate, alkylphenol polyoxyethylene ether and sulfobetaine, and the cleaning liquid is pure water.

4. A method for extending the service life of a graphite boat according to claim 1, It is characterized in that In step S2, the following steps are included: S21, placing the cleaned and dried silicon wafer into the silicon wafer mounting groove of the graphite boat, and clamping the silicon wafer into the silicon wafer mounting groove through the circular clamping point of the graphite boat, so that the silicon wafer is completely mounted on the graphite boat; S22, placing the graphite boat on a push boat, and the push boat carries the graphite boat and sends it into the reaction chamber of the tubular PECVD device; S23, closing the coating furnace door of the reaction chamber, checking the sealing of the coating furnace, and after confirming that the sealing is good, extracting the air in the coating furnace; S24, introducing nitrogen into the coating furnace, checking the sealing of the coating furnace again, and after confirming that the sealing is good, introducing silane and inert gas ammonia into the coating furnace, and maintaining the temperature in the coating furnace at 430° C. to 480° C., reacting under the conditions of radio frequency current 8A to 12A, voltage 400V to 420V, and power 1.5 to 2.7kW, silane and ammonia react to generate silicon nitride, and the generated silicon nitride is deposited on the silicon wafer, and a first layer of silicon film is plated on the silicon wafer by a plasma enhanced chemical vapor deposition method; S25, after purging the coated silicon wafers, the push boat pushes the graphite boat out of the tubular PECVD device, performs quality inspection on the coated silicon wafers, and removes unqualified products; S26, repeating steps S24 and S25 twice, and coating a second silicon film and a third silicon film on the silicon wafer by plasma enhanced chemical vapor deposition; S27, under the protection of inert gas, slowly raising the temperature in the coating furnace to 900° C. to 960° C., crystallizing the amorphous silicon film on the silicon wafer to obtain a crystalline silicon film; S28. Under the protection of inert gas, wait for the graphite boat to cool to room temperature, and then use a push boat to push the graphite boat out of the tubular PECVD device.

5. A method for extending the service life of a graphite boat according to claim 1, It is characterized in that The tubular PECVD device comprises a furnace body (1), a furnace door (2), a furnace tail (3), an internal thermocouple (4), a graphite boat assembly (5), a support member (6), a quartz tube (9) and a thermal insulation layer (11); one end of the inner wall of the furnace body (1) is fixedly mounted to one end of the internal thermocouple (4); a plurality of external thermocouples (8) are fixedly connected to the outer wall of the furnace body (1); and a plurality of auxiliary heating assemblies (12) are symmetrically fixedly mounted on the inner wall of the furnace body (1).

6. A method for extending the service life of a graphite boat according to claim 5, It is characterized in that The quartz tube (9) is sleeved on the outer wall of the furnace body (1), and a resistance heating wire (10) is fixedly mounted on the outer wall of the quartz tube (9), and the thermal insulation layer (11) is sleeved on the outer side of the resistance heating wire (10).

7. A method for extending the service life of a graphite boat according to claim 5, It is characterized in that The inner wall of the furnace body (1) is fixedly mounted to both ends of the support member (6), and support flanges (13) are symmetrically welded to the outer sides of both ends of the furnace body (1).

8. A method for extending the service life of a graphite boat according to claim 5, It is characterized in that One end of the furnace body (1) is fixedly mounted to one end of a furnace door (2), and the other end of the furnace body (1) is fixedly mounted to one end of a furnace tail (3); a sealing and water-cooling flange (7) is fixedly mounted on one end of the furnace door (2), and an air inlet flange (14) is fixedly connected to one end of the furnace tail (3).

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