Novel diffusion process for gradient deposition and diffusion of high sheet resistance

Abstract

The invention discloses a novel diffusion process for gradient deposition and diffusion of high sheet resistance, and relates to the field of boron diffusion of solar cells, and the novel diffusion process comprises the following steps: in a tubular diffusion furnace, BCl3 enters from the furnace during ventilation, boron trichloride is decomposed at a high temperature and reacts with Si to generate elemental boron, and the elemental boron is diffused into a silicon substrate to form a PN junction; diffusion is divided into three steps: pre-diffusion, diffusion and redistribution, limited surface source diffusion is adopted, impurities introduced by pre-diffusion and diffusion are used as diffusion sources, and diffusion is carried out at a relatively high concentration so as to control the surface concentration and the diffusion depth. According to the novel gradient deposition diffusion high sheet resistance diffusion process, the high surface concentration and shallow junction depth design is adopted, the shallow junction depth design can effectively reduce the impurity recombination center of the surface, the survival rate of surface minority carriers is improved, meanwhile, the response of short waves is increased, Isc and Uoc are effectively increased based on the design, and therefore the performance of the diffusion process is improved. And the purpose of improving efficiency is achieved.

Description

Technical Field

[0001] The invention relates to the field of boron diffusion of solar cell sheets, and in particular to a new type of gradient deposition diffusion high square resistance diffusion process. Background Art

[0002] At present, the boron diffusion preparation methods of solar cells in the market are divided into two technical routes: single boron diffusion and boron diffusion + oxidation. The cells of these two processes are suitable for conventional component production. Compared with the process of secondary boron diffusion cells, the single boron diffusion process using 300Ω square resistance cells increases by about 0.056%. The original intention of the design of this technology is to cancel the SE+oxidation process, which can effectively reduce the production time and improve production efficiency. At the same time, the process time can be shortened and efficiency can be improved by optimizing the boron flow, nitrogen, oxygen, temperature, process time, etc. The most direct impact of adjusting the temperature, time, and boron flow is that the junction depth becomes shallower and the square resistance of the cell is increased. Summary of the invention

[0003] The main purpose of the present invention is to provide a new type of gradient deposition diffusion high square resistance diffusion process, which can effectively solve the problems in the background technology.

[0004] To achieve the above object, the technical solution adopted by the present invention is: A new type of gradient deposition diffusion high square resistance diffusion process includes the following steps: S1: Place the silicon wafer to be diffused in a diffusion furnace, raise the temperature to 780°C, and simultaneously introduce 3000sccm of large N2 and 1000sccm of small N2 to close the tube and pump down the pressure; S2: After the temperature stabilizes at 780°C, the temperature of each temperature zone in the furnace is raised to 810°C, and 2000sccm of large N2 and 1000sccm of small N2 are introduced at the same time for 300s, and the tube pressure is controlled at 200mbar; S3: Continue to control the temperature of each temperature zone in the furnace at 823°C, and introduce 2000sccm of large N2, 2500sccm of O2 and 1000sccm of small N2 at the same time, the time is 270s, and the tube pressure is controlled at 200mbar; S4: Continue to control the temperature of each temperature zone in the furnace at 823°C, and simultaneously introduce 4200 sccm of large N2, 650 sccm of O2, 135 sccm of BCl3 and 1000 sccm of small N2 for 200 s, and control the tube pressure at 200 mbar; S5: After the temperature is stabilized, the temperature of each temperature zone in the furnace is raised to 838°C, and 4200sccm of large N2, 650sccm of O2, 140sccm of BCl3 and 1000sccm of small N2 are introduced for 150s, and the tube pressure is controlled at 200mbar; S6: Continue to control the temperature of each temperature zone in the furnace at 853°C, and introduce 4200 sccm of large N2 and 650 sccm of small O 2和 145sccm BCl3 and 600sccm N2, time is 180s, tube pressure is controlled at 200mbar; S7: Continue to control the temperature of each temperature zone in the furnace at 878°C, and simultaneously introduce 4200 sccm of large N2 and 1000 sccm of small N2 for 210 s, and control the tube pressure at 200 mbar; S8: After the temperature is stabilized, stabilize the temperature zones in the furnace to 878°C, and introduce 15000sccm of large N2 and 2000sccm of small N at the same time. 2， The time is 60s, and the pipe pressure is controlled at 900mbar; S9: Continue to raise the temperature of each temperature zone in the furnace to 1000°C, and at the same time introduce 23000sccm of large O 2， and 3000sccm of small N2, the time is 720s, and the tube pressure is controlled at 900mbar; S10: Continue to raise the temperature of each temperature zone in the furnace to 1040°C, and introduce 25000sccm of large O 2， and 2000sccm of small N2, the time is 3624s, and the tube pressure is controlled at 900mbar; S11: Continue to lower the temperature of each temperature zone in the furnace to 1030°C, and introduce 2500 sccm of N 2和 25000sccm Big O 2， and 2000sccm of small N2, the time is 420s, and the tube pressure is controlled at 900mbar; S12: The temperature of each temperature zone in the furnace is lowered to 780°C, and 15000sccm of large N2 and 2000sccm of small N2 are introduced at the same time for 60s, and the tube pressure is controlled at 900mbar; S13: The temperature of each temperature zone in the furnace is lowered to 780°C, and 3000sccm of large N2 and 2000sccm of small N2 are introduced at the same time for 1410s. After the tube pressure is controlled at 900mbar, the silicon wafer is taken out to complete the diffusion.

[0005] Preferably, S4 is a pre-diffusion step.

[0006] Preferably, S5 is a diffusion step.

[0007] Preferably, S6 is a redistribution step.

[0008] Compared with the prior art, the present invention has the following beneficial effects: It can effectively improve the battery conversion efficiency. This process adopts a high surface concentration and shallow junction depth design. The shallow junction depth design can effectively reduce the impurity recombination center on the surface, improve the survival rate of surface minority carriers, and increase the short-wave response. Based on this, Isc and Uoc are effectively increased to achieve the purpose of improving efficiency. At the same time, the high surface concentration significantly reduces the surface sheet resistance, improves the contact between the battery surface and the silver paste and reduces Rs. At the same time, due to the increase in doping concentration, FF can be effectively improved. The gradient deposition diffusion process uses a higher surface concentration and a shallow junction depth design to improve Uoc and Isc while effectively improving FF, which can achieve the purpose of improving efficiency by 0.05%. DETAILED DESCRIPTION

[0009] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only 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. Specific embodiment one: The invention relates to a novel gradient deposition diffusion high square resistance diffusion process. In a tubular diffusion furnace, BCl3 enters the furnace during ventilation, and boron trichloride is decomposed at high temperature and reacts with Si to generate elemental boron, which diffuses into a silicon substrate to form a PN junction. The diffusion is divided into three steps: pre-diffusion, diffusion and redistribution. Pre-diffusion: at a relatively low temperature, boron trichloride is introduced and then deposited on the surface of a silicon wafer, and a constant surface source diffusion method is adopted. Diffusion: the source and deposition temperatures are increased, and boron trichloride is introduced and then deposited and diffused on the surface of the silicon wafer. Redistribution: the deposition diffusion temperature is further increased, and limited surface source diffusion is adopted, and impurities introduced by pre-diffusion and diffusion are used as diffusion sources. Diffusion is carried out at a higher concentration to control the surface concentration and diffusion depth. Since the whole diffusion process is divided into three steps of deposition and diffusion, the deposition and diffusion temperature is also a gradient heating process, which ensures that a gradient doping concentration will be formed in the tube during this process. In order to eliminate this effect, it is necessary to increase the gas flow rate of bulk nitrogen and furnace nitrogen to reduce the deposition of boron in the oxide layer in the early stage of the reaction, and increase the gas flow rate of pre-oxygen so that more boron atoms can be more evenly diffused on the silicon wafer surface when passing through the oxide layer. At the same time, the uniformity of the square resistance value can be improved. High-temperature oxidation is used to promote the reaction to ensure the depth of the PN junction, optimize the surface doping concentration, and increase the square resistance. Specific embodiment 2: The present invention relates to a novel gradient deposition diffusion high square resistance diffusion process, comprising the following steps: S1: Place the silicon wafer to be diffused in a diffusion furnace, raise the temperature to 780°C, and simultaneously introduce 3000sccm of large N2 and 1000sccm of small N2 to close the tube and pump down the pressure; S2: After the temperature stabilizes at 780°C, the temperature of each temperature zone in the furnace is raised to 810°C, and 2000sccm of large N2 and 1000sccm of small N2 are introduced at the same time for 300s, and the tube pressure is controlled at 200mbar; S3: Continue to control the temperature of each temperature zone in the furnace at 823°C, and introduce 2000sccm of large N2, 2500sccm of O2 and 1000sccm of small N2 at the same time, the time is 270s, and the tube pressure is controlled at 200mbar; S4: Continue to control the temperature of each temperature zone in the furnace at 823°C, and introduce 4200sccm of large N2, 650sccm of O2, 135sccm of BCl3 and 1000sccm of small N2 at the same time, the time is 200s, and the tube pressure is controlled at 200mbar. This is the pre-diffusion step; S5: After the temperature is stabilized, the temperature of each temperature zone in the furnace is raised to 838°C, and 4200sccm of large N2, 650sccm of O2, 140sccm of BCl3 and 1000sccm of small N2 are introduced for 150s, and the tube pressure is controlled at 200mbar. This is the diffusion step; S6: Continue to control the temperature of each temperature zone in the furnace at 853°C, and introduce 4200 sccm of large N2 and 650 sccm of small O 2和 145sccm BCl3 and 600sccm small N2, time is 180s, tube pressure is controlled at 200mbar, this is the redistribution step; S7: Continue to control the temperature of each temperature zone in the furnace at 878°C, and simultaneously introduce 4200 sccm of large N2 and 1000 sccm of small N2 for 210 s, and control the tube pressure at 200 mbar; S8: After the temperature is stabilized, stabilize the temperature zones in the furnace to 878°C, and introduce 15000sccm of large N2 and 2000sccm of small N at the same time. 2， The time is 60s, and the pipe pressure is controlled at 900mbar; S9: Continue to raise the temperature of each temperature zone in the furnace to 1000°C, and at the same time introduce 23000sccm of large O 2， and 3000sccm of small N2, the time is 720s, and the tube pressure is controlled at 900mbar; S10: Continue to raise the temperature of each temperature zone in the furnace to 1040°C, and introduce 25000sccm of large O 2， and 2000sccm of small N2, the time is 3624s, and the tube pressure is controlled at 900mbar; S11: Continue to lower the temperature of each temperature zone in the furnace to 1030°C, and introduce 2500 sccm of N 2和 25000sccm Big O 2， and 2000sccm of small N2, the time is 420s, and the tube pressure is controlled at 900mbar; S12: The temperature of each temperature zone in the furnace is lowered to 780°C, and 15000sccm of large N2 and 2000sccm of small N2 are introduced at the same time for 60s, and the tube pressure is controlled at 900mbar; S13: The temperature of each temperature zone in the furnace is lowered to 780°C, and 3000sccm of large N2 and 2000sccm of small N2 are introduced at the same time for 1410s. After the tube pressure is controlled at 900mbar, the silicon wafer is taken out to complete the diffusion: Specific embodiment three: The present invention relates to a novel gradient deposition diffusion high square resistance diffusion process, comprising the following steps: S1: Place the silicon wafer to be diffused in a diffusion furnace, raise the temperature to 780°C, and simultaneously introduce 3000sccm of large N2 and 1000sccm of small N2 to close the tube and pump down the pressure; S2: After the temperature stabilizes, the temperature of each temperature zone in the furnace is raised to 810°C, and 2000sccm of large N2 and 1000sccm of small N2 are introduced at the same time for 300s, and the tube pressure is controlled at 200mbar; S3: Continue to control the temperature of each temperature zone in the furnace at 823°C, and introduce 2000sccm of large N2, 2500sccm of O2 and 1000sccm of small N2 at the same time, the time is 270s, and the tube pressure is controlled at 200mbar; S4: Continue to control the temperature of each temperature zone in the furnace at 823°C, and simultaneously introduce 4200 sccm of large N2, 650 sccm of O2, 135 sccm of BCl3 and 1000 sccm of small N2 for 200 s, and control the tube pressure at 200 mbar; S5: After the temperature is stabilized, the temperature of each temperature zone in the furnace is raised to 838°C, and 4200sccm of large N2, 650sccm of O2, 140sccm of BCl3 and 1000sccm of small N2 are introduced for 150s, and the tube pressure is controlled at 200mbar; S6: Continue to control the temperature of each temperature zone in the furnace at 853°C, and introduce 4200 sccm of large N2 and 650 sccm of small O 2和 145sccm BCl3 and 600sccm N2, time is 180s, tube pressure is controlled at 200mbar; S7: Continue to control the temperature of each temperature zone in the furnace at 878°C, and simultaneously introduce 4200 sccm of large N2 and 1000 sccm of small N2 for 210 s, and control the tube pressure at 200 mbar; S8: After the temperature is stabilized, stabilize the temperature zones in the furnace to 878°C, and introduce 15000sccm of large N2 and 2000sccm of small N at the same time. 2， The time is 60s, and the pipe pressure is controlled at 900mbar; S9: Continue to raise the temperature of each temperature zone in the furnace to 1000°C, and at the same time introduce 23000sccm of large O 2， and 3000sccm of small N2, the time is 720s, and the tube pressure is controlled at 900mbar; S10: Continue to raise the temperature of each temperature zone in the furnace to 1040°C, and introduce 25000sccm of large O 2， and 2000sccm of small N2, the time is 3624s, and the tube pressure is controlled at 900mbar; S11: Continue to lower the temperature of each temperature zone in the furnace to 1030°C, and at the same time introduce 2500sccm of N2 and 25000sccm of O 2， and 2000sccm of small N2, the time is 420s, and the tube pressure is controlled at 900mbar; S12: The temperature of each temperature zone in the furnace is lowered to 780°C, and 15000sccm of large N2 and 2000sccm of small N2 are introduced at the same time for 60s, and the tube pressure is controlled at 900mbar; S13: The temperature of each temperature zone in the furnace is reduced to 780°C, and 3000sccm of large N2 and 2000sccm of small N2 are introduced at the same time for 1410s. The tube pressure is controlled at 900mbar, and the silicon wafer is taken out.

[0012] The silicon wafer to be diffused is a single crystal silicon wafer. The cell manufactured using this gradient deposition diffusion process has a square resistance of 340Ω.

[0013] The present invention can effectively improve the battery conversion efficiency. The process adopts a high surface concentration and shallow junction depth design. The shallow junction depth design can effectively reduce the impurity recombination center on the surface, improve the survival rate of surface minority carriers, and increase the short-wave response. Based on this, Isc and Uoc are effectively increased to achieve the purpose of improving efficiency. At the same time, the high surface concentration significantly reduces the surface sheet resistance, improves the contact between the battery surface and the silver paste and reduces Rs. At the same time, due to the increase in doping concentration, FF can be effectively improved. The gradient deposition diffusion process uses a higher surface concentration and a shallow junction depth design to effectively improve FF while improving Uoc and Isc, and can achieve the purpose of improving efficiency by 0.05%; It can minimize the recombination efficiency in solar cells, optimize the emitter, optimize the metal contact ohmic resistance, and minimize the series resistance. First, to optimize the emitter, it is necessary to minimize the dark current density in its emitter region. Under the same emitter concentration, the cell efficiency decreases with the increase of junction depth. When it exceeds a certain peak value, this performance decreases rapidly, because the higher the concentration in the emitter, the shorter the lifetime of photogenerated carriers, the greater the probability of recombination, and the current cell density decreases. The deeper the emitter junction depth, the more light is absorbed by the emitter, and the greater this effect. At the same time, because the current cell density decreases, the open circuit voltage will also decrease, so the junction depth can effectively improve the cell conversion efficiency; The metal contact ohmic resistance is optimized. By increasing the surface concentration of the battery, the surface sheet resistance is significantly reduced, the contact between the battery surface and the silver paste is improved, and the purpose of reducing Rs is achieved. At the same time, due to the increase in doping concentration, FF can be effectively improved, so high surface concentration can effectively improve the battery conversion efficiency; Because at the same emitter doping concentration, the front surface recombination is the largest, and the square resistance for obtaining higher battery efficiency is also larger. This is because a large square resistance corresponds to a shallow junction depth, and the shallower the emitter, the less light is absorbed by the emitter, thereby reducing the probability of photogenerated carriers being affected by the surface and recombining. Therefore, theoretically, the junction depth and surface concentration can be adjusted through a gradient deposition diffusion process to control the surface concentration and junction depth, thereby affecting the size of the square resistance. For example, square resistance values ​​of 360Ω, 380Ω, 400Ω, and 450Ω can have a direct impact on efficiency.

[0014] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A new type of gradient deposition diffusion high square resistance diffusion process, characterized by: The steps include: S1: Place the silicon wafer to be diffused in a diffusion furnace, raise the temperature to 780°C, and simultaneously introduce 3000sccm of large N2 and 1000sccm of small N2 to close the tube and pump down the pressure; S2: After the temperature stabilizes at 780°C, the temperature of each temperature zone in the furnace is raised to 810°C, and 2000sccm of large N2 and 1000sccm of small N2 are introduced at the same time for 300s, and the tube pressure is controlled at 200mbar; S3: Continue to control the temperature of each temperature zone in the furnace at 823°C, and introduce 2000sccm of large N2, 2500sccm of O2 and 1000sccm of small N2 at the same time, the time is 270s, and the tube pressure is controlled at 200mbar; S4: Continue to control the temperature of each temperature zone in the furnace at 823°C, and simultaneously introduce 4200 sccm of large N2, 650 sccm of O2, 135 sccm of BCl3 and 1000 sccm of small N2 for 200 s, and control the tube pressure at 200 mbar; S5: After the temperature is stabilized, the temperature of each temperature zone in the furnace is raised to 838°C, and 4200sccm of large N2, 650sccm of O2, 140sccm of BCl3 and 1000sccm of small N2 are introduced for 150s, and the tube pressure is controlled at 200mbar; S6: Continue to control the temperature of each temperature zone in the furnace at 853°C, and introduce 4200 sccm of large N2 and 650 sccm of small O 2和 145sccm BCl3 and 600sccm N2, time is 180s, tube pressure is controlled at 200mbar; S7: Continue to control the temperature of each temperature zone in the furnace at 878°C, and simultaneously introduce 4200 sccm of large N2 and 1000 sccm of small N2 for 210 s, and control the tube pressure at 200 mbar; S8: After the temperature is stabilized, stabilize the temperature zones in the furnace to 878°C, and introduce 15000sccm of large N2 and 2000sccm of small N at the same time. 2， The time is 60s, and the pipe pressure is controlled at 900mbar; S9: Continue to raise the temperature of each temperature zone in the furnace to 1000°C, and at the same time introduce 23000sccm of large O 2， and 3000sccm of small N2, the time is 720s, and the tube pressure is controlled at 900mbar; S10: Continue to raise the temperature of each temperature zone in the furnace to 1040°C, and introduce 25000sccm of large O 2， and 2000sccm of small N2, the time is 3624s, and the tube pressure is controlled at 900mbar; S11: Continue to lower the temperature of each temperature zone in the furnace to 1030°C, and introduce 2500 sccm of N 2和 25000sccm Big O 2， and 2000sccm of small N2, the time is 420s, and the tube pressure is controlled at 900mbar; S12: The temperature of each temperature zone in the furnace is lowered to 780°C, and 15000sccm of large N2 and 2000sccm of small N2 are introduced at the same time for 60s, and the tube pressure is controlled at 900mbar; S13: The temperature of each temperature zone in the furnace is lowered to 780°C, and 3000sccm of large N2 and 2000sccm of small N2 are introduced at the same time for 1410s. After the tube pressure is controlled at 900mbar, the silicon wafer is taken out to complete the diffusion.

2. According to claim 1, a new type of gradient deposition diffusion high square resistance diffusion process is characterized by: The S4 is a pre-diffusion step.

3. According to claim 1, a new type of gradient deposition diffusion high square resistance diffusion process is characterized by: The S5 is a diffusion step.

4. According to claim 1, a new type of gradient deposition diffusion high square resistance diffusion process is characterized by: The S6 is a redistribution step.