A tubular variable-temperature boron diffusion deposition process

Abstract

The present invention discloses a tube-type variable-temperature boron diffusion deposition process, belonging to the technical field of solar cells. This method combines a multi-step source supply deposition process and a variable-temperature junction pushing process to achieve the boron diffusion process; specifically, it includes 7 steps: nitrogen inlet into the boat, pre-oxidation treatment, multi-step source supply deposition, variable-temperature junction pushing, high-temperature oxidation, cooling oxidation, and nitrogen outlet from the boat, and the 7 steps are completed under different temperature conditions. During the boron diffusion process, through the variable-temperature process treatment, the drawback of uneven diffusion easily existing in the interface region is overcome; at the same time, in the form of multi-step source supply deposition, the interface uniformity of boron diffusion deposition is better repaired, while optimizing the boron diffusion uniformity, the conversion efficiency of the battery is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of solar cells, and in particular relates to a tubular variable temperature boron diffusion deposition process. Background Art

[0002] The heart of a solar cell is a PN junction. A characteristic of silicon crystals is that atoms are held together by covalent bonds. The four valence electrons of a silicon atom form four shared electron pairs with its four neighboring atoms. These shared electron pairs are called "covalent bonds." When boron is doped into a silicon wafer, since the boron atom has three valence electrons in its outermost shell, one of the valence bonds must be missing an electron, creating a vacancy. We call this vacancy a "hole." Semiconductors that rely on holes for conductivity are called hole-type semiconductors, or P-type semiconductors for short. Similarly, phosphorus (P) atoms have five valence electrons in their outermost shell, but only four participate in covalent bonds, while the remaining electron is not present and becomes a free electron. Semiconductors doped with phosphorus primarily conduct electricity through the free electrons provided by phosphorus. Semiconductors that rely on electrons for conductivity are called electron-type semiconductors, or N-type semiconductors for short.

[0003] If this N-type silicon wafer is placed in a quartz furnace, heated to a certain temperature, and a boron-containing compound is introduced, the boron will decompose onto the wafer's surface, coating the surface and then diffusing into the wafer. The side with boron penetration becomes P-type, while the side without penetration remains the original N-type. This creates the desired PN junction within the wafer, a process known as diffusion. The purpose of diffusion is to create a PN junction. The process of diffusing an N-type substrate wafer with boron trichloride as a dopant source is known as boron diffusion. The conventional process for boron diffusion is a constant-temperature push-junction process, which can lead to uneven diffusion at the interface. Summary of the Invention

[0004] In response to the problems existing in the prior art, a technical problem to be solved by the present invention is to provide a tubular variable temperature boron diffusion deposition process. The variable temperature process is used during the boron diffusion process to overcome the disadvantage that the interface area is prone to uneven diffusion. At the same time, a multi-step through-source deposition method is used to better repair the interface uniformity of the boron diffusion deposition, thereby optimizing the boron diffusion uniformity and improving the conversion efficiency of the battery.

[0005] In order to solve the above problems, the technical solutions adopted by the present invention are as follows:

[0006] A tubular variable temperature boron diffusion deposition process adopts a multi-step through-source deposition process combined with a variable temperature push-junction process to realize the boron diffusion process.

[0007] For the tube-type variable-temperature boron diffusion deposition process, the multi-step source feeding deposition process is as follows: Deposition is carried out under the conditions of a temperature of 860 °C, a nitrogen flow rate of 3000 sccm, an oxygen flow rate of 2000 sccm, and a boron trichloride flow rate of 300 sccm. The deposition time for the first step is 300 s; deposition is carried out under the conditions of a temperature of 870 °C, a nitrogen flow rate of 4000 sccm, an oxygen flow rate of 3000 sccm, and a boron trichloride flow rate of 200 sccm. The deposition time for the second step is 240 s; deposition is carried out under the conditions of a temperature of 880 °C, a nitrogen flow rate of 5000 sccm, an oxygen flow rate of 4000 sccm, and a boron trichloride flow rate of 100 sccm. The deposition time for the third step is 180 s.

[0008] For the tube-type variable-temperature boron diffusion deposition process, the variable-temperature push sintering process is as follows: Push sintering is carried out under the conditions of a temperature of 930 - 990 °C, a nitrogen flow rate of 6000 sccm, and an oxygen flow rate of 2000 sccm. The temperature is increased by 10 °C every 300 s, and the total push sintering time is 2100 s. According to the time gradient, the time for each step is gradually decreased and the temperature is gradually increased to achieve the effect of variable temperature, so that the sheet resistance uniformity of the silicon wafer after the process is better.

[0009] The tube-type variable-temperature boron diffusion deposition process includes the following steps:

[0010] (1) Feed nitrogen into the boat. Place the quartz boat loaded with silicon wafers on the silicon carbide slurry, send it into the furnace tube, and ensure that the inside of the tube is in a positive pressure state.

[0011] (2) Pre-oxidation treatment. Heat up to the oxidation temperature and carry out oxidation under certain nitrogen and oxygen flow rates.

[0012] (3) Multi-step source feeding deposition,

[0013] (4) Variable-temperature push sintering,

[0014] (5) High-temperature oxidation. Carry out oxidation under the conditions of a temperature of 1040 °C and certain nitrogen and oxygen flow rates.

[0015] (6) Cooling oxidation. Carry out oxidation under the conditions of a temperature of 800 °C and certain nitrogen and oxygen flow rates.

[0016] (7) Feed nitrogen out of the boat. Place the quartz boat of the silicon wafer after the process treatment on the silicon carbide slurry, send it out of the furnace tube, and ensure that the inside of the tube is in a positive pressure state.

[0017] For the tube-type variable-temperature boron diffusion deposition process, the boat feeding temperature in step (1) is 780 - 800 °C, the boat feeding rate is 150 mm / s, the inside of the tube is ensured to be in a positive pressure state according to a nitrogen flow rate of 10000 sccm, and the boat feeding time is 720 s.

[0018] For the tube-type variable-temperature boron diffusion deposition process, in step (2), maintain the boat temperature at 840 - 850 °C, heat up to 860 °C at a rate of 20 °C / min for oxidation, perform oxidation under the conditions of a nitrogen flow rate of 3000 sccm and an oxygen flow rate of 2000 sccm, and the oxidation time is 300 s.

[0019] For the tube-type variable-temperature boron diffusion deposition process, in step (5), perform oxidation under the conditions of a nitrogen flow rate of 2000 sccm and an oxygen flow rate of 18000 sccm, and the oxidation time is 7200 s.

[0020] For the tube-type variable-temperature boron diffusion deposition process, in step (6), perform oxidation under the conditions of a nitrogen flow rate of 5000 sccm and an oxygen flow rate of 10000 sccm, and the temperature is reduced by 20 °C every 300 s, and the total oxidation time is 3900 s.

[0021] For the tube-type variable-temperature boron diffusion deposition process, in step (7), maintain the boat-out temperature at 780 - 800 °C, the boat-out speed is 150 mm / s, ensure a positive pressure state inside the tube according to a nitrogen flow rate of 10000 sccm, and the boat-out time is 720 s.

[0022] Beneficial effects: Compared with the existing technology, the advantages of the present invention include:

[0023] The present invention adopts a variable-temperature push-junction process. During deposition, the boron trichloride gradient decreases, improving the carrier lifetime in the silicon wafer, reducing the non-uniformity of the diffusion sheet resistance, reducing the low-efficiency discreteness of the finished battery, and improving the battery efficiency as the electrical performance parameters are improved. Specific embodiments

[0024] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following detailed description of the specific embodiments of the present invention is provided in conjunction with specific examples.

[0025] Example 1

[0026] A tube-type variable-temperature boron diffusion deposition process, the specific implementation process is as follows:

[0027] In step (1), introduce nitrogen and load the boat. Place the quartz boat loaded with silicon wafers on the silicon carbide slurry, maintain the boat-loading temperature at 780 - 800 °C, send it into the furnace tube at a speed of 150 mm / s to prepare for the process, and ensure a positive pressure state inside the tube according to a nitrogen flow rate of 10000 sccm, and the loading time is 720 s.

[0028] In step (2), perform pre-oxidation treatment. Maintain the boat temperature at 840 - 850 °C, heat up to 860 °C at a rate of 20 °C / min for oxidation, perform oxidation under the conditions of a nitrogen flow rate of 3000 sccm and an oxygen flow rate of 2000 sccm, and the oxidation time is 300 s.

[0029] Step (3) Multi-step source deposition is carried out under the conditions of a temperature of 860 °C, a nitrogen flow rate of 3000 sccm, an oxygen flow rate of 2000 sccm, and a boron trichloride flow rate of 300 sccm. The deposition time for the first step is 300 s. Deposition is carried out under the conditions of a temperature of 870 °C, a nitrogen flow rate of 4000 sccm, an oxygen flow rate of 3000 sccm, and a boron trichloride flow rate of 200 sccm. The deposition time for the second step is 240 s. Deposition is carried out under the conditions of a temperature of 880 °C, a nitrogen flow rate of 5000 sccm, an oxygen flow rate of 4000 sccm, and a boron trichloride flow rate of 100 sccm. The deposition time for the third step is 180 s.

[0030] Step (4) Variable-temperature push sintering is carried out under the conditions of a temperature of 930 - 990 °C, a nitrogen flow rate of 6000 sccm, and an oxygen flow rate of 2000 sccm. The temperature is increased by 10 °C every 300 s, and the total push sintering time is 2100 s.

[0031] Step (5) High-temperature oxidation is carried out under the conditions of a temperature of 1040 °C, a nitrogen flow rate of 2000 sccm, and an oxygen flow rate of 18000 sccm. The oxidation time is 7200 s.

[0032] Step (6) Cooling oxidation is carried out under the conditions of a temperature of 800 °C, a nitrogen flow rate of 5000 sccm, and an oxygen flow rate of 10000 sccm. The temperature is decreased by 20 °C every 300 s, and the total oxidation time is 3900 s.

[0033] Step (7) Nitrogen purging and boat unloading: Place the quartz boat of the silicon wafer after process treatment on the silicon carbide slurry, maintain the boat unloading temperature at 780 - 800 °C, send it out of the furnace tube at a speed of 150 mm / s, and ensure a positive pressure state inside the tube according to a nitrogen flow rate of 10000 sccm. The boat unloading time is 720 s.

[0034] Comparative Example 1

[0035] The specific process flow of a traditional boron diffusion process is as follows:

[0036] Step (1) Nitrogen purging and boat loading: Place the quartz boat loaded with silicon wafers on the silicon carbide slurry, maintain the boat loading temperature at 780 - 800 °C, send it into the furnace tube at a speed of 150 mm / s to prepare for the process, and ensure a positive pressure state inside the tube according to a nitrogen flow rate of 10000 sccm. The boat loading time is 720 s.

[0037] Step (2) Pre-oxidation treatment: Maintain the boat temperature at 840 - 850 °C, and increase the temperature to 860 °C at a rate of 20 °C / min for oxidation. Oxidation is carried out under the conditions of a nitrogen flow rate of 3000 sccm and an oxygen flow rate of 2000 sccm. The oxidation time is 300 s.

[0038] Step (3) single-step source deposition is carried out under the conditions of a temperature of 870 °C, a nitrogen flow rate of 9000 sccm, an oxygen flow rate of 6000 sccm, and a boron trichloride flow rate of 300 sccm, with a deposition time of 6000 s.

[0039] Step (4) constant-temperature pushing and sintering: First, heat up to 990 °C under vacuum, with a heating-up time of 1800 s. Then, carry out pushing and sintering under the conditions of a nitrogen flow rate of 6000 sccm and an oxygen flow rate of 2000 sccm. The temperature rises by 10 °C every 300 s, and the total pushing and sintering time is 2100 s.

[0040] Step (5) high-temperature oxidation is carried out under the conditions of a temperature of 1040 °C, a nitrogen flow rate of 2000 sccm, and an oxygen flow rate of 18000 sccm, with an oxidation time of 7200 s.

[0041] Step (6) cooling oxidation is carried out under the conditions of a temperature of 800 °C, a nitrogen flow rate of 5000 sccm, and an oxygen flow rate of 10000 sccm. The temperature drops by 20 °C every 300 s, and the total oxidation time is 3900 s.

[0042] Step (7) nitrogen purging and boat taking out: Place the quartz boat of the silicon wafer after process treatment on the silicon carbide slurry, keep the boat-taking-out temperature at 780 - 800 °C, send it out of the furnace tube at a speed of 150 mm / s, and ensure a positive pressure state inside the tube according to a nitrogen flow rate of 10000 sccm, with a boat-taking-out time of 720 s.

[0043] Table 1 Comparison of the uniformity of silicon wafers produced by traditional boron diffusion process and variable-temperature boron diffusion process

[0044] Project In-chip uniformity (%) Traditional boron diffusion process 5.6 Temperature-variable push-junction process 4.5

[0045] Table 2 Comparison of the sheet resistance data of silicon wafers produced by traditional boron diffusion process and variable-temperature boron diffusion process

[0046]

[0047] Among them, the data unit in the table is Ω.

[0048] For the traditional boron diffusion process, when the sheet resistance value reaches 141.7 Ω, the in-wafer uniformity STD is 5.6%; for the variable-temperature boron diffusion process, when the sheet resistance value reaches 141 Ω, the in-wafer uniformity STD is 4.5%. Comparing the two, the uniformity of the variable-temperature boron diffusion process is smaller, the discreteness of the finished products completed by this process is more concentrated, and the conversion efficiency is better.

Claims

1. A tube-type variable-temperature boron diffusion deposition process, characterized in that The boron diffusion process is realized by combining a multi-step through-source deposition process with a variable temperature push-through process, including the following steps: (1) Pass nitrogen into the boat, place the quartz boat loaded with silicon wafers on the silicon carbide paddle, and send it into the furnace tube, and ensure that the tube is in a positive pressure state; (2) Pre-oxidation treatment: heating to oxidation temperature and oxidizing under a certain flow rate of nitrogen and oxygen; (3) Multi-step source deposition; The multi-step through-source deposition process is as follows: deposition is performed at a temperature of 860°C, a nitrogen flow rate of 3000 sccm, an oxygen flow rate of 2000 sccm, and a boron trichloride flow rate of 300 sccm, with a first deposition time of 300 s; deposition is performed at a temperature of 870°C, a nitrogen flow rate of 4000 sccm, an oxygen flow rate of 3000 sccm, and a boron trichloride flow rate of 200 sccm, with a second deposition time of 240 s; deposition is performed at a temperature of 880°C, a nitrogen flow rate of 5000 sccm, an oxygen flow rate of 4000 sccm, and a boron trichloride flow rate of 100 sccm, with a third deposition time of 180 s. (4) Temperature-variable push-in; The variable temperature push-bonding process is as follows: push-bonding is carried out at a temperature of 930-990°C, a nitrogen flow rate of 6000 sccm, and an oxygen flow rate of 2000 sccm. The temperature is increased by 10°C every 300 seconds, and the total push-bonding time is 2100 seconds. (5) High temperature oxidation: oxidation is carried out at a temperature of 1040°C under certain nitrogen and oxygen flow conditions; (6) Cooling oxidation: oxidation is carried out at a temperature of 800°C under certain nitrogen and oxygen flow conditions; (7) Nitrogen is passed out of the boat, and the quartz boat containing the processed silicon wafers is placed on the silicon carbide paddle, and sent out of the furnace tube, and the positive pressure inside the tube is ensured.

2. The tube-type variable-temperature boron diffusion deposition process according to claim 1, wherein In step (1), the boat feeding temperature is 780-800°C, the boat feeding speed is 150 mm / s, the nitrogen flow rate is 10000 sccm to ensure that the tube is in a positive pressure state, and the boat feeding time is 720 s.

3. The tube-type variable-temperature boron diffusion deposition process according to claim 1, characterized in that, Step (2): maintaining the boat temperature at 840-850°C, heating it to 860°C at a rate of 20°C / min for oxidation, and performing oxidation at a nitrogen flow rate of 3000 sccm and an oxygen flow rate of 2000 sccm for 300 s.

4. The tube-type variable-temperature boron diffusion deposition process according to claim 1, wherein In step (5), oxidation was performed under the conditions of a nitrogen flow rate of 2000 sccm and an oxygen flow rate of 18000 sccm, and the oxidation time was 7200 s.

5. The tube-type variable-temperature boron diffusion deposition process according to claim 1, wherein In step (6), oxidation was performed under the conditions of a nitrogen flow rate of 5000 sccm and an oxygen flow rate of 10000 sccm, the temperature was reduced by 20°C every 300 s, and the total oxidation time was 3900 s.

6. The tube-type variable-temperature boron diffusion deposition process according to claim 1, wherein Step (7) maintains the temperature out of the boat at 780-800°C, the speed out of the boat at 150 mm / s, and a nitrogen flow rate of 10,000 sccm to ensure positive pressure in the tube. The time out of the boat is 720 s.

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