A method of boron diffusion for forming a junction

Abstract

The application provides a boron diffusion preparation method, which comprises the following steps: (1) after the texturing of a silicon wafer, the silicon wafer is subjected to surface oxidation in a diffusion device by introducing O2; then small N2 carrying a boron source is introduced into the diffusion device to react with O2, and large N2 is introduced to transport the boron source and O2 to the surface of the silicon wafer, so that BSG pre-deposition is carried out on the surface of the silicon wafer; after the completion, the flow rates of O2, small N2 and large N2 are adjusted, and BSG deposition and promotion are continuously carried out on the surface of the silicon wafer; after the completion, the silicon wafer in the diffusion device is purged; (2) the silicon wafer after the completion of the purging is transferred to a chain oxidation device to perform rapid heat treatment under a protective atmosphere, and boron diffusion is completed after the removal of the back BSG layer; the method rapidly completes BSG deposition and short-time pre-promotion in a tube diffusion device, and further completes the promotion by means of a rapid heat treatment device, so that the uniformity of the silicon wafer is ensured, the boron diffusion preparation time is greatly saved, and the production efficiency is improved.

Description

Technical Field

[0001] This invention belongs to the field of photovoltaics, and particularly relates to the preparation of boron diffusion PN junctions for solar cells, and especially to a method for boron diffusion junction preparation. Background Technology

[0002] Currently, there are generally four methods for boron diffusion in the photovoltaic industry to prepare emitters: tubular BBr3 or BCl3 diffusion, spin-coating boron source + diffusion, APCVD boron source + diffusion, and ion implantation + annealing. Among them, tubular diffusion has become the mainstream boron diffusion technology due to its high cost-effectiveness, avoidance of metal ion contamination, high minority carrier lifetime, and ease of implementation.

[0003] Boron doping is achieved using tubular thermal diffusion. The specific method typically involves inserting a silicon wafer into a quartz boat carrier and performing a deposition-then-propellant process at high temperatures. First, at a relatively low temperature, nitrogen gas carries BBr3 or BCl3 to react with O2 to form a borosilicate glass (BSG) layer on the silicon wafer surface. Then, the temperature is increased for high-temperature propulsion (above 950°C) to obtain the desired boron emitter. While this tubular deposition and propulsion diffusion method can meet the requirements for preparing boron emitters, it still has several unresolved drawbacks, such as high process temperatures leading to energy waste, slow boron propulsion resulting in long processing times and insufficient production capacity; the B2O3 produced after the tubular reaction of BBr3 or BCl3 with O2 has a boiling point above 1800°C, and when it adheres to the silicon wafer surface in liquid form during the reaction, uneven deposition can lead to poor uniformity of the doped junction.

[0004] CN113972130A discloses a boron doping method, a solar cell, and a method for fabricating the same, relating to the field of photovoltaic technology. This method facilitates the doping of boron into silicon wafers, reducing the difficulty of boron doping. The boron doping method includes the following steps: providing a silicon substrate; forming an auxiliary layer on the silicon substrate, the auxiliary layer being made of titanium dioxide; forming a boron-containing slurry layer on the auxiliary layer; and using a laser to propel boron impurities in the boron-containing slurry layer through the auxiliary layer into the silicon substrate, thereby doping the silicon substrate. The boron doping method, solar cell, and method for fabricating the same are used in solar cell manufacturing, but excessively long oxygen permeation times lead to low efficiency.

[0005] CN109545893A discloses a multi-step boron diffusion process for N-type solar cells, comprising the following steps: (a) selecting an N-type silicon wafer as the substrate material and forming a pyramidal textured surface on the wafer surface through alkaline etching; (b) performing RCA cleaning and drying on the treated silicon wafer surface; (c) placing the dried N-type silicon wafer in a diffusion furnace tube and forming a PN junction on the surface through a multi-step boron diffusion process; (d) further processing the silicon wafer with subsequent N-type cell manufacturing processes. This process proposes a novel method for boron diffusion, solving the problem of preparing PN junctions on the surface of N-type solar cells. It can produce PN junctions with good uniformity and excellent contact performance, reducing the lateral contact resistance of the solar cell. Simultaneously, by adjusting parameters such as the flow rate of nitrogen carrying the boron source, the driving time, and the temperature, different surface doping concentrations and junction depths can be obtained, matching different metallization processes, which can further improve the conversion efficiency of N-type cells. However, this process requires multiple passes to ensure junction uniformity, resulting in excessively long production time and low efficiency.

[0006] In 2006, Huaju Group discussed the application and mechanism of rapid thermal processing technology in the phosphorus diffusion process of silicon wafers (see "Application of Rapid Thermal Processing in Solar Cells", Zhejiang University, Master's Thesis), proving that after the silicon wafer is rapidly heated, the surface non-equilibrium state and the high-energy photon enhanced diffusion can accelerate the phosphorus diffusion process.

[0007] Therefore, it is necessary to develop a production process that can quickly and efficiently achieve boron diffusion and form a uniform PN junction. Summary of the Invention

[0008] To address the problems of long processing time and uneven deposition affecting yield in existing tubular diffusion-based junction formation technologies, this invention proposes a boron diffusion-based junction formation method. By rapidly completing BSG deposition and short-time pre-propulsion in tubular diffusion, a high concentration of active boron (B) in the BSG layer is ensured. Simultaneously, rapid push-junction is achieved using a rapid heat treatment device, thereby improving production efficiency and product quality.

[0009] To achieve this objective, the present invention adopts the following technical solution:

[0010] This invention provides a method for boron diffusion junction formation, the method comprising the following steps:

[0011] (1) After texturing, the silicon wafer is oxidized by introducing O2 into the diffusion device; then, a small N2 carrying a boron source is introduced into the diffusion device to react with the O2, while a large N2 is introduced to transport the boron source and O2 to the surface of the silicon wafer for BSG pre-deposition; after the BSG pre-deposition is completed, the flow rates of O2, small N2 and large N2 are adjusted to continue BSG deposition and propagation on the surface of the silicon wafer; after the BSG deposition and propagation are completed, the silicon wafer in the diffusion device is purged.

[0012] (2) After the silicon wafer is purged, it is transferred to a chain oxidation device and subjected to rapid heat treatment under a protective atmosphere to remove the back BSG layer and complete the boron diffusion process.

[0013] This invention provides a boron diffusion junction formation method, which improves both the boron deposition step and the junction pushing step. In the boron deposition step, tubular diffusion is used for preliminary junction pushing and BSG layer deposition. Simultaneously, the BSG layer is deposited throughout the entire through-source reaction process. Before the silicon wafer is pushed forward, it is in a boron-rich state. During the tubular diffusion process, the high-temperature pushing time is short, and it can be completed in as little as 5 minutes. The subsequent junction pushing step is completed by a rapid thermal treatment process, which greatly saves the time of tubular boron diffusion. The new equipment introduced for rapid thermal treatment is a chain oxidation furnace, which can be seamlessly connected with the industry-standard chain BSG removal machine. After the junction pushing is completed, the silicon wafer continues to advance on the roller to complete the BSG layer removal step on the back side. This solution can be directly mass-produced without adding additional equipment and time costs.

[0014] In this invention, rapid heat treatment refers to the ability of a halogen tungsten lamp thermal infrared tube to rapidly heat the surface of a silicon wafer to over 1000°C in an extremely short time. This extremely rapid heating of the silicon wafer surface causes a non-equilibrium state, generating a large number of holes and interstitial atoms, which promotes the diffusion of boron. Simultaneously, under the influence of the instantaneous enhanced diffusion effect of high-energy photons, the bonding can be completed rapidly within 70-200 seconds.

[0015] In this invention, there are no special restrictions on the temperature and method of texturing and removing the BSG layer on the back side; conventional operations can be used, or adjustments can be made according to the actual process. Small N2 refers to a path of N2 that carries BBr3 after being introduced into the BBr3 boron source, or that is mixed with BCl3 boron source gas and introduced into the furnace tube. Large N2 refers to a path of N2 located at the tail of the furnace, with separate gas intake, used for back pressure, maintaining the inert gas atmosphere in the furnace and assisting in the transport and redistribution of the boron source in the tube.

[0016] Preferably, the type of diffusion device in step (1) includes a quartz diffusion device.

[0017] Preferably, the silicon wafer is inserted into the quartz boat carrier and then transferred to the diffusion device.

[0018] Preferably, the diffusion device is evacuated before the surface oxidation.

[0019] Preferably, the pressure in the vacuum diffusion device is ≤100mbar, for example, it can be 100mbar, 90mbar, 80mbar, 70mbar, 60mbar or 50mbar, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0020] Preferably, the surface oxidation temperature in step (1) is 780-860℃, for example, it can be 780℃, 800℃, 820℃, 850℃ or 860℃, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0021] Preferably, the flow rate of O2 in the surface oxidation is 1000-3000 sccm, for example, it can be 1000 sccm, 1500 sccm, 2000 sccm, 2500 sccm or 3000 sccm, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0022] Preferably, the surface oxidation time is 300-600s, for example, 300s, 400s, 500s or 600s, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0023] Preferably, during the BSG pre-deposition in step (1), the pressure in the diffusion device is 150-400 mbar, for example, it can be 150 mbar, 200 mbar, 250 mbar, 300 mbar, 350 mbar or 400 mbar, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0024] Preferably, the BSG pre-deposition temperature is 850-900℃, for example, it can be 850℃, 860℃, 870℃, 880℃, 890℃ or 900℃, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0025] Preferably, the boron source includes BBr3 and / or BCl3.

[0026] Preferably, the concentration of the boron source in the small N2 containing the boron source is (2.79-8.9)×10⁻⁶. -3 mol / L, for example, could be 2.79 × 10⁻⁶. -3 mol / L, 2.8×10 -3 mol / L, 3×10 -3 mol / L, 3.5×10 -3 mol / L, 4×10 -3 mol / L, 4.5×10 -3 mol / L, 5×10 -3 mol / L, 5.5×10 -3 mol / L, 6×10 -3 mol / L, 6.5×10 -3 mol / L, 7×10 -3mol / L, 8×10 -3 mol / L or 8.9×10 -3 The value is mol / L, but is not limited to the listed values; other unlisted values ​​within this range also apply.

[0027] Preferably, the volumetric flow rate ratio of O2 to small N2 carrying a boron source is (1-3):1, for example, it can be 1:1, 1.2:1, 1.25:1, 1.5:1, 1.8:1, 2:1, 2.5:1 or 3:1, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0028] Preferably, the flow rate of the small N2 is 800-3000 sccm, for example, it can be 800 sccm, 1000 sccm, 1200 sccm, 1500 sccm, 1800 sccm, 2000 sccm, 2200 sccm, 2500 sccm, 2800 sccm or 3000 sccm, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0029] Preferably, the flow rate of the large N2 is 10-15 slm, for example, it can be 10 slm, 11 slm, 12 slm, 13 slm, 14 slm or 15 slm, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0030] Preferably, the BSG pre-deposition time is 600-1200s, for example, it can be 600s, 700s, 800s, 900s, 1000s, 1100s or 1200s, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0031] Preferably, during BSG deposition and propulsion in step (1), the pressure in the diffusion device is 150-400 mbar, for example, it can be 150 mbar, 200 mbar, 250 mbar, 300 mbar, 350 mbar or 400 mbar, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0032] Preferably, the temperature for BSG deposition and propagation is 950-1000°C, for example, 950°C, 960°C, 970°C, 980°C, 990°C or 1000°C, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0033] Preferably, the boron source includes BBr3 and / or BCl3.

[0034] Preferably, the concentration of the boron source in the small N2 containing the boron source is (2.79-8.9)×10⁻⁶. -3 mol / L, for example, could be 2.79 × 10⁻⁶. -3 mol / L, 2.8×10 -3 mol / L, 3×10 -3 mol / L, 3.5×10 -3 mol / L, 4×10 -3 mol / L, 4.5×10 -3 mol / L, 5×10 -3 mol / L, 5.5×10 -3 mol / L, 6×10 -3 mol / L, 6.5×10 -3 mol / L, 7×10 -3 mol / L, 8×10 -3 mol / L or 8.9×10 -3 The value is mol / L, but is not limited to the listed values; other unlisted values ​​within this range also apply.

[0035] Preferably, the volumetric flow rate ratio of O2 to small N2 carrying a boron source is 1:(2-4), for example, it can be 1:2, 1:2.2, 1:2.5, 1:2.8, 1:3, 1:3.5 or 1:4, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0036] Preferably, the flow rate of the small N2 is 2000-3000 sccm, for example, it can be 2000 sccm, 2200 sccm, 2500 sccm, 2800 sccm or 3000 sccm, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0037] Preferably, the flow rate of the large N2 is 10-15 slm, for example, it can be 10 slm, 11 slm, 12 slm, 13 slm, 14 slm or 15 slm, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0038] In this invention, the preferred volumetric flow rate ratio of O2 to N2 carrying the boron source is adopted according to the BSG deposition process. Its advantage is that when depositing BSG at low temperature, excess oxygen is selected to ensure that the boron source reacts completely, and some of the generated elemental B is further oxidized to B2O3, reducing the risk of excessive dead layer on the silicon wafer surface. When continuing to heat up and deposit BSG and advance, selecting excess boron source can deposit enough B source for the subsequent chain oxidation process.

[0039] Preferably, the BSG deposition and propagation time is 300-900s, for example, it can be 300s, 400s, 500s, 600s, 700s, 800s or 900s, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0040] Preferably, the introduction of small amounts of N2 and O2 is stopped before the purging in step (1).

[0041] Preferably, after stopping the introduction of small amounts of N2 and O2, the temperature of the diffusion device is maintained at 840-860°C, for example, 840°C, 845°C, 850°C, 855°C or 860°C, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0042] Preferably, after stopping the flow of small amounts of N2 and O2, the pressure of the diffusion device is kept ≤100 mbar, for example, it can be 100 mbar, 90 mbar, 80 mbar, 70 mbar, 60 mbar or 50 mbar, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0043] Preferably, the purging includes purging the diffuser by introducing nitrogen and water vapor.

[0044] Preferably, the purging time is 200-600s, for example, it can be 200s, 300s, 400s, 500s or 600s, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0045] Preferably, after the purging is completed, a large amount of N2 is introduced into the diffusion device, and the pressure is returned to normal to end the silicon wafer deposition.

[0046] Preferably, the rapid heat treatment in step (2) includes the following steps: the silicon wafer is carried into the chain oxidation device by a roller conveyor belt and is subjected to rapid heat treatment and bonding by thermal infrared lamps.

[0047] Preferably, the chain oxidation device in step (2) is equipped with a thermal infrared lamp tube that emits high-energy photons.

[0048] Preferably, the type of thermal infrared lamp tube includes halogen tungsten filament thermal infrared lamp tubes.

[0049] Preferably, the power of a single thermal infrared lamp tube is ≥3KW, for example, it can be 3KW, 3.1KW, 3.2KW, 3.3KW, 3.4KW or 3.5KW, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0050] Preferably, the temperature of the rapid heat treatment is 850-1000℃, for example, it can be 850℃, 900℃, 950℃ or 1000℃, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0051] Preferably, the belt speed of the roller conveyor belt is ≤3.5m / min, for example, it can be 3.5m / min, 3.4m / min, 3.3m / min, 3.2m / min or 3.1m / min, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0052] Preferably, the rapid heat treatment push-bonding time is ≥70s, for example, it can be 70s, 80s, 100s, 120s, 150s, 180s or 200s, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0053] Preferably, the protective atmosphere includes any one or a combination of at least two of Ar, N2, or O2, with N2 being the most preferred.

[0054] Preferably, the flow rate of the protective atmosphere is ≥60L / min, for example, it can be 60L / min, 70L / min, 80L / min, 90L / min or 100L / min, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0055] Preferably, the rapid heat treatment time is 70-200s, for example, it can be 70s, 80s, 100s, 120s, 150s, 180s or 200s, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0056] As a preferred technical solution of the present invention, the method includes the following steps:

[0057] (1) The texturized silicon wafer is transferred into a quartz diffusion apparatus. A vacuum is evacuated from the quartz diffusion apparatus to a pressure ≤100 mbar. O2 at 1000-3000 sccm is introduced at 780-860℃ for 300-600 s for surface oxidation. Subsequently, BSG pre-deposition is performed. Small amounts of N2 carrying BBr3 and / or BCl3 and O2 are introduced into the diffusion apparatus at a pressure of 150-400 mbar and a temperature of 850-900℃. The volumetric flow rate ratio of O2 to small amounts of N2 carrying a boron source is (1-3):1, and the flow rate of the small amounts of N2 is (2.79-8.9) × 10⁻⁶. -3A mol / L solution of nitrogen (N2) is introduced, and 10-15 slm of nitrogen is simultaneously introduced to transport the boron source and O2 to the silicon wafer surface. BSG pre-deposition is then performed on the silicon wafer surface for 600-1200 s. After the BSG pre-deposition is completed, the temperature in the diffusion device is raised to 950-1000℃, and the volumetric flow rate ratio of O2 to the nitrogen carrying the boron source is adjusted to 1:(2-4). Simultaneously, 10-15 slm of nitrogen is introduced to transport the boron source and O2 to the silicon wafer surface, and BSG deposition and propagation continue on the silicon wafer surface for 300-900 s. After the BSG deposition and propagation are completed, the introduction of nitrogen and O2 is stopped, and the temperature of the diffusion device is maintained at 840-860℃, and the pressure ≤100 mbar. Nitrogen (N2) and water vapor are introduced to purge the diffusion device for 200-600 s. After purging, nitrogen (N2) is introduced into the diffusion device, and the pressure is returned to atmospheric pressure, ending the silicon wafer deposition.

[0058] (2) The silicon wafer after purging is carried into the chain oxidation device by a roller conveyor belt. The chain oxidation device is equipped with a halogen tungsten wire thermal infrared lamp tube with the function of emitting high-energy photons. The power of a single halogen tungsten wire thermal infrared lamp tube is ≥3KW. The rapid heat treatment push-bonding is carried out by the thermal infrared lamp tube at a temperature of 850-1000℃. The belt speed of the roller conveyor belt is ≤3.5m / min. The rapid heat treatment push-bonding time is ≥70s. The rapid heat treatment is carried out for 70-200s in N2 atmosphere. After removing the back BSG layer, the boron diffusion process is completed.

[0059] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0060] (1) The boron diffusion junction method provided by the present invention deposits a BSG layer throughout the entire through-source reaction process, ensuring the uniformity of the surface BSG layer, the sheet resistance non-uniformity is ≤2.5%, the fill factor is increased by more than 0.31%, the photoelectric conversion efficiency is increased by more than 0.009%, and a B enrichment state is created to facilitate efficient subsequent junction pushing.

[0061] (2) The boron diffusion junction method provided by the present invention uses rapid heat treatment for junction pushing, which greatly reduces the junction pushing time and improves production efficiency.

[0062] (3) The boron diffusion junction method provided by the present invention can be directly connected to the existing equipment with the newly added rapid heat treatment equipment, with little modification and effective cost saving. Detailed Implementation

[0063] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0064] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0065] In one specific embodiment, the present invention provides a method for boron diffusion junction formation, the method comprising the following steps:

[0066] (1) After texturing, the silicon wafer is transferred into a quartz diffusion device. The device is evacuated to a pressure ≤100 mbar, and O2 at 1000-3000 sccm is introduced at 780-860℃ for 300-600 s surface oxidation. Subsequently, BSG pre-deposition is performed. Small N2 carrying BBr3 and / or BCl3 and O2 are introduced into the diffusion device at a pressure of 150-400 mbar and a temperature of 850-900℃. The volumetric flow rate ratio of O2 to small N2 carrying a boron source is (1-3):1, and the flow rate of the small N2 is 800-3000 sccm. Simultaneously, 10-15 slm of large N2 is introduced to transport the boron source and O2 to the silicon wafer surface. A 600- BSG pre-deposition for 1200s; after the BSG pre-deposition is completed, the temperature in the diffusion device is raised to 950-1000℃, the volume flow rate ratio of O2 to small N2 carrying boron source is adjusted to 1:(2-4), and at the same time, 10-15slm of large N2 is introduced to transport the boron source and O2 to the silicon wafer surface, and BSG deposition and propagation on the silicon wafer surface continues for 300-900s; after the BSG deposition and propagation is completed, the introduction of small N2 and O2 is stopped, the temperature of the diffusion device is maintained at 840-860℃, the pressure is ≤100mbar, and large N2 and water vapor are introduced to purge the diffusion device for 200-600s. After the purging is completed, large N2 is introduced into the diffusion device, the pressure is returned to normal pressure, and the silicon wafer deposition is ended;

[0067] (2) The silicon wafer after purging is carried into the chain oxidation device by a roller conveyor belt. The chain oxidation device is equipped with a halogen tungsten wire thermal infrared lamp tube with the function of emitting high-energy photons. The power of a single halogen tungsten wire thermal infrared lamp tube is ≥3KW. The rapid heat treatment push-bonding is carried out by the thermal infrared lamp tube at a temperature of 850-1000℃. The belt speed of the roller conveyor belt is ≤3.5m / min. The rapid heat treatment push-bonding time is ≥70s. The rapid heat treatment is carried out for 70-200s in N2 atmosphere. After removing the back BSG layer, the boron diffusion process is completed.

[0068] It should be clarified that any use of the process provided in the embodiments of the present invention or any substitution or change of conventional data falls within the protection and disclosure scope of the present invention.

[0069] In all the following examples and comparative examples, N-type single-crystal silicon wafers with a resistivity range of 0.4–1.1 ohm·cm, a thickness of 160–170 μm, and a size of 182 mm * 182 mm were used. Dust and dirt on the surface of the silicon wafers were removed in a mixture of NaOH and H₂O₂. Then, double-sided texturing was performed in a 2% (w / w) NaOH and texturing additive solution to form a pyramidal textured surface on the silicon wafer. The size of the pyramidal textured surface was controlled to be 0.7–3.5 μm. After texturing, PN junctions were prepared using the methods of the following examples and comparative examples.

[0070] Example 1

[0071] This embodiment provides a method for boron diffusion junction formation, the method comprising the following steps:

[0072] (1) The texturized silicon wafer is transferred into a quartz diffusion apparatus. A vacuum is evacuated in the quartz diffusion apparatus to a pressure of 50 mbar. O2 is introduced at 800°C at a flow rate of 2200 sccm for 480 s for surface oxidation. Subsequently, BSG pre-deposition is performed. Small N2 carrying BCl3 and O2 are introduced into the diffusion apparatus at a pressure of 250 mbar and a temperature of 900°C. The volumetric flow rate ratio of O2 to small N2 carrying a boron source is 2.5:1, and the flow rate of the small N2 is 800 sccm. Simultaneously, 13 slm of large N2 is introduced to transport the boron source and O2 to the silicon wafer surface. BSG pre-deposition is then performed on the silicon wafer surface for 900 s. After BSG pre-deposition, the temperature in the diffusion device is raised to 970℃. The volumetric flow rate ratio of O2 to small N2 carrying the boron source is adjusted to 1:3.125. At the same time, 15slm of large N2 is introduced to transport the boron source and O2 to the silicon wafer surface. BSG deposition and propagation on the silicon wafer surface continues for 600s. After the BSG deposition and propagation are completed, the introduction of small N2 and O2 is stopped. The temperature of the diffusion device is maintained at 850℃ and the pressure is ≤100mbar. Large N2 and water vapor are introduced to purge the diffusion device for 400s. After purging, 30slm of large N2 is introduced into the diffusion device, and the pressure is returned to normal pressure to end the silicon wafer deposition.

[0073] (2) The silicon wafer after purging is conveyed into the chain oxidation device via a roller conveyor belt. The chain oxidation device is equipped with a halogen tungsten filament thermal infrared lamp tube with the function of emitting high-energy photons. The power of a single halogen tungsten filament thermal infrared lamp tube is 3KW. The rapid heat treatment push-bonding is carried out at a temperature of 920℃ by the thermal infrared lamp tube. N2 is introduced at a rate of 80L / min as a protective gas. The belt speed of the roller conveyor belt is ≤3.5m / min. The rapid heat treatment push-bonding time is ≥70s. The rapid heat treatment is carried out for 100s in N2 atmosphere. After removing the back BSG layer, the boron diffusion process is completed.

[0074] Example 2

[0075] This embodiment provides a method for boron diffusion junction formation, the method comprising the following steps:

[0076] (1) The texturized silicon wafer is transferred into a quartz diffusion apparatus. A vacuum is evacuated from the apparatus to a pressure ≤100 mbar. O2 at 780°C and 3000 sccm is introduced for 300 s surface oxidation. Subsequently, BSG pre-deposition is performed. Small N2 carrying BCl3 and O2 are introduced into the diffusion apparatus at a pressure of 150 mbar and a temperature of 850°C. The volumetric flow rate ratio of O2 to small N2 carrying a boron source is 3:1, and the flow rate of the small N2 is 1000 sccm. Simultaneously, 15 slm of large N2 is introduced to transport the boron source and O2 to the silicon wafer surface. BSG pre-deposition is then performed on the silicon wafer surface for 900 s. Deposition; After the BSG pre-deposition is completed, the temperature in the diffusion device is raised to 950℃, the volumetric flow rate ratio of O2 to small N2 carrying the boron source is adjusted to 1:2, and 15slm of large N2 is introduced to transport the boron source and O2 to the silicon wafer surface, and BSG deposition and propagation on the silicon wafer surface continues for 900s; After the BSG deposition and propagation is completed, the introduction of small N2 and O2 is stopped, the temperature of the diffusion device is maintained at 840℃, the pressure is ≤100mbar, and large N2 and water vapor are introduced to purge the diffusion device for 600s. After the purging is completed, large N2 is introduced into the diffusion device, the pressure is returned to normal pressure, and the silicon wafer deposition ends;

[0077] (2) The silicon wafer after purging is carried into the chain oxidation device by a roller conveyor belt. The chain oxidation device is equipped with a halogen tungsten filament thermal infrared lamp tube with the function of emitting high-energy photons. The power of a single halogen tungsten filament thermal infrared lamp tube is ≥3KW. The rapid heat treatment push-bonding is carried out by the thermal infrared lamp tube at a temperature of 850℃. The belt speed of the roller conveyor belt is ≤3.5m / min. The rapid heat treatment push-bonding time is ≥70s. The rapid heat treatment is carried out for 200s in N2 atmosphere. After removing the back BSG layer, the boron diffusion process is completed.

[0078] Example 3

[0079] This embodiment provides a method for boron diffusion junction formation, the method comprising the following steps:

[0080] (1) After texturing, the silicon wafer is transferred into a quartz diffusion device. The device is evacuated to a pressure ≤100 mbar, and surface oxidation is performed for 600 s at 860°C with 1000 sccm of O2. Subsequently, BSG pre-deposition is performed. Small N2 carrying BBr3 and O2 are introduced into the diffusion device at a pressure of 400 mbar and a temperature of 900°C. The volumetric flow rate ratio of O2 to small N2 carrying the boron source is 1:1, and the flow rate of the small N2 is 800 sccm. Simultaneously, 10 slm of large N2 is introduced to transport the boron source and O2 to the silicon wafer surface. BSG pre-deposition is then performed on the silicon wafer surface for 1200 s. Deposition; After the BSG pre-deposition is completed, the temperature in the diffusion device is raised to 1000℃, the volume flow ratio of O2 to small N2 carrying the boron source is adjusted to 1:4, and 10slm of large N2 is introduced to transport the boron source and O2 to the silicon wafer surface. BSG deposition and propagation on the silicon wafer surface continues for 300s; After the BSG deposition and propagation is completed, the introduction of small N2 and O2 is stopped, the temperature of the diffusion device is maintained at 860℃, and the pressure is ≤100mbar. Large N2 and water vapor are introduced to purge the diffusion device for 200s. After the purging is completed, large N2 is introduced into the diffusion device, and the pressure is returned to normal pressure to end the silicon wafer deposition;

[0081] (2) The silicon wafer after purging is carried into the chain oxidation device by a roller conveyor belt. The chain oxidation device is equipped with a halogen tungsten wire thermal infrared lamp tube with the function of emitting high-energy photons. The power of a single halogen tungsten wire thermal infrared lamp tube is ≥3KW. The rapid heat treatment push-bonding is carried out by the thermal infrared lamp tube at a temperature of 1000℃. The belt speed of the roller conveyor belt is ≤3.5m / min. The rapid heat treatment push-bonding time is ≥70s. The rapid heat treatment is carried out for 150s in N2 atmosphere. After removing the back BSG layer, the boron diffusion process is completed.

[0082] Example 4

[0083] This embodiment provides a method for boron diffusion junction formation. The only difference between this method and Embodiment 1 is that in step (1), the ratio of O2 flow rate to source-carrying small N2 flow rate in the BSG pre-deposition is 4:1.

[0084] Example 5

[0085] This embodiment provides a method for boron diffusion junction formation. The only difference between this method and Embodiment 1 is that in step (1) of BSG pre-deposition, the ratio of O2 flow rate to source-carrying small N2 flow rate is 0.5:1.

[0086] Comparative Example 1

[0087] This comparative example provides a method for boron diffusion junction formation. The only difference between this method and Example 1 is that the rapid heat treatment push junction in step (2) is not performed. Instead, only the BSG pre-deposition step and the BSG deposition and push junction in step (1) are performed. After step (1) is completed, the push junction is maintained at a high temperature of 1000-1050℃ and continuously pushed for 3500s to complete the boron diffusion.

[0088] Comparative Example 2

[0089] This comparative example provides a method for boron diffusion junction formation, wherein the method uses a tubular boron diffusion furnace as described in the specific embodiment of CN114664643A to perform the boron diffusion process.

[0090] The silicon wafers obtained in Examples 1-5 and Comparative Example 1 were processed into N-type PERC cells. After boron diffusion, the sheet resistance was kept as uniform as possible. Comparative Example 2 directly adopted the diffusion scheme mentioned in CN114664643A, performing a tubular boron diffusion process. The total process time of boron diffusion on the silicon wafers, the uniformity of sheet resistance within the wafer, and the electrical performance of the cells were tested, as shown in Table 1. The total process time and sheet resistance uniformity after diffusion for Examples 1-5 and Comparative Examples 1-2 were statistically analyzed. For the sheet resistance test, five locations were tested on a single wafer: the four corners and the center. The non-uniformity of the sheet resistance after diffusion was calculated using the following formula:

[0091]

[0092] Table 1

[0093]

[0094] Note: When using a chain conveyor, different rapid heat treatment times are achieved by adjusting the belt speed of the conveyor rollers. There are also feeding and cooling areas before and after the conveyor. Adjusting the belt speed affects the total chain conveyor duration.

[0095] As shown in Table 2, the electrical performance parameters of Examples 1-5 and Comparative Example 1 were obtained using the PERC battery manufactured by the industry-common boron diffusion process as a benchmark. Comparative Example 2 is not listed in Table 2 because its sheet resistance control is much lower than that of Examples 1 and 2, and therefore its electrical performance does not meet the comparison conditions.

[0096] Table 2

[0097]

[0098] From the data in Tables 1 and 2, we can see that:

[0099] (1) The boron diffusion junction method provided in Examples 1-3 rapidly completes BSG deposition and short-time pre-propulsion in tubular diffusion, and then completes the push junction with the help of a rapid heat treatment device. The resulting PERC cell has good surface uniformity, sheet resistance non-uniformity ≤2.5%, fill factor increased by more than 0.31%, and photoelectric conversion efficiency increased by more than 0.009%.

[0100] (2) As can be seen from the combined results of Examples 1 and 4-5, the ratio of O2 flow rate to source-carrying small N2 flow rate in the BSG pre-deposition of Example 1 is 2.5:1, while the flow rates in Examples 4-5 are 4:1 and 0.5:1, respectively. Example 1 uses an excess oxygen method in the BSG pre-deposition, which ultimately yields a battery cell with higher uniformity. The sheet resistance non-uniformity of Example 1 is only 1.7%, the fill factor is increased by 0.31%, and the photoelectric conversion efficiency is increased by 0.01%. In contrast, the sheet resistance non-uniformity of Examples 4-5 is as high as 7.1% and 9.8%, respectively, the fill factor is only increased by 0.17% and 0.24%, respectively, and the photoelectric conversion efficiency is decreased by 0.01% and 0.02%, respectively. This proves that using the oxygen flow rate of this application in the BSG pre-deposition stage can achieve better oxidation effect, thereby obtaining better uniformity.

[0101] (3) Based on the comprehensive results of Example 1 and Comparative Examples 1-2, it can be seen that in Example 1, the diffusion reaction continuously deposits the BSG layer, and then rapid thermal treatment is used for bonding. In contrast, Comparative Example 1 directly bonds after diffusion, and Comparative Example 2 uses a tubular boron diffusion furnace for bonding. The time spent in the diffusion furnace for Example 1 is only 7200s, the sheet resistance non-uniformity is only 1.7%, the fill factor is increased by 0.31%, and the photoelectric conversion efficiency is increased by 0.01%. In contrast, the sheet resistance non-uniformity of Comparative Examples 1-2 is as high as 7.5% and 3.2%, respectively. The time spent in the diffusion furnace for Comparative Example 1 is 11200s, and the time spent in the diffusion furnace for Comparative Example 2 is 9500s. This proves that using rapid thermal treatment for bonding effectively improves the performance and processing efficiency of battery products.

[0102] In summary, the boron diffusion junction formation method provided by this invention ensures good surface uniformity of the silicon wafer by rapidly completing BSG deposition and short-time pre-propulsion in tubular diffusion. Simultaneously, it utilizes a rapid thermal processing device to achieve fast and efficient junction pushing, saving more than 1 hour of total process time per tube and increasing theoretical throughput by 30%, thus improving production efficiency. Furthermore, as shown in the sheet resistance non-uniformity statistics of Examples 1-3, the rapid thermal processing device-assisted boron junction pushing significantly improves the overall sheet resistance uniformity. Compared with the mainstream tubular boron diffusion method, the electrical performance is slightly improved in efficiency. This process is suitable for industrial production.

[0103] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for boron diffusion junction formation, characterized in that, The method includes the following steps: (1) After texturing, the silicon wafer is oxidized by introducing O2 into the diffusion device; then, a small N2 carrying a boron source is introduced into the diffusion device to react with O2, while a large N2 is introduced to transport the boron source and O2 to the surface of the silicon wafer, and BSG pre-deposition is performed on the surface of the silicon wafer; after the BSG pre-deposition is completed, the flow rates of O2, small N2 and large N2 are adjusted to continue BSG deposition and propulsion on the surface of the silicon wafer; after the BSG deposition and propulsion are completed, the silicon wafer in the diffusion device is purged. The BSG pre-deposition temperature is 850-900℃; during BSG pre-deposition, the volumetric flow rate ratio of O2 to small N2 carrying the boron source is (1-3):1; the flow rate of the small N2 is 800-3000 sccm; and the flow rate of the large N2 is 10-15 slm. The BSG deposition and propulsion temperature is 950-1000℃; during BSG deposition and propulsion, the volumetric flow rate ratio of O2 to small N2 carrying the boron source is 1:(2-4); the flow rate of the small N2 is 800-3000 sccm; and the flow rate of the large N2 is 10-15 slm. (2) After the silicon wafer is purged, it is transferred to the chain oxidation device and subjected to rapid heat treatment under a protective atmosphere to remove the back BSG layer and complete the boron diffusion process.

2. The method according to claim 1, characterized in that, The type of diffusion device mentioned in step (1) includes a quartz diffusion device.

3. The method according to claim 1, characterized in that, The diffusion device is evacuated before the surface oxidation.

4. The method according to claim 3, characterized in that, The pressure in the vacuum diffusion device is ≤100mbar.

5. The method according to claim 1, characterized in that, The surface oxidation temperature in step (1) is 780-860℃.

6. The method according to claim 1, characterized in that, The flow rate of O2 in the surface oxidation is 1000-3000 sccm.

7. The method according to claim 1, characterized in that, The surface oxidation time is 300-600s.

8. The method according to claim 1, characterized in that, During the BSG pre-deposition described in step (1), the pressure in the diffusion device is 150-400 mbar.

9. The method according to claim 1, characterized in that, During the BSG pre-deposition, the boron source includes BBr3 and / or BCl3.

10. The method according to claim 1, characterized in that, During the BSG pre-deposition, the concentration of the boron source in the small N2 containing the boron source is (2.79-8.9)×10⁻⁶. -3 mol / L.

11. The method according to claim 1, characterized in that, The BSG pre-deposition time is 600-1200s.

12. The method according to claim 1, characterized in that, During BSG deposition and propulsion in step (1), the pressure in the diffusion device is 150-400 mbar.

13. The method according to claim 1, characterized in that, During BSG deposition and propulsion, the boron source includes BBr3 and / or BCl3.

14. The method according to claim 1, characterized in that, During the BSG deposition and propagation, the concentration of the boron source in the small N2 carrying the boron source is (2.79-8.9) ×10⁻¹⁰. -3 mol / L.

15. The method according to claim 1, characterized in that, The BSG deposition and propagation time is 300-900 s.

16. The method according to claim 1, characterized in that, Before purging as described in step (1), stop introducing small amounts of N2 and O2.

17. The method according to claim 16, characterized in that, After stopping the introduction of small amounts of N2 and O2, the temperature of the diffusion device is maintained at 840-860℃.

18. The method according to claim 16, characterized in that, After stopping the flow of small amounts of N2 and O2, the pressure of the diffusion device is maintained at ≤100 mbar.

19. The method according to claim 1, characterized in that, The purging process includes introducing nitrogen and water vapor to purge the diffuser.

20. The method according to claim 1, characterized in that, The purging time is 200-600 seconds.

21. The method according to claim 1, characterized in that, After the purging process is completed, a large amount of N2 is introduced into the diffusion device, and the pressure is returned to normal to end the silicon wafer deposition.

22. The method according to claim 1, characterized in that, The rapid heat treatment described in step (2) includes the following steps: The silicon wafers are conveyed into the chain oxidation unit by a roller conveyor belt, where they undergo rapid heat treatment and bonding by irradiation with thermal infrared lamps.

23. The method according to claim 8, characterized in that, The chain oxidation device described in step (2) is equipped with a thermal infrared lamp tube that emits high-energy photons.

24. The method according to claim 22, characterized in that, The types of thermal infrared lamps include halogen tungsten filament thermal infrared lamps.

25. The method according to claim 22, characterized in that, The power of a single thermal infrared lamp tube is ≥3KW.

26. The method according to claim 1, characterized in that, The rapid heat treatment temperature is 850-1000℃.

27. The method according to claim 22, characterized in that, The belt speed of the roller conveyor belt is ≤3.5m / min.

28. The method according to claim 1, characterized in that, The rapid heat treatment push-bonding time is ≥70s.

29. The method according to claim 1, characterized in that, The protective atmosphere includes any one or a combination of at least two of Ar, N2, or O2.

30. The method according to claim 29, characterized in that, The protective atmosphere is N2.

31. The method according to claim 1, characterized in that, The flow rate of the protective atmosphere is ≥60L / min.

32. The method according to claim 1, characterized in that, The rapid heat treatment time is 70-200s.

33. The method according to claim 1, characterized in that, The method includes the following steps: (1) After texturing, the silicon wafer is transferred into a quartz diffusion device. The quartz diffusion device is evacuated to a pressure ≤100mbar. O2 is introduced at 780-860℃ at a flow rate of 1000-3000sccm for 300-600s for surface oxidation. Subsequently, BSG pre-deposition is performed. Small N2 carrying BBr3 and / or BCl3 and O2 are introduced into the diffusion device at a pressure of 150-400mbar and a temperature of 850-900℃. The volume flow rate ratio of O2 to small N2 carrying boron source is (1-3):

1. The flow rate of small N2 is 800-3000sccm. At the same time, large N2 at a flow rate of 10-15slm is introduced to transport the boron source and O2 to the surface of the silicon wafer. The process is carried out on the surface of the silicon wafer for 600-1200s. BSG pre-deposition; after the BSG pre-deposition is completed, the temperature in the diffusion device is raised to 950-1000℃, the volume flow rate ratio of O2 to small N2 carrying boron source is adjusted to 1:(2-4), and at the same time, 10-15slm of large N2 is introduced to transport the boron source and O2 to the silicon wafer surface, and BSG deposition and propagation are continued on the silicon wafer surface for 300-900s; after the BSG deposition and propagation is completed, the introduction of small N2 and O2 is stopped, the temperature of the diffusion device is maintained at 840-860℃, the pressure is ≤100mbar, and large N2 and water vapor are introduced to purge the diffusion device for 200-600s. After the purging is completed, large N2 is introduced into the diffusion device, the pressure is returned to normal pressure, and the silicon wafer deposition is ended; (2) The silicon wafer after purging is carried into the chain oxidation device by a roller conveyor belt. The chain oxidation device is equipped with a halogen tungsten wire thermal infrared lamp tube with the function of emitting high-energy photons. The power of a single halogen tungsten wire thermal infrared lamp tube is ≥3KW. The rapid heat treatment push-bonding is carried out by the thermal infrared lamp tube at a temperature of 850-1000℃. The belt speed of the roller conveyor belt is ≤3.5m / min. The rapid heat treatment push-bonding time is ≥70s. The rapid heat treatment is carried out for 70-200s in N2 atmosphere. After removing the back BSG layer, the boron diffusion process is completed.

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