Method for boron diffusion and boron diffusion apparatus for solar cells

Abstract

The application discloses a boron diffusion method and a boron diffusion device for a solar cell, and the method is used for preparing a boron emitter of a TOPCon solar cell, and the steps are front oxygen treatment, low-temperature boron deposition, temperature rising supplementary deposition, first-order temperature change promotion, oxygen-free constant-temperature promotion, second-order temperature rising promotion, high-temperature oxygen-containing promotion and low-temperature junction control tailing in sequence. Through the process design of multi-step deposition and multi-section temperature change promotion, the industry pain point that surface doping concentration and junction depth are difficult to be cooperatively controlled in the preparation of a high sheet resistance boron emitter is solved, the high sheet resistance boron emitter with a sheet resistance of 450 omega / sq to 480 omega / sq can be stably prepared, low interface recombination and low contact resistance are considered, the core electrical performance of the TOPCon solar cell is significantly improved, the process is fully adapted to the existing mass production equipment, the control window is wide, and the mass production stability is high.

Description

Technical Field

[0001] This invention belongs to the field of solar cell fabrication technology, specifically relating to a boron diffusion method and a boron diffusion device for solar cells. Background Technology

[0002] Crystalline silicon solar cells, especially N-type TOPCon solar cells, utilize boron diffusion to form the P-type doped region and the PN junction emitter during fabrication. The quality of the boron emitter determines key performance indicators of the cell, such as open-circuit voltage (Voc), fill factor (FF), and photoelectric conversion efficiency. While traditional boron diffusion processes can create a certain doped region, it is difficult to simultaneously achieve high uniformity and precise control of the doping concentration gradient. Especially when pursuing higher sheet resistance, it is difficult to avoid sheet resistance inhomogeneity within and between cells, which leads to poorer consistency in cell performance.

[0003] While traditional processes can meet this requirement to some extent, they typically sacrifice doping uniformity. In such cases, sheet resistance deviations between and within cells can be significant, leading to greater performance variations within batches of cells. Furthermore, achieving high sheet resistance requires precise control of the doping concentration gradient to avoid increased contact resistance due to excessive surface doping concentration or increased interfacial recombination due to insufficient surface doping. However, existing processes struggle to simultaneously optimize both of these key performance indicators under high sheet resistance conditions.

[0004] Furthermore, existing horizontal tubular boron diffusion devices primarily utilize a single-end centralized gas inlet combined with a gradient-aperture gas homogenization design to transport the boron source gas. However, this method presents a problem in practical applications: during the transport of silicon wafers within the furnace tube, the boron source gas easily forms a significant concentration gradient. The obstruction effect of the carrier and the turbulence within the furnace tube further exacerbate this concentration unevenness, resulting in significant intra-wafer and inter-wafer differences in sheet resistance after doping. This not only affects doping uniformity but also further increases the complexity and difficulty of high sheet resistance processes.

[0005] Therefore, in order to address the aforementioned technical problems, it is necessary to provide a boron diffusion method and a boron diffusion apparatus for solar cells.

[0006] The information disclosed in this background section is intended only to enhance the understanding of the overall background of the invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0007] The purpose of this invention is to provide a boron diffusion method and a boron diffusion apparatus for solar cells, which can solve the technical problems mentioned in the background art.

[0008] To achieve the above objectives, a specific embodiment of the present invention provides the following technical solution:

[0009] A boron diffusion method for solar cells, used in the fabrication of boron emitters for TOPCon solar cells, includes the following steps:

[0010] S1. Place the silicon wafer to be processed in a diffusion furnace, heat it to the pre-oxidation process temperature, introduce oxygen to perform pre-oxidation treatment, and grow a silicon oxide layer on the surface of the silicon wafer.

[0011] S2. Lower the furnace temperature of the diffusion furnace to the low-temperature deposition temperature, introduce boron source precursor and oxygen into the furnace, and perform low-temperature boron deposition on the silicon wafer surface to form a uniform shallow boron doped layer.

[0012] S3. Based on the low-temperature deposition temperature, increase the furnace temperature, maintain the continuous introduction of boron source precursor and oxygen, perform temperature increase to replenish deposition, increase the boron atom doping concentration on the silicon wafer surface, and provide sufficient boron source for subsequent processes.

[0013] S4. Stop the introduction of boron source precursor and oxygen, and raise the furnace temperature from the replenishment deposition temperature to the first-order propulsion temperature. During the heating process, the temperature-dependent propulsion of boron atoms is completed simultaneously.

[0014] S5. At the first-order propulsion temperature, oxygen-free isothermal propulsion is carried out to regulate the impurity distribution of boron doping and initially control the doping junction depth.

[0015] S6. Raise the furnace temperature of the diffusion furnace from the first-stage propulsion temperature to the second-stage high-temperature propulsion temperature to complete the second-stage heating process;

[0016] S7. At the second-order high-temperature propulsion temperature, oxygen is introduced into the furnace to carry out high-temperature oxygen diffusion treatment, which increases the solid solubility of boron and controls the boron doping concentration on the silicon wafer surface.

[0017] S8. The furnace temperature of the diffusion furnace is reduced to the low-temperature controlled junction temperature. Oxygen is first introduced into the furnace for aerobic propulsion, and then oxygen-free propulsion is carried out. The junction depth of the PN junction and the boron doping concentration on the silicon wafer surface are precisely controlled, and finally a high sheet resistance boron emitter structure is prepared on the silicon wafer surface.

[0018] In one or more embodiments of the present invention, in step S1, the pre-oxidation process temperature is 780℃~820℃, the oxygen flow rate is 1500sccm~2500sccm, the pre-oxidation treatment duration is 200s~300s, and the thickness of the silicon oxide layer is 1nm~3nm.

[0019] In one or more embodiments of the present invention, in step S2, the low-temperature deposition temperature is 780℃~820℃, the boron source precursor is boron trichloride, the boron trichloride flow rate is 100sccm~180sccm, the oxygen flow rate is 500sccm~900sccm, and the low-temperature boron deposition time is 100s~200s.

[0020] In one or more embodiments of the present invention, in step S3, the furnace temperature after heating is increased by 15°C to 25°C compared to the low temperature deposition temperature, the flow rate of the boron source precursor and oxygen is kept consistent with that in step S2, and the heating and replenishment deposition time is 200s to 300s.

[0021] In one or more embodiments of the present invention, in step S4, the first-stage propulsion temperature is 880℃~920℃, and the heating process lasts for 300s~350s.

[0022] In one or more embodiments of the present invention, in step S8, the low-temperature controlled junction temperature is 780℃~820℃, the oxygen flow rate for aerobic propulsion is 18000sccm~22000sccm, the aerobic propulsion duration is 1300s~1500s, and the anaerobic propulsion duration is 400s~500s; the final boron emitter has a sheet resistance of 450Ω / sq~480Ω / sq, and the PN junction depth is controlled at 0.5μm~0.7μm.

[0023] To achieve the above objectives, a specific embodiment of the present invention provides the following technical solution:

[0024] A boron diffusion device for solar cells includes a boron diffusion device body, a diffusion furnace fixedly connected inside the boron diffusion device body, a sealing cover matching the diffusion furnace rotatably connected to the boron diffusion device body, and a gas equalization device, the gas equalization device including a gas distribution plate, one end of the gas distribution plate being fixedly connected to a gas supply main pipe, and the other end being used to connect to a first gas source.

[0025] Multiple inner tubes are fixedly connected to the air distribution plate. The air distribution plate and the inner tubes are in communication. Multiple evenly distributed air nozzles are fixedly connected to the inner tubes. A guide ring is slidably connected inside the air nozzle. A sealing plug is fixedly connected to the guide ring. A sealing part matching the air nozzle is fixedly connected to the sealing plug. A venting part is provided on the guide ring.

[0026] An outer tube is fitted around the inner tube, and the outer tube seals the inner end of the inner tube located inside the diffusion furnace. The outer tube has multiple evenly distributed air outlet holes.

[0027] It also includes an in-situ detection module corresponding to the doping partition. The in-situ detection module includes a temperature detection unit and a gas detection unit. The temperature detection unit is used to collect the actual surface temperature of the silicon wafer in the corresponding doping partition, and the gas detection unit is used to collect the boron source atmosphere concentration and furnace pressure parameters in the corresponding doping partition.

[0028] In one or more embodiments of the present invention, a gas supply pipe matching the outer pipe is installed inside the diffusion furnace, a main gas supply pipe is connected to the gas supply pipe, and a second gas source is connected to the end of the main gas supply pipe away from the gas supply pipe.

[0029] In one or more embodiments of the present invention, a doping partition is formed between adjacent gas supply pipes, an exhaust pipe is installed in the doping partition, a main exhaust pipe is installed on the exhaust pipe, an air extraction system is connected to the end of the main exhaust pipe away from the exhaust pipe, and valves are installed on both the main exhaust pipe and the main gas supply pipe.

[0030] In one or more embodiments of the present invention, the temperature detection unit includes a quartz-sheathed thermocouple and a non-contact infrared temperature probe. The quartz-sheathed thermocouple is embedded in the slot of the silicon wafer carrier, and the temperature measuring end is attached to the edge of the silicon wafer. The furnace wall of the diffusion furnace cavity is provided with sapphire temperature measuring windows corresponding to the doping partitions. The non-contact infrared temperature probe collects the surface temperature of the silicon wafer through the sapphire temperature measuring windows. The gas detection unit includes a quartz pressure tube, a boron source concentration sensor, and a pressure sensor. One end of the quartz pressure tube extends into the corresponding doping partition, and the other end is led out to the ambient temperature zone outside the furnace, and is connected to the boron source concentration sensor and the pressure sensor.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] By using a gas equalization device located in the center of the furnace cavity, a boron-containing doped mixed gas is introduced into the furnace cavity and diffused uniformly after passing through multiple stages of equalization. The pressure difference adaptive constant flow structure of the gas nozzle on the inner tube is used to compensate for the pressure difference between the front and rear ends of the inner tube. Combined with the full-area isobaric pressure stabilizing chamber of the outer tube and the gas outlet with a gas equalization structure, the axial concentration gradient of the traditional gas inlet structure is eliminated from the root.

[0033] Meanwhile, parameters are collected in real time by an in-situ detection module that corresponds to each doping zone. With the help of an independent gas supply pipe, the target zone with insufficient boron source concentration is accurately supplied with gas to correct local atmosphere deviation. The gas supply parameters can also be adjusted synchronously based on the silicon wafer surface temperature parameters. The difference in doping reaction rate caused by temperature fluctuation is compensated by the boron source concentration, which greatly improves the uniformity and consistency of boron doping in the entire furnace cavity.

[0034] By deploying exhaust pipes that correspond one-to-one with each doping zone, the exhaust volume of each zone and the pressure throughout the furnace cavity are simultaneously controlled. This, combined with the gas replenishment action, maintains the flow field stability of each doping zone and avoids the problems of axial pressure gradient and flow field distortion in the furnace cavity caused by traditional exhaust methods. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 This is a schematic diagram of the boron diffusion method and boron diffusion device for a solar cell according to an embodiment of the present invention;

[0037] Figure 2 This is a schematic diagram of the gas equalization device in one embodiment of the present invention. Figure 1 ;

[0038] Figure 3 This is a partial cross-sectional view of the gas equalization device in one embodiment of the present invention;

[0039] Figure 4 This is a schematic diagram of the gas equalization device in one embodiment of the present invention. Figure 2 .

[0040] Explanation of key figure labels:

[0041] 1. Main body of boron diffusion device; 101. Sealing cover; 2. Diffusion furnace; 3. Gas equalization device; 4. Gas distribution plate; 5. Main gas supply pipe; 6. Outer pipe; 601. Gas outlet; 7. Inner pipe; 8. Gas nozzle; 9. Guide ring; 901. Gas vent; 10. Sealing plug; 1001. Sealing part; 11. Gas supply pipe; 12. Main gas supply pipe; 13. Doping zone; 14. Exhaust pipe; 15. Main exhaust pipe; 16. Valve. Detailed Implementation

[0042] To enable those skilled in the art to better understand the technical solutions in this disclosure, the technical solutions in the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this disclosure.

[0043] like Figures 1-4As shown, in one embodiment of the present invention, a boron diffusion device for a solar cell includes a boron diffusion device body 1, a horizontal diffusion furnace 2 fixedly connected inside the boron diffusion device body 1, the diffusion furnace 2 being a furnace tube made of high-purity quartz material, forming a sealed furnace cavity inside; a sealing cover 101 matching the furnace opening of the diffusion furnace 2 is rotatably connected to the end of the boron diffusion device body 1, the sealing cover 101 adopting a high-temperature resistant vacuum sealing structure to ensure the airtightness of the furnace cavity during the process.

[0044] The boron diffusion device also includes a gas equalization device 3, which is installed inside the furnace cavity of the diffusion furnace 2. The gas equalization device 3 includes a gas distribution plate 4, which is connected to multiple inner tubes 7. The end of the inner tube 7 away from the gas supply main pipe 5 extends into the diffusion furnace 2. The gas distribution plate 4 is equipped with a gas supply main pipe 5, which is used to connect to a first gas source. The first gas source is a boron-containing doped mixed gas supply system that can provide nitrogen-carried boron tribromide or trimethyl borate doped gas.

[0045] Multiple air nozzles 8 are fixedly connected to the inner tube 7. A guide ring 9 is slidably connected inside the air nozzle 8. A sealing plug 10 is fixedly connected to the guide ring 9. A sealing part 1001 that matches the inner wall of the air nozzle 8 is fixedly connected to the sealing plug 10. The outer wall of the sealing part 1001 contacts the inner wall of the air nozzle 8 to achieve a seal. A vent 901 is provided on the guide ring 9. When air enters the inner tube 7, the gas pushes outward against the sealing plug 10, forcing the sealing plug 10 and the air nozzle 8 to lose their connection, and the gas can be discharged from the air nozzle 8.

[0046] Among them, the air nozzle 8 is perpendicular to the horizontal plane. When the sealing plug 10 is pushed out, the air pressure in the inner tube 7 decreases. Under the action of gravity, the sealing plug 10 can be inserted back into the air nozzle 8.

[0047] However, it is worth noting that the air pressure at the front and rear ends of the inner tube 7 is inconsistent, and this should be considered in practical applications. Specifically, for the front nozzle 8 with higher air pressure, the high pressure inside the tube can only push open the sealing plug 10 to create a limited flow gap. The air output is throttled and locked by the fixed diameter of the vent 901 of the guide ring 9, preventing a sudden increase in air output due to the high pressure at the front. For the rear nozzle 8 with lower air pressure, as long as the air pressure inside the tube reaches a uniform opening threshold, the sealing plug 10 can be opened to achieve stable air output. The throttling design of the vent 901 ensures that the air output of a single nozzle 8 will not decrease significantly due to a slight decrease in the rear air pressure.

[0048] like Figures 2-3As shown, an outer tube 6 is fitted around the inner tube 7. The outer tube 6 completely wraps around one end of the inner tube 7 located inside the diffusion furnace 2. The outer tube 6 has an outlet hole 601 facing the battery cell. A gas equalization structure is installed on the outlet hole 601. Specifically, the gas equalization structure is a high-purity quartz sintered porous medium layer or a slit laminar flow gas equalization structure. The gas can be evenly discharged from the outer tube 6 through the gas equalization structure.

[0049] In the non-ventilated state, the sealing part 1001 of the sealing plug 10 is tightly fitted to the inner wall of the air nozzle 8, and the air nozzle 8 is in a normally closed state, which can completely prevent borosilicate glass deposits and dust in the furnace from flowing back into the inner tube 7 and causing blockage of the channel.

[0050] When the doped mixed gas is introduced into the inner tube 7 and the gas pressure inside the tube reaches the opening threshold, the gas pressure pushes the sealing plug 10 and the guide ring 9 outward, causing the sealing part 1001 to disengage from the inner wall of the nozzle 8. The doped mixed gas flows out of the nozzle 8 through the vent 901 on the guide ring 9 and enters the annular pressure stabilizing chamber between the inner tube 7 and the outer tube 6.

[0051] This chamber is a large-volume, full-area isobaric chamber, which can quickly eliminate airflow fluctuations in a single nozzle 8 and slight air output deviations in nozzles 8 at different positions, so that the mixed gas pressure and boron source concentration inside the entire outer tube 6 are completely equal along the entire axis, thus eliminating the axial concentration gradient of the traditional air intake structure from the root.

[0052] Finally, the uniform mixed gas in the pressure stabilizing chamber is discharged through the vent 601 on the outer tube 6 facing the silicon wafer. The high-purity quartz sintered porous dielectric layer or slit laminar flow uniform gas structure matched at the vent 601 can transform the concentrated airflow into a uniform and gentle planar laminar flow, uniformly covering the front and back surfaces of the M10 / M12 large-size silicon wafer, avoiding the problems of excessive doping at the edge of the silicon wafer and turbulence disturbance in the tube caused by direct airflow, and realizing the uniform diffusion of the doped atmosphere throughout the entire area.

[0053] like Figures 1-4 As shown, multiple gas supply pipes 11 are evenly distributed along the circumference of the inner wall of the diffusion furnace 2. Each gas supply pipe 11 is equipped with a main gas supply pipe 12. The gas supply pipes 11 are made of high-purity quartz material that matches the furnace body of the diffusion furnace 2. They can withstand high-temperature conditions of 900-1100℃ and strong corrosive environment of boron source. Their axial extension length is completely matched with the effective bearing length of the silicon wafer carrier in the furnace cavity, ensuring that the gas supply range fully covers the process range where all silicon wafers are located, with no blind spots in control.

[0054] Each gas supply pipe 11 has its inlet end sealed and connected to an independent main gas supply pipe 12. The main gas supply pipe 12 extends along the axial direction of the diffusion furnace 2 towards the tail end of the boron diffusion device body 1, and passes through the tail furnace wall of the boron diffusion device body 1 through a high-temperature resistant sealing structure, extending to the ambient temperature area outside the furnace. Each main gas supply pipe 12 has an independent valve 16 installed outside the furnace. The valve 16 preferably adopts a high-precision mass flow control valve, which can independently and accurately control the gas supply on / off, gas flow rate, and gas rate of the corresponding gas supply pipe 11. The end of the main gas supply pipe 12 away from the gas supply pipe 11 is uniformly connected to a second gas source outside the furnace. The second gas source can provide independently proportioned boron-containing mixed gas, inert protective gas, or oxidizing cleaning gas according to process requirements, forming a completely independent dual-supply system with the first gas source of the gas equalization device 3, avoiding gas supply interference between the main gas equalization supply and the zoned gas supply, and ensuring the parameter stability of the two gas supplies.

[0055] Along the axial direction of diffusion furnace 2, an independent doping zone 13 is defined between two adjacent gas supply pipes 11. All doping zones 13 are arranged sequentially along the axial direction of the furnace cavity, completely covering the entire process area. Each doping zone 13 corresponds to a set of gas supply pipes 11, an in-situ detection module, and an exhaust pipe 14, forming an independent control unit of "one zone, one monitoring; one zone, one gas supply; one zone, one exhaust".

[0056] Each gas supply pipe 11 has a gas supply outlet hole on its pipe wall facing the center of the furnace cavity, which matches the range of the corresponding doping zone 13. The gas supply outlet hole is equipped with a gas uniform structure, preferably a high-purity quartz sintered porous dielectric layer or a slit laminar flow gas uniform structure, which allows the gas supply airflow to diffuse into the target doping zone 13 in a soft and uniform planar flow field, avoiding direct airflow impacting the silicon wafer and causing fragmentation, while preventing local turbulence from disturbing the stable flow field environment inside the furnace.

[0057] In the actual process, two adjacent gas supply pipes 11 can work together to control the atmosphere of the intermediate doping zone 13: when the in-situ detection module reports that the boron source atmosphere concentration in a certain doping zone 13 is lower than the process set threshold, or when the doping reaction rate needs to be compensated due to local temperature field fluctuations, the overall control system can precisely control the gas supply pipes 11 on both sides of the doping zone 13, and synchronously adjust the opening of the corresponding valves 16 to supplement the target doping zone 13 with a boron-containing mixed gas of a set flow rate and concentration, and quickly correct the local atmosphere deviation; or, according to the actual deviation, the gas supply pipe 11 on one side can be controlled separately to perform micro-gas supply compensation, so as to achieve full-gradient precise control from large-scale correction to micro-fine adjustment, and maintain a high degree of consistency in the boron source concentration and doping reaction rate of all doping zones 13 in the entire furnace cavity.

[0058] In addition, during the cleaning process after a single batch of processes is completed, a cleaning mixture of high-temperature oxygen and inert gas can be independently introduced through each gas supply pipe 11, and the exhaust pipe 14 of the corresponding zone can be used to independently exhaust the gas, so as to achieve segmented purging and cleaning of each doped zone 13 in the furnace cavity, accurately remove borosilicate glass deposits in the corresponding area, avoid the cleaning blind spots that exist in traditional overall purging, and further extend the continuous operation cycle of the equipment.

[0059] Specifically, the in-situ detection module includes a temperature detection unit and a gas detection unit that work together. The temperature detection unit is used to collect the actual surface temperature of the silicon wafer within the corresponding doped partition 13. A dual-redundant temperature measurement architecture using quartz-clad thermocouples and non-contact infrared temperature probes ensures both the accuracy of temperature measurement and full-coverage monitoring of the entire temperature of the M10 / M12 large-size silicon wafer, as detailed below:

[0060] Quartz-clad thermocouples are pre-embedded in the wafer slots of the quartz boat carrier that holds the silicon wafers. At least two sets of quartz-clad thermocouples are installed in each doping zone 13, with their sensing ends directly and tightly fitted to the edge of the silicon wafer within the slot, allowing for direct and real-time acquisition of the actual temperature of the silicon wafer. The thermocouple protective sheaths are made of high-purity quartz, capable of withstanding the high temperatures and strong boron corrosion conditions of the boron diffusion process, preventing metal contamination of the silicon wafer and avoiding temperature drift and shortened lifespan issues caused by boron penetration. The thermocouple signal cables are led out along the quartz boat and furnace wall to the ambient temperature zone outside the furnace, where they are electrically connected to the main control system. There are no active electronic components in the high-temperature zone inside the furnace, completely eliminating the risk of high-temperature failure.

[0061] The non-contact infrared temperature probe complements the quartz-clad thermocouple. To address the radial temperature difference monitoring needs of large-size silicon wafers, sapphire temperature measurement windows with inert gas purging protection are installed on the furnace wall of diffusion furnace 2, corresponding to each doping zone 13. The sapphire material is high-temperature resistant, corrosion-resistant, and has stable infrared transmittance, ensuring long-term stability of temperature measurement accuracy. The non-contact infrared temperature probe is fixedly installed in the ambient temperature zone outside the furnace. Through the sapphire temperature measurement window, it non-contactly collects the surface temperature of the central region of the silicon wafer within the corresponding doping zone 13. This temperature difference is verified and complemented by the edge temperature of the silicon wafer collected by the quartz-clad thermocouple, allowing simultaneous monitoring of the radial temperature difference of a single silicon wafer and the axial temperature difference of the entire furnace cavity.

[0062] The gas detection unit includes a quartz pressure tube, a boron source concentration sensor, and a pressure sensor, each corresponding to one of the doping zones 13. The quartz pressure tube is made of high-purity quartz, with one end open and extending into the furnace cavity of the corresponding doping zone 13. The opening is positioned directly above the gap between the silicon wafers in that zone, allowing for accurate acquisition of the actual atmosphere parameters within that zone without pipeline delay or concentration distortion. The other end of the quartz pressure tube passes through the furnace wall of the diffusion furnace 2 via a high-temperature resistant sealing structure and extends to the ambient temperature area outside the furnace, where it is sealed and connected to the boron source concentration sensor and the pressure sensor, respectively.

[0063] Among them, the pressure sensor can monitor the furnace pressure in the corresponding doping zone 13 in real time, providing data support for zone linkage pressure stabilization and exhaust, ensuring the linkage balance between gas supply and exhaust actions, and avoiding the disruption of flow field uniformity caused by furnace pressure fluctuations; the boron source concentration sensor can detect the boron source gas phase concentration in the corresponding zone in real time, accurately capture the deviation of local boron source concentration, and provide direct control basis for differentiated zone gas supply. When the concentration is detected to be lower than the process set threshold, the overall control system can immediately trigger the gas supply action of the corresponding gas supply pipe 11 to achieve rapid correction of the deviation.

[0064] All concentration and pressure detection elements are kept in a normal temperature environment outside the furnace throughout the process, without coming into contact with the high temperature and highly corrosive atmosphere inside the furnace. This eliminates the problems of detection accuracy drift and element failure caused by boron source corrosion and high temperature aging, ensuring the detection stability and reliability of long-term operation and significantly reducing equipment calibration and maintenance costs.

[0065] All parameters collected by the temperature detection unit and the gas detection unit are transmitted to the main control system in real time. Based on the preset process parameter thresholds, the main control system synchronously controls the gas supply pipe 11, the exhaust pipe 14 and the furnace heating system of the corresponding doping zone 13 to ensure the uniformity and consistency of the doping process in the entire furnace cavity.

[0066] like Figures 2-4 As shown, exhaust pipes 14 are specifically installed within each independent doping zone 13. Exhaust pipes 14 are made of high-purity quartz material compatible with diffusion furnace 2, capable of withstanding high temperatures of 900-1100℃ and strong corrosive atmospheres such as boron sources and hydrogen bromide, posing no risk of metal contamination and suitable for all boron diffusion process conditions. Exhaust pipes 14 are connected to the main exhaust pipe 15, and all exhaust pipes 14 are uniformly connected to the main exhaust pipe 15 via independent valves 16. The end of the main exhaust pipe 15 is directly connected to the plant's extraction system and tail gas treatment system, achieving unified collection and harmless treatment of tail gas within the furnace.

[0067] A boron diffusion method for a solar cell according to an embodiment of the present invention includes the following steps:

[0068] S1. Pre-oxidation treatment: The silicon wafer to be treated is placed in a diffusion furnace, heated to the pre-oxidation process temperature, and oxygen is introduced to perform pre-oxidation treatment, growing a silicon oxide layer on the surface of the silicon wafer.

[0069] The pre-oxidation process involves a temperature of 780℃~820℃, an oxygen flow rate of 1500sccm~2500sccm, and a pre-oxidation treatment duration of 200s~300s; the thickness of the silicon oxide layer is 1nm~3nm. This ultrathin silicon oxide layer, grown through this step, allows for precise control of the initial diffusion rate of boron atoms, improving the uniformity of doping across the entire wafer, while also acting as a lattice getter, reducing surface defects on the silicon wafer.

[0070] S2. Low-temperature boron deposition: The furnace temperature of the diffusion furnace is lowered to the low-temperature deposition temperature, and boron source precursor and oxygen are introduced into the furnace to perform low-temperature boron deposition on the silicon wafer surface to form a uniform shallow boron doped layer.

[0071] The low-temperature deposition temperature is 780℃~820℃, the boron source precursor is boron trichloride, the boron trichloride flow rate is 100sccm~180sccm, the oxygen flow rate is 500sccm~900sccm, and the low-temperature boron deposition time is 100s~200s. Through low-temperature and gentle deposition, a uniform and controllable shallow boron-doped layer is formed on the silicon wafer surface, avoiding the problems of uneven doping and uncontrolled junction depth caused by high-temperature deposition, thus laying a uniform boron source foundation for subsequent processes.

[0072] S3. Heating and Deposition Supplementation: Based on the low-temperature deposition temperature, the furnace temperature is increased to maintain the continuous flow of boron source precursor and oxygen, and heating and deposition supplementation is carried out to increase the boron atom doping concentration on the silicon wafer surface, so as to provide sufficient boron source for subsequent processes.

[0073] In this process, the furnace temperature after heating is increased by 15°C to 25°C above the low-temperature deposition temperature. The flow rates of the boron source precursor and oxygen are kept consistent with those in step S2, and the heating and replenishment deposition time is 200s to 300s. By slightly increasing the temperature, the deposition rate of boron atoms and the solid solubility of the silicon lattice are improved. Without compromising doping uniformity, the amount of boron atoms adsorbed on the silicon wafer surface is further increased. This provides a sufficient and uniform boron source for subsequent multi-stage processes, avoiding problems such as insufficient doping and increased contact resistance caused by insufficient boron source in high sheet resistance processes.

[0074] S4, First-order temperature-dependent propulsion: Stop the introduction of boron source precursor and oxygen, raise the furnace temperature from the replenishment deposition temperature to the first-order propulsion temperature, and simultaneously complete the temperature-dependent propulsion of boron atoms during the heating process.

[0075] The first-order propagation temperature is 880℃~920℃, and the heating process lasts for 300s~350s. During the slow heating process under an inert protective atmosphere, shallow and gradual propagation of boron atoms is achieved simultaneously, avoiding the uncontrolled junction depth caused by subsequent high-temperature concentrated propagation. At the same time, the doping concentration gradient is optimized to reduce interface recombination.

[0076] S5. Oxygen-free isothermal propulsion: Under the first-order propulsion temperature, oxygen-free isothermal propulsion is carried out to regulate the impurity distribution of boron doping and initially control the doping junction depth;

[0077] The duration of the oxygen-free isothermal propulsion is 400s~500s. By using isothermal propulsion in a low-temperature oxygen-free environment, the smooth internal diffusion of boron atoms is achieved, the impurity distribution of boron doping is precisely controlled, the doping junction depth range is initially locked, and the problems of excessive junction depth and sheet resistance loss caused by high-temperature propulsion are avoided.

[0078] S6, Second-stage heating and propulsion: The furnace temperature of the diffusion furnace is raised from the first-stage propulsion temperature to the second-stage high-temperature propulsion temperature to complete the second-stage heating process;

[0079] The second-order high-temperature propulsion temperature is 1000℃~1040℃, and the heating process lasts for 2000s~2200s. Through long-term slow heating, the gradient propulsion of boron atoms is realized simultaneously during the heating process, continuously optimizing the doping concentration gradient and forming an ideal doped structure with "low surface concentration and gradually changing distribution in the bulk", which takes into account both passivation effect and contact performance.

[0080] S7. High-temperature oxygen propulsion: At the second-order high-temperature propulsion temperature, oxygen is introduced into the furnace to carry out high-temperature oxygen diffusion treatment, which increases the solid solubility of boron and controls the boron doping concentration on the silicon wafer surface.

[0081] The oxygen flow rate was 18000 sccm to 22000 sccm, and the total duration of high-temperature oxygen diffusion was 1800 s to 2000 s. This high-temperature oxygen environment increased the solid solubility of boron in the silicon lattice, ensuring that the doping concentration on the silicon wafer surface met the low contact resistance requirements of the subsequent metal electrodes. Simultaneously, the high-temperature oxidation process allowed for precise control of the surface doping concentration, preventing the formation of heavily doped dead layers and reducing interfacial recombination losses.

[0082] S8. Low-Temperature Controlled Junction Finishing: The furnace temperature of the diffusion furnace is reduced to the low-temperature controlled junction temperature. Oxygen is first introduced into the furnace for aerobic propulsion, and then oxygen-free propulsion is carried out. The junction depth of the PN junction and the boron doping concentration on the silicon wafer surface are precisely controlled, and finally a high sheet resistance boron emitter structure is prepared on the silicon wafer surface.

[0083] The cryogenic junction temperature was 780℃~820℃, the oxygen flow rate for aerobic propulsion was 18000sccm~22000sccm, the aerobic propulsion duration was 1300s~1500s, and the anaerobic propulsion duration was 400s~500s. The final boron emitter had a sheet resistance of 450Ω / sq~480Ω / sq, and the PN junction depth was controlled at 0.5μm~0.7μm.

[0084] The beneficial effects of the boron diffusion method of the present invention include:

[0085] By employing a low-temperature two-step deposition process, multi-stage temperature-controlled advancement, and low-temperature controlled junction finishing process, a high sheet resistance boron emitter with a sheet resistance of 380 Ω / sq can be stably fabricated. At the same time, the PN junction depth is precisely controlled at around 0.6 μm, and the boron doping concentration on the silicon wafer surface is stably controlled within the optimal range. This eliminates the interface recombination loss caused by the heavily doped dead layer and fully ensures the low contact resistance requirement between the metal electrode and the silicon wafer, thus balancing low recombination and low contact resistance.

[0086] The step-by-step process design of this invention significantly improves the tolerance to fluctuations in furnace temperature field and gas source flow rate, effectively ensuring doping uniformity. The 380Ω / sq boron emitter prepared by this process can have its sheet resistance uniformity deviation within 2% and its sheet resistance deviation between wafers in the same batch controlled within 3%, with strong batch-to-batch performance consistency, fully meeting the yield requirements for large-scale production of TOPCon batteries.

[0087] It will be apparent to those skilled in the art that this disclosure is not limited to the details of the exemplary embodiments described above, and that this disclosure can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of this disclosure is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within this disclosure. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0088] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A boron diffusion method for solar cells, characterized in that, The fabrication of a boron emitter for TOPCon solar cells includes the following steps: S1. Place the silicon wafer to be processed in a diffusion furnace, heat it to the pre-oxidation process temperature, introduce oxygen to perform pre-oxidation treatment, and grow a silicon oxide layer on the surface of the silicon wafer. S2. Lower the furnace temperature of the diffusion furnace to the low-temperature deposition temperature, introduce boron source precursor and oxygen into the furnace, and perform low-temperature boron deposition on the silicon wafer surface to form a uniform shallow boron doped layer. S3. Based on the low-temperature deposition temperature, increase the furnace temperature, maintain the continuous introduction of boron source precursor and oxygen, perform temperature increase to replenish deposition, increase the boron atom doping concentration on the silicon wafer surface, and provide sufficient boron source for subsequent processes. S4. Stop the introduction of boron source precursor and oxygen, and raise the furnace temperature from the replenishment deposition temperature to the first-order propulsion temperature. During the heating process, the temperature-dependent propulsion of boron atoms is completed simultaneously. S5. At the first-order propulsion temperature, oxygen-free isothermal propulsion is carried out to regulate the impurity distribution of boron doping and initially control the doping junction depth. S6. Raise the furnace temperature of the diffusion furnace from the first-stage propulsion temperature to the second-stage high-temperature propulsion temperature to complete the second-stage heating process; S7. At the second-order high-temperature propulsion temperature, oxygen is introduced into the furnace to carry out high-temperature oxygen diffusion treatment, which increases the solid solubility of boron and controls the boron doping concentration on the silicon wafer surface. S8. The furnace temperature of the diffusion furnace is reduced to the low-temperature controlled junction temperature. Oxygen is first introduced into the furnace for aerobic propulsion, and then oxygen-free propulsion is carried out. The junction depth of the PN junction and the boron doping concentration on the silicon wafer surface are precisely controlled, and finally a high sheet resistance boron emitter structure is prepared on the silicon wafer surface.

2. The boron diffusion method for solar cells according to claim 1, characterized in that, In step S1, the pre-oxidation process temperature is 780℃~820℃, the oxygen flow rate is 1500sccm~2500sccm, and the pre-oxidation treatment time is 200s~300s; the thickness of the silicon oxide layer is 1nm~3nm.

3. The boron diffusion method for solar cells according to claim 1, characterized in that, In step S2, the low-temperature deposition temperature is 780℃~820℃, the boron source precursor is boron trichloride, the boron trichloride flow rate is 100sccm~180sccm, the oxygen flow rate is 500sccm~900sccm, and the low-temperature boron deposition time is 100s~200s.

4. The boron diffusion method for solar cells according to claim 1, characterized in that, In step S3, the furnace temperature after heating is increased by 15°C to 25°C compared to the low-temperature deposition temperature. The flow rates of the boron source precursor and oxygen are kept the same as in step S2. The heating and replenishment deposition time is 200s to 300s.

5. The boron diffusion method for solar cells according to claim 1, characterized in that, In step S4, the first-stage propulsion temperature is 880℃~920℃, and the heating process lasts for 300s~350s.

6. The boron diffusion method for solar cells according to claim 1, characterized in that, In step S8, the low-temperature controlled junction temperature is 780℃~820℃, the oxygen flow rate for aerobic propulsion is 18000sccm~22000sccm, the aerobic propulsion duration is 1300s~1500s, and the anaerobic propulsion duration is 400s~500s. The final boron emitter has a sheet resistance of 450Ω / sq to 480Ω / sq and a PN junction depth controlled at 0.5μm to 0.7μm.

7. A boron diffusion apparatus for a solar cell, used to perform the boron diffusion method for a solar cell according to any one of claims 1 to 6, comprising a boron diffusion apparatus body, wherein a diffusion furnace is fixedly connected inside the boron diffusion apparatus body, and a sealing cover matching the diffusion furnace is rotatably connected to the boron diffusion apparatus body, characterized in that, It also includes a gas equalization device, which includes a gas distribution plate. One end of the gas distribution plate is fixedly connected to a gas supply pipe, and the other end is used to connect to a first gas source. Multiple inner tubes are fixedly connected to the air distribution plate. The air distribution plate and the inner tubes are in communication. Multiple evenly distributed air nozzles are fixedly connected to the inner tubes. A guide ring is slidably connected inside the air nozzle. A sealing plug is fixedly connected to the guide ring. A sealing part matching the air nozzle is fixedly connected to the sealing plug. A venting part is provided on the guide ring. An outer tube is fitted around the inner tube, and the outer tube seals the inner end of the inner tube located inside the diffusion furnace. The outer tube has multiple evenly distributed air outlet holes. It also includes an in-situ detection module corresponding to the doping partition. The in-situ detection module includes a temperature detection unit and a gas detection unit. The temperature detection unit is used to collect the actual surface temperature of the silicon wafer in the corresponding doping partition, and the gas detection unit is used to collect the boron source atmosphere concentration and furnace pressure parameters in the corresponding doping partition.

8. The boron diffusion device for a solar cell according to claim 7, characterized in that, The diffusion furnace is equipped with a gas supply pipe that matches the outer pipe. A main gas supply pipe is connected to the gas supply pipe, and a second gas source is connected to the end of the main gas supply pipe away from the gas supply pipe.

9. The boron diffusion device for a solar cell according to claim 8, characterized in that, A doping zone is formed between adjacent gas supply pipes. An exhaust pipe is installed in the doping zone. A main exhaust pipe is installed on the exhaust pipe. An air extraction system is connected to the end of the main exhaust pipe away from the exhaust pipe. Valves are installed on both the main exhaust pipe and the main gas supply pipe.

10. The boron diffusion device for a solar cell according to claim 9, characterized in that, The temperature detection unit includes a quartz-armored thermocouple and a non-contact infrared temperature probe. The quartz-armored thermocouple is embedded in the slot of the silicon wafer carrier, and the temperature measuring end is attached to the edge of the silicon wafer. The diffusion furnace cavity has sapphire temperature measurement windows on its furnace wall that correspond one-to-one with the doping zones. The non-contact infrared temperature measurement probe collects the surface temperature of the silicon wafer through the sapphire temperature measurement windows. The gas detection unit includes a quartz pressure tube, a boron source concentration sensor, and a pressure sensor. One end of the quartz pressure tube extends into the corresponding doping zone, and the other end extends to the ambient temperature zone outside the furnace, where it is connected to the boron source concentration sensor and the pressure sensor.

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