Method for boron diffusion with high uniformity of high sheet resistance for TOPCon cell

Abstract

This invention provides a method for achieving high sheet resistance uniformity in boron diffusion for TOPCon solar cells. The method includes sequential steps such as wafer loading, heating, vacuuming, pre-oxygenation, multi-step power supply, variable-temperature multi-step junction pushing, variable-pressure annealing, re-pressure, and wafer unloading. The variable-temperature multi-step junction pushing includes sequential oxygen-free and oxygen-containing junction pushing. The temperature of oxygen-free junction pushing is lower than that of oxygen-containing junction pushing, the time of oxygen-free junction pushing is shorter than that of oxygen-containing junction pushing, the furnace pressure during oxygen-free junction pushing is lower than that during oxygen-containing junction pushing, and the oxygen flow rate during oxygen-containing junction pushing is 18000-23000 sccm. This invention improves the uniformity of boron content distribution by introducing a variable-temperature multi-step junction pushing process that combines oxygen-free followed by oxygen-containing junction pushing with multi-step power supply and variable-pressure annealing. This results in a P+ emitter with lower surface doping concentration and shallower junction depth, while significantly improving the sheet resistance uniformity after boron diffusion, achieving high sheet resistance uniformity under high sheet resistance targets.

Description

Technical Field

[0001] This invention belongs to the field of photovoltaic technology, specifically relating to a method for high sheet resistance uniform boron expansion of TOPCon cells. Background Technology

[0002] TOPCon (tunneling oxide passivated contact) solar cells, with their excellent photoelectric conversion efficiency and potential low cost advantages, have become an important development direction for next-generation high-efficiency crystalline silicon cells. One of their core structures is the P+ emitter formed on the front surface of the cell through a boron diffusion process. This process aims to introduce boron atoms into the surface of the N-type silicon wafer to form a P-type layer, thereby constructing a high-quality PN junction, which is a key step that determines the cell's open-circuit voltage, short-circuit current, and final efficiency.

[0003] Today, the photovoltaic industry requires high-efficiency TOPCon cells to have high sheet resistance and shallow junction depth at the emitter. This typically means precisely controlling and appropriately reducing the total amount of boron doping near the silicon wafer surface (i.e., boron content). However, in tubular high-temperature diffusion processes, the pursuit of reducing boron content and increasing sheet resistance conflicts significantly with maintaining excellent sheet resistance uniformity. This non-uniformity in sheet resistance directly causes differences in electrical performance across the cell, leading to decreased parallel resistance and increased local recombination, severely restricting the improvement of cell efficiency and production yield.

[0004] Therefore, how to solve the problem of uneven boron content distribution in existing technologies when reducing boron content, and achieve high sheet resistance uniformity under high sheet resistance target, is an urgent technical problem to be solved. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a method for achieving high sheet resistance uniformity in boron diffusion in TOPCon solar cells. This invention introduces a variable-temperature, multi-step junction-pushing process with a "first oxygen-free, then oxygen-containing" approach, combined with multi-step source-through and variable-pressure annealing. This modulates the diffusion kinetics and surface chemical reactions of boron atoms within the silicon wafer, fundamentally improving the uniformity of boron content distribution. This results in a P+ emitter with lower surface doping concentration and shallower junction depth, while significantly enhancing the sheet resistance uniformity after boron diffusion, achieving high sheet resistance uniformity at a high sheet resistance target. Based on this, TOPCon solar cells exhibit a stronger short-wavelength spectral response. Furthermore, the process itself reduces lattice damage to the silicon wafer surface, effectively weakens the recombination effect of photogenerated carriers, reduces internal defects in the silicon wafer, and achieves higher cell conversion efficiency. In addition, this process helps shorten the overall process time, reduce process costs, and has high repeatability, providing a reliable technical path for the efficient and stable mass production of TOPCon solar cells.

[0006] To achieve this objective, the present invention employs the following technical solution: This invention provides a method for high sheet resistance uniform boron expansion of TOPCon cells. The method includes sequentially performing silicon wafer loading, heating, vacuuming, pre-oxygenation, multi-step power supply, variable temperature multi-step junction pushing, variable voltage annealing, re-pressure, and silicon wafer unloading.

[0007] The variable-temperature multi-step bonding process includes sequential oxygen-free bonding and aerobic bonding; the temperature of the oxygen-free bonding is lower than the temperature of the aerobic bonding, the time of the oxygen-free bonding is shorter than the time of the aerobic bonding, the furnace pressure during the oxygen-free bonding is lower than the furnace pressure during the aerobic bonding, and the oxygen flow rate during the aerobic bonding is 18000-23000 sccm.

[0008] This invention introduces a variable-temperature, multi-step junction-pushing process with an initial oxygen-free phase followed by an oxygen-containing phase, combined with multi-step source-through and variable-pressure annealing. This process controls the diffusion kinetics and surface chemical reactions of boron atoms within the silicon wafer, fundamentally improving the uniformity of boron content distribution. This results in a P+ emitter with lower surface doping concentration and shallower junction depth, while significantly enhancing the sheet resistance uniformity after boron diffusion, achieving high sheet resistance uniformity even at high sheet resistance targets. Based on this, TOPCon cells exhibit a stronger short-wavelength spectral response. Furthermore, the process itself reduces lattice damage to the silicon wafer surface, effectively mitigating the recombination effect of photogenerated carriers, reducing internal defects in the silicon wafer, and achieving higher cell conversion efficiency. In addition, this process helps shorten the overall process time, reduce process costs, and offers high repeatability, providing a reliable technical path for the efficient and stable mass production of TOPCon cells.

[0009] In this invention, the oxygen-free push-junction stage is carried out under relatively low temperature, time, and pressure conditions, primarily for the initial diffusion and redistribution of boron atoms, providing a more uniform boron atom base for subsequent oxygen-based push-junction. In the oxygen-based push-junction stage, oxygen participates in the reaction, not only promoting further diffusion of boron atoms but also reacting with impurities on and inside the silicon wafer surface, improving the quality and uniformity of the PN junction. By precisely controlling the process parameters of oxygen-free and oxygen-based push-junctions, the advantages of both are maximized synergistically, contributing to the acquisition of PN junctions with higher uniformity and quality.

[0010] In this invention, the oxygen flow rate during the oxygen-driven junction push-off stage is 18,000-23,000 sccm, for example, 18,000 sccm, 19,000 sccm, 20,000 sccm, 21,000 sccm, 22,000 sccm, or 23,000 sccm. Using an appropriate oxygen flow rate during the oxygen-driven junction push-off stage allows for the growth of a uniform and dense oxide layer on the silicon wafer surface. This oxide layer effectively shields environmental impurities and improves surface passivation quality. Furthermore, oxygen participation in the reaction promotes the orderly and uniform propagation of boron atoms within the silicon lattice, while simultaneously combining with certain metallic impurities in the silicon and being expelled with the gas flow, thus playing a cleaning role. Therefore, precise control of the oxygen flow rate can achieve the target junction depth and sheet resistance while avoiding excessive oxidation or lattice stress caused by excessive oxygen content, thereby improving PN junction uniformity while minimizing carrier recombination losses.

[0011] This invention limits the furnace pressure during oxygen-free push-junction to be lower than that during oxygen-containing push-junction. This provides a crucial process environment for achieving high sheet resistance uniformity under high sheet resistance targets. The lower pressure environment allows boron atoms to disperse more freely and fully in the initial lateral and longitudinal directions under oxygen-free conditions, laying the foundation for achieving excellent sheet resistance uniformity in subsequent oxygen-containing push-junction under high sheet resistance targets.

[0012] Preferably, the temperature for the oxygen-free bonding is 870-900℃, for example, 870℃, 880℃, 890℃ or 900℃, and the time is 10-20min, for example, 10min, 15min or 20min.

[0013] In the oxygen-free push-junction stage, the present invention uses the above-mentioned temperature in combination with a specific time to achieve sufficient and gentle initial propagation of boron atoms while ensuring the stability of the silicon wafer structure. This effectively reduces the surface peak concentration, forms a uniform and controllable shallow pre-diffusion layer, and avoids various defects caused by excessively high temperature or excessively long time.

[0014] Preferably, the temperature of the aerobic bonding is 1000-1100℃, for example, 1000℃, 1050℃ or 1100℃, and the time is 70-100min, for example, 70min, 80min, 90min or 100min.

[0015] In the oxygen-driven junction stage, the present invention uses the above-mentioned temperature in combination with a specific time to achieve stable and uniform deep penetration of boron atoms into the silicon wafer to form the target PN junction; it can also promote the growth of a high-quality and dense oxide layer and effectively remove impurities, thereby achieving the required electrical performance while greatly optimizing the quality and interface characteristics of the PN junction.

[0016] Preferably, the furnace pressure during oxygen-free sintering is 100-800 mbar, for example, it can be 100 mbar, 200 mbar, 300 mbar, 400 mbar, 500 mbar, 600 mbar, 700 mbar or 800 mbar.

[0017] Preferably, the furnace pressure during aerobic sintering is 700-800 mbar, for example, it can be 700 mbar, 750 mbar or 800 mbar.

[0018] Preferably, during the transition from anaerobic to aerobic bonding, the rate of increase of oxygen flow rate is 10,000-20,000 sccm / min, for example, it can be 10,000 sccm / min, 12,000 sccm / min, 14,000 sccm / min, 16,000 sccm / min, 18,000 sccm / min or 20,000 sccm / min, etc.

[0019] In this invention, during the transition from oxygen-free to oxygen-enriched junction bonding, the rate of increase of oxygen flow is limited to meet certain conditions, which can ensure a smooth transition of PN junction depth from shallow to deep and improve the uniformity of sheet resistance on the silicon wafer surface.

[0020] Preferably, after the oxygen-free push junction, the PN junction depth on the silicon wafer surface is 0.05-0.15μm, for example, it can be 0.05μm, 0.1μm or 0.15μm, etc.

[0021] Preferably, after the oxygen-free push-junction, the average sheet resistance of the silicon wafer is 550-580 Ω / sq, for example, it can be 550 Ω / sq, 560 Ω / sq, 570 Ω / sq or 580 Ω / sq, etc.

[0022] Preferably, after the oxygen-induced junction push-in, the PN junction depth on the silicon wafer surface is 0.6-0.9 μm, for example, it can be 0.6 μm, 0.7 μm, 0.8 μm, or 0.9 μm, etc.

[0023] Preferably, after the oxygen push-junction, the average sheet resistance of the silicon wafer is 380-460 Ω / sq, for example, it can be 380 Ω / sq, 400 Ω / sq, 420 Ω / sq, 440 Ω / sq or 460 Ω / sq, etc.

[0024] In this invention, the aforementioned performance characteristics obtained in the oxygen-free and oxygen-enriched bonding stages lay a solid foundation for achieving the core objective of high uniformity under high sheet resistance.

[0025] Preferably, the multi-step power supply steps include: (a) A diffusion source is introduced under the condition of the first source temperature to pre-deposit a first boron-rich layer on the silicon wafer surface.

[0026] (b) Heat to the second source temperature and then introduce a diffusion source to pre-deposit a second boron-rich layer on the surface of the first boron-rich layer.

[0027] (c) Heat to the third source temperature and then introduce a diffusion source to pre-deposit the third boron-rich layer on the surface of the second boron-rich layer.

[0028] The boron atom concentrations of the first, second, and third boron-rich layers increase sequentially.

[0029] Preferably, the first power supply temperature is 805-815℃, for example, it can be 805℃, 810℃ or 815℃.

[0030] Preferably, the second power supply temperature is 815-825℃, for example, it can be 815℃, 820℃ or 825℃.

[0031] Preferably, the third power source temperature is 825-835℃, for example, it can be 825℃, 830℃ or 835℃, etc.

[0032] In this invention, the boron deposition kinetics are more precisely controlled by progressively increasing the temperature at each step through a "low temperature, narrow range, and step-by-step" heating strategy. This ensures the full decomposition and adsorption of the boron source while suppressing problems such as premature diffusion of boron atoms into the silicon body, poor uniformity of the surface deposition layer, and aggravated thermal damage to the silicon wafer caused by excessive temperature rise or excessive temperature. This lays the foundation for achieving a highly uniform PN junction.

[0033] Preferably, during the multi-step power supply process, the furnace pressure is kept constant at 200-250 mbar, for example, it can be 200 mbar, 300 mbar, 400 mbar or 500 mbar.

[0034] Preferably, the diffusion sources in steps (a), (b), and (c) all include an inert gas, oxygen, and a boron source. For example, the inert gas may be nitrogen or argon, and the boron source may be boron tribromide, boron trichloride, etc.

[0035] Preferably, the boron atom concentration in the first boron-rich layer is 0.1 × 10⁻⁶. 20 cm -3 -0.3×10 20 cm -3 For example, it could be 0.1 × 10 20 cm -3 0.2×10 20 cm -3 Or 0.3×10 20 cm-3 wait.

[0036] Preferably, the boron atom concentration in the second boron-rich layer is 0.3 × 10⁻⁶. 20 cm -3 -0.6×10 20 cm -3 For example, it could be 0.3 × 10 20 cm -3 0.4×10 20 cm -3 0.5×10 20 cm -3 Or 0.6×10 20 cm -3 wait.

[0037] Preferably, the boron atom concentration in the third boron-rich layer is 0.6 × 10⁻⁶. 20 cm -3 -0.9×10 20 cm -3 For example, it could be 0.6 × 10 20 cm -3 0.7×10 20 cm -3 0.8×10 20 cm -3 Or 09×10 20 cm -3 wait.

[0038] Preferably, in step (a), the flow rate ratio of the inert gas, oxygen, and boron source is (25-40):(6.25-10):1, wherein the inert gas selection range "25-40" can be, for example, 25, 30, 35, or 40, and the oxygen selection range "6.25-10" can be, for example, 6.25, 7, 8, 9, or 10.

[0039] Preferably, in step (b), the flow rate ratio of the inert gas, oxygen, and boron source is (20-100):(5-25):1, wherein the inert gas selection range "20-100" can be, for example, 20, 40, 60, 80, or 100, and the oxygen selection range "5-25" can be, for example, 5, 10, 15, 20, or 25.

[0040] Preferably, in step (c), the flow rate ratio of the inert gas, oxygen, and boron source is (50-200):(12.5-50):1, wherein the inert gas selection range "50-200" can be, for example, 50, 100, 150, or 200, and the oxygen selection range "12.5-50" can be, for example, 12.5, 15, 20, 30, 40, or 50.

[0041] Preferably, the variable pressure annealing step includes: Under the pressure conditions of the first furnace, the first step of annealing is carried out, then the pressure is reduced to the pressure conditions of the second furnace, and then the second step of annealing is carried out.

[0042] Preferably, during the variable pressure annealing process, the annealing temperature is 750-900℃, for example, it can be 750℃, 800℃, 850℃ or 900℃.

[0043] Preferably, the pressure inside the first furnace is 700-800 mbar, for example, it can be 700 mbar, 750 mbar or 800 mbar.

[0044] Preferably, the pressure inside the second furnace is 550-700 mbar, for example, it can be 550 mbar, 600 mbar, 650 mbar or 700 mbar.

[0045] Preferably, the atmosphere for the first annealing step is an inert atmosphere. For example, it can be nitrogen or argon.

[0046] Preferably, the atmosphere for the second annealing step is a mixed atmosphere containing an active gas and an inert gas. The active gas includes hydrogen, and the volume fraction of the active gas is 0.1-5%, for example, 0.1%, 0.5%, 1%, 2%, 3%, 4%, or 5%. Exemplarily, the inert gas may be nitrogen or argon.

[0047] In this invention, the introduction of a certain volume fraction of hydrogen can passivate the dangling bonds on the silicon wafer surface and within the wafer, reducing the recombination center density. Specifically, hydrogen can reduce local fluctuations in carrier mobility, ensuring on-chip consistency of electrical performance under high sheet resistance conditions.

[0048] Preferably, the time for the silicon wafer to enter the boat is 8-15 minutes, for example, it can be 8 minutes, 10 minutes, 12 minutes or 15 minutes.

[0049] Preferably, in the heating step, the heating time is ≤3min, for example, it can be 3min, 2min or 1min, and the temperature after heating is 805-815℃, for example, it can be 805℃, 810℃ or 815℃.

[0050] Preferably, the pressure inside the furnace after vacuuming is 200-250 mbar, for example, 200 mbar, 210 mbar, 220 mbar, 230 mbar, 240 mbar or 250 mbar, and the pressure holding time is 5-10 min, for example, 5 min, 6 min, 7 min, 8 min, 9 min or 10 min.

[0051] Preferably, in the pre-oxygenation step, an inert gas and oxygen are introduced at a flow rate ratio of (2-4):(1-3) for 3-6 minutes, for example, 3 minutes, 4 minutes, 5 minutes, or 6 minutes. For example, the inert gas selection range "2-4" can be 2, 3, or 4, and the oxygen selection range "1-3" can be 1, 2, or 3. The inert gas can be, for example, nitrogen or argon.

[0052] Preferably, after the back pressure step, the average sheet resistance of the boron-expanded silicon wafer is 380-460 Ω / sq, for example, it can be 380 Ω / sq, 390 Ω / sq, 400 Ω / sq, 410 Ω / sq, 420 Ω / sq, 430 Ω / sq, 440 Ω / sq, 450 Ω / sq, 460 Ω / sq, etc., and the sheet resistance uniformity between wafers is ≤8%, for example, it can be 8%, 7%, 6%, 5%, 4%, 3%, 2% or 1%, etc.

[0053] Preferably, the method includes the following steps: (1) Silicon wafers are loaded onto the ship: The silicon wafers are inserted back-to-back into the quartz boat and loaded into the tube diffusion furnace.

[0054] (2) Heating: Under an inert atmosphere, the tubular diffusion furnace is heated to a first source temperature of 805-815℃ within ≤3 minutes.

[0055] (3) Vacuuming and leak detection: While keeping the temperature of the tubular diffusion furnace constant, evacuate the furnace to a pump pressure of 200-250 mbar. After holding the pressure for 5-10 minutes, perform a leak test on the tubular diffusion furnace.

[0056] (4) Pre-oxygen: Keeping the temperature of the tubular diffusion furnace constant, an inert gas and oxygen with a flow rate ratio of (2-4):(1-3) are introduced for 3-6 minutes to prepare a silicon oxide layer on the silicon wafer surface.

[0057] (5) Multi-step source connection: (5-1) Under the condition of the first power-on temperature, an inert gas, oxygen, and boron source with a flow ratio of (25-40):(6.25-10):1 are introduced for ≤5 min (e.g., 5 min, 4 min, 3 min, 2 min, or 1 min, etc.) to pre-deposit a boron atom concentration of 0.1 × 10⁻⁶ on the silicon wafer surface. 20 cm -3 -0.3×10 20 cm -3 The first boron-rich layer.

[0058] (5-2) Heat to the second source temperature, then introduce an inert gas, oxygen, and boron source at a flow ratio of (20-100):(5-25):1 for ≤5 min (e.g., 5 min, 4 min, 3 min, 2 min, or 1 min, etc.), thereby pre-depositing a boron atom concentration of 0.3 × 10⁻⁶ on the surface of the first boron-rich layer. 20 cm -3 -0.6×10 20 cm -3 The second boron-rich layer; the second source temperature is 815-825℃.

[0059] (5-3) Heat to the third source temperature, then introduce an inert gas, oxygen, and boron source at a flow ratio of (50-200):(12.5-50):1 for ≤5 min (e.g., 5 min, 4 min, 3 min, 2 min, or 1 min, etc.) to pre-deposit a boron atom concentration of 0.6 × 10⁻⁶ on the surface of the second boron-rich layer. 20 cm -3 -0.9×10 20 cm -3 The third boron-rich layer; the third source temperature is 825-835℃.

[0060] The boron atom concentrations of the first, second, and third boron-rich layers increase sequentially; during the multi-step power supply process, the furnace pressure remains constant at 200-250 mbar.

[0061] (6) Variable temperature multi-step bonding: (6-1) Under an oxygen-free atmosphere of 850-950℃ and 100-800mbar in the furnace, perform oxygen-free push junction for 10-20min to make the PN junction depth on the silicon wafer surface 0.05-0.15μm and the average sheet resistance of the silicon wafer 500-580Ω / sq.

[0062] (6-2) Heat to 1000-1100℃ and pressurize to 700-800mbar in the furnace. At the same time, introduce oxygen into the tubular diffusion furnace and control the oxygen flow rate to increase by 10000-20000sccm / min until the oxygen flow rate is 18000-23000sccm. Then, perform oxygen-induced junction pushing for 70-100min to make the PN junction depth on the silicon wafer surface 0.6-0.9μm and the average sheet resistance of the silicon wafer 380-460Ω / sq.

[0063] (7) Variable pressure annealing: The first annealing is carried out in an inert atmosphere at 700-800 mbar and 750-900℃ for a time ≤40 min (e.g., 40 min, 30 min, 20 min, or 10 min). Then, the pressure is reduced to 550-700 mbar, and the second annealing is carried out in a mixed atmosphere containing active and inert gases at 750-900℃ for a time ≤40 min (e.g., 40 min, 30 min, 20 min, or 10 min).

[0064] In the inert atmosphere, the flow rate of the inert gas is ≤18000 sccm (e.g., 18000 sccm, 16000 sccm, 14000 sccm, 12000 sccm, or 10000 sccm, etc.); in the mixed atmosphere, the volume fraction of the active gas is 0.1-5%, and the flow rate of the inert gas is ≤18000 sccm (e.g., 18000 sccm, 16000 sccm, 14000 sccm, 12000 sccm, or 10000 sccm, etc.); the active gas includes hydrogen.

[0065] (8) Back pressure and silicon wafer unloading: After the pressure inside the tubular diffusion furnace is reduced to differential pressure, the boron-expanded silicon wafers are removed. The average sheet resistance of the boron-expanded silicon wafers is 380-460 Ω / sq, and the sheet resistance uniformity between wafers is ≤8%.

[0066] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0067] Compared with the prior art, the present invention has the following beneficial effects: This invention introduces a variable-temperature, multi-step junction-pushing process with an initial oxygen-free phase followed by an oxygen-containing phase, combined with multi-step source-through and variable-pressure annealing. This process controls the diffusion kinetics and surface chemical reactions of boron atoms within the silicon wafer, fundamentally improving the uniformity of boron content distribution. This results in a P+ emitter with lower surface doping concentration and shallower junction depth, while significantly enhancing the sheet resistance uniformity after boron diffusion, achieving high sheet resistance uniformity even at high sheet resistance targets. Based on this, TOPCon cells exhibit a stronger short-wavelength spectral response. Furthermore, the process itself reduces lattice damage to the silicon wafer surface, effectively mitigating the recombination effect of photogenerated carriers, reducing internal defects in the silicon wafer, and achieving higher cell conversion efficiency. In addition, this process helps shorten the overall process time, reduce process costs, and offers high repeatability, providing a reliable technical path for the efficient and stable mass production of TOPCon cells. Detailed Implementation

[0068] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention.

[0069] Example 1 This embodiment provides a method for high sheet resistance uniform boron diffusion in TOPCon batteries, the method comprising the following steps; (1) Silicon wafers are loaded onto the ship: The silicon wafers are inserted back-to-back into the quartz boat and loaded into the tube diffusion furnace.

[0070] (2) Heating: Under a nitrogen atmosphere, the tubular diffusion furnace is heated to a first source temperature of 810°C within 2 minutes.

[0071] (3) Vacuuming and leak detection: While keeping the temperature of the tubular diffusion furnace constant, a vacuum was drawn to achieve a pump pressure of 225 mbar. After holding the pressure for 8 minutes, the tubular diffusion furnace was leak-tested.

[0072] (4) Pre-oxygen: Keeping the temperature of the tubular diffusion furnace constant, nitrogen and oxygen are introduced at a flow ratio of 3:2 for 5 minutes to prepare a silicon oxide layer with a thickness of 2 nm on the silicon wafer surface.

[0073] (5) Multi-step source connection: (5-1) Under the condition of the first power-on temperature, nitrogen, oxygen and boron trichloride were introduced in a flow ratio of 30:8:1 for 4 minutes to pre-deposit a boron atom concentration of 0.2×10 on the silicon wafer surface. 20 cm -3 The first boron-rich layer.

[0074] (5-2) The temperature is raised to the second source temperature, and then nitrogen, oxygen and boron trichloride are introduced in a flow ratio of 60:15:1 for 4 minutes, thereby pre-depositing a boron atom concentration of 0.45 × 10⁻⁶ on the surface of the first boron-rich layer. 20 cm -3 The second boron-rich layer; the second source temperature is 820°C.

[0075] (5-3) The temperature is raised to the third source temperature, and then nitrogen, oxygen and boron trichloride are introduced in a flow ratio of 125:30:1 for 4 minutes, thereby pre-depositing a boron atom concentration of 0.75 × 10⁻⁶ on the surface of the second boron-rich layer. 20 cm -3 The third boron-rich layer; the third source temperature is 830°C.

[0076] The boron atom concentrations of the first, second, and third boron-rich layers increase sequentially; during the multi-step power supply process, the furnace pressure remains constant at 225 mbar.

[0077] (6) Variable temperature multi-step bonding: (6-1) Under an oxygen-free atmosphere of 900℃ and 100mbar in the furnace, oxygen-free bonding was carried out for 15 minutes, so that the PN junction depth on the silicon wafer surface was 0.1μm and the average sheet resistance of the silicon wafer was 580Ω / sq.

[0078] (6-2) Heat to 1050℃ and pressurize to 750mbar in the furnace. At the same time, oxygen is introduced into the tubular diffusion furnace. The oxygen flow rate is controlled to increase by 10000sccm / min until the oxygen flow rate is 20000sccm. Then, oxygen-induced junction pushing is performed for 85 minutes to make the PN junction depth on the silicon wafer surface 0.6μm and the average sheet resistance of the silicon wafer 460Ω / sq.

[0079] (7) Variable pressure annealing: The first annealing was carried out in a nitrogen atmosphere at 750 mbar and 775 °C for 20 min. Then, the pressure was reduced to 600 mbar and the second annealing was carried out in a mixed atmosphere of hydrogen and nitrogen at 775 °C for 20 min.

[0080] In the nitrogen atmosphere, the nitrogen flow rate is 16000 sccm; in the mixed atmosphere, the hydrogen volume fraction is 2.5%, and the nitrogen flow rate is 16000 sccm.

[0081] (8) Back pressure and silicon wafer unloading: After the pressure inside the tubular diffusion furnace is reduced to differential pressure, the boron-expanded silicon wafers are removed; the average sheet resistance of the boron-expanded silicon wafers is 460Ω / sq, and the sheet resistance uniformity between wafers is 8%.

[0082] Example 2 This embodiment provides a method for high sheet resistance uniform boron diffusion in TOPCon batteries, the method comprising the following steps; (1) Silicon wafers are loaded onto the ship: The silicon wafers are inserted back-to-back into the quartz boat and loaded into the tube diffusion furnace.

[0083] (2) Heating: Under a nitrogen atmosphere, the tubular diffusion furnace is heated to a first source temperature of 810°C within 2 minutes.

[0084] (3) Vacuuming and leak detection: While keeping the temperature of the tubular diffusion furnace constant, a vacuum was drawn to achieve a pump pressure of 200 mbar. After holding the pressure for 8 minutes, the tubular diffusion furnace was leak-tested.

[0085] (4) Pre-oxygen: Keeping the temperature of the tubular diffusion furnace constant, nitrogen and oxygen are introduced at a flow ratio of 2:3 for 3 minutes to prepare a silicon oxide layer with a thickness of 2 nm on the silicon wafer surface.

[0086] (5) Multi-step source connection: (5-1) Under the condition of the first power-on temperature, nitrogen, oxygen and boron trichloride are introduced in a flow ratio of 25:10:1 for 4 minutes to pre-deposit a boron atom concentration of 0.1×10 on the silicon wafer surface. 20 cm -3 The first boron-rich layer.

[0087] (5-2) The temperature is raised to the second source temperature, and then nitrogen, oxygen and boron trichloride are introduced in a flow ratio of 20:25:1 for 4 minutes, thereby pre-depositing a boron atom concentration of 0.3 × 10⁻⁶ on the surface of the first boron-rich layer. 20 cm -3 The second boron-rich layer; the second source temperature is 815°C.

[0088] (5-3) The temperature is raised to the third source temperature, and then nitrogen, oxygen and boron trichloride are introduced in a flow ratio of 50:50:1 for 4 minutes, thereby pre-depositing a boron atom concentration of 0.6 × 10⁻⁶ on the surface of the second boron-rich layer. 20 cm -3 The third boron-rich layer; the third source temperature is 825°C.

[0089] The boron atom concentrations of the first, second, and third boron-rich layers increase sequentially; during the multi-step power supply process, the furnace pressure remains constant at 200 mbar.

[0090] (6) Variable temperature multi-step bonding: (6-1) Under an oxygen-free atmosphere of 850℃ and 200mbar in the furnace, oxygen-free bonding was carried out for 10 minutes, so that the PN junction depth on the silicon wafer surface was 0.05μm and the average sheet resistance of the silicon wafer was 550Ω / sq.

[0091] (6-2) Heat to 1000℃ and pressurize to 720mbar in the furnace. At the same time, oxygen is introduced into the tubular diffusion furnace. The oxygen flow rate is controlled to increase at a rate of 20000sccm / min. After the oxygen flow rate reaches 20000sccm, oxygen-induced junction pushing is performed for 70 minutes to make the PN junction depth on the silicon wafer surface 0.9μm and the average sheet resistance of the silicon wafer 386Ω / sq.

[0092] (7) Variable pressure annealing: The first annealing was carried out in a nitrogen atmosphere at 720 mbar and 750 °C for 30 min. Then, the pressure was reduced to 550 mbar and the second annealing was carried out in a mixed atmosphere of hydrogen and nitrogen at 750 °C for 30 min.

[0093] In the nitrogen atmosphere, the nitrogen flow rate is 16000 sccm; in the mixed atmosphere, the hydrogen volume fraction is 0.5%, and the nitrogen flow rate is 16000 sccm.

[0094] (8) Back pressure and silicon wafer unloading: After the pressure inside the tubular diffusion furnace is reduced to differential pressure, the boron-expanded silicon wafers are removed; the average sheet resistance of the boron-expanded silicon wafers is 386Ω / sq, and the sheet resistance uniformity between wafers is 5.5%.

[0095] Example 3 This embodiment provides a method for high sheet resistance uniform boron diffusion in TOPCon batteries, the method comprising the following steps; (1) Silicon wafers are loaded onto the ship: The silicon wafers are inserted back-to-back into the quartz boat and loaded into the tube diffusion furnace.

[0096] (2) Heating: Under a nitrogen atmosphere, the tubular diffusion furnace is heated to a first source temperature of 810°C within 2 minutes.

[0097] (3) Vacuuming and leak detection: While keeping the temperature of the tubular diffusion furnace constant, a vacuum was drawn to achieve a pump pressure of 250 mbar. After holding the pressure for 8 minutes, the tubular diffusion furnace was leak-tested.

[0098] (4) Pre-oxygen: Keeping the temperature of the tubular diffusion furnace constant, nitrogen and oxygen were introduced at a flow ratio of 4:1 for 6 minutes to prepare a silicon oxide layer with a thickness of 2 nm on the silicon wafer surface.

[0099] (5) Multi-step source connection: (5-1) Under the condition of the first power-on temperature, nitrogen, oxygen and boron trichloride were introduced in a flow ratio of 40:6.25:1 for 4 minutes, thereby pre-depositing a boron atom concentration of 0.3×10 on the silicon wafer surface. 20 cm -3 The first boron-rich layer.

[0100] (5-2) The temperature is raised to the second source temperature, and then nitrogen, oxygen and boron trichloride are introduced in a flow ratio of 100:5:1 for 4 minutes, thereby pre-depositing a boron atom concentration of 0.6×10 on the surface of the first boron-rich layer. 20 cm -3 The second boron-rich layer; the second source temperature is 825°C.

[0101] (5-3) The temperature is raised to the third source temperature, and then nitrogen, oxygen and boron trichloride are introduced at a flow rate ratio of 200:12.5:1 for 4 minutes, thereby pre-depositing a boron atom concentration of 0.9 × 10⁻⁶ on the surface of the second boron-rich layer. 20 cm -3 The third boron-rich layer; the third source temperature is 835°C.

[0102] The boron atom concentrations of the first, second, and third boron-rich layers increase sequentially; during the multi-step power supply process, the furnace pressure remains constant at 250 mbar.

[0103] (6) Variable temperature multi-step bonding: (6-1) Under an oxygen-free atmosphere of 950℃ and 200mbar in the furnace, oxygen-free bonding was carried out for 20 minutes, so that the PN junction depth on the silicon wafer surface was 0.15μm and the average sheet resistance of the silicon wafer was 550Ω / sq.

[0104] (6-2) Heat to 1100℃ and pressurize to 800mbar in the furnace. At the same time, oxygen is introduced into the tubular diffusion furnace. The oxygen flow rate is controlled to increase at a rate of 20000sccm / min. After the oxygen flow rate reaches 20000sccm, oxygen-induced junction pushing is performed for 100min to make the PN junction depth on the silicon wafer surface 0.7μm and the average sheet resistance of the silicon wafer 420Ω / sq.

[0105] (7) Variable pressure annealing: The first annealing step was carried out in a nitrogen atmosphere at 800 mbar and 900 °C for 10 min. Then, the pressure was reduced to 700 mbar and the second annealing step was carried out in a mixed atmosphere of hydrogen and nitrogen at 900 °C for 10 min.

[0106] In the nitrogen atmosphere, the nitrogen flow rate is 16000 sccm; in the mixed atmosphere, the hydrogen volume fraction is 5%, and the nitrogen flow rate is 16000 sccm.

[0107] (8) Back pressure and silicon wafer unloading: After the pressure inside the tubular diffusion furnace is reduced to differential pressure, the boron-expanded silicon wafers are removed. The average sheet resistance of the boron-expanded silicon wafers is 420 Ω / sq, and the sheet resistance uniformity between wafers is 3.2%.

[0108] Example 4 The difference between this embodiment and Embodiment 1 is that the first power supply temperature is 815°C, the second power supply temperature is 840°C, and the third power supply temperature is 860°C.

[0109] The remaining methods and parameters are consistent with those in Example 1.

[0110] Example 5 The difference between this embodiment and embodiment 1 is that after oxygen-free push junction in step (6-1), the PN junction depth on the silicon wafer surface is 0.2μm.

[0111] The remaining methods and parameters are consistent with those in Example 1.

[0112] Example 6 The difference between this embodiment and Embodiment 1 is that in step (6-2), the oxygen flow rate increases at a rate of 25000 sccm / min.

[0113] The remaining methods and parameters are consistent with those in Example 1.

[0114] Example 7 The difference between this embodiment and embodiment 1 is that in step (7), the atmosphere for the second annealing step is a pure nitrogen atmosphere.

[0115] The remaining methods and parameters are consistent with those in Example 1.

[0116] Example 8 The difference between this embodiment and embodiment 1 is that in step (7), the volume fraction of hydrogen in the mixed atmosphere is 6%.

[0117] The remaining methods and parameters are consistent with those in Example 1.

[0118] Comparative Example 1 The difference between this comparative example and Example 1 is that in step (6-1), the anaerobic push-junction is replaced with the aerobic push-junction, and the oxygen flow rate is the same as that in step (6-2).

[0119] The remaining methods and parameters are consistent with those in Example 1.

[0120] Comparative Example 2 The difference between this comparative example and Example 1 is that the furnace pressure in step (6-1) for oxygen-free push-bonding is equal to the furnace pressure in step (6-2) for oxygen-free push-bonding, both being 750 mbar.

[0121] The remaining methods and parameters are consistent with those in Example 1.

[0122] Comparative Example 3 The difference between this comparative example and Example 1 is that, in step (6-2), the oxygen flow rate of the aerobic pusher is 15000 sccm.

[0123] The remaining methods and parameters are consistent with those in Example 1.

[0124] Comparative Example 4 The difference between this comparative example and Example 1 is that, in step (6-2), the oxygen flow rate of the aerobic pusher is 25000 sccm.

[0125] The remaining methods and parameters are consistent with those in Example 1.

[0126] Performance testing A four-probe tester was used to test the sheet resistance of the boron-expanded silicon wafers prepared in the above examples and comparative examples, and the sheet resistance uniformity between wafers was calculated. The specific values ​​are shown in Table 1.

[0127] Table 1 analyze: As shown in Table 1, this invention, by introducing a variable-temperature multi-step junction pushing process of "oxygen-free first, oxygen-containing later," combined with multi-step source-through and variable-pressure annealing, regulates the diffusion kinetics and surface chemical reactions of boron atoms within the silicon wafer. This fundamentally improves the uniformity of boron content distribution, resulting in a P+ emitter with lower surface doping concentration and shallower junction depth. Simultaneously, it significantly enhances the sheet resistance uniformity after boron diffusion, achieving high sheet resistance uniformity under high sheet resistance targets. The average sheet resistance of the boron-diffused silicon wafer is 300-460 Ω / sq, with inter-wafer sheet resistance uniformity ≤8%. Based on this, TOPCon cells exhibit a stronger short-wavelength spectral response. Furthermore, the process itself reduces lattice damage to the silicon wafer surface, effectively weakens the recombination effect of photogenerated carriers, reduces internal defects in the silicon wafer, and achieves higher cell conversion efficiency, reaching up to 27.25%.

[0128] As can be seen from the comparison between Example 1 and Example 4, if the temperature increase between the first source temperature, the second source temperature and the third source temperature is too large, it will destroy the smoothness and compactness of the boron-rich layer deposition, resulting in increased interlayer stress and decreased interface quality, which will cause local disturbances in the diffusion front during subsequent bonding and ultimately damage the sheet resistance uniformity.

[0129] A comparison between Example 1 and Example 5 shows that if the PN junction depth on the silicon wafer surface is too deep after oxygen-free junction pushing, it indicates that boron atoms diffuse excessively during the oxygen-free junction pushing stage, weakening the process's ability to control the final junction depth and uniformity.

[0130] As can be seen from the comparison between Example 1 and Example 6, if the rate of increase of oxygen flow is too large during the transition from oxygen-free push junction to oxygen-containing push junction, it will lead to violent and uneven oxidation reaction on the silicon wafer surface, causing local thermal stress and uneven oxide layer thickness, and ultimately damaging sheet resistance uniformity.

[0131] As can be seen from the comparison between Example 1 and Example 7, if the atmosphere of the second annealing step does not contain active gas during the transformer annealing process, the defects in the silicon wafer and its interface cannot be effectively treated, resulting in more residual composite centers, which limits the improvement of the photoelectric performance of the battery.

[0132] As can be seen from the comparison between Example 1 and Example 8, if the volume fraction of active gas in the atmosphere of the second annealing step is too large during the voltage transformation annealing process, it may introduce new problems due to excessive modification, which may degrade the junction region and even interfere with the already formed uniform doping distribution, thus negatively affecting the efficiency of the battery.

[0133] As can be seen from the comparison between Example 1 and Comparative Example 1, if the entire process of the variable-temperature multi-step bonding stage is in an oxygen-rich environment, the boron atoms are blocked by the rapidly growing oxide layer on the surface from the beginning, making the final doping distribution more sensitive to the initial deposition inhomogeneity, thus making it difficult to achieve excellent sheet resistance uniformity under high sheet resistance.

[0134] As can be seen from the comparison between Example 1 and Comparative Example 2, if the furnace pressure of oxygen-free sintering is equal to that of oxygen-containing sintering, the effect of oxygen-free sintering in optimizing the longitudinal concentration distribution is weakened, which is not conducive to achieving the goal of high sheet resistance uniformity.

[0135] As can be seen from the comparison between Example 1 and Comparative Examples 3-4, if the oxygen flow rate of the oxygen-driven junction is too small, it is insufficient to grow a continuous, dense and uniform oxide layer on the silicon wafer surface, resulting in a poor passivation and impurity shielding effect. At the same time, the role of oxygen in promoting uniform boron diffusion and impurity removal is not fully utilized. If the oxygen flow rate of the oxygen-driven junction is too large, the oxidation reaction on the silicon wafer surface will be too intense, hindering the further propagation of boron atoms. It may also introduce large lattice stress and interface defects, degrading the quality of the PN junction and the improvement of electrical performance.

[0136] It should be noted that the present invention is illustrated through the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, additions of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for high sheet resistance uniform boron diffusion in TOPCon batteries, characterized in that, The method includes sequentially performing silicon wafer loading, heating, vacuuming, pre-oxygenation, multi-step power supply, variable temperature multi-step junction pushing, variable pressure annealing, re-pressure, and silicon wafer unloading. The variable-temperature multi-step bonding process includes sequential oxygen-free bonding and aerobic bonding; the temperature of the oxygen-free bonding is lower than the temperature of the aerobic bonding, the time of the oxygen-free bonding is shorter than the time of the aerobic bonding, the furnace pressure during the oxygen-free bonding is lower than the furnace pressure during the aerobic bonding, and the oxygen flow rate during the aerobic bonding is 18000-23000 sccm.

2. The method according to claim 1, characterized in that, The oxygen-free bonding temperature is 870-900℃, and the time is 10-20 min; And / or, the temperature of the aerobic bonding is 1000-1100℃ and the time is 70-100min; And / or, the furnace pressure during the oxygen-free push-bonding process is 100-800 mbar; And / or, the furnace pressure during the aerobic sintering process is 700-800 mbar; And / or, during the transition from anaerobic to aerobic shovel bonding, the oxygen flow rate increases at a rate of 10,000-20,000 sccm / min.

3. The method according to claim 1 or 2, characterized in that, After oxygen-free push-junction, the PN junction depth on the silicon wafer surface is 0.05-0.15μm; And / or, after the oxygen-free push junction, the average sheet resistance of the silicon wafer is 550-580 Ω / sq; And / or, after the oxygen-induced junction push-in, the PN junction depth on the silicon wafer surface is 0.6-0.9 μm; And / or, after the oxygen push-junction, the average sheet resistance of the silicon wafer is 380-460 Ω / sq.

4. The method according to any one of claims 1-3, characterized in that, The multi-step source connection process includes: (a) A diffusion source is introduced under the condition of the first source temperature to pre-deposit a first boron-rich layer on the silicon wafer surface; (b) Heat to the second source temperature, and then introduce a diffusion source to pre-deposit a second boron-rich layer on the surface of the first boron-rich layer; (c) Heat to the third source temperature, and then introduce a diffusion source to pre-deposit the third boron-rich layer on the surface of the second boron-rich layer; The boron atom concentrations of the first, second, and third boron-rich layers increase sequentially.

5. The method according to claim 4, characterized in that, The first power source temperature is 805-815℃; And / or, the second power supply temperature is 815-825℃; And / or, the third power source temperature is 825-835℃; And / or, during the multi-step power supply process, the pressure inside the furnace is kept constant at 200-250 mbar; And / or, the diffusion sources in steps (a), (b) and (c) all include inert gas, oxygen and boron sources; And / or, in the first boron-rich layer, the boron atom concentration is 0.1 × 10⁻⁶. 20 cm -3 -0.3×10 20 cm -3 ; And / or, in the second boron-rich layer, the boron atom concentration is 0.3 × 10⁻⁶. 20 cm -3 -0.6×10 20 cm -3 ; And / or, in the third boron-rich layer, the boron atom concentration is 0.6 × 10⁻⁶. 20 cm -3 -0.9×10 20 cm -3 .

6. The method according to claim 5, characterized in that, In step (a), the flow rate ratio of the inert gas, oxygen and boron source is (25-40):(6.25-10):1; And / or, in step (b), the flow rate ratio of the inert gas, oxygen and boron source is (20-100):(5-25):1; And / or, in step (c), the flow rate ratio of the inert gas, oxygen and boron source is (50-200):(12.5-50):

1.

7. The method according to any one of claims 1-6, characterized in that, The variable pressure annealing step includes: Under the pressure conditions of the first furnace, the first step of annealing is carried out, then the pressure is reduced to the pressure conditions of the second furnace, and then the second step of annealing is carried out.

8. The method according to claim 7, characterized in that, During the variable pressure annealing process, the annealing temperature is 750-900℃; And / or, the pressure inside the first furnace is 700-800 mbar; And / or, the pressure inside the second furnace is 550-700 mbar; And / or, the atmosphere for the first annealing step is an inert atmosphere; And / or, the atmosphere for the second annealing step is a mixed atmosphere containing an active gas and an inert gas, wherein the active gas includes hydrogen and the volume fraction of the active gas is 0.1-5%.

9. The method according to any one of claims 1-8, characterized in that, The time for the silicon wafer to be fed into the boat is 8-15 minutes; And / or, in the heating step, the heating time is ≤3 min, and the temperature after heating is 805-815℃; And / or, the pressure inside the furnace after vacuuming is 200-250 mbar, and the pressure holding time is 5-10 min; And / or, in the pre-oxygenation step, an inert gas and oxygen are introduced at a flow rate ratio of (2-4):(1-3) for a duration of 3-6 min; And / or, after the back pressure step, the average sheet resistance of the boron-expanded silicon wafer is 380-460 Ω / sq, and the sheet resistance uniformity between wafers is ≤8%.

10. The method according to any one of claims 1-9, characterized in that, The method includes the following steps: (1) Silicon wafers are loaded onto the ship: The silicon wafers are inserted into the quartz boat in a "back-to-back" manner and loaded into the tube diffusion furnace; (2) Heating: Under an inert atmosphere, the tubular diffusion furnace is heated to a first source temperature of 805-815℃ within ≤3 minutes. (3) Vacuuming and leak detection: While keeping the temperature of the tubular diffusion furnace constant, evacuate the furnace to a pump pressure of 200-250 mbar. After holding the pressure for 5-10 minutes, check the tubular diffusion furnace for leaks. (4) Pre-oxygen: Keeping the temperature of the tubular diffusion furnace constant, an inert gas and oxygen with a flow ratio of (2-4):(1-3) are introduced for 3-6 minutes to prepare a silicon oxide layer on the silicon wafer surface. (5) Multi-step source connection: (5-1) Under the condition of the first source temperature, an inert gas, oxygen and boron source with a flow ratio of (25-40):(6.25-10):1 are introduced for ≤5 min, thereby pre-depositing a boron atom concentration of 0.1×10 on the silicon wafer surface. 20 cm -3 -0.3×10 20 cm -3 The first boron-rich layer; (5-2) Heat to the second source temperature, then introduce an inert gas, oxygen, and boron source at a flow ratio of (20-100):(5-25):1 for ≤5 min, thereby pre-depositing a boron atom concentration of 0.3×10 on the surface of the first boron-rich layer. 20 cm -3 -0.6×10 20 cm -3 The second boron-rich layer; the second source temperature is 815-825℃; (5-3) Heat to the third source temperature, then introduce an inert gas, oxygen, and boron source at a flow ratio of (50-200):(12.5-50):1 for ≤5 min, thereby pre-depositing a boron atom concentration of 0.6×10 on the surface of the second boron-rich layer. 20 cm -3 -0.9×10 20 cm -3 The third boron-rich layer; the third source temperature is 825-835℃; Among them, the boron atom concentration of the first boron-rich layer, the second boron-rich layer and the third boron-rich layer increases sequentially; during the multi-step source-passing process, the furnace pressure is kept constant at 200-250 mbar. (6) Variable temperature multi-step bonding: (6-1) Under an oxygen-free atmosphere of 850-950℃ and 100-800mbar in the furnace, perform oxygen-free push junction for 10-20min to make the PN junction depth on the silicon wafer surface 0.05-0.15μm and the average sheet resistance of the silicon wafer 550-580Ω / sq. (6-2) Heat to 1000-1100℃ and pressurize to 700-800mbar in the furnace. At the same time, oxygen is introduced into the tubular diffusion furnace. The oxygen flow rate is controlled to increase by 10000-20000sccm / min until the oxygen flow rate is 18000-23000sccm. Then, oxygen-induced junction pushing is performed for 70-100min to make the PN junction depth on the silicon wafer surface 0.6-0.9μm and the average sheet resistance of the silicon wafer 380-460Ω / sq. (7) Variable pressure annealing: The first annealing is carried out in an inert atmosphere at 700-800 mbar and 750-900℃ for a time of ≤40 min. Then, the pressure is reduced to 550-700 mbar and the second annealing is carried out in a mixed atmosphere containing active and inert gases at 750-900℃ for a time of ≤40 min. In the inert atmosphere, the flow rate of the inert gas is ≤18000 sccm; in the mixed atmosphere, the volume fraction of the active gas is 0.1-5%, and the flow rate of the inert gas is ≤18000 sccm; the active gas includes hydrogen. (8) Back pressure and silicon wafer unloading: After the pressure inside the tubular diffusion furnace is reduced to differential pressure, the boron-expanded silicon wafers are removed. The average sheet resistance of the boron-expanded silicon wafers is 380-460 Ω / sq, and the sheet resistance uniformity between wafers is ≤8%.

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