Boron diffusion method, TOPCon battery and preparation method of TOPCon battery
By using a boron diffusion method that controls temperature and atmosphere in stages, the problems of excessive boron concentration and diffusion dead layer in TOPCon cells were solved, resulting in higher cell efficiency and yield, and ensuring device performance and process consistency.
Patent Information
- Application Number
- CN202511111025.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-08
- Publication Date
- 2025-11-14
AI Technical Summary
Existing boron diffusion processes in TOPCon cells result in excessively high boron concentrations on the silicon wafer surface, low peak doping, and the formation of diffusion dead layers, affecting device performance and the consistency of subsequent processes, leading to low cell efficiency and yield.
A boron diffusion method with staged temperature and atmosphere control is adopted, including surface deposition, cooling diffusion propagation, and oxidation redistribution. By controlling the temperature gradient and gas flow rate, the boron concentration on the silicon wafer surface is reduced, the generation of diffusion dead layer is avoided, the peak doping concentration is increased, and the wafer sheet resistance is reduced.
It effectively reduces the boron concentration on the silicon wafer surface, avoids diffusion dead layers, improves the efficiency and yield of TOPCon cells, and ensures the consistency of device performance and subsequent processes.
Smart Images
Figure CN120954968A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of photovoltaic cell technology, and in particular to a boron diffusion method, a TOPCon cell, and a method for preparing the same. Background Technology
[0002] With the development of high-efficiency solar cells, the high-efficiency crystalline silicon solar cell—the tunnel oxide passivated contact solar cell (TOPCon)—has become one of the next-generation mainstream cell structures due to its excellent carrier selectivity and passivation performance. TOPCon cells are an advanced crystalline silicon solar cell technology designed to achieve efficient carrier selective transport and surface passivation by introducing an ultra-thin tunnel oxide layer and a doped polycrystalline silicon layer on the back of the cell. This design significantly improves the cell's conversion efficiency and reduces energy loss.
[0003] Boron diffusion is an important technology in semiconductor manufacturing, particularly in solar cell and integrated circuit manufacturing. It is primarily used to form a p-type doped layer on the surface of silicon wafers to create pn junctions or improve electrical contact characteristics. Existing boron diffusion processes typically employ a heated deposition and heated advance approach. This method has a simple process path, is suitable for standard tube diffusion furnaces, and is easy to integrate into production lines.
[0004] However, the inventors discovered that due to the temperature coupling between the diffusion deposition process and the propulsion process, the boron concentration on the silicon wafer surface is too high, the peak doping is low, and an unnecessary thickness of borosilicate glass is formed, which affects the device performance and the consistency of subsequent processes, ultimately resulting in low efficiency and yield of TOPCon cells. Summary of the Invention
[0005] This application provides a boron diffusion method, a TOPCon cell and its fabrication method, which reduces the boron concentration on the silicon wafer surface, avoids the formation of diffusion dead layers, increases the peak doping concentration of the boron residual layer and reduces the sheet resistance, ensures the consistency of device performance and subsequent processes, and improves the efficiency and yield of the finished TOPCon cell.
[0006] The embodiments of this application are implemented as follows:
[0007] In a first aspect, the present invention provides a boron diffusion method, comprising the following steps:
[0008] S1, Raw material preparation: Providing silicon wafers and precursors;
[0009] S2, Preparatory Steps: Place the silicon wafer in the diffusion furnace;
[0010] S3, Surface deposition: Introduce precursor, oxygen and nitrogen, and heat to a first temperature and maintain for a first preset time;
[0011] S4, Diffusion Propulsion: Introduce nitrogen gas, cool to a second temperature and maintain for a second preset time;
[0012] S5, Oxidation and redistribution: Introduce oxygen and nitrogen, raise the temperature to the third temperature and maintain it for the third preset time;
[0013] Wherein, the second temperature is lower than the first temperature, and the first temperature is lower than the third temperature.
[0014] In an optional embodiment, the first temperature is 830–870°C, the second temperature is 780–820°C, and the third temperature is 1030–1050°C.
[0015] In an optional embodiment, the cooling rate from the first temperature to the second temperature is 3 to 8 °C / min.
[0016] In an optional implementation, the first preset time is 10-20 minutes, the second preset time is 15-30 minutes, and the third preset time is 30-60 minutes.
[0017] In an optional implementation, the oxygen flow rate in step S3 is less than the oxygen flow rate in step S5.
[0018] And / or,
[0019] The flow rate of nitrogen is the same in steps S3, S4 and S5.
[0020] In an optional implementation, in step S3, the oxygen flow rate is 400-600 sccm, and the precursor flow rate is 100-140 sccm.
[0021] In step S5, the oxygen flow rate is 15000–25000 sccm;
[0022] In steps S3, S4 and S5, the flow rate of nitrogen is 2000-4000 sccm.
[0023] In an optional implementation, after step S5, the boron diffusion method further includes the step of:
[0024] S6, the surface borosilicate glass is removed by wet etching or dry processing.
[0025] In an optional implementation, a liquid boron source, boron trichloride, or boron tribromide is used as a precursor.
[0026] Secondly, the present invention provides a method for preparing a TOPCon battery, including a boron diffusion process, wherein the boron diffusion process employs the boron diffusion method described in any of the foregoing embodiments.
[0027] Thirdly, the present invention provides a TOPCon battery, which is manufactured by the TOPCon battery preparation method described in the foregoing embodiments.
[0028] The advantages of this application compared to the prior art include:
[0029] By heating to a first temperature and maintaining surface deposition for a first preset time, a boron source material (borosilicate glass, BSG) can be deposited on the silicon wafer surface. This serves as the boron source for subsequent migration of boron atoms into the silicon wafer interior. Subsequently, the temperature is lowered to a second temperature, which is lower than the first temperature, and diffusion is advanced for a second preset time. This achieves deep diffusion of boron atoms into the silicon wafer interior, resulting in gradient doping. The oxygen-free process of cooling and advancing the temperature prevents oxidation. Then, the temperature is raised to a third temperature, which is higher than the first temperature, and oxidation redistribution is performed for a third preset time. This reduces the boron atom concentration on the silicon wafer surface, allowing boron atoms to migrate into the silicon wafer interior. Through cooling and oxidation redistribution, the boron atom concentration on the silicon wafer surface is reduced, thereby avoiding excessive boron accumulation, reducing the boron concentration on the silicon wafer surface, preventing the formation of diffusion dead layers, increasing the peak doping concentration of the boron residue layer, and reducing the sheet resistance. This ensures the consistency of device performance and subsequent processes, and improves the efficiency and yield of the finished TOPCon cell. Attached Figure Description
[0030] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.
[0031] Figure 1 This is a comparison chart showing the peak doping concentration of a boron-doped layer obtained by a boron diffusion method according to one embodiment of this application and a boron-doped layer from Comparative Example 1. Detailed Implementation
[0032] As used in this article:
[0033] "Prepared from" is synonymous with "comprising". The terms "comprising", "including", "having", "containing", or any other variations thereof as used herein are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.
[0034] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1–5” is disclosed, the described range should be interpreted as including ranges “1–4”, “1–3”, “1–2”, “1–2 and 4–5”, “1–3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.
[0035] In these embodiments, unless otherwise specified, the parts and amounts are by weight.
[0036] The embodiments of this application will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of this application. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.
[0037] This application discloses a boron diffusion method, which includes the following steps S1 to S5:
[0038] S1, Raw material preparation: Provide silicon wafers and precursors; the silicon wafers are monocrystalline N-type silicon wafers with a crystal orientation of [missing information]. <100> The resistivity is 1 to 3 Ω·cm, and the precursor is a liquid boron source, boron tribromide, or boron tribromide.
[0039] S2, Preparatory Steps: Place the silicon wafer in the diffusion furnace;
[0040] S3, Surface deposition: Introduce precursor, oxygen and nitrogen, and heat to a first temperature and maintain for a first preset time;
[0041] S4, Diffusion Propulsion: Introduce nitrogen gas, cool to a second temperature and maintain for a second preset time;
[0042] S5, Oxidation and redistribution: Introduce oxygen and nitrogen, raise the temperature to the third temperature and maintain it for the third preset time;
[0043] The second temperature is lower than the first temperature, and the first temperature is lower than the third temperature.
[0044] In this way, by heating to a first temperature and maintaining surface deposition for a first preset time, a boron source material (borosilicate glass, BSG) can be deposited on the silicon wafer surface as a boron source for subsequent migration of boron atoms into the silicon wafer. Then, the temperature is lowered to a second temperature, which is lower than the first temperature, and diffusion is advanced for a second preset time to achieve deep diffusion of boron atoms into the silicon wafer, achieving a gradient doping effect. The cooling and oxygen-free process prevents oxidation. Then, the temperature is raised to a third temperature, which is higher than the first temperature, and oxidation redistribution is performed for a third preset time to reduce the boron atom concentration on the silicon wafer surface, allowing boron atoms to migrate into the silicon wafer. This cooling and oxidation redistribution process reduces the boron atom concentration on the silicon wafer surface, thereby avoiding excessive boron accumulation, reducing the boron concentration on the silicon wafer surface, avoiding the formation of a diffusion dead layer, increasing the peak doping concentration of the boron residue layer, and reducing the sheet resistance, ensuring the consistency of device performance and subsequent processes, and improving the efficiency and yield of the finished TOPCon cell.
[0045] The initial temperature affects the quantity and speed of boron atom deposition. The higher the temperature, the more boron atoms are enriched on the silicon wafer surface, resulting in a faster and denser boron-enriched layer. The initial temperature can be selected from 830 to 870°C, such as 830°C, 840°C, 850°C, 860°C, or 870°C, etc., which fall within the range of 830 to 570°C. This ensures that the reaction is not too low, resulting in incomplete reaction and uneven BSG deposition, which would cause boron atoms to exist in an inactive form and affect the subsequent boron doping concentration. At the same time, it avoids excessive boron atom deposition due to excessively high temperatures, which would lead to an overabundance of boron atoms on the surface, thus ensuring sufficient reaction, uniform BSG deposition, and the activity of boron atoms.
[0046] The magnitude of the second temperature affects the diffusion rate, diffusion uniformity, and boron doping activation rate of boron atoms diffusing from BSG into the silicon wafer. The second temperature can be selected from 780 to 820°C, such as 780°C, 790°C, 800°C, 810°C, or 820°C, etc., any value within this range. This ensures that the diffusion rate and boron doping activation rate are not too low, and that the diffusion is not too uniform, nor is the boron concentration on the silicon wafer surface too high. This guarantees the diffusion rate, diffusion uniformity, boron doping activation rate, and peak concentration of boron atoms diffusing from the silicon wafer surface into the silicon wafer, preventing the formation of a diffusion dead layer on the silicon wafer surface.
[0047] The cooling rate from the first temperature to the second temperature affects the uniformity of boron diffusion. The cooling rate from the first temperature to the second temperature can be selected as 3 to 8 °C / min, such as 3 °C / min, 4 °C / min, 5 °C / min, 6 °C / min, 7 °C / min or 8 °C / min, etc., which are all within the range of 3 to 8 °C / min. This ensures that the process time is not prolonged due to the cooling rate being too small, the production efficiency is not reduced, and the excessive diffusion of impurities is not caused by the high temperature being held for too long. On the other hand, it also ensures that the cooling rate is too large, which may lead to thermal stress risk, uneven doping distribution, lattice defects and excessive enrichment of boron atoms on the surface. This ensures the uniformity and efficiency of boron diffusion and avoids excessive enrichment of boron atoms on the surface.
[0048] The third temperature affects the boron atom concentration on and inside the silicon wafer. The third temperature can be selected from 1030 to 1050°C, such as 1030°C, 1035°C, 1050°C, 1045°C or 1050°C, etc., which are all within the range of 1030 to 1050°C. This temperature will not be too low, which would prevent boron atoms from precipitating and doping from the silicon-rich layer, thus affecting the diffusion of boron atoms and causing excessive local recombination and excessive boron concentration on the silicon wafer surface. Nor will it be too high, which would cause the boron atom concentration on the silicon wafer surface to be too low, affecting recombination loss. This will further reduce the surface boron concentration, allowing boron atoms to migrate into the silicon wafer, making the boron distribution more uniform, and at the same time, it will help passivate the silicon wafer surface.
[0049] Of course, it is understandable that the first temperature, second temperature, third temperature and cooling rate are not limited to the above range values, as long as the temperature setting satisfies the process of first heating up for deposition, then cooling down for diffusion and then oxidation.
[0050] The first preset time affects the total amount of boron source on the silicon wafer surface. The first preset time can be selected from 10 to 20 minutes, such as 10 minutes, 12 minutes, 15 minutes, 18 minutes or 20 minutes, which are any values within the range of 10 to 20 minutes. This can avoid the situation where the deposition time is too long, resulting in too many boron atoms deposited on the silicon wafer surface and too high surface boron concentration, which leads to a large junction depth and too high concentration after subsequent diffusion-driven deposition. This may result in overdoping, causing an increase in recombination rate, reducing the passivation effect and making it difficult to remove BSG in the future. On the other hand, it can avoid the situation where the deposition time is too short, resulting in insufficient number of boron atoms on the silicon wafer surface, which leads to insufficient number of boron atoms migrating into the silicon wafer, resulting in insufficient peak doping concentration, a narrower p+ region, and higher sheet resistance.
[0051] The second preset time affects the diffusion depth. The second preset time can be selected from 15 to 30 minutes, such as 15 minutes, 20 minutes, 25 minutes, or 30 minutes, any value within this range. This avoids situations where the diffusion time is too short, resulting in insufficient boron atoms diffusing into the silicon wafer, leading to a shallow junction depth and potentially excessively high doping concentration on the surface, causing severe recombination. Conversely, it avoids situations where the diffusion time is too long, resulting in excessive boron diffusion, increased junction depth, and lower sheet resistance.
[0052] The third preset time affects the redistribution and passivation effects. The third preset time can be selected from 30 to 60 minutes, such as 30 minutes, 40 minutes, 50 minutes, or 60 minutes, which are any values within this range. This can avoid the following: if the post-oxidation time is too short, the number of boron atoms diffused will be small, the junction depth will be shallow, and the sheet resistance will be high; if the post-oxidation time is too long, the number of boron atoms diffused will be large, the junction depth will be large, and the sheet resistance will be low.
[0053] Of course, it is understandable that the first, second, and third preset times are not limited to the above range values, as long as they can meet the duration requirements of the three stages.
[0054] In step S3, the oxygen flow rate is less than that in step S5 to ensure high-temperature oxidation during the oxidation and redistribution process in step S5. The nitrogen flow rates in steps S3, S4, and S5 are all the same to ensure good verification results.
[0055] In step S3, nitrogen acts as a carrier gas, while simultaneously diluting oxygen to control the reaction rate, thereby controlling the boron source concentration and deposition rate. The nitrogen flow rate can be selected from 2000 to 4000 sccm, such as 2000 sccm, 3000 sccm, or 4000 sccm, all falling within this range. This avoids both excessive flow rate, which would dilute the boron source precursor, slow the deposition rate, and result in a thin BSG layer, and excessive flow rate, which would lead to a high boron source concentration, causing over-deposition or even segregation, affecting diffusion uniformity.
[0056] In step S3, oxygen plays a role in stabilizing the BSG. The oxygen flow rate can be selected as 400-600 sccm, such as 400 sccm, 500 sccm or 600 sccm, which are any values within the range of 400-600 sccm. This can avoid the problem of excessive flow rate inhibiting the deposition efficiency of boron and resulting in low doping concentration, while also avoiding the problem of insufficient flow rate causing BSG instability and boron accumulation that leads to surface defects.
[0057] In step S3, the precursor primarily serves as a boron source, providing the dopant. The precursor flow rate can be selected from 100 to 140 sccm; for example, 100 sccm, 110 sccm, 120 sccm, 130 sccm, or 140 sccm are all values within this range. This avoids the formation of a highly doped layer due to excessively high boron concentration, resulting in a decrease in sheet resistance, while also avoiding insufficient doping due to excessively low flow rate, which would prevent the formation of an effective p+ contact layer and lead to high sheet resistance.
[0058] In step S4, nitrogen provides inert protection and also assists in purging the reaction gases, diluting residual boron sources or reaction byproducts, and ensuring interface cleanliness. The nitrogen flow rate can be selected from 400 to 600 sccm, such as 400 sccm, 500 sccm, or 600 sccm, any value within this range. This avoids excessive flow rate causing a sudden drop in local temperature and affecting the uniformity of the BSG layer, while also avoiding insufficient flow rate leading to incomplete removal of residual precursors or oxygen and abnormal surface boron concentration.
[0059] In step S5, nitrogen acts as a carrier gas to control uniformity. The nitrogen flow rate can be selected from 2000 to 4000 sccm, such as 2000 sccm, 3000 sccm, or 4000 sccm, which are any values within this range. This avoids both excessive flow rate, which dilutes the oxygen concentration and affects the oxidation rate, disturbs the silicon wafer surface, or causes the redistribution of boron by BSG, and causes local temperature differences on the silicon wafer; and excessive flow rate, which leads to uneven gas mixing, excessively high local oxygen concentration, unstable intracranial atmosphere, and uneven oxidation.
[0060] In step S5, oxygen is used to oxidize BRL to generate boron dioxide, which in turn oxidizes BRL to BSG. Boron atoms expand inward to form the emitter. The oxygen flow rate can be selected from 15,000 to 25,000 sccm. For example, any value within the range of 15,000 to 25,000 sccm, such as 15,000 sccm, 17,000 sccm, 20,000 sccm, 23,000 sccm, or 25,000 sccm, can avoid the problem of excessive flow rate causing a sudden drop in intracranial temperature, excessively fast oxidation rate, and excessively thick BSG that affects subsequent cleaning and diffusion. On the other hand, it can also avoid the problem of insufficient BSG generation, incomplete conversion of BRL resulting in high concentrations of residual boron, and insufficient boron redistribution that affects the quality of the emitter.
[0061] Of course, it is understandable that the flow rate range values of each atmosphere in steps S3 to S5 above do not limit the specific selection range of each atmosphere flow rate.
[0062] It should be noted that BSG residue can lead to carrier recombination on the front side of the battery, contact deterioration, and optical loss. Specifically, this manifests as a significant reduction in open circuit voltage (Voc), fill factor (FF), short circuit current (Isc), and darkening of electroluminescence (EL) appearance.
[0063] Therefore, in this application, after step S5, the boron diffusion method further includes the following step S6:
[0064] S6, the surface borosilicate glass is removed by wet etching or dry processing.
[0065] The purpose is to remove the BSG formed during the diffusion process to avoid its adverse effects on subsequent processes (such as passivation and metallization).
[0066] This application also discloses a method for preparing a TOPCon battery, which includes a boron diffusion process using the boron diffusion method described above.
[0067] This application also discloses a TOPCon battery, which is made by the above-described TOPCon battery preparation method.
[0068] The boron diffusion method of this application will be further described in detail below with reference to the embodiments.
[0069] Example 1
[0070] 1. Take a single-crystal N-type silicon wafer (crystal orientation) <100> (resistivity 1–3 Ω·cm);
[0071] 2. Boron trichloride was used as the diffusion precursor;
[0072] 3. Place the silicon wafer in a tube diffusion furnace and introduce an oxygen / nitrogen mixed atmosphere;
[0073] 4. Heat to 830℃, oxygen flow rate 400, nitrogen flow rate 2000, precursor flow rate 100, and maintain boron source deposition during the process for 10 minutes;
[0074] 5. Cool down to 780℃, nitrogen flow rate 2000, diffusion propulsion during the process, lasting 15 minutes; cooling rate 3℃ / min;
[0075] 6. Oxidation and redistribution are carried out during the heating process to 1030℃, with an oxygen flow rate of 15000 and a nitrogen flow rate of 2000, for 30 minutes;
[0076] 7. After the process is completed, the surface borosilicate glass is removed by wet etching or dry treatment.
[0077] Example 2
[0078] 1. Take a single-crystal N-type silicon wafer (crystal orientation) <100> (resistivity 1–3 Ω·cm);
[0079] 2. Boron trichloride was used as the diffusion precursor;
[0080] 3. Place the silicon wafer in a tube diffusion furnace and introduce an oxygen / nitrogen mixed atmosphere;
[0081] 4. Heat to 850℃, oxygen flow rate 500, nitrogen flow rate 3200, precursor flow rate 120, and maintain boron source deposition during the process for 15 minutes;
[0082] 5. Cool down to 800℃, nitrogen flow rate 3200, diffusion propulsion during the process, for 25 minutes; cooling rate 6℃ / min;
[0083] 6. Oxidation and redistribution are carried out during the heating process to 1040℃, with an oxygen flow rate of 20,000 and a nitrogen flow rate of 3,200, for 45 minutes;
[0084] 7. After the process is completed, the surface borosilicate glass is removed by wet etching or dry treatment.
[0085] Example 3
[0086] 1. Take a single-crystal N-type silicon wafer (crystal orientation) <100> (resistivity 1–3 Ω·cm);
[0087] 2. Boron trichloride was used as the diffusion precursor;
[0088] 3. Place the silicon wafer in a tube diffusion furnace and introduce an oxygen / nitrogen mixed atmosphere;
[0089] 4. Heat to 870℃, oxygen flow rate 600, nitrogen flow rate 4000, precursor flow rate 140, and maintain boron source deposition during the process for 20 minutes;
[0090] 5. Cool down to 820℃, nitrogen flow rate 4000, diffusion propulsion during the process, for 30 minutes; cooling rate 8℃ / min;
[0091] 6. Oxidation and redistribution are carried out during the heating process to 1050℃, with an oxygen flow rate of 25,000 and a nitrogen flow rate of 4,000, for 60 minutes;
[0092] 7. After the process is completed, the surface borosilicate glass is removed by wet etching or dry treatment.
[0093] Example 4
[0094] 1. Take a single-crystal N-type silicon wafer (crystal orientation) <100> (resistivity 1–3 Ω·cm);
[0095] 2. Boron trichloride was used as the diffusion precursor;
[0096] 3. Place the silicon wafer in a tube diffusion furnace and introduce an oxygen / nitrogen mixed atmosphere;
[0097] 4. Heat to 820℃, oxygen flow rate 350, nitrogen flow rate 1900, precursor flow rate 90, and maintain boron source deposition during the process for 5 minutes;
[0098] 5. Cool down to 770℃, nitrogen flow rate 1900, diffusion propulsion during the process, lasting 5 minutes; cooling rate 10℃ / min;
[0099] 6. Oxidation and redistribution are carried out during the process of heating to 1020℃, with an oxygen flow rate of 14000 and a nitrogen flow rate of 1900, for 25 minutes;
[0100] 7. After the process is completed, the surface borosilicate glass is removed by wet etching or dry treatment.
[0101] Example 5
[0102] 1. Take a single-crystal N-type silicon wafer (crystal orientation) <100> (resistivity 1–3 Ω·cm);
[0103] 2. Boron trichloride was used as the diffusion precursor;
[0104] 3. Place the silicon wafer in a tube diffusion furnace and introduce an oxygen / nitrogen mixed atmosphere;
[0105] 4. Heat to 880℃, oxygen flow rate 650, nitrogen flow rate 4500, precursor flow rate 150, and maintain boron source deposition during the process for 25 minutes;
[0106] 5. Cool down to 830℃, nitrogen flow rate 4500, diffusion propulsion during the process, lasting 35 minutes; cooling rate 2.5℃ / min;
[0107] 6. Oxidation and redistribution are carried out during the heating process to 1060℃, with an oxygen flow rate of 26,000 and a nitrogen flow rate of 4,500 for 70 minutes;
[0108] 7. After the process is completed, the surface borosilicate glass is removed by wet etching or dry treatment.
[0109] Comparative Example
[0110] 1. Take a single-crystal N-type silicon wafer ( <100> (resistivity 1–3 Ω·cm);
[0111] 2. Boron trichloride was used as the diffusion precursor;
[0112] 3. Place the silicon wafer in a tube diffusion furnace and introduce an oxygen / nitrogen mixed atmosphere;
[0113] 4. Heat to 850℃, oxygen flow rate 500, nitrogen flow rate 3200, precursor flow rate 120, and maintain boron source deposition during the process for 10 minutes;
[0114] 5. Heat to 890℃, nitrogen flow rate 3200, diffusion propulsion during the process, for 15 minutes;
[0115] 6. Oxidation and redistribution are carried out during the heating process to 1040℃, with an oxygen flow rate of 20,000 and a nitrogen flow rate of 3,000, for 60 minutes;
[0116] 7. After the process is completed, the surface borosilicate glass is removed by wet etching or dry treatment.
[0117] The peak doping concentration, sheet resistance, and efficiency of the finished batteries fabricated from Examples 1-5 and Comparative Example 1 were tested. The performance test results are shown in Table 1 below.
[0118] Table 1
[0119]
[0120] Combining Table 1 above and the appendix Figure 1 As can be seen, the peak doping concentrations of Examples 1-5 of this application are all greater than those of Comparative Example 1, and the sheet resistance is all lower than that of Comparative Example 1. The efficiency of the batteries fabricated based on Examples 1-5 is also higher than that of the battery fabricated based on Comparative Example 1. It is evident that the boron diffusion process driven by cooling in this application is superior to the boron diffusion process driven by heating in the comparative example. Therefore, it can effectively avoid excessive boron accumulation and the formation of diffusion dead layers, thereby improving the efficiency and yield of the final finished wafer.
[0121] The above are merely specific embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.
Claims
1. A boron diffusion method, characterized in that, Includes the following steps: S1, Raw material preparation: Providing silicon wafers and precursors; S2, Preparatory Steps: Place the silicon wafer in the diffusion furnace; S3, Surface deposition: Introduce precursor, oxygen and nitrogen, and heat to a first temperature and maintain for a first preset time; S4, Diffusion Propulsion: Introduce nitrogen gas, cool to a second temperature and maintain for a second preset time; S5, Oxidation and redistribution: Introduce oxygen and nitrogen, raise the temperature to the third temperature and maintain it for the third preset time; Wherein, the second temperature is lower than the first temperature, and the first temperature is lower than the third temperature.
2. The boron diffusion method according to claim 1, characterized in that, The first temperature is 830–870°C, the second temperature is 780–820°C, and the third temperature is 1030–1050°C.
3. The boron diffusion method according to claim 1 or 2, characterized in that, The cooling rate from the first temperature to the second temperature is 3–8 °C / min.
4. The boron diffusion method according to claim 2, characterized in that, The first preset time is 10-20 minutes, the second preset time is 15-30 minutes, and the third preset time is 30-60 minutes.
5. The boron diffusion method according to claim 1, characterized in that, The oxygen flow rate in step S3 is less than the oxygen flow rate in step S5. And / or, The flow rate of nitrogen is the same in steps S3, S4 and S5.
6. The boron diffusion method according to claim 1 or 5, characterized in that, In step S3, the oxygen flow rate is 400–600 sccm, and the precursor flow rate is 100–140 sccm. In step S5, the oxygen flow rate is 15000–25000 sccm; In steps S3, S4 and S5, the flow rate of nitrogen is 2000-4000 sccm.
7. The boron diffusion method according to claim 1, characterized in that, Following step S5, the boron diffusion method further includes the following steps: S6, the surface borosilicate glass is removed by wet etching or dry processing.
8. The boron diffusion method according to claim 1, characterized in that, Liquid boron source, boron trichloride, or boron tribromide are used as precursors.
9. A method for preparing a TOPCon battery, characterized in that, Includes a boron diffusion process, wherein the boron diffusion process employs the boron diffusion method according to any one of claims 1-8.
10. A TOPCon battery, characterized in that, It is made by the TOPCon battery preparation method according to claim 9.