A method for boron diffusion of single crystal silicon

Abstract

The application provides a method for boron diffusion of monocrystalline silicon, which comprises the following steps: pretreating monocrystalline silicon, growing a boron-affinity thin film layer on the monocrystalline silicon to obtain monocrystalline silicon with a boron-affinity thin film layer on the surface; reacting the monocrystalline silicon with the boron-affinity thin film layer on the surface in the presence of oxygen and a boron source to obtain a B2O3 thin film layer covering the boron-affinity thin film layer; performing a first boron diffusion reaction on the monocrystalline silicon with the two thin film layers under an oxygen-free condition, cooling, removing the film, performing a second boron diffusion reaction in the presence of oxygen, and then performing a boron removal reaction on the monocrystalline silicon in the presence of nitrogen and hydrogen to obtain boron-diffused monocrystalline silicon. The boron-affinity thin film layer and hydrogen-assisted propulsion technology are used to realize deep PN junction and high boron diffusion effect of sheet resistance under the condition that the temperature is not higher than 940 DEG C, the damage of high temperature to the silicon wafer body is effectively avoided, the conversion efficiency of the solar cell is improved, and convenience is provided for subsequent production of solar cells with complex structures.

Description

Technical Field

[0001] This application belongs to the field of industrial chemistry, and in particular relates to a method for boron diffusion of single-crystal silicon. Background Technology

[0002] In the field of solar cell technology, with the increasing global demand for renewable energy and the growing awareness of environmental protection, improving the conversion efficiency of solar cells, reducing production costs, and adapting to more complex structural designs have become research hotspots. Solar cells, devices that directly convert sunlight into electrical energy, rely on an artificially constructed PN junction structure to effectively separate photogenerated carriers (i.e., electrons and holes generated by photoexcitation), thereby creating a potential difference across the PN junction and driving current generation.

[0003] In the production of solar cells, the formation of the PN junction is crucial, directly affecting the cell's photoelectric conversion efficiency. Currently, boron diffusion on the N-type silicon surface is the mainstream method for forming high-quality PN junctions. The boron diffusion process not only determines the depth of the PN junction but also affects the doping concentration and sheet resistance of the monocrystalline silicon surface; these factors collectively influence the performance of the solar cell.

[0004] Specifically, the junction depth of the PN junction is a crucial indicator of its quality. A deeper PN junction structure effectively prevents the paste from damaging the PN junction during subsequent screen printing, ensuring the stability and reliability of the cell. Meanwhile, higher sheet resistance is also a key factor in improving solar cell efficiency. Sheet resistance, as a physical quantity measuring the conductivity of monocrystalline silicon surfaces, is directly related to the recombination rate on the monocrystalline silicon surface. Generally, lower surface concentration and higher sheet resistance help reduce surface recombination, thereby improving photoelectric conversion efficiency. However, this also means that while pursuing high sheet resistance, it is necessary to ensure that the PN junction has a certain depth to achieve the optimal performance balance. Summary of the Invention

[0005] Existing technologies often use long durations and high temperatures for boron diffusion, resulting in single-crystal silicon with low doping concentration, deep junction depth, and sheet resistance reaching 300 Ω / □, which is a relatively ideal impurity distribution. However, as the diffusion time and temperature decrease, the surface concentration increases, the junction depth becomes shallower, and the sheet resistance decreases, directly leading to a reduction in the conversion efficiency of solar cells. Furthermore, prolonged high-temperature diffusion can cause some damage to the silicon substrate itself, and high temperatures can easily destroy structures such as tunneling oxide layers. This means that when designing and fabricating more complex cell structures such as BC, the boron diffusion process must be completed first, which presents significant limitations.

[0006] To address the aforementioned technical problems, this application provides a method for boron diffusion in single-crystal silicon.

[0007] The specific technical solution of this application is as follows:

[0008] A method for boron diffusion into single-crystal silicon, comprising:

[0009] Monocrystalline silicon is pretreated and grown with a boron-loving thin film layer to obtain monocrystalline silicon with a boron-loving thin film layer on the surface.

[0010] Single-crystal silicon with a boron-loving thin film layer on its surface was reacted in the presence of oxygen and a boron source to obtain a B2O3 thin film layer covered with the boron-loving thin film layer.

[0011] The monocrystalline silicon, which has undergone two thin film layer growths, is subjected to a first boron diffusion reaction under oxygen-free conditions. After cooling and film removal, a second boron diffusion reaction is carried out in the presence of oxygen. Then, the monocrystalline silicon undergoes a boron elimination reaction under nitrogen and hydrogen conditions to obtain boron-diffused monocrystalline silicon.

[0012] Furthermore, the pretreatment is either double-sided texturing or double-sided polishing.

[0013] Furthermore, the growth of the boron-loving thin film layer includes: reacting the single-crystal silicon in the presence of SiH4, B2H6, Ar and H2 to form a first boron-loving thin film layer on the surface of the single-crystal silicon; and reacting the single-crystal silicon with the first boron-loving thin film layer on its surface in the presence of SiH4, B2H6, Ar and N2O at a reaction temperature of 300-400°C to obtain a second boron-loving thin film layer covering the first boron-loving thin film layer.

[0014] Furthermore, the thickness of the first boron-loving thin film layer is 5–10 nm, and the thickness of the second boron-loving thin film layer is 5–10 nm.

[0015] Furthermore, the single-crystal silicon with a boron-loving thin film layer on its surface is reacted in the presence of oxygen and a boron source at a reaction temperature of 800–830°C and a reaction pressure of 90 Pa–150 Pa.

[0016] Furthermore, the thickness of the B2O3 thin film layer is 5–10 nm.

[0017] Furthermore, the reaction temperature of the first boron diffusion reaction is 900–960 °C, and the reaction time is 10–30 min.

[0018] Furthermore, the membrane removal is a wet process.

[0019] Furthermore, the reaction temperature of the second boron diffusion reaction is 900–940 °C, and the reaction time is 20–40 min.

[0020] Furthermore, the boron elimination reaction is carried out at a temperature of 900–940°C for 10–20 minutes.

[0021] Furthermore, after the boron elimination reaction, the process also includes a step of etching the boron-diffused single-crystal silicon using HF.

[0022] Furthermore, this application also provides a boron-diffused monocrystalline silicon obtained according to the above-described method for boron diffusion of monocrystalline silicon.

[0023] The effects of the invention

[0024] This application utilizes a boron-philic thin film layer to assist in the first boron diffusion reaction. Compared to the traditional method of directly depositing B2O3 on the single-crystal silicon surface, this method can dope more boron into the single-crystal silicon surface during the first deposition and oxygen-free propagation process. The high boron concentration in this region serves as the boron source for the second propagation step, enabling the fabrication of deeper PN junctions under low-temperature propagation conditions. Furthermore, hydrogen is used as an auxiliary gas for the second boron diffusion. Taking advantage of the rapid diffusion rate of boron impurities in a hydrogen atmosphere, the high-concentration boron deposition of SiO2 and the outermost surface of the single-crystal silicon is accelerated. The reduced boron content in the SiO2 film increases its protective properties and expands the adjustment window for subsequent wet processes. The reduced boron concentration on the single-crystal silicon surface effectively increases sheet resistance, improves the passivation effect of the boron diffusion process, and the lower surface boron concentration is also beneficial for processes such as laser mold making. Detailed Implementation

[0025] The present application is further illustrated below with reference to embodiments. It should be understood that the embodiments are only used to further illustrate and explain the present application and are not intended to limit the present application.

[0026] Unless otherwise defined, technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art. While similar or identical methods and materials may be applied in experimental or practical applications, materials and methods are described herein. In case of conflict, the definitions included herein shall prevail. Furthermore, materials, methods, and examples are for illustrative purposes only and are not intended to be limiting. The present application is further described below with reference to specific embodiments, but is not intended to limit the scope of the application.

[0027] This application provides a method for boron diffusion into single-crystal silicon, comprising:

[0028] Monocrystalline silicon is pretreated and grown with a boron-loving thin film layer to obtain monocrystalline silicon with a boron-loving thin film layer on the surface.

[0029] Single-crystal silicon with a boron-loving thin film layer on its surface was reacted in the presence of oxygen and a boron source to obtain a B2O3 thin film layer covered with the boron-loving thin film layer.

[0030] The monocrystalline silicon, which has undergone two thin film layer growths, is subjected to a first boron diffusion reaction under oxygen-free conditions. After cooling and film removal, a second boron diffusion reaction is carried out in the presence of oxygen. Then, the monocrystalline silicon undergoes a boron elimination reaction under nitrogen and hydrogen conditions to obtain boron-diffused monocrystalline silicon.

[0031] In one specific embodiment, the pretreatment is either double-sided texturing or double-sided polishing. Double-sided texturing increases the roughness of the monocrystalline silicon surface, thereby more effectively capturing and absorbing sunlight, improving solar energy conversion efficiency. It also enhances the adhesion between the monocrystalline silicon surface and subsequent coatings, ensuring the stability and durability of the coating, and helps the monocrystalline silicon dissipate heat better during subsequent operations, reducing the impact of temperature on battery performance. Double-sided polishing ensures consistent quality on both surfaces of the material, avoiding differences that may occur after single-sided polishing. Furthermore, double-sided polishing can reduce the curvature of the monocrystalline silicon, improving its optical properties.

[0032] In one specific embodiment, the boron-loving thin film layer is grown by reacting the single-crystal silicon in the presence of SiH4, B2H6, Ar and H2 to form a first boron-loving thin film layer on the surface of the single-crystal silicon; the single-crystal silicon with the first boron-loving thin film layer on the surface is reacted in the presence of SiH4, B2H6, Ar and N2O to obtain a second boron-loving thin film layer covering the first boron-loving thin film layer. The reaction temperature is 300-400℃, for example, 300℃, 305℃, 310℃, 315℃, 320℃, 325℃, 330℃, 335℃, 340℃, 345℃, 350℃, 355℃, 360℃, 365℃, 370℃, 375℃, 380℃, 385℃, 390℃, 395℃, or 400℃. Boron atoms migrate much faster in a boron-philic thin film compared to diffuse directly on the monocrystalline silicon surface, allowing them to penetrate the silicon interior more easily and quickly, thus improving diffusion efficiency. The presence of the boron-philic thin film enables deeper diffusion of boron atoms into the monocrystalline silicon, facilitating the formation of a deeper PN junction. This prevents the paste from damaging the PN junction structure during subsequent processes such as screen printing, ensuring the stability and conversion efficiency of the solar cell. By growing a boron-philic thin film on the monocrystalline silicon surface, good boron diffusion can be achieved at a relatively low temperature (around 900℃), avoiding damage to the monocrystalline silicon at high temperatures and reducing production costs. Furthermore, the boron-philic thin film helps achieve a deeper PN junction and higher sheet resistance at lower temperatures, thereby improving the photoelectric conversion efficiency of the solar cell.

[0033] In one specific embodiment, the thickness of the first boron-loving thin film layer is 5 to 10 nm, for example, it can be 5 nm, 5.3 nm, 5.5 nm, 5.8 nm, 6 nm, 6.3 nm, 6.5 nm, 6.8 nm, 7 nm, 7.3 nm, 7.5 nm, 7.8 nm, 8 nm, 8.3 nm, 8.5 nm, 8.8 nm, 9 nm, 9.3 nm, 9.5 nm, 9.8 nm, or 10 nm. The thickness of the second boron-philic thin film layer is 5–10 nm, for example, 5 nm, 5.3 nm, 5.5 nm, 5.8 nm, 6 nm, 6.3 nm, 6.5 nm, 6.8 nm, 7 nm, 7.3 nm, 7.5 nm, 7.8 nm, 8 nm, 8.3 nm, 8.5 nm, 8.8 nm, 9 nm, 9.3 nm, 9.5 nm, 9.8 nm, and 10 nm. When the thickness of the boron-philic thin film layer is in the range of 5–10 nm, it can more effectively promote the diffusion of boron atoms on the surface of single-crystal silicon. It not only provides a good diffusion path for boron, but also maintains sufficient film stability, avoiding the obstruction of boron diffusion caused by excessive thickness or the inability of boron to be effectively retained on the surface of single-crystal silicon caused by excessive thinness. At the same time, after fulfilling its function of assisting diffusion, the boron-philic thin film layer can be easily removed by wet process. The thinner film layer can reduce the time of wet processing and the consumption of chemical reagents, thereby reducing production costs.

[0034] In one specific embodiment, monocrystalline silicon with a boron-philic thin film layer on its surface is reacted in the presence of oxygen and a boron source at a reaction temperature of 800–830°C, for example, 800°C, 802°C, 804°C, 806°C, 808°C, 810°C, 812°C, 814°C, 816°C, 818°C, 820°C, 822°C, 824°C, 826°C, 828°C, or 830°C. Boron diffuses rapidly through the boron-philic thin film layer and reacts with oxygen to form a B₂O₃ thin film layer. This B₂O₃ thin film layer not only stably immobilizes the boron but also further ensures the uniformity of boron distribution on the surface of the monocrystalline silicon. By performing boron diffusion on the boron-philic thin film layer, effective boron diffusion can be achieved at a relatively low temperature, which helps to reduce the damage to the monocrystalline silicon substrate caused by high temperatures and protects the integrity and performance of the monocrystalline silicon.

[0035] In one specific embodiment, monocrystalline silicon with a boron-philic thin film layer on its surface is reacted in the presence of oxygen and a boron source to obtain a B2O3 thin film layer covering the boron-philic thin film layer. This B2O3 thin film layer serves as the main carrier of the boron source. By covering it onto the boron-philic thin film layer, it ensures that the boron source can effectively diffuse into the monocrystalline silicon through the boron-philic thin film layer during subsequent heat treatment. Furthermore, the B2O3 thin film layer acts as a storage and transport layer for the boron source, while the boron-philic thin film layer accelerates the migration rate of boron atoms. Together, these two factors significantly improve the efficiency and depth of boron diffusion. Simultaneously, the B2O3 thin film layer provides a certain degree of protection to the boron-philic thin film layer, preventing unnecessary damage or destruction to the boron-philic thin film layer during subsequent heat treatment.

[0036] In one specific embodiment, the thickness of the B2O3 thin film layer is 5–10 nm, for example, it can be 5 nm, 5.3 nm, 5.5 nm, 5.8 nm, 6 nm, 6.3 nm, 6.5 nm, 6.8 nm, 7 nm, 7.3 nm, 7.5 nm, 7.8 nm, 8 nm, 8.3 nm, 8.5 nm, 8.8 nm, 9 nm, 9.3 nm, 9.5 nm, 9.8 nm, or 10 nm. A thinner B2O3 layer helps ensure the uniformity of boron diffusion. An excessively thick B2O3 layer may increase the resistance to boron atom diffusion, leading to uneven diffusion and affecting the quality of the PN junction. This thickness can well balance the diffusion rate and uniformity, and the energy couple can be more easily and completely removed during the subsequent wet film removal process, reducing the surface stress and damage to the single crystal silicon that may be caused by an excessively thick film layer.

[0037] In one specific embodiment, the reaction temperature of the first boron diffusion reaction is 900–960°C. For example, it can be 900°C, 903°C, 905°C, 908°C, 910°C, 913°C, 915°C, 918°C, 920°C, 923°C, 925°C, 928°C, 930°C, 933°C, 935°C, 938°C, 940°C, 943°C, 945°C, 948°C, 950°C, 953°C, 955°C, 958°C, or 960°C. Compared to the high temperatures of over 1000℃ required for traditional boron diffusion, setting the temperature between 900 and 960℃ can significantly reduce the thermal stress experienced by monocrystalline silicon during diffusion, thereby reducing damage to the monocrystalline silicon substrate. Furthermore, the low-temperature environment helps protect other structures within the monocrystalline silicon, preventing damage caused by high temperatures. This is particularly important for the subsequent production of solar cells with complex structures. At the same time, excessively high temperatures may accelerate the boron diffusion rate at the edges of the monocrystalline silicon, leading to excessively high doping concentrations in the edge regions. The reaction time is 10–30 min, for example, 10 min, 10.5 min, 11.5 min, 12 min, 12.5 min, 13 min, 13.5 min, 14 min, 14.5 min, 15 min, 15.5 min, 16 min, 16.5 min, 17 min, 17.5 min, 18 min, 18.5 min, 19 min, 19.5 min, 20 min, 20.5 min, 21 min, 21.5 min, 22 min, 22.5 min, 23 min, 23.5 min, 24 min, 24.5 min, 25 min, 25.5 min, 26 min, 26.5 min, 27 min, 27.5 min, 28 min, 28.5 min, 29 min, 29.5 min, and 30 min. Too short a reaction time may not allow boron to diffuse sufficiently, while too long a reaction time can increase the diffusion depth, but it will also increase production costs and equipment downtime. Within this reaction time, the boron concentration on the surface of the monocrystalline silicon can be controlled to avoid excessively high surface concentrations that could lead to difficulties in subsequent processing or affect battery performance.

[0038] In one specific embodiment, the film removal is a wet process that removes the boron-loving thin film layer and B2O3 layer from the surface of the monocrystalline silicon. These thin film layers play an auxiliary role in the boron diffusion process, but if they are not removed, they may become impurities that affect the performance of the solar cell.

[0039] In one specific embodiment, the wet process for removing the film involves dissolving the boron-loving thin film layer and the B2O3 layer using HF or a mixture thereof.

[0040] In one specific embodiment, prior to the second boron diffusion reaction, the de-filmed monocrystalline silicon is reacted in the presence of BCl3 and O2 to grow a 5nm-10nm thick B2O3 film on the monocrystalline silicon. This B2O3 film serves as a supplementary boron source during the subsequent second boron diffusion reaction, preventing the back diffusion of boron that has already diffused into the monocrystalline silicon to the outside of the monocrystalline silicon, thus avoiding insufficient boron concentration within the monocrystalline silicon.

[0041] In one specific embodiment, the reaction temperature of the second boron diffusion reaction is 900–940°C, for example, 900°C, 903°C, 905°C, 908°C, 910°C, 913°C, 915°C, 918°C, 920°C, 923°C, 925°C, 928°C, 930°C, 933°C, 935°C, 938°C, or 940°C. Within this temperature range, the diffusion rate of boron atoms in monocrystalline silicon remains relatively fast, effectively propelling boron atoms into the interior of the monocrystalline silicon to form a deeper PN junction, while maintaining high diffusion efficiency. The low temperature range of 900–940°C significantly reduces thermal damage to the monocrystalline silicon substrate, protecting its integrity and making the process more gentle, which is beneficial for producing high-quality solar cells. The reaction time is 20–40 min, for example, 20 min, 20.5 min, 21 min, 21.5 min, 22 min, 22.5 min, 23 min, 23.5 min, 24 min, 24.5 min, 25 min, 25.5 min, 26 min, 26.5 min, 27 min, 27.5 min, 28 min, 28.5 min, 29 min, 29.5 min, 30 min, 30.5 min, 31 min, 31.5 min, 32 min, 32.5 min, 33 min, 33.5 min, 34 min, 34.5 min, 35 min, 35.5 min, 36 min, 36.5 min, 37 min, 37.5 min, 38 min, 38.5 min, 39 min, 39.5 min, and 40 min. During this period, boron atoms have sufficient time to diffuse within the monocrystalline silicon, ensuring that the PN junction depth meets requirements. At the same time, maintaining a uniform distribution of boron concentration within the monocrystalline silicon is beneficial for improving the photoelectric conversion efficiency of solar cells. Furthermore, the low-temperature diffusion process, by optimizing the diffusion time, avoids potential thermal damage to the monocrystalline silicon substrate caused by excessively long diffusion times, thus protecting the integrity of the monocrystalline silicon.

[0042] In one specific embodiment, during the second boron diffusion reaction, by controlling the amount of oxygen introduced and the temperature, a SiO2 film can be formed on the surface of the monocrystalline silicon. This SiO2 film has good insulation and stability, which can protect the boron-doped region of the monocrystalline silicon. Furthermore, in an oxygen environment, some of the high-concentration boron on the surface of the monocrystalline silicon will continue to diffuse into the interior of the monocrystalline silicon, while some will enter the newly formed SiO2 film. This diffusion effect further deepens the penetration depth of boron in the silicon wafer, which is beneficial to the quality of the PN junction. This results in a more reasonable distribution of boron atoms inside the monocrystalline silicon and in the SiO2 film, forming an ideal impurity concentration distribution with a lower surface boron concentration and a gradually increasing concentration towards the interior.

[0043] In one specific embodiment, the boron elimination reaction temperature is 900–940°C, for example, 900°C, 903°C, 905°C, 908°C, 910°C, 913°C, 915°C, 918°C, 920°C, 923°C, 925°C, 928°C, 930°C, 933°C, 935°C, 938°C, or 940°C. By reducing the boron concentration on the surface of monocrystalline silicon, the number of surface recombination centers can be reduced, thereby improving the passivation effect of monocrystalline silicon, reducing energy loss during solar cell operation, and improving photoelectric conversion efficiency. Furthermore, within this temperature range, the diffusion rate of boron impurities in the SiO2 film layer is accelerated. In the presence of hydrogen, boron impurities can more effectively volatilize from the SiO2 film layer and the monocrystalline silicon surface into the external air, helping to reduce the boron concentration on the monocrystalline silicon surface and in the SiO2 film layer, thereby achieving a higher sheet resistance. The reaction time is 10–20 min, for example, 10 min, 10.5 min, 11.5 min, 12 min, 12.5 min, 13 min, 13.5 min, 14 min, 14.5 min, 15 min, 15.5 min, 16 min, 16.5 min, 17 min, 17.5 min, 18 min, 18.5 min, 19 min, 19.5 min, and 20 min. This reaction time allows boron impurities to diffuse effectively in a hydrogen atmosphere and accelerates the precipitation of high-concentration boron from SiO2 onto the outermost surface of the silicon wafer. Furthermore, the diffusion rate of boron impurities reaches a high level, effectively promoting the volatilization of boron to the outside, thereby reducing the boron concentration on the silicon wafer surface and in the SiO2 film.

[0044] In one specific embodiment, the boron elimination reaction can be performed as follows:

[0045] In one specific embodiment, after the boron removal reaction, the process further includes etching the boron-diffused single-crystal silicon using HF. During the boron removal reaction, most of the boron impurities have been volatilized through an oxygen-free process using nitrogen and hydrogen, but a SiO2 film layer remains on the single-crystal silicon surface. This film layer needs to be removed to expose the treated single-crystal silicon surface for subsequent processes. HF can effectively etch away the SiO2 film layer with minimal damage to the single-crystal silicon itself, and HF etching can further adjust the boron doping distribution on the single-crystal silicon surface.

[0046] This application utilizes a boron-philic thin film layer to assist in the first boron diffusion reaction. Compared to the traditional method of directly depositing B2O3 on the single-crystal silicon surface, this method can dope more boron into the single-crystal silicon surface during the first deposition and oxygen-free propagation process. The high boron concentration in this region serves as the boron source for the second propagation step, enabling the fabrication of deeper PN junctions under low-temperature propagation conditions. Furthermore, hydrogen is used as an auxiliary gas for the second boron diffusion. Taking advantage of the rapid diffusion rate of boron impurities in a hydrogen atmosphere, the high-concentration boron deposition of SiO2 and the outermost surface of the single-crystal silicon is accelerated. The reduced boron content in the SiO2 film increases its protective properties and expands the adjustment window for subsequent wet processes. The reduced boron concentration on the single-crystal silicon surface effectively increases sheet resistance, improves the passivation effect of the boron diffusion process, and the lower surface boron concentration is also beneficial for processes such as laser mold making.

[0047] Example

[0048] The following specific embodiments illustrate and explain the implementation of this application in detail, but the following content should not be construed as limiting this application in any way. Unless otherwise specified, all substances used in the embodiments are commercially available products.

[0049] Example

[0050] Prepare silicon wafers: Select N-type silicon wafers with a resistivity of 12Ω·cm and a thickness of 130μm. Perform double-sided polishing to ensure that the surface of the silicon wafer is flat and free of impurities. Thoroughly clean the silicon wafers with deionized water and a mixture of dilute hydrofluoric acid and nitric acid to remove surface stains and oxides.

[0051] Boron-affinity thin film growth: A double-sided polished silicon wafer is placed in a boron diffusion apparatus. Under conditions of 200°C, 15W RF power, and 13.56MHz RF frequency, SiH4, B2H6, Ar, and H2 are introduced to grow a 5nm thick boron-containing hydrogenated amorphous silicon boron-affinity thin film on both sides of the silicon wafer. The temperature is then increased to 300°C, and SiH4, B2H6, Ar, and N2O are introduced to coat the wafer with a 5-10nm thick layer of BSG. The wafer is then cooled to room temperature and removed.

[0052] B2O3 thin film growth: BCl3 and O2 were introduced into a boron diffusion apparatus at 90 Pa and 800 °C to grow a 5 nm thick B2O3 thin film on a boron-loving thin film layer.

[0053] Oxygen-free propulsion: Continue oxygen-free propulsion at 900℃ for 10-30 minutes to allow boron to enter the silicon wafer surface area through the boron-loving layer.

[0054] Film removal: After cooling to room temperature, remove B2O3 and BSG from the surface with 1% hydrochloric acid and 5% hydrofluoric acid. Then, perform alkaline washing with 0.1% low-concentration NaOH solution. Finally, treat the surface with ozone and hydrofluoric acid to remove the polycrystalline silicon film.

[0055] Oxygen-assisted propulsion: The silicon wafer is placed in a high-temperature furnace tube. First, BCl3 and O2 are introduced at 90 Pa and 800 °C to grow a 5 nm thick B2O3 film. Then, the temperature is raised to 900 °C and a large amount of oxygen is introduced. The temperature is kept constant for 20 minutes to generate a SiO2 film and promote further diffusion of boron.

[0056] Oxygen-free propulsion and boron removal: After oxygen is extracted, nitrogen and hydrogen are introduced and kept at 900℃ for 10 minutes to promote the volatilization of boron impurities and reduce the surface boron concentration.

[0057] Etching the SiO2 film: The SiO2 film on the surface is etched away using a 5% HF hydrofluoric acid solution to obtain the desired low-temperature boron diffusion sample.

[0058] Example 1

[0059] The only difference between this embodiment and Embodiment 1 is that the reaction temperature for growing the first boron-loving thin film layer is 250°C.

[0060] Example 2

[0061] The only difference between this embodiment and Embodiment 1 is that the reaction temperature for growing the first boron-loving thin film layer is 300°C.

[0062] Example 3

[0063] The only difference between this embodiment and Embodiment 1 is that the reaction temperature for growing the second boron-loving thin film layer is 350°C.

[0064] Example 4

[0065] The only difference between this embodiment and Embodiment 1 is that the reaction temperature for growing the second boron-loving thin film layer is 400°C.

[0066] Example 5

[0067] The only difference between this embodiment and Embodiment 1 is that the reaction temperature for growing the B2O3 thin film is 815°C.

[0068] Example 6

[0069] The only difference between this embodiment and Embodiment 1 is that the reaction temperature for growing the B2O3 thin film is 830°C.

[0070] Example 7

[0071] The only difference between this embodiment and Embodiment 1 is that the reaction temperature of the first boron diffusion reaction is 930°C.

[0072] Example 8

[0073] The only difference between this embodiment and Embodiment 1 is that the reaction temperature of the first boron diffusion reaction is 960°C.

[0074] Example 9

[0075] The only difference between this embodiment and Embodiment 1 is that the reaction temperature of the second boron diffusion reaction is 920°C.

[0076] Example 10

[0077] The only difference between this embodiment and Embodiment 1 is that the reaction temperature of the second boron diffusion reaction is 940°C.

[0078] Example 11

[0079] The only difference between this embodiment and Example 1 is that the reaction temperature for the boron elimination reaction is 920°C.

[0080] Example 12

[0081] The only difference between this embodiment and Example 1 is that the reaction temperature for the boron elimination reaction is 940°C.

[0082] Comparative Example 1

[0083] The only difference between this comparative example and Example 1 is that the reaction temperature for growing the first boron-loving thin film layer is 100°C.

[0084] Comparative Example 2

[0085] The only difference between this comparative example and Example 1 is that the reaction temperature for growing the first boron-loving thin film layer is 400°C.

[0086] Comparative Example 3

[0087] The only difference between this comparative example and Example 1 is that the reaction temperature for growing the second boron-loving thin film layer is 200°C.

[0088] Comparative Example 4

[0089] The only difference between this comparative example and Example 1 is that the reaction temperature for growing the second boron-loving thin film layer is 500°C.

[0090] Comparative Example 5

[0091] The only difference between this comparative example and Example 1 is that the reaction temperature for growing the B2O3 thin film is 700°C.

[0092] Comparative Example 6

[0093] The only difference between this comparative example and Example 1 is that the reaction temperature for growing the B2O3 thin film is 900°C.

[0094] Comparative Example 7

[0095] The only difference between this comparative example and Example 1 is that the reaction temperature of the first boron diffusion reaction is 800°C.

[0096] Comparative Example 8

[0097] The only difference between this comparative example and Example 1 is that the reaction temperature of the first boron diffusion reaction is 1000°C.

[0098] Comparative Example 9

[0099] The only difference between this comparative example and Example 1 is that the reaction temperature of the second boron diffusion reaction is 800°C.

[0100] Comparative Example 9

[0101] The only difference between this comparative example and Example 1 is that the reaction temperature of the second boron diffusion reaction is 1000°C.

[0102] Comparative Example 11

[0103] The only difference between this comparative example and Example 1 is that the reaction temperature for the boron elimination reaction is 900°C.

[0104] Comparative Example 12

[0105] The only difference between this comparative example and Example 1 is that the reaction temperature for the boron elimination reaction is 940°C.

[0106] Comparative Example 13

[0107] The only difference between this comparative example and Example 1 is that no boron-loving thin film layer was grown.

[0108] Comparative Example 14

[0109] The only difference between this comparative example and Example 1 is that no B2O3 thin film layer was grown.

[0110]

[0111]

[0112] The above description is merely a preferred experimental example of this application and is not intended to limit this application in any other way. Any person skilled in the art may use the disclosed technical content to make changes or modifications to create equivalent experimental examples. However, any simple modifications, equivalent changes, and modifications made to the above experimental examples based on the technical essence of this application, without departing from the content of the technical solution of this application, shall still fall within the protection scope of the technical solution of this application.

Claims

1. A method for boron diffusion into single-crystal silicon, wherein, include: Monocrystalline silicon is pretreated and grown with a boron-loving thin film layer to obtain monocrystalline silicon with a boron-loving thin film layer on the surface. Single-crystal silicon with a boron-loving thin film layer on its surface was reacted in the presence of oxygen and a boron source to obtain a B2O3 thin film layer covered with the boron-loving thin film layer. The monocrystalline silicon that has undergone two thin film layer growths is subjected to the first boron diffusion reaction under oxygen-free conditions, cooled, and after film removal, it is subjected to the second boron diffusion reaction in the presence of oxygen. Then, the monocrystalline silicon is subjected to the boron elimination reaction under nitrogen and hydrogen conditions to obtain boron-diffused monocrystalline silicon. The single-crystal silicon is reacted in the presence of SiH4, B2H6, Ar and H2 at a reaction temperature of 200~300℃ to form a first boron-loving thin film layer on the surface of the single-crystal silicon. The single-crystal silicon with a first boron-loving thin film layer on its surface is reacted in the presence of SiH4, B2H6, Ar and N2O at a reaction temperature of 300~400℃ to obtain a second boron-loving thin film layer covering the first boron-loving thin film layer.

2. The method according to claim 1, wherein, The pretreatment is either double-sided texturing or double-sided polishing.

3. The method according to claim 1, wherein, The thickness of the first boron-loving thin film layer is 5~10 nm, and the thickness of the second boron-loving thin film layer is 5~10 nm.

4. The method according to claim 1, wherein, The process involves reacting monocrystalline silicon with a boron-loving thin film layer on its surface in the presence of oxygen and a boron source at a temperature of 800-830°C and a pressure of 90-150Pa.

5. The method according to claim 4, wherein, The thickness of the B2O3 thin film layer is 5~10 nm.

6. The method according to claim 1, wherein, The reaction temperature of the first boron diffusion reaction is 900~960℃, and the reaction time is 10~30min.

7. The method according to claim 1, wherein, The membrane removal process is a wet membrane removal process.

8. The method according to claim 1, wherein, The reaction temperature for the second boron diffusion reaction is 900~940℃, and the reaction time is 20~40min.

9. The method according to claim 1, wherein, The boron elimination reaction is carried out at a temperature of 900-940℃ for 10-20 minutes.

10. The method according to claim 1, wherein, The process includes etching the boron-diffused single-crystal silicon using HF after the boron elimination reaction.

11. Boron-diffused monocrystalline silicon obtained by the method of boron diffusion of monocrystalline silicon according to any one of claims 1 to 10.

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