Low temperature boron diffusion method
By employing a three-stage variable-temperature boron diffusion and wet oxygen oxidation method, the problem of excessively high boron diffusion temperature was solved, extending the machine's lifespan, reducing costs, improving the quality of boron source deposition on the silicon wafer surface and the uniformity of sheet resistance, and enhancing power generation efficiency.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SHANGRAO JIETAI NEW ENERGY TECH CO LTD
- Filing Date
- 2022-06-28
- Publication Date
- 2026-07-21
Smart Images
Figure CN115083893B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of boron diffusion, and in particular to a low-temperature boron diffusion method. Background Technology
[0002] High-efficiency, low-cost crystalline silicon solar cells represent the future direction of the photovoltaic industry. Their aim is to reduce the surface concentration of the emitter junction, effectively decrease the recombination rate on the cell surface, thereby improving the minority carrier lifetime and the short-wavelength spectral response of the device. Combined with dense wire mesh technology, this can effectively increase the short-circuit current and open-circuit voltage, achieving higher efficiency and power output. In recent years, N-type solar cells have attracted increasing attention from major manufacturers due to their advantages such as lower light attenuation, higher stability, and bifacial power generation, and their market share is growing.
[0003] However, the current boron diffusion process has a high temperature (>1000℃), which causes significant damage to the equipment. Prolonged high temperatures will reduce the service life of the equipment and quartz carrier, increase costs, and seriously affect production capacity.
[0004] Therefore, finding a method to reduce the diffusion temperature and extend the machine life without affecting the quality of boron diffusion is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention
[0005] The purpose of this invention is to provide a low-temperature boron diffusion method to solve the problem that the boron diffusion temperature is too high in the prior art, which leads to a reduction in the service life of the equipment.
[0006] To solve the above technical problems, the present invention provides a low-temperature boron diffusion method, comprising:
[0007] The textured N-type silicon wafer is placed in a boron diffusion furnace and subjected to initial boron diffusion deposition at a first temperature.
[0008] The ambient temperature is raised from the first temperature to the second temperature to perform secondary boron diffusion deposition;
[0009] The ambient temperature was increased from the second temperature to the third temperature, and boron diffusion deposition was performed three times.
[0010] The ambient temperature is raised from the third temperature to the propulsion temperature to propel the N-type silicon wafer that has undergone the three boron diffusion processes.
[0011] The ambient temperature is lowered from the advance temperature to the post-oxidation temperature to perform through-source oxidation on the advanced N-type silicon wafer.
[0012] Optionally, in the low-temperature boron diffusion method, during the process of reducing the advance temperature to the post-oxidation temperature, the advanced N-type silicon wafer is subjected to through-source oxidation.
[0013] Optionally, in the low-temperature boron diffusion method, the oxygen used in the through-source oxidation process is wet oxygen.
[0014] Optionally, in the low-temperature boron diffusion method, the range of the high oxygen flow rate in the through-source oxidation process is 500 sccm to 1000 sccm, including the endpoint value; the range of the low oxygen flow rate in the through-source oxidation process is 500 sccm to 1000 sccm, including the endpoint value.
[0015] Optionally, in the low-temperature boron diffusion method, the time range of the through-source oxidation is 15 to 20 minutes, including the endpoint value.
[0016] Optionally, in the low-temperature boron diffusion method, the post-oxidation temperature ranges from 850 degrees Celsius to 950 degrees Celsius, including the endpoint values.
[0017] Optionally, in the low-temperature boron diffusion method, the first temperature ranges from 785 degrees Celsius to 850 degrees Celsius, including the endpoint value; the time for the first boron diffusion deposition is from 2 minutes to 4 minutes, including the endpoint value.
[0018] Optionally, in the low-temperature boron diffusion method, the difference between the second temperature and the first temperature ranges from 5 degrees Celsius to 20 degrees Celsius, including the endpoint value; the time for the secondary boron diffusion deposition is from 3 minutes to 5 minutes, including the endpoint value.
[0019] Optionally, in the low-temperature boron diffusion method, the difference between the third temperature and the second temperature ranges from 5 degrees Celsius to 20 degrees Celsius, including the endpoint value; the time for the secondary boron diffusion deposition is from 1 minute to 3 minutes, including the endpoint value.
[0020] Optionally, in the aforementioned low-temperature boron diffusion method, prior to the first boron diffusion deposition, the following steps are further included:
[0021] The N-type silicon wafer is pre-oxidized at a pre-oxidation temperature to obtain a surface oxide layer; wherein the pre-oxidation temperature is lower than the first temperature;
[0022] Accordingly, after the aforementioned source oxidation, the process further includes:
[0023] Remove the surface oxide layer.
[0024] The low-temperature boron diffusion method provided by this invention involves placing a textured N-type silicon wafer into a boron diffusion furnace for initial boron diffusion deposition at a first temperature; raising the ambient temperature from the first temperature to a second temperature for a second boron diffusion deposition; raising the ambient temperature from the second temperature to a third temperature for a third boron diffusion deposition; raising the ambient temperature from the third temperature to a advance temperature to advance the N-type silicon wafer after the three boron diffusions; and lowering the ambient temperature from the advance temperature to a post-oxidation temperature to perform source oxidation on the advanced N-type silicon wafer. This invention employs a three-stage variable-temperature deposition process, ensuring sufficient boron source deposition on the silicon wafer surface. Therefore, the advance temperature corresponding to the subsequent high-temperature advance can be optimized and reduced, improving the service life of the equipment and quartz carrier, reducing costs. Simultaneously, the continuous introduction of a boron source during the oxidation process further improves deposition quality and optimizes sheet resistance uniformity. Attached Figure Description
[0025] To more clearly illustrate the technical solutions of the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0026] Figure 1 A schematic flowchart illustrating a specific embodiment of the low-temperature boron diffusion method provided by the present invention;
[0027] Figure 2 A schematic flowchart illustrating a specific embodiment of the low-temperature boron diffusion method provided by the present invention;
[0028] Figure 3 This is a flowchart illustrating a specific embodiment of the low-temperature boron diffusion method provided by the present invention. Detailed Implementation
[0029] To enable those skilled in the art to better understand the present invention, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0030] The core of this invention is to provide a low-temperature boron diffusion method, the flowchart of one specific embodiment of which is shown below. Figure 1 As shown, this is referred to as Specific Implementation Method One, which includes:
[0031] S101: Place the textured N-type silicon wafer into a boron diffusion furnace and perform the first boron diffusion deposition at the first temperature.
[0032] Specifically, in the first boron diffusion deposition, the boron source is BCl3, the flow rate of the boron source ranges from 100 sccm to 200 sccm, the flow rate of the high nitrogen source ranges from 2000 sccm to 2500 sccm, the flow rate of the oxygen source ranges from 300 sccm to 800 sccm, and the first temperature ranges from 785 degrees Celsius to 850 degrees Celsius, including endpoint values such as any one of 785.0 degrees Celsius, 802.0 degrees Celsius, and 850.0 degrees Celsius; the time of the first boron diffusion deposition is from 2 minutes to 4 minutes, including endpoint values such as any one of 2.0 minutes, 2.5 minutes, or 4.0 minutes.
[0033] S102: Raise the ambient temperature from the first temperature to the second temperature to perform secondary boron diffusion deposition.
[0034] Specifically, in the secondary boron diffusion deposition, the boron source flow rate ranges from 200 sccm to 400 sccm, the nitrogen flow rate ranges from 1800 sccm to 2300 sccm, and the oxygen flow rate ranges from 500 sccm to 1000 sccm; the difference between the second temperature and the first temperature ranges from 5 degrees Celsius to 20 degrees Celsius, including endpoint values such as any one of 5.0 degrees Celsius, 10.0 degrees Celsius, or 20.0 degrees Celsius; and the secondary boron diffusion deposition time is from 3 minutes to 5 minutes, including endpoint values such as any one of 3.0 minutes, 4.2 minutes, or 5.0 minutes.
[0035] S103: Increase the ambient temperature from the second temperature to the third temperature and perform three boron diffusion depositions.
[0036] Specifically, in the tertiary boron diffusion deposition, the boron source flow rate ranges from 100 sccm to 300 sccm, the nitrogen flow rate ranges from 2000 sccm to 2500 sccm, and the oxygen flow rate ranges from 400 sccm to 800 sccm; the difference between the third temperature and the second temperature ranges from 5 degrees Celsius to 20 degrees Celsius, including endpoint values such as 5.0 degrees Celsius, 10.0 degrees Celsius, or 20.0 degrees Celsius; the time for the secondary boron diffusion deposition is from 1 minute to 3 minutes, including endpoint values such as any one of 1.0 minute, 1.6 minutes, or 3.0 minutes.
[0037] S104: Raise the ambient temperature from the third temperature to the propulsion temperature to propel the N-type silicon wafer that has undergone the three boron diffusions.
[0038] During the propulsion process (also known as high-temperature propulsion), the flow rate of nitrogen ranges from 2000 sccm to 3500 sccm, the propulsion temperature ranges from 900 degrees Celsius to 960 degrees Celsius, and the propulsion time ranges from 15 minutes to 30 minutes.
[0039] S105: Reduce the ambient temperature from the advance temperature to the post-oxidation temperature and perform through-source oxidation on the advanced N-type silicon wafer.
[0040] In a preferred embodiment, during the process of reducing the propulsion temperature to the post-oxidation temperature, the N-type silicon wafer that has been propulsed is subjected to through-source oxidation. In other words, through-source oxidation begins as the ambient temperature gradually decreases to the propulsion temperature, making the through-source oxidation process a variable-temperature process. This eliminates the waiting time during the cooling process, greatly improves diffusion efficiency, shortens the process time, and increases production capacity.
[0041] Specifically, the post-oxidation temperature ranges from 850 degrees Celsius to 950 degrees Celsius, including endpoint values such as any one of 850.0 degrees Celsius, 900.2 degrees Celsius, or 950.0 degrees Celsius.
[0042] The low-temperature boron diffusion method provided by this invention involves placing a textured N-type silicon wafer into a boron diffusion furnace for initial boron diffusion deposition at a first temperature; raising the ambient temperature from the first temperature to a second temperature for a second boron diffusion deposition; raising the ambient temperature from the second temperature to a third temperature for a third boron diffusion deposition; raising the ambient temperature from the third temperature to a advance temperature to advance the N-type silicon wafer after the three boron diffusions; and lowering the ambient temperature from the advance temperature to a post-oxidation temperature to perform source oxidation on the advanced N-type silicon wafer. This invention employs a three-stage variable-temperature deposition process, ensuring sufficient boron source deposition on the silicon wafer surface. Therefore, the advance temperature corresponding to the subsequent high-temperature advance can be optimized and reduced, improving the service life of the equipment and quartz carrier, reducing costs. Simultaneously, the continuous introduction of a boron source during the oxidation process further improves deposition quality and optimizes sheet resistance uniformity.
[0043] Based on Specific Implementation Method 1, further preprocessing of the N-type silicon wafer is performed to obtain Specific Implementation Method 2, the flowchart of which is shown below. Figure 2 As shown, it includes:
[0044] S201: The N-type silicon wafer is pre-oxidized at a pre-oxidation temperature to obtain a surface oxide layer; wherein the pre-oxidation temperature is lower than the first temperature.
[0045] Specifically, the pre-oxidation temperature ranges from 770 degrees Celsius to 785 degrees Celsius, including endpoint values such as any one of 770.0 degrees Celsius, 779.5 degrees Celsius, or 785.0 degrees Celsius; during the pre-oxidation process, the oxygen flow rate ranges from 900 sccm to 1600 sccm, the nitrogen flow rate ranges from 1000 sccm to 1500 sccm, and the pre-oxidation time ranges from 2 minutes to 3 minutes.
[0046] S202: The N-type silicon wafer that has undergone the pre-oxidation process is placed in a boron diffusion furnace, and the first boron diffusion deposition is performed at a first temperature.
[0047] S203: Raise the ambient temperature from the first temperature to the second temperature to perform secondary boron diffusion deposition.
[0048] S204: Raise the ambient temperature from the second temperature to the third temperature and perform three boron diffusion depositions.
[0049] S205: Raise the ambient temperature from the third temperature to the propulsion temperature to propel the N-type silicon wafer that has undergone the three boron diffusions.
[0050] S206: Reduce the ambient temperature from the advance temperature to the post-oxidation temperature and perform through-source oxidation on the advanced N-type silicon wafer.
[0051] S207: Remove the surface oxide layer.
[0052] The difference between this specific embodiment and the above specific embodiments is that, in this specific embodiment, the surface oxide layer is pre-formed on the surface of the N-type silicon wafer. The other steps are the same as those in the above specific embodiments, and will not be elaborated further in this invention.
[0053] Because a surface oxide layer, which is the last layer to be removed and does not contribute to the final silicon wafer structure, is set on the surface of the N-type silicon wafer, the boron source used in the first three low-temperature deposition steps is deposited as much as possible in this surface oxide layer. This provides sufficient boron source for subsequent steps while avoiding the problems of excessively high boron concentration, poor sheet resistance uniformity, severe carrier recombination, and low power generation efficiency caused by boron diffusion processes in existing technologies. This achieves the effects of reducing the concentration on the silicon wafer surface, optimizing sheet resistance uniformity, reducing dead layers, lowering dark current, and improving power generation efficiency.
[0054] Based on Specific Implementation Method Two, further pre-processing is performed on the N-type silicon wafer to obtain Specific Implementation Method Three, the flowchart of which is shown below. Figure 3 As shown, it includes:
[0055] S301: The N-type silicon wafer is pre-oxidized at a pre-oxidation temperature to obtain a surface oxide layer; wherein the pre-oxidation temperature is lower than the first temperature.
[0056] S302: The N-type silicon wafer that has undergone the pre-oxidation process is placed in a boron diffusion furnace and subjected to the first boron diffusion deposition at a first temperature.
[0057] S303: Raise the ambient temperature from the first temperature to the second temperature to perform secondary boron diffusion deposition.
[0058] S304: Raise the ambient temperature from the second temperature to the third temperature and perform three boron diffusion depositions.
[0059] S305: Raise the ambient temperature from the third temperature to the propulsion temperature to propel the N-type silicon wafer that has undergone the three boron diffusions.
[0060] S306: The ambient temperature is lowered from the advance temperature to the post-oxidation temperature to perform through-source oxidation on the advanced N-type silicon wafer; wherein the oxygen used in the through-source oxidation process is wet oxygen.
[0061] S307: Remove the surface oxide layer.
[0062] The difference between this specific embodiment and the above specific embodiments is that, in this specific embodiment, the oxygen in the post-oxidation process (i.e., the through-source oxidation) is specifically limited to wet oxygen. The remaining steps are the same as those in the above specific embodiments, and will not be elaborated here.
[0063] In this specific embodiment, the oxygen used in the source oxidation step is wet oxygen. Specifically, wet oxygen refers to oxygen carrying water vapor that flows through a pure water bottle (at a constant temperature of about 30 degrees Celsius).
[0064] In one specific implementation, the boron source flow rate of the through-source oxidation is in the range of 100 sccm-200 sccm, and the nitrogen flow rate is in the range of 1000 sccm-1500 sccm.
[0065] The high oxygen flow rate during the source oxidation process ranges from 500 sccm to 1000 sccm, including endpoint values such as 500.0 sccm, 658.2 sccm, or 1000.0 sccm; the low oxygen flow rate during the source oxidation process ranges from 500 sccm to 1000 sccm, including endpoint values such as 500.0 sccm, 856.7 sccm, or 1000.0 sccm; and the source oxidation time ranges from 15 minutes to 20 minutes, including endpoint values such as 15.0 minutes, 17.5 minutes, or 20.0 minutes.
[0066] The oxidation method described in this specific embodiment uses wet oxygen cooling and variable temperature oxidation to improve the oxidation rate, reduce process time, increase production capacity, and optimize the uniformity of the oxide film. In other existing technologies, the post-oxidation time exceeds 1 hour, while the post-oxidation time of this invention can be reduced to less than 20 minutes, which greatly reduces process time and increases production capacity.
[0067] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to in the method section.
[0068] Table 1 compares the sheet resistance and BSG thickness uniformity of the experimental group using the present invention with those of the normal production line process. As can be seen from Table 1, under the condition that the average sheet resistance and oxide layer thickness are basically the same, the sheet resistance uniformity and oxide layer uniformity of the experimental group are improved by 1%.
[0069] Table 1 Comparison of sheet resistance and oxide layer thickness uniformity between the experimental group and the normal production line.
[0070]
[0071] Table 2 compares the electrical performance of the experimental group with that of the normal production line process. As shown in Table 2, the present invention uses a multi-temperature deposition method to reduce the surface concentration, thus the open voltage has an advantage of 0.03V compared with the production line. At the same time, the filling capacity is slightly reduced due to the increase in contact resistance, and the overall efficiency is improved by 0.06% compared with the normal production line process.
[0072] Table 2 Comparison of Electrical Performance Between Experimental Group and Normal Production Line Process
[0073] plan Eta(%) Voc(V) lsc(A) FF (%) experimental group 24.68 0.713 13.784 83.05 control group 24.62 0.71 13.783 83.09 difference 0.06 0.003 0.001 -0.04
[0074] It should be noted that, in this specification, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.
[0075] The low-temperature boron diffusion method provided by this invention has been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of this invention. It should be noted that those skilled in the art can make several improvements and modifications to this invention without departing from the principles of this invention, and these improvements and modifications also fall within the protection scope of the claims of this invention.
Claims
1. A low-temperature boron diffusion method, characterized in that, include: The textured N-type silicon wafer is placed in a boron diffusion furnace and subjected to initial boron diffusion deposition at a first temperature. The boron source is BCl3, the flow rate of the boron source ranges from 100 sccm to 200 sccm, the flow rate of the high nitrogen source ranges from 2000 sccm to 2500 sccm, the flow rate of the oxygen source ranges from 300 sccm to 800 sccm, the first temperature ranges from 785 degrees Celsius to 850 degrees Celsius, including the endpoint values; the time for the first boron diffusion deposition is from 2 minutes to 4 minutes, including the endpoint values. Prior to the initial boron diffusion deposition, the following is also included: The N-type silicon wafer is pre-oxidized at a pre-oxidation temperature to obtain a surface oxide layer; wherein the pre-oxidation temperature is lower than the first temperature; The ambient temperature is raised from the first temperature to the second temperature to perform secondary boron diffusion deposition; The boron source flow rate ranges from 200 sccm to 400 sccm, the nitrogen flow rate ranges from 1800 sccm to 2300 sccm, and the oxygen flow rate ranges from 500 sccm to 1000 sccm; the difference between the second temperature and the first temperature ranges from 5 degrees Celsius to 20 degrees Celsius, including the endpoint; the secondary boron diffusion deposition time is from 3 minutes to 5 minutes, including the endpoint. The ambient temperature was increased from the second temperature to the third temperature, and boron diffusion deposition was performed three times. In the tertiary boron diffusion deposition, the boron source flow rate ranges from 100 sccm to 300 sccm, the nitrogen flow rate ranges from 2000 sccm to 2500 sccm, and the oxygen flow rate ranges from 400 sccm to 800 sccm; the difference between the third temperature and the second temperature ranges from 5 degrees Celsius to 20 degrees Celsius, including the endpoint; and the time for the secondary boron diffusion deposition is from 1 minute to 3 minutes, including the endpoint. The ambient temperature is raised from the third temperature to the propulsion temperature to propel the N-type silicon wafer that has undergone the three boron diffusion processes. The flow rate of large nitrogen ranges from 2000 sccm to 3500 sccm, the propulsion temperature ranges from 900 degrees Celsius to 960 degrees Celsius, and the propulsion time ranges from 15 minutes to 30 minutes; The ambient temperature is lowered from the advance temperature to the post-oxidation temperature to perform through-source oxidation on the advanced N-type silicon wafer; During the process of reducing the advance temperature to the post-oxidation temperature, the N-type silicon wafer that has been advanced is subjected to through-source oxidation. The oxygen used in the circulating oxidation process is wet oxygen; Accordingly, after the aforementioned source oxidation, the process further includes: Remove the surface oxide layer.
2. The low-temperature boron diffusion method as described in claim 1, characterized in that, The range of boron source flow rate for the circulating oxidation is 100 sccm-200 sccm, and the range of nitrogen flow rate is 1000 sccm-1500 sccm. The high oxygen flow rate in the through-source oxidation process ranges from 500 sccm to 1000 sccm, including the endpoint value; the low oxygen flow rate in the through-source oxidation process ranges from 500 sccm to 1000 sccm, including the endpoint value.
3. The low-temperature boron diffusion method as described in claim 1, characterized in that, The time range for the source oxidation is 15 to 20 minutes, including the endpoint value.
4. The low-temperature boron diffusion method as described in claim 1, characterized in that, The post-oxidation temperature ranges from 850 degrees Celsius to 950 degrees Celsius, including the endpoint values.