Solar cell and diffusion method
Through the diffusion process of solar batteries, the cooling of two times and gradually decreased in the cooling level, solving the problem of bending and high cost of silicon wafers, and achieved the effect of reducing losses and production costs.
Patent Information
- Application Number
- CN202310915251.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-07-24
- Publication Date
- 2025-01-28
AI Technical Summary
In the prior art, the silicon wafer is prone to bending in the diffusion process of solar cells, resulting in losses, or the vertical or flat insertion method is used, and the cost is higher.
After controlling the diffusion furnace for the first cooling of the diffusion furnace after the oxidation process of the silicon wafer constant temperature, the cooling range is 130 ° C to 140 ° C, and then the second cooling is performed. Avoid thermal stress.
This method effectively reduces the bending of the silicon wafer, reduces production costs, and simplifies the cooling process, avoiding losses caused by thermal stress.
Smart Images
Figure CN119381251A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the field of photovoltaic technology, in particular to a solar cell and a diffusion method. Background Art
[0002] Solar cells can directly convert light energy into electrical energy. Their application is clean, environmentally friendly and pollution-free. In the production process of solar cells, diffusion is an important process, the purpose of which is to form a PN junction. At present, the thermal diffusion method is usually used to make the junction.
[0003] With the development of photovoltaic technology, the size of silicon wafers has become larger and larger, making it easy for the silicon wafers to bend when affected by external forces. In the prior art, when the diffusion process adopts the method of horizontal insertion, the temperature reduction step and the boat discharge step of the diffusion process are natural cooling, and the cooling rate cannot be adjusted. The furnace mouth and the furnace tail of the diffusion furnace cool down faster than the furnace. The furnace mouth and the furnace tail temperature zones are at the outermost side of the temperature zone distribution of the diffusion furnace tube. When cooling, the heating power is zero and is not controlled by the temperature control module. The heat loss is the largest and the cooling is the fastest, which is not conducive to the elimination of thermal stress. There are other temperature zones on both sides of the temperature zone in the furnace, the temperature loss is relatively small, the cooling rate is relatively stable, and the cooling is slow, which is conducive to the elimination of thermal stress. The temperature changes at the furnace mouth and the furnace tail are fast, and thermal stress is easily generated, resulting in deformation of the contact position between the silicon wafer at the furnace mouth and the furnace tail and the quartz boat teeth, which may cause EL (ElectroLuminescence, electroluminescence) boat tooth marks, and even cause obvious bending of the silicon wafer. Since the subsequent process cannot repair the deformation of the silicon wafer, and the bent silicon wafer in the subsequent process will also cause the rupture of other silicon wafers, it can only be processed as fragments, that is, scrapped, resulting in great losses. When the diffusion process adopts the method of vertical or flat insertion, thermal stress can be prevented from acting on the surface of the silicon wafer, reducing the bending of the silicon wafer. However, the vertical or flat insertion quartz boat requires the use of a small boat and a boat support. It is cumbersome to get on and off the boat during cleaning, the quartz boat is easily damaged, and the cost of replacing the quartz boat is high. In addition, when the diffusion process adopts the method of flat insertion, if the silicon wafer is large in size, the silicon wafer will bend to a certain extent due to the influence of gravity. Summary of the invention
[0004] The present invention provides a solar cell and a diffusion method, aiming to solve the problem that in the diffusion process of the prior art, a silicon wafer is easy to bend or a silicon wafer is not easy to bend but the cost is high.
[0005] In a first aspect, the present invention provides a diffusion method, the diffusion method comprising: after a constant temperature oxidation process of a silicon wafer, controlling a diffusion furnace to perform a first temperature reduction, wherein the first temperature reduction has a temperature reduction range of 130° C. to 140° C.;
[0006] After the first temperature reduction, the diffusion furnace is controlled to perform a second temperature reduction, wherein the second temperature reduction has a temperature reduction range of 110° C. to 130° C.
[0007] In the present invention, after the constant temperature oxidation process of the silicon wafer, the diffusion furnace is controlled to perform the first cooling, and the cooling range of the first cooling is 130°C to 140°C; after the first cooling, the diffusion furnace is controlled to perform the second cooling, and the cooling range of the second cooling is 110°C to 130°C. In the case of two-step cooling, the cooling range can be reduced. The furnace mouth and furnace tail cool faster than the furnace. The cooling is carried out twice, and the cooling range of each cooling is small, so as to avoid a large cooling range in one cooling, which leads to too fast temperature change at the furnace mouth and furnace tail, and generates thermal stress, and then the silicon wafer at the furnace mouth and furnace tail and the boat teeth contact position are prone to bending and deformation, causing losses, and at the same time, it can avoid the complexity of the cooling process; the cooling range of the first cooling is 130℃ to 140℃, and the cooling range of the second cooling is 110℃ to 130℃, which can ensure that the temperature of the process after the second cooling meets the process requirements, avoid too small cooling range, affect the overall cooling range of the two coolings, and cause the temperature after the second cooling to not drop to the temperature of the process after the second cooling, and at the same time, avoid too large cooling range, and the silicon wafer is prone to bending and deformation. In addition, the cooling range is small, and after the temperature of the furnace mouth and furnace tail drops to the set temperature, there can be a period of constant temperature process at the furnace mouth and furnace tail, which is conducive to the elimination of thermal stress. Furthermore, by adopting the diffusion method in the embodiment of the present invention, the problem that the silicon wafer is prone to bending is improved by cooling the temperature twice, without adding additional devices, and the cost is low.
[0008] Optionally, the first cooling time is 1500s to 1600s;
[0009] The second cooling time is from 1200s to 1300s.
[0010] Optionally, after the second cooling, the diffusion method further comprises a boat exiting step;
[0011] In the boat-out step, the temperature is 700°C to 720°C.
[0012] Optionally, in the boat-out step, the time is 660s to 720s.
[0013] Optionally, the boat-out step includes: opening a furnace door of a diffusion furnace;
[0014] After the boat exiting step, the diffusion method further comprises a temperature raising step;
[0015] The temperature raising step includes: closing the furnace door.
[0016] Optionally, in the heating step, the temperature is 770°C to 780°C.
[0017] Optionally, in the heating step, the time is 120s to 180s.
[0018] Optionally, the diffusion method is used for boron diffusion.
[0019] Optionally, the diffusion method is used to diffuse single crystal silicon wafers.
[0020] In a second aspect, the present invention further provides a solar cell, comprising a silicon wafer, wherein the silicon wafer comprises a conductive region, and the conductive region of the silicon wafer is diffused by the diffusion method described in the first aspect. BRIEF DESCRIPTION OF THE DRAWINGS
[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative labor.
[0022] Figure 1 A flowchart of a diffusion method according to an embodiment of the present invention is shown;
[0023] Figure 2 A flow chart showing the steps of another diffusion method in an embodiment of the present invention is shown. DETAILED DESCRIPTION
[0024] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.
[0025] Reference Figure 1 , Figure 1 A flow chart of steps of a diffusion method in an embodiment of the present invention is shown, and the method includes:
[0026] Step 101, after the constant temperature oxidation process of the silicon wafer, controlling the diffusion furnace to perform the first temperature reduction, wherein the first temperature reduction has a temperature reduction range of 130° C. to 140° C.
[0027] Step 102, after the first temperature reduction, controlling the diffusion furnace to perform a second temperature reduction, wherein the second temperature reduction has a temperature reduction range of 110°C to 130°C.
[0028] In the production process of solar cells, the diffusion process is an important process, and its purpose is to form a PN junction. The diffusion process is generally carried out in a diffusion furnace, and the temperature in the diffusion furnace is increased or decreased by setting the temperature of the diffusion furnace. After the constant temperature oxidation process of the silicon wafer, the diffusion furnace is controlled to cool down for the first time, and the first cooling range is 130℃ to 140℃; after the first cooling, the diffusion furnace is controlled to cool down for the second time, and the second cooling range is 110℃ to 130℃. In the case of cooling in two steps, the cooling range can be reduced, the furnace mouth and the furnace tail cool faster than the furnace, and the cooling is carried out in two steps, and the cooling range of each cooling is small, so as to avoid a large cooling range in one cooling, which leads to too fast temperature change at the furnace mouth and the furnace tail, and generates thermal stress, and then the silicon wafer at the furnace mouth and the furnace tail and the boat teeth contact position are prone to bending deformation, causing losses, and at the same time, the cooling process can be avoided to be complicated; the cooling range of the first cooling is 130℃ (Celsius) to 140℃, and the cooling range of the second cooling is 110℃ to 130℃. For example, the cooling range of the first cooling can be 130℃, or 132℃, or 134℃, or 136℃, or 138℃, or 140℃, and the cooling range of the second cooling can be 110℃, or 115℃, or 120℃, or 125℃, or 128℃, or 130℃. The first cooling range is 130℃ to 140℃, and the second cooling range is 110℃ to 130℃, which can ensure the temperature of the process after the second cooling, avoid too small a cooling range, and the temperature after the second cooling will not reach the temperature of the process after the second cooling. At the same time, avoid too large a cooling range, which may cause the silicon wafer to bend and deform easily. For example, the cooling is after the constant temperature oxidation process and before the inflation back pressure process. The temperature of the constant temperature oxidation process is 1030℃, and the temperature of the inflation back pressure process is 780℃. The first cooling range can be 130℃, and the second cooling range can be 120℃, ensuring that the temperature of the inflation back pressure process is 780℃.
[0029] The inventors have discovered that in the prior art, when the diffusion process adopts the method of horizontal inserts, the cooling step and the boat-out step of the diffusion process are natural cooling, and the cooling rate cannot be adjusted. The furnace mouth and furnace tail temperature zones are at the outermost sides of the furnace tube temperature zone distribution. The heating power is zero during cooling and is not controlled by the temperature control module. The heat loss is the largest and the cooling is the fastest. There are other temperature zones on both sides of the temperature zone in the furnace, and the temperature loss is relatively small. The cooling rate is relatively stable and the cooling is slow. The temperature changes at the furnace mouth and furnace tail are fast, which is easy to produce thermal stress, causing the silicon wafers at the furnace mouth and furnace tail to be easily deformed at the contact positions with the quartz boat teeth, which may cause EL boat tooth marks, and even cause obvious bending of the silicon wafers, which can only be processed as fragments, that is, scrapped, resulting in large losses. When the diffusion process adopts the method of vertical or flat insertion, thermal stress can be prevented from acting on the surface of the silicon wafer, reducing the bending of the silicon wafer. However, the vertical or flat insertion quartz boat requires the use of a small boat and a boat support. It is cumbersome to get on and off the boat during cleaning, the quartz boat is easily damaged, and the cost of replacing the quartz boat is high. In addition, when the diffusion process adopts the method of flat insertion, if the silicon wafer is large in size, the silicon wafer will bend to a certain extent due to the influence of gravity.
[0030] In response to the above problems, in an embodiment of the present invention, after the constant temperature oxidation process of the silicon wafer, the diffusion furnace is controlled to perform the first cooling, and the cooling amplitude of the first cooling is 130°C to 140°C; after the first cooling, the diffusion furnace is controlled to perform the second cooling, and the cooling amplitude of the second cooling is 110°C to 130°C. In the case of two-step cooling, the cooling range can be reduced. The furnace mouth and furnace tail cool faster than the furnace. The cooling is carried out twice, and the cooling range of each cooling is small, so as to avoid a large cooling range in one cooling, which leads to too fast temperature change at the furnace mouth and furnace tail, and generates thermal stress, and then the silicon wafer at the furnace mouth and furnace tail and the boat teeth contact position are prone to bending and deformation, causing losses, and at the same time, it can avoid the complexity of the cooling process; the cooling range of the first cooling is 130℃ to 140℃, and the cooling range of the second cooling is 110℃ to 130℃, which can ensure that the temperature of the process after the second cooling meets the process requirements, avoid too small cooling range, affect the overall cooling range of the two coolings, and cause the temperature after the second cooling to not drop to the temperature of the process after the second cooling, and at the same time, avoid too large cooling range, and the silicon wafer is prone to bending and deformation. In addition, the cooling range is small, and after the temperature of the furnace mouth and furnace tail drops to the set temperature, there can be a period of constant temperature process at the furnace mouth and furnace tail, which is conducive to the elimination of thermal stress. Furthermore, by adopting the diffusion method in the embodiment of the present invention, the problem that the silicon wafer is prone to bending is improved by cooling the temperature twice, without adding additional devices, and the cost is low.
[0031] Optionally, the first cooling time is 1500s (seconds) to 1600s; the second cooling time is 1200s to 1300s. For example, the first cooling time can be 1500s, or 1520s, or 1540s, or 1560s, or 1580s, or 1600s; the second cooling time is 1200s, or 1220s, or 1240s, or 1260s, or 1280s, or 1300s. The first cooling time is 1500s to 1600s, which can ensure that the overall temperature in the diffusion furnace after the first cooling can meet the process setting requirements, and at the same time, avoid the process time being too long; the second cooling time is 1200s to 1300s, which can ensure that the overall temperature in the diffusion furnace after the second cooling can meet the process setting requirements, and at the same time, avoid the process time being too long.
[0032] Optionally, after the second temperature reduction, the diffusion method further comprises a step of removing the mixture from the boat; in the step of removing the mixture from the boat, the temperature is 700° C. to 720° C. For example, in the step of removing the mixture from the boat, the temperature may be 700° C., or 705° C., or 710° C., or 712° C., or 715° C., or 720° C. In the boat-out step, the temperature is 700°C to 720°C. The temperature of the boat-out step is relatively low, so that the boat and the silicon wafers in the boat can maintain a relatively low temperature in the boat-out step. At the same time, when the boat is out of the furnace mouth, since the furnace door is open, the furnace mouth temperature zone is directly connected to the atmosphere. When the temperature set in the boat-out step is high, the temperature of the furnace mouth temperature zone will be reduced more relative to other temperature zones. In the boat-out step, the temperature is 700°C to 720°C. The set temperature is relatively low, and the temperature of other temperature zones is reduced. The difference in the temperature reduction range of the furnace mouth temperature zone relative to other temperature zones becomes smaller, which can reduce the temperature difference between the furnace mouth temperature zone and other temperature zones, reduce the silicon wafer bending caused by the high temperature silicon wafer in the furnace suddenly dropping too much when reaching the furnace mouth in the boat-out step, and reduce the risk of bending at the contact position between the silicon wafer and the boat teeth. In addition, avoid too low a temperature to affect the initial temperature of the next diffusion process.
[0033] Optionally, in the boat-out step, the time is 660s to 720s. For example, in the boat-out step, the time can be 660s, or 670s, or 680s, or 690s, or 700s, or 720s. In the boat-out step, the time is 660s to 720s, which can ensure that the boat-out action is completed within this time range.
[0034] Optionally, the boat-out step includes: opening the furnace door of the diffusion furnace; after the boat-out step, the diffusion method further includes a heating step; the heating step includes: closing the furnace door. The boat-out step includes opening the furnace door of the diffusion furnace so that the boat and the silicon wafer in the boat can be taken out. The diffusion method uses a diffusion furnace, which can conveniently control the temperature and provide a diffusion environment. The boat-out step includes a heating step after the boat-out step, which can reduce the heating time before the next diffusion process. The heating step includes closing the furnace door, which can save the time of closing the furnace door.
[0035] Optionally, in the temperature raising step, the temperature is 770° C. to 780° C. For example, in the temperature raising step, the temperature may be 770° C., or 772° C., or 774° C., or 776° C., or 778° C., or 780° C. In the temperature raising step, the temperature is 770° C. to 780° C., and a higher temperature can further reduce the temperature raising time before the next diffusion process.
[0036] Optionally, in the heating step, the time is 120s to 180s. For example, in the heating step, the time can be 120s, or 130s, or 140s, or 150s, or 160s, or 180s. In the heating step, the time is 120s to 180s, which can ensure that the action of closing the furnace door is completed within this time range.
[0037] Optionally, the diffusion method is used for boron diffusion. The temperature required for boron diffusion is relatively high. The diffusion method is used for boron diffusion, which can improve the bending of the silicon wafer caused by thermal stress generated by rapid temperature changes during the boron diffusion process. Optionally, the boron source is boron trichloride. When boron trichloride is used as the boron source, the diffusion byproducts have little damage to the carrier quartz boat, which can extend the service life of the quartz boat.
[0038] Optionally, the diffusion method is used to diffuse a single crystal silicon wafer. Compared with a polycrystalline silicon wafer, a single crystal silicon wafer has fewer defects. Diffusion is performed on the single crystal silicon wafer, and the solar cell prepared by using the diffused single crystal silicon wafer has better performance.
[0039] The present invention also provides a solar cell, comprising a silicon wafer, wherein the silicon wafer comprises a conductive region, and the conductive region of the silicon wafer is diffused by the above diffusion method. The above diffusion method can improve the situation that the silicon wafer is easily bent in the cooling step and the boat-out step of the diffusion process, thereby avoiding affecting the performance of the solar cell.
[0040] The present invention is further explained below in conjunction with specific embodiments.
[0041] Example 1
[0042] Embodiment 1 is another diffusion method in the embodiment of the present invention, referring to Figure 2 , Figure 2 A flow chart of steps of another diffusion method in an embodiment of the present invention is shown. The diffusion method is used for boron diffusion, the boron source is boron trichloride, the silicon wafer type is an N-type silicon wafer, and the diffusion furnace is provided with six temperature zones, namely, temperature zone 1, temperature zone 2, temperature zone 3, temperature zone 4, temperature zone 5, and temperature zone 6, and the six temperature zones are distributed along the lateral direction of the diffusion furnace, wherein temperature zone 1 is located at the furnace mouth, and temperature zone 6 is located at the furnace tail. Specifically, the following steps are included:
[0043] (1) Start: The time is 25 s, the temperature is set to 830°C, and the temperatures of the six temperature zones are the same. The flow rate of nitrogen is 8000 sccm (standard cubic centimeter per minute), the flow rates of boron trichloride and oxygen are both 0 sccm, and the furnace pressure is 990 mbar (millibar);
[0044] (2) Entering the boat: Open the furnace door, and the quartz boat carrying the silicon wafer enters the diffusion furnace. Close the furnace door. The time is 660 seconds, the temperature is set to 830°C, and the temperature of the six temperature zones is the same. The flow rate of nitrogen is 5000 sccm, the flow rates of boron trichloride and oxygen are both 0 sccm, and the furnace tube pressure is 990 mbar;
[0045] (3) Vacuuming: the time is 580 s, the temperature is set to 855 °C, and the temperature of the six temperature zones is the same. The flow rates of nitrogen, boron trichloride and oxygen are all 0 sccm, and the furnace tube pressure is 180 mbar;
[0046] (4) Leak detection: The time is 30 s, the temperature is set to 855°C, and the temperature of the six temperature zones is the same. The flow rates of nitrogen, boron trichloride and oxygen are all 0 sccm, and the furnace tube pressure is 180 mbar;
[0047] (5) Pre-oxidation: time is 280 s, temperature is set to 855 °C, and the temperature of the six temperature zones is the same, the flow rate of nitrogen is 500 sccm, the flow rate of boron trichloride is 0 sccm, the flow rate of oxygen is 2000 sccm, and the furnace pressure is 200 mbar;
[0048] (6) Diffusion: time is 500 s, temperature is set to 855-875 °C, the temperature of the six temperature zones is set according to the actual preparation situation, the flow rate of nitrogen is 1800 sccm, the flow rate of boron trichloride is 120 sccm, the flow rate of oxygen is 500 sccm, and the furnace pressure is 180 mbar;
[0049] (7) Primary heating: the time is 180 s, the temperature is set to 920 °C, and the temperature of the six temperature zones is the same, the flow rate of nitrogen is 2400 sccm, the flow rates of boron trichloride and oxygen are both 0 sccm, and the furnace tube pressure is 180 mbar;
[0050] (8) First push: the time is 720 s, the temperature is set to 970-990 °C, the temperatures of the six temperature zones are set according to the actual preparation conditions, the flow rate of nitrogen is 10000 sccm, the flow rates of boron trichloride and oxygen are both 0 sccm, and the furnace pressure is 800 mbar;
[0051] (9) Second push: time is 300 s, temperature is set to 970-990 °C, the temperature of the six temperature zones is set according to the actual preparation situation, the flow rate of nitrogen is 15000 sccm, the flow rates of boron trichloride and oxygen are both 0 sccm, and the furnace pressure is 850 mbar;
[0052] (10) Temperature rise oxidation: the time is 720 s, the temperature is set to 1030 °C, and the temperature of the six temperature zones is the same, the flow rates of nitrogen and boron trichloride are both 0 sccm, the flow rate of oxygen is 15000 sccm, and the furnace pressure is 800 mbar;
[0053] (11) Constant temperature oxidation: the time is 3600 s, the temperature is set to 1030 °C, and the temperature of the six temperature zones is the same, the flow rates of nitrogen and boron trichloride are both 0 sccm, the flow rate of oxygen is 15000 sccm, and the furnace pressure is 800 mbar;
[0054] (12) First cooling: the time is 1500s, the temperature is set to 900°C, and the temperature of the six temperature zones is the same. The flow rates of nitrogen and boron trichloride are both 0sccm, the flow rate of oxygen is 15000sccm, and the furnace tube pressure is 800mbar;
[0055] (13) Second cooling: time is 1200 s, temperature is set to 780 °C, and the temperature of the six temperature zones is the same, the flow rate of nitrogen is 18000 sccm, the flow rates of boron trichloride and oxygen are both 0 sccm, and the furnace tube pressure is 800 mbar;
[0056] (14) Gas back pressure: time is 60 s, temperature is set to 780 °C, and the temperature of the six temperature zones is the same, the flow rate of nitrogen is 5000 sccm, the flow rates of boron trichloride and oxygen are both 0 sccm, and the furnace tube pressure is 990 mbar;
[0057] (15) Boat exit step: Open the furnace door, and the quartz boat carrying the silicon wafer is taken out of the diffusion furnace. The time is 660 s, the temperature is set to 700°C, and the temperature of the six temperature zones is the same. The flow rate of nitrogen is 1800 sccm, the flow rates of boron trichloride and oxygen are both 0 sccm, and the furnace tube pressure is 990 mbar;
[0058] (16) Heating step: close the furnace door, the time is 180 s, the temperature is set to 780 °C, and the temperature of the six temperature zones is the same, the flow rate of nitrogen is 1800 sccm, the flow rates of boron trichloride and oxygen are both 0 sccm, and the furnace tube pressure is 990 mbar.
[0059] In the above steps, nitrogen is an auxiliary gas, which refers to pure nitrogen gas, and is mainly used to maintain the gas atmosphere in the furnace tube of the diffusion furnace.
[0060] In step (1), the time can be 25-45s, the temperature can be set to 830-850°C, the flow rate of large nitrogen can be 8000-12000sccm, and the furnace tube pressure can be 990-1000mbar; in step (2), the time can be 660-680s, the temperature can be set to 830-850°C, the flow rate of large nitrogen can be 5000-8000sccm, and the furnace tube pressure can be 990-1000mbar; in step (3), the time can be 580-600s, the temperature can be set to 855-875°C, and the furnace tube pressure can be 180-200mbar; in step (4), the time can be 30-60s, the temperature can be set to The temperature of the furnace tube can be 855-875°C, and the furnace tube pressure can be 180-200 mbar; in step (5), the time can be 280-300 s, the temperature can be set to 855-875°C, and the flow rate of the large nitrogen can be 500-1000 sccm; in step (6), the time can be 500-540 s, the flow rate of the large nitrogen can be 1800-2200 sccm, the flow rate of boron trichloride can be 120-150 sccm, the flow rate of oxygen can be 500-1000 sccm, and the furnace tube pressure can be 180-200 mbar; in step (7), the time can be 180-200 s, the temperature can be set to 920-925°C, the flow rate of the large nitrogen can be 2400 -2600sccm, the furnace tube pressure can be 180-200mbar; in step (8), the time can be 700-720s, the flow rate of large nitrogen can be 10000-15000sccm, and the furnace tube pressure can be 800-850mbar; in step (9), the time can be 240-300s, the flow rate of large nitrogen can be 10000-15000sccm, and the furnace tube pressure can be 800-850mbar; in step (10), the time can be 720-900s, the flow rate of oxygen can be 15000-18000sccm, and the furnace tube pressure can be 800-850mbar; in step (11), the time can be 3600 -3800s, the oxygen flow rate can be 15000-18000sccm, and the furnace tube pressure can be 800-850mbar; in step (12), the temperature can be set to 890-900°C, the oxygen flow rate can be 15000-18000sccm, the introduction of oxygen can reduce the doping concentration on the surface of the silicon wafer, and the furnace tube pressure can be 800-850mbar; in step (13), the temperature can be set to 770-780°C, the nitrogen flow rate can be 15000-18000sccm, and the introduction of a large flow of low-temperature nitrogen can take away part of the heat in the diffusion furnace and accelerate the cooling rate of the second cooling; the furnace tube pressure can be 800-850mbar;In step (14), the time can be 60-90s, the temperature can be set to 770-780°C, the flow rate of bulk nitrogen can be 5000-8000sccm, and the furnace tube pressure can be 990-1000mbar; in step (15), the flow rate of bulk nitrogen can be 1800-2000sccm, and the furnace tube pressure can be 990-1000mbar; in step (16), the flow rate of bulk nitrogen can be 1800-2000sccm, and the furnace tube pressure can be 990-1000mbar. ;
[0061] Comparative Example 1
[0062] The difference from Example 1 is that in step (12), the temperature is set to 780°C for the first cooling; steps (15) and (16) are combined into one boat exiting step, specifically, the furnace door is opened, the quartz boat carrying the silicon wafer is taken out of the diffusion furnace, the furnace door is closed, the time is 840s, the temperature is set to 780°C, and the temperatures of the six temperature zones are the same, the flow rate of nitrogen is 1800sccm, the flow rates of boron trichloride and oxygen are both 0sccm, and the furnace tube pressure is 990mbar.
[0063] The other steps and process parameters are the same as those in Example 1.
[0064] During the diffusion process of Comparative Example 1 and Example 1, the temperature of six temperature zones was measured under the same measurement conditions. The measurement results are as follows:
[0065] Table 1 Temperature comparison table of Example 1 and Comparative Example 1
[0066]
[0067]
[0068] In Table 1 above, the unit of each numerical value is ℃, and the actual temperatures are the temperatures measured after the corresponding steps are completed. It can be seen from Table 1 above that the extreme difference of the first cooling, that is, the maximum temperature difference, is 69℃ for Comparative Example 1, and 30℃ for Example 1; the maximum temperature difference of the boat-out step is 65℃ for Comparative Example 1, and 37℃ for Example 1. Compared with Comparative Example 1, the temperature extreme difference of the six temperature zones in Example 1 is reduced, and the thermal stress is also reduced, which can reduce the probability of bending and deformation of the silicon wafer when it is out of the boat.
[0069] Example 2
[0070] The difference from Example 1 is that: in step (12), the temperature is set to 895° C. for the first cooling; in step (13), the temperature is set to 775° C. for the second cooling;
[0071] The other steps and process parameters are the same as those in Example 1.
[0072] Comparative Example 2
[0073] The difference from Example 2 is that in step (12), the temperature is set to 775°C for the first cooling; steps (15) and (16) are combined into one boat exiting step, specifically: the furnace door is opened, the quartz boat carrying the silicon wafer is taken out of the diffusion furnace, the furnace door is closed, the time is 840s, the temperature is set to 775°C, and the temperatures of the six temperature zones are the same, the flow rate of nitrogen is 1800sccm, the flow rates of boron trichloride and oxygen are both 0sccm, and the furnace tube pressure is 990mbar.
[0074] The other steps and process parameters are the same as those in Example 2.
[0075] During the diffusion process of Comparative Example 2 and Example 2, the temperature of six temperature zones was measured under the same measurement conditions. The measurement results are as follows:
[0076] Table 2 Temperature comparison table of Example 2 and Comparative Example 2
[0077]
[0078]
[0079] In Table 2 above, the unit of each numerical value is ℃, and the actual temperatures are the temperatures measured after the completion of the corresponding steps. It can be seen from Table 2 above that the maximum temperature difference of the first cooling is 73℃ for Comparative Example 2, and 35℃ for Example 2; the maximum temperature difference of the boat-out step is 65℃ for Comparative Example 2, and 42℃ for Example 2. Compared with Comparative Example 2, the temperature extremes of the six temperature zones in Example 2 are reduced, and the thermal stress is also reduced, which can reduce the probability of bending and deformation of the silicon wafer when it is out of the boat.
[0080] Example 3
[0081] The difference from Example 1 is that: in step (12), the temperature is set to 890° C. for the first cooling; in step (13), the temperature is set to 770° C. for the second cooling;
[0082] The other steps and process parameters are the same as those in Example 1.
[0083] Comparative Example 3
[0084] The difference from Example 3 is that in step (12), the temperature is set to 770°C for the first cooling; steps (15) and (16) are combined into one boat exiting step, specifically, the furnace door is opened, the quartz boat carrying the silicon wafer is taken out of the diffusion furnace, the furnace door is closed, the time is 840s, the temperature is set to 770°C, and the temperatures of the six temperature zones are the same, the flow rate of nitrogen is 1800sccm, the flow rates of boron trichloride and oxygen are both 0sccm, and the furnace tube pressure is 990mbar.
[0085] The other steps and process parameters are the same as those in Example 3.
[0086] During the diffusion process of Comparative Example 3 and Example 3, the temperature of six temperature zones was measured under the same measurement conditions. The measurement results are as follows:
[0087] Table 3 Temperature comparison table of Example 3 and Comparative Example 3
[0088]
[0089]
[0090] In Table 3 above, the unit of each numerical value is ℃, and the actual temperatures are the temperatures measured after the completion of the corresponding steps. It can be seen from Table 3 above that the maximum temperature difference of the first cooling is 71℃ for Comparative Example 3, and 28℃ for Example 3; the maximum temperature difference of the boat-out step is 63℃ for Comparative Example 3, and 46℃ for Example 3. Compared with Comparative Example 3, the temperature extremes of the six temperature zones in Example 3 are reduced, and the thermal stress is also reduced, which can reduce the probability of bending and deformation of the silicon wafer when it is out of the boat.
[0091] In the embodiment of the present invention, the bent piece refers to: the silicon wafer is deformed at the contact position with the quartz boat teeth. The bent piece is easy to break. The bent piece is mainly manifested by the deformation of the silicon wafer at the contact position with the boat teeth, and then after the robot slicing and subsequent processes, diagonal fragments with fixed positions will be formed, which will cause frequent jamming of fragments in subsequent processes, affecting the yield and fragmentation rate. The above-mentioned methods of Example 1 and Comparative Example 1 were used for diffusion, and then the fragmentation data were compared. The specific temperature setting values of Example 1 and Comparative Example 1 are shown in Table 4.
[0092] Table 4 Comparison of set temperatures of Example 1 and Comparative Example 1
[0093]
[0094]
[0095] In Table 4 above, the unit of each value is ° C. The fragment data is statistically analyzed, and the statistical results are shown in Table 5.
[0096] Table 5 Fragmentation data comparison table
[0097]
[0098] In Table 5 above, the capacity refers to the total number of silicon wafers that undergo boron diffusion, and the number of fragments refers to the number of silicon wafers that undergo deformation and fragmentation. As can be seen from Table 5 above, the average fragmentation rate of Comparative Example 1 is 0.047%, and the average fragmentation rate of Example 1 is 0.034%. Compared with Comparative Example 1, the average fragmentation rate of Example 1 is reduced by 0.013%. It is shown that the above-mentioned diffusion method of the embodiment of the present invention can improve the situation in which the silicon wafer is prone to bending in the cooling step and the boat discharge step of the diffusion process, reduce the proportion of silicon wafer bending, and thus reduce the fragmentation rate and reduce losses.
[0099] It should be noted that the aforementioned diffusion method and solar cell can refer to each other in their related parts and can achieve the same or similar effects.
[0100] It should be noted that, for the method embodiments, for the sake of simplicity of description, they are all expressed as a series of action combinations, but those skilled in the art should be aware that the embodiments of the present application are not limited by the described order of actions, because according to the embodiments of the present application, certain steps can be performed in other orders or simultaneously. Secondly, those skilled in the art should also be aware that the embodiments described in the specification are all preferred embodiments, and the actions involved are not necessarily required by the embodiments of the present application.
[0101] It should be noted that, in this article, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the existence of other identical elements in the process, method, article or device including the element.
[0102] Through the description of the above implementation methods, those skilled in the art can clearly understand that the above-mentioned embodiment methods can be implemented by means of software plus a necessary general hardware platform, and of course by hardware, but in many cases the former is a better implementation method. Based on such an understanding, the technical solution of the present invention, or the part that contributes to the prior art, can be embodied in the form of a software product, which is stored in a storage medium (such as ROM / RAM, a magnetic disk, or an optical disk), and includes a number of instructions for enabling a terminal (which can be a mobile phone, a computer, a server, an air conditioner, or a network device, etc.) to execute the methods described in each embodiment of the present invention.
[0103] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation modes, which are merely illustrative rather than restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the present invention and the claims, all of which are within the protection of the present invention.
Claims
1. A diffusion method, characterized in that: The diffusion method includes: After the constant temperature oxidation process of the silicon wafer, the diffusion furnace is controlled to perform a first temperature reduction, wherein the first temperature reduction has a temperature reduction range of 130° C. to 140° C.; After the first temperature reduction, the diffusion furnace is controlled to perform a second temperature reduction, wherein the second temperature reduction has a temperature reduction range of 110° C. to 130° C.
2. The diffusion method according to claim 1, characterized in that: The first cooling time is 1500s to 1600s; The second cooling time is from 1200s to 1300s.
3. The diffusion method according to claim 1, characterized in that: After the second cooling, the diffusion method further comprises a boat exiting step; In the boat-out step, the temperature is 700°C to 720°C.
4. The diffusion method according to claim 3, characterized in that: In the boat-out step, the time is 660s to 720s.
5. The diffusion method according to claim 3, characterized in that: The boat unloading step includes: opening a furnace door of the diffusion furnace; After the boat exiting step, the diffusion method further comprises a temperature raising step; The temperature raising step includes: closing the furnace door.
6. The diffusion method according to claim 5, characterized in that: In the temperature increasing step, the temperature is 770°C to 780°C.
7. The diffusion method according to claim 5, characterized in that: In the temperature increasing step, the time is 120s to 180s.
8. The diffusion method according to any one of claims 1 to 7, characterized in that: The diffusion method is used to perform boron diffusion.
9. The diffusion method according to any one of claims 1 to 7, characterized in that: The diffusion method is used to diffuse single crystal silicon wafers.
10. A solar cell, characterized in that: It comprises a silicon wafer, wherein the silicon wafer comprises a conductive region, and the conductive region of the silicon wafer is diffused by using the diffusion method described in any one of claims 1 to 9.