Boron diffusion method
By forming an oxide layer, depositing a boron source, cleaning, and advancing the process during boron diffusion, the problem of uneven boron content distribution was solved, improving the sheet resistance uniformity of silicon wafers and cell performance, and ensuring the consistency of silicon wafers and the maintenance cycle of equipment.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- 三一硅能(朔州)有限公司
- Filing Date
- 2022-09-28
- Publication Date
- 2026-06-16
AI Technical Summary
In existing technologies, when reducing boron content, the boron content distribution is uneven, which affects the performance and efficiency of N-type crystalline silicon solar cells, and the consistency between different silicon wafers is poor.
A boron diffusion method is employed, which includes forming an oxide layer in a diffusion furnace, depositing a boron source, removing reaction products, performing a first-pass process, cleaning the silicon wafer surface, controlling the boron diffusion depth with water vapor, and finally adjusting the temperature and pressure to ensure uniformity.
This achieved a uniform distribution of boron content, improved the uniformity of sheet resistance within the silicon wafer and the performance of the battery, ensured parameter control for subsequent processes, and extended the service life of the equipment.
Smart Images
Figure CN115547818B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of photovoltaic cell technology, and in particular to a boron diffusion method. Background Technology
[0002] In the fabrication of N-type crystalline silicon solar cells, the PN junction is typically created using a boron diffusion process. For this process, not only does the boron content in the resulting PN junction significantly impact the performance and efficiency of the N-type crystalline silicon solar cell, but the uniformity of boron diffusion also affects the parameter control of subsequent fabrication processes.
[0003] To ensure the performance and efficiency of N-type crystalline silicon solar cells, the boron content is typically controlled to prevent excessive boron content from increasing sheet resistance. However, in existing technologies, reducing boron content and increasing sheet resistance often leads to uneven boron source distribution, resulting in inconsistent boron content within individual silicon wafers, and poor consistency in boron content across different wafers within the same diffusion furnace. This unevenness in boron content becomes even more pronounced with increased production volume and wafer size.
[0004] Therefore, how to solve the problem of uneven boron content distribution in the existing technology when reducing boron content has become an important technical problem to be solved by those skilled in the art. Summary of the Invention
[0005] This invention provides a boron diffusion method to solve the defect of uneven boron content distribution in the prior art when reducing boron content.
[0006] This invention provides a boron diffusion method, comprising:
[0007] The silicon wafer is placed into the diffusion furnace, and the temperature and pressure inside the diffusion furnace are adjusted.
[0008] A pre-oxidation operation is performed on the silicon wafer to form an oxide layer on the surface of the silicon wafer;
[0009] Oxygen and boron sources are introduced into the diffusion furnace to perform deposition treatment;
[0010] The gaseous reaction products from the deposition process, along with the remaining boron source, are discharged to the outside of the diffusion furnace.
[0011] Increase the temperature and pressure inside the diffusion furnace to perform a single propulsion process to diffuse the target amount of boron into the silicon wafer;
[0012] Steam is introduced into the diffusion furnace to clean the surface of the silicon wafer;
[0013] The temperature inside the diffusion furnace is increased to perform a secondary propulsion process;
[0014] Adjust the temperature and pressure inside the diffusion furnace, and remove the silicon wafer from the diffusion furnace.
[0015] According to a boron diffusion method provided by the present invention, the step of introducing water vapor into the diffusion furnace includes:
[0016] Nitrogen and water vapor are introduced into the diffusion furnace, with the flow rate of nitrogen being greater than the flow rate of water vapor.
[0017] According to a boron diffusion method provided by the present invention, the volumetric flow rate of the water vapor is 100-2000 sccm.
[0018] According to a boron diffusion method provided by the present invention, the boron source is boron trichloride gas, the volumetric flow rate of the boron trichloride gas is 50-1000 sccm, and the volumetric flow rate of the oxygen is 100-5000 sccm.
[0019] According to a boron diffusion method provided by the present invention, the primary propulsion process is carried out in a nitrogen atmosphere.
[0020] According to a boron diffusion method provided by the present invention, the secondary propulsion process is carried out in an atmosphere of nitrogen and oxygen.
[0021] According to a boron diffusion method provided by the present invention, the step of introducing oxygen and a boron source into the diffusion furnace includes:
[0022] A mixture of nitrogen, oxygen, and boron source is introduced into the diffusion furnace.
[0023] According to a boron diffusion method provided by the present invention, nitrogen gas is continuously introduced into the diffusion furnace when the silicon wafer is placed into the diffusion furnace and when the silicon wafer is removed from the diffusion furnace.
[0024] According to a boron diffusion method provided by the present invention, adjusting the temperature and pressure inside the diffusion furnace includes:
[0025] The diffusion furnace is evacuated to reduce the pressure inside the furnace to the target pressure.
[0026] Raise the temperature inside the diffusion furnace to the target temperature.
[0027] According to a boron diffusion method provided by the present invention, after reducing the pressure inside the diffusion furnace to a target pressure, the method further includes:
[0028] The airtightness of the diffusion furnace was tested.
[0029] In the boron diffusion method provided by this invention, a silicon wafer is placed in a diffusion furnace, and the temperature and pressure inside the furnace are adjusted to the target temperature and pressure. Then, a pre-oxidation operation is performed on the silicon wafer to form an oxide layer on its surface. Afterward, oxygen and a boron source are introduced into the diffusion furnace for deposition. To ensure sufficient boron is deposited at all locations on each silicon wafer within the diffusion furnace, the excessive introduction of the boron source can be controlled. After deposition, the gaseous reaction products (including boron oxide and chlorine) and any remaining boron source are discharged outside the diffusion furnace. Then, the temperature and pressure inside the diffusion furnace are increased to perform a propulsion process, allowing boron to diffuse into the silicon wafer until the target amount of boron is reached. After the first pass, steam is introduced into the diffusion furnace to clean the silicon wafer surface, removing any residual boron (including not only elemental boron but also potentially undischarged boron oxide and boron sources). The temperature inside the diffusion furnace is then increased for a second pass to further increase the diffusion depth of boron into the silicon wafer, reaching the target junction depth. Finally, the temperature and pressure inside the diffusion furnace are adjusted, and the silicon wafer is removed, yielding the boron-doped silicon wafer. This setup, by introducing excess boron and oxygen during deposition, ensures sufficient boron levels at all locations within the diffusion furnace. After the first pass introduces the required amount of elemental boron into the silicon wafer, steam cleaning removes excess boron from the wafer surface, preventing further diffusion of boron adhering to the surface during the second pass. This reduces the impact of excessive boron source on the boron content within the wafer, preventing excessively high boron content and resolving the uneven boron content distribution problem present in existing technologies when reducing boron content. Attached Figure Description
[0030] To more clearly illustrate the technical solutions in this 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 some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.
[0031] Figure 1 This is a flowchart of the boron diffusion method provided by the present invention. Detailed Implementation
[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.
[0033] The following is combined Figure 1 The boron diffusion method of the present invention is described.
[0034] like Figure 1 As shown, the boron diffusion method provided in this embodiment of the invention includes the following steps:
[0035] Step 110: Place the silicon wafer into the diffusion furnace and adjust the temperature and pressure inside the diffusion furnace.
[0036] Before performing boron diffusion on silicon wafers, the wafers need to be cleaned and texturized.
[0037] Open the door of the diffusion furnace, insert the texturized silicon wafer into the quartz boat, and send the silicon wafer and the quartz boat into the diffusion furnace together.
[0038] The diffusion furnace in this embodiment may be, but is not limited to, a quartz tube.
[0039] When placing the silicon wafer into the diffusion furnace, nitrogen gas can be continuously introduced into the furnace. The introduction of nitrogen increases the pressure inside the furnace, thereby reducing the amount of outside air entering and minimizing its impact on the furnace's cleanliness. The volumetric flow rate of the nitrogen gas can be controlled between 2000-20000 sccm; specifically, a flow rate of 5000 sccm is suitable.
[0040] It should be noted that oxygen and nitrogen are generally involved in the various steps of the boron diffusion process. Introducing nitrogen into the diffusion furnace when placing the silicon wafer inside will not affect the cleanliness of the furnace. Furthermore, since the air we breathe daily contains 78% nitrogen, introducing nitrogen in this step, compared to introducing other gases, reduces the impact on the operator.
[0041] After placing the silicon wafer into the diffusion furnace, close the furnace door to seal the furnace. Then adjust the temperature and pressure inside the diffusion furnace to the target temperature and pressure.
[0042] The target temperature and target pressure mentioned above are the temperature and pressure required for the deposition process in the following steps. Generally, the target temperature is controlled at 800-950 degrees Celsius, and the target pressure is controlled at 50-300 mbar. Specifically, the target temperature can be 880 degrees Celsius, and the target pressure can be 100 mbar.
[0043] Step 120: Perform a pre-oxidation operation on the silicon wafer to form an oxide layer on the surface of the silicon wafer.
[0044] After the temperature and pressure inside the diffusion furnace stabilize at the target values, the silicon wafer undergoes a pre-oxidation process. Specifically, oxygen is introduced into the diffusion furnace, causing the silicon on the wafer surface to react with the oxygen to generate silicon dioxide, forming an oxide layer on the wafer surface.
[0045] The oxide layer has an adsorption effect on the boron source, causing the boron source to be adsorbed on the silicon wafer surface, which helps to improve the uniformity of the boron source in the diffusion furnace.
[0046] During the aforementioned pre-oxidation process, the volumetric flow rate of oxygen introduced into the diffusion furnace can be controlled at 500-5000 sccm, and the introduction time can be controlled at 100-1000 seconds. Specifically, in step 120, the volumetric flow rate of oxygen introduced into the diffusion furnace is 3000 sccm, and the introduction time is 500 seconds.
[0047] Step 130: Introduce oxygen and boron sources into the diffusion furnace for deposition treatment.
[0048] After the oxide layer is formed on the surface of the silicon wafer, and before step 130, nitrogen and oxygen are introduced into the diffusion furnace to change the gas atmosphere inside the furnace. The volumetric flow rate of nitrogen is controlled at 500-5000 sccm, the volumetric flow rate of oxygen is controlled at 500-5000 sccm, and the introduction time is controlled at 30-1000 seconds. Specifically, the volumetric flow rate of nitrogen is 2000 sccm, the volumetric flow rate of oxygen is 900 sccm, and the introduction time is 30 seconds.
[0049] Then, oxygen and a boron source are introduced into the diffusion furnace for deposition. To ensure sufficient boron is deposited at all locations within the diffusion furnace, the amount of boron source introduced can be controlled to be excessive.
[0050] Specifically, boron trichloride gas can be used as the boron source mentioned above. The following explanation uses boron trichloride gas as an example of the introduced boron source.
[0051] In the aforementioned deposition process, boron trichloride gas, oxygen, and silicon react to produce boron, silicon oxide, boron oxide, and chlorine. Boron and silicon oxide adhere to the surface of the silicon wafer, boron diffuses into the wafer, and chlorine and boron oxide are distributed within the diffusion furnace.
[0052] During the deposition process, the volumetric flow rate of oxygen introduced into the diffusion furnace is controlled at 100-5000 sccm, the volumetric flow rate of boron trichloride gas is controlled at 50-1000 sccm, and the deposition time is controlled at 30-2000 seconds. Specifically, in step 130, the volumetric flow rate of oxygen introduced into the diffusion furnace is 900 sccm, the volumetric flow rate of boron trichloride gas is 210 sccm, and the deposition time is 700 seconds.
[0053] The relatively small volumetric flow rates of boron trichloride and oxygen can easily lead to insufficient distribution of boron trichloride in certain locations within the diffusion furnace, making it difficult to ensure the uniformity of boron trichloride and oxygen distribution within the furnace. In this embodiment, nitrogen gas is also introduced into the diffusion furnace along with oxygen and boron trichloride. That is, oxygen and boron trichloride gas are introduced into the diffusion furnace by introducing a mixture of nitrogen, oxygen, and boron trichloride.
[0054] Nitrogen, as the carrier gas for oxygen and boron trichloride, needs to have a relatively large volumetric flow rate. Adjusting the flow rate and reaction rate of oxygen and boron trichloride is beneficial for the uniform diffusion of boron trichloride and oxygen at various locations within the diffusion furnace.
[0055] In step 130, the volumetric flow rate of nitrogen introduced into the diffusion furnace is controlled at 1000-5000 sccm. Specifically, the volumetric flow rate of nitrogen can be 3200 sccm.
[0056] Step 140: Discharge the gaseous reaction products from the deposition process and the remaining boron source to the outside of the diffusion furnace.
[0057] After the above deposition process is completed, unreacted boron trichloride, as well as gaseous reaction products such as chlorine and boron oxide, are distributed in the diffusion furnace. Before the process is advanced, the gaseous reaction products and the remaining boron trichloride need to be discharged to the outside of the diffusion furnace to prevent the boron oxide and the remaining boron trichloride from affecting the subsequent processes.
[0058] Specifically, nitrogen and oxygen can be introduced into the diffusion furnace while maintaining constant temperature and pressure to remove the gaseous reaction products and residual boron trichloride generated during the deposition process.
[0059] In step 140, the volumetric flow rate of nitrogen introduced into the diffusion furnace is controlled at 1000-5000 sccm, and the volumetric flow rate of oxygen is controlled at 500-5000 sccm, with the introduction time controlled at 30-1000 seconds. Specifically, the volumetric flow rate of nitrogen introduced into the diffusion furnace is 4000 sccm, the volumetric flow rate of oxygen is 900 sccm, and the introduction time is 30 seconds.
[0060] Steps 120, 130 and 140 are all performed at the target temperature and target pressure.
[0061] Step 150: Increase the temperature and pressure inside the diffusion furnace to perform a propulsion process until the target amount of boron is diffused into the silicon wafer.
[0062] After removing the gaseous reaction products and remaining boron trichloride from the deposition process, the temperature inside the diffusion furnace is increased to 900-1000 degrees Celsius, and the pressure inside the diffusion furnace is increased to 200-900 mbar. Specifically, the temperature inside the diffusion furnace is increased to 950 degrees Celsius, and the pressure is increased to 500 mbar.
[0063] The pressure inside the diffusion furnace can be increased by introducing nitrogen gas. In step 150, the volumetric flow rate of nitrogen gas introduced into the diffusion furnace is controlled at 2000-20000 sccm, and the introduction time is controlled at 100-1000 seconds. Specifically, the volumetric flow rate of nitrogen gas introduced into the diffusion furnace can be 10000 sccm first, with the time controlled at 80 seconds, and then the volumetric flow rate of nitrogen gas introduced into the diffusion furnace can be 15000 sccm, with the time controlled at 100 seconds.
[0064] After raising the temperature and pressure inside the diffusion furnace, nitrogen gas is introduced into the diffusion furnace. Under the nitrogen atmosphere, a propulsion process is carried out to diffuse boron from the surface of the silicon wafer into the interior of the silicon wafer until the boron inside the silicon wafer reaches the target amount.
[0065] Step 160: Pass water vapor into the diffusion furnace to clean the surface of the silicon wafer.
[0066] After the initial diffusion process described above, excess boron (including not only elemental boron but also potentially unremoved boron oxide and boron trichloride) remains on the surface of the silicon wafer. At this point, steam is introduced into the diffusion furnace to clean the silicon wafer surface, removing the residual boron. This prevents further diffusion of boron adhering to the wafer surface into the wafer during the second diffusion process, thus reducing the boron content within the wafer. Furthermore, it prevents the formation of boron-rich regions, reduces damage to the silicon wafer's lattice, and improves passivation effectiveness.
[0067] In step 160, the volumetric flow rate of steam introduced into the diffusion furnace is controlled at 100-2000 sccm, and the introduction time is controlled at 50-2000 seconds. Specifically, the volumetric flow rate of steam introduced into the diffusion furnace is 500 sccm, and the introduction time is 900 seconds.
[0068] The small volumetric flow rate of water vapor hinders its diffusion to various locations within the diffusion furnace, making it difficult to ensure effective cleaning of silicon wafers at different locations within the furnace. In this embodiment, nitrogen gas is also introduced into the diffusion furnace along with water vapor; that is, water vapor is introduced into the diffusion furnace by introducing a mixture of nitrogen and water vapor.
[0069] Nitrogen, as the carrier gas for water vapor, needs to have a relatively large volumetric flow rate. Specifically, the volumetric flow rate of nitrogen should be greater than that of water vapor to facilitate the uniform diffusion of water vapor to various locations within the diffusion furnace.
[0070] In step 160, the volumetric flow rate of nitrogen introduced into the diffusion furnace is controlled at 2000-20000 sccm. Specifically, the volumetric flow rate of nitrogen can be 5000 sccm.
[0071] The aforementioned water vapor can be obtained by heating liquid water at high temperature or by using an ignition device to react hydrogen and oxygen.
[0072] Specifically, a steam delivery pipe can be connected to the diffusion furnace.
[0073] For methods that obtain steam by heating liquid water, a container can be connected to the inlet end of a steam delivery pipe. Liquid water is added to the container, and the steam delivery pipe extends above the liquid surface in the container. A nitrogen delivery pipe is also connected to the container, extending below the liquid surface inside the container. The liquid water in the container is heated to approximately 90 degrees Celsius by a heater. Nitrogen gas is then delivered through the nitrogen delivery pipe. The nitrogen gas carries the steam as it passes through the liquid water and enters the diffusion furnace through the steam delivery pipe.
[0074] For methods that generate water vapor by reacting hydrogen and oxygen, a reactor can be connected to the inlet end of a water vapor delivery pipe. The reactor is also externally connected to a hydrogen inlet pipe and an oxygen inlet pipe. Hydrogen and oxygen are added to the reactor through these pipes, and the hydrogen and oxygen react by ignition or heating to generate water vapor. The generated water vapor then enters a diffusion furnace through the water vapor delivery pipe.
[0075] In an alternative embodiment, water vapor generated at other locations within the plant can also be used in step 160 of the boron diffusion method provided in this embodiment.
[0076] Step 170: Increase the temperature inside the diffusion furnace and perform a secondary propulsion process.
[0077] After cleaning away the boron residue on the silicon wafer surface, while keeping the pressure inside the diffusion furnace constant, the temperature inside the diffusion furnace is increased to the temperature required for high-temperature propulsion processing, allowing the boron inside the silicon wafer to diffuse further into the silicon wafer.
[0078] The temperature inside the diffusion furnace needs to be controlled between 1000 and 1100 degrees Celsius. Specifically, the temperature inside the diffusion furnace can be raised to 1030 degrees Celsius.
[0079] During the secondary diffusion process, nitrogen and oxygen are introduced into the diffusion furnace. The secondary diffusion process is carried out in an oxygen atmosphere to increase the diffusion depth of boron into the silicon wafer, reaching the target junction depth.
[0080] The volumetric flow rate of nitrogen gas is controlled between 0 and 20,000 sccm, the volumetric flow rate of oxygen gas is controlled between 0 and 20,000 sccm, and the infusion time is controlled between 1,000 and 10,000 seconds. Specifically, the volumetric flow rate of nitrogen gas is 5,000 sccm, the volumetric flow rate of oxygen gas is 3,000 sccm, and the infusion time is 6,500 seconds.
[0081] It should be noted that after cleaning the boron residue from the silicon wafer surface, before raising the temperature inside the diffusion furnace, nitrogen gas needs to be introduced to expel water vapor and change the atmosphere within the furnace. The volumetric flow rate of nitrogen introduced into the diffusion furnace should be controlled between 2000-20000 sccm, and the introduction time should be controlled between 100-1000 seconds. Specifically, the volumetric flow rate of nitrogen introduced is 5000 sccm, and the introduction time is 500 seconds.
[0082] Step 180: Adjust the temperature and pressure inside the diffusion furnace and remove the silicon wafer from the diffusion furnace.
[0083] After the secondary propulsion process is completed, the temperature inside the diffusion furnace is lowered to 750-850 degrees Celsius, specifically 750 degrees Celsius. The pressure inside the diffusion furnace is increased to match atmospheric pressure in preparation for removing the silicon wafers from the furnace.
[0084] Specifically, the temperature inside the diffusion furnace can be lowered first, and then the pressure inside the diffusion furnace can be increased.
[0085] When lowering the temperature inside the diffusion furnace, nitrogen and oxygen can be introduced into the diffusion furnace. The volumetric flow rate of nitrogen is 10,000 sccm, the volumetric flow rate of oxygen is 3,000 sccm, and the introduction time is 2,100 seconds.
[0086] When increasing the pressure inside the diffusion furnace, nitrogen gas can be introduced into the diffusion furnace at a volumetric flow rate of 20,000 sccm for 200 seconds.
[0087] When removing the silicon wafer from the diffusion furnace, after opening the furnace door, nitrogen needs to be continuously introduced into the diffusion furnace. The volumetric flow rate of the nitrogen can be 20,000 sccm. The introduction of nitrogen can increase the pressure inside the diffusion furnace, thereby reducing the amount of air from outside entering the diffusion furnace and reducing the impact of air on the cleanliness of the inside of the diffusion furnace.
[0088] When removing the silicon wafer from the diffusion furnace, the quartz boat is taken out together with the silicon wafer to allow the silicon wafer to cool further. Then the silicon wafer is removed from the quartz boat to obtain the boron-doped silicon wafer.
[0089] This setup, by introducing excess boron trichloride and oxygen during deposition, ensures that the boron content at all locations within the diffusion furnace meets the requirements. After the first pass through the silicon wafer to deliver the required amount of boron, the wafer surface is cleaned with steam to remove excess boron. This prevents further diffusion of boron adhering to the wafer surface into the wafer during the second pass, thereby reducing the impact of excess boron trichloride on the boron content within the wafer. This avoids excessively high boron content, ensures the sheet resistance of the wafer, and solves the problem of uneven boron content distribution that exists in existing technologies when reducing boron content.
[0090] It should be noted that during the deposition process, the reaction of boron trichloride, oxygen, and silicon produces boron oxide and other byproducts, which are discharged outside the diffusion furnace in step 140. As the temperature decreases, these byproducts condense on the inner wall of the conveying pipes outside the diffusion furnace, easily leading to blockage. In this embodiment, after cleaning the silicon wafer surface with steam, the steam, after being discharged outside the diffusion furnace, reacts with the boron oxide and other byproducts as it passes through the aforementioned conveying pipes to generate boric acid, which has a low melting point, low boiling point, and is soluble in water. This alleviates the blockage problem in the conveying pipes and extends the maintenance cycle and service life of the equipment.
[0091] In this embodiment, the primary propulsion process is performed under a nitrogen atmosphere, which facilitates the rapid entry of boron into the surface layer of the silicon wafer. The secondary propulsion process is performed under a nitrogen and oxygen atmosphere, which facilitates further diffusion of boron and adjusts the diffusion distribution curve of boron in the surface layer of the silicon wafer.
[0092] In this embodiment, when adjusting the temperature and pressure inside the diffusion furnace in step 110, the diffusion furnace can first be evacuated to reduce the pressure inside the furnace to the target pressure, and then the temperature inside the diffusion furnace can be increased to the target temperature. The above evacuation process can be achieved using an evacuation pump, with the evacuation time controlled between 100 and 1000 seconds.
[0093] After the pressure inside the diffusion furnace is reduced to the target pressure, the airtightness of the diffusion furnace needs to be tested. Specifically, the air pump can be turned off and no gas should be introduced into the diffusion furnace. Observe the pressure change inside the diffusion furnace for 60 seconds. If the pressure increase inside the diffusion furnace does not exceed 2 mbar, it indicates that the airtightness of the diffusion furnace is good.
[0094] After raising the temperature of the diffusion furnace to the target temperature, nitrogen gas is introduced into the furnace to purge any air that may have entered due to the opening and closing of the furnace door. During the nitrogen introduction process, a vacuum pump can be turned on to maintain stable pressure inside the diffusion furnace. The volumetric flow rate of the introduced nitrogen should be controlled at 1000-5000 sccm, and the introduction time should be controlled at 100-1000 seconds.
[0095] In step 110, after adjusting the temperature and pressure to the target temperature and pressure, the temperature is stabilized for a certain period of time to allow the power of the heating wire in the diffusion furnace and the actual temperature inside the diffusion furnace to stabilize.
[0096] The following content, combined with data from the experimental and control groups, further illustrates the effectiveness of the boron diffusion method in the embodiments of the present invention.
[0097] Two experimental groups and one control group were set up, and boron diffusion treatment was carried out in each group.
[0098] The data for test group 1 and test group 2 were strictly carried out according to each step of the boron diffusion method provided in the embodiments of the present invention. The only difference between test group 1 and test group 2 is the time for introducing water vapor in step 160 (the volume flow rate of the introduced water vapor is the same). The time for introducing water vapor in test group 2 is 100 seconds less than the time for introducing water vapor in test group 1.
[0099] Compared to experimental groups 1 and 2, the control group reduced the volumetric flow rates of boron trichloride and oxygen in step 130 and eliminated step 160. The data in all other steps remained consistent with those of the experimental groups.
[0100] After the boron diffusion treatment was completed in experimental groups 1, 2, and the control group, the sheet resistance of each silicon wafer in each group was tested at the center, lower right, lower left, upper left, and upper right positions (corresponding to detection points 1, 2, 3, 4, and 5 below), and the following data were obtained:
[0101] The data for experimental group 1 are shown in the table below:
[0102]
[0103] The data for experimental group 2 are shown in the table below:
[0104]
[0105] The data from the control group are shown in the table below:
[0106]
[0107] Since the boron content within a silicon wafer cannot be directly measured, sheet resistance (SRP) is used as a characterization of boron content in this embodiment. SRP is inversely proportional to boron content; a higher SRP indicates less boron content in the silicon wafer, and a lower SRP indicates more boron content.
[0108] The above-mentioned average sheet resistance within the wafer refers to the average sheet resistance of each detection point on a single silicon wafer.
[0109] The above-mentioned intra-wafer sheet resistance uniformity refers to the uniformity of sheet resistance within a single silicon wafer, and the calculation formula is as follows:
[0110]
[0111] That is, the smaller the value of the sheet resistance uniformity within the chip, the better the sheet resistance uniformity within the chip.
[0112] The above average sheet resistance refers to the average of the average sheet resistance of each chip.
[0113] The above-mentioned uniformity of sheet resistance within the entire chip refers to the average value of the uniformity of sheet resistance within each chip.
[0114] The aforementioned inter-wafer sheet resistance uniformity refers to the uniformity of sheet resistance among all silicon wafers, and the calculation formula is as follows: Inter-chip sheet resistance uniformity
[0115] That is, the smaller the value of the sheet resistance uniformity between wafers, the better the sheet resistance uniformity between wafers.
[0116] By comparing and analyzing the above data, the following conclusions can be drawn:
[0117] Since excessive boron trichloride and oxygen were introduced during the deposition process in both Experimental Group 1 and Experimental Group 2, and the silicon wafers were cleaned with water vapor after one advance process, the uniformity of sheet resistance within and between wafers in Experimental Group 1 and Experimental Group 2 was good.
[0118] Since the steam passage time in test group 1 is longer than that in test group 2, the amount of boron remaining on the silicon wafer surface in test group 1 is less than that in test group 2. Therefore, the sheet resistance of test group 1 is greater than that of test group 2.
[0119] Since the boron trichloride and oxygen introduced during the deposition process in the control group were not excessive and no water vapor was introduced, the uniformity of the total sheet resistance within the control group and the uniformity of the sheet resistance between the sheets were both poor. The sheet resistance in the control group was less than that in the experimental group one, and the sheet resistance in the control group was about the same as that in the experimental group two.
[0120] In summary, the sheet resistance value, the overall uniformity within the wafers, and the uniformity of sheet resistance between wafers are all related to whether the amount of boron trichloride and oxygen introduced during the deposition process is excessive, whether water vapor is introduced after the first propulsion process, and the flow rate of the introduced water vapor. Therefore, during the boron diffusion process, the flow rate parameters of boron trichloride and oxygen introduced during the deposition process, as well as the flow rate parameters of water vapor introduced after the first propulsion process, can be adjusted according to the uniformity requirements and the required boron content.
[0121] In this embodiment, after completing the above tests, 100 silicon wafers were randomly selected from both the experimental group 2 and the control group for the standard TOPCon process (back etching - tunneling oxidation - doped amorphous silicon - annealing - decoupling - alumina - positive film - back film). Five wafers were then selected to test their implicit open-circuit voltage, followed by sintering. The implicit open-circuit voltage was then tested again, and the remaining wafers were printed. The test results are shown in the table below:
[0122]
[0123] By comparing and analyzing the above data, the following conclusions can be drawn:
[0124] The sheet resistance of experimental group 2 was similar to that of the control group, and the performance of the battery made from the silicon wafers of experimental group 2 was better than that of the battery made from the silicon wafers of the control group.
[0125] In summary, when processing boron-doped silicon wafers using the boron diffusion method described in this embodiment, it exhibits good uniformity in improving the sheet resistance of the silicon wafer and facilitates the control of parameters in subsequent processes after boron diffusion. Furthermore, it contributes to improving battery performance to a certain extent.
[0126] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims
1. A method of boron diffusion, characterized by, include: The silicon wafer is placed into the diffusion furnace, and the temperature and pressure inside the diffusion furnace are adjusted. A pre-oxidation operation is performed on the silicon wafer to form an oxide layer on the surface of the silicon wafer; Oxygen and boron sources are introduced into the diffusion furnace to perform deposition treatment; The gaseous reaction products from the deposition process, along with the remaining boron source, are discharged to the outside of the diffusion furnace. The temperature and pressure inside the diffusion furnace are increased to perform a first-pass process to diffuse the target amount of boron into the silicon wafer. The first-pass process is performed in a nitrogen atmosphere. Nitrogen and water vapor are introduced into the diffusion furnace to clean the surface of the silicon wafer, removing the boron remaining on the surface of the silicon wafer and preventing the boron adhering to the surface of the silicon wafer from further diffusing into the silicon wafer during the secondary propulsion process. The flow rate of the nitrogen is greater than the flow rate of the water vapor. The temperature inside the diffusion furnace is increased to perform the secondary propulsion process, which further diffuses boron into the silicon wafer to increase the diffusion depth of boron into the silicon wafer to the target junction depth. The secondary propulsion process is performed in an atmosphere of nitrogen and oxygen. Adjust the temperature and pressure inside the diffusion furnace, and remove the silicon wafer from the diffusion furnace.
2. The boron diffusion method according to claim 1, wherein, The volumetric flow rate of the water vapor is 100-2000 sccm.
3. The boron diffusion method according to claim 1, wherein, The boron source is boron trichloride gas, the volumetric flow rate of the boron trichloride gas is 50-1000 sccm, and the volumetric flow rate of the oxygen is 100-5000 sccm.
4. The boron diffusion method of claim 1, wherein The process of introducing oxygen and boron sources into the diffusion furnace includes: A mixture of nitrogen, oxygen, and boron source is introduced into the diffusion furnace.
5. The boron diffusion method of claim 1, wherein Nitrogen gas is continuously introduced into the diffusion furnace during the process of placing the silicon wafer into the diffusion furnace and removing the silicon wafer from the diffusion furnace.
6. The boron diffusion method of claim 1, wherein, Adjusting the temperature and pressure inside the diffusion furnace includes: The diffusion furnace is evacuated to reduce the pressure inside the furnace to the target pressure. Raise the temperature inside the diffusion furnace to the target temperature.
7. The boron diffusion method according to claim 6, wherein, After reducing the pressure inside the diffusion furnace to the target pressure, the process further includes: The airtightness of the diffusion furnace was tested.