Oxidation treatment method and solar cell

Abstract

The present application relates to the field of photovoltaic technology, and in particular to an oxidation treatment method and a solar cell, wherein the oxidation treatment method comprises the following steps: placing a silicon wafer to be oxidized in an oxidation furnace, wherein the silicon wafer to be oxidized comprises a base layer and an emitter region disposed on the surface of the base layer; performing a primary oxidation treatment on the surface of the emitter region using oxygen that has passed through a pure water bath during the heating stage of the oxidation furnace; performing a secondary oxidation treatment on the surface of the emitter region using oxygen that has passed through a pure water bath during the constant temperature stage of the oxidation furnace; performing a tertiary oxidation treatment on the surface of the emitter region using dry oxygen during the cooling stage of the oxidation furnace, and an oxide layer is formed on the surface of the emitter region. The oxidation treatment method provided by the present application reduces the cleaning times of the oxidation furnace and the diaphragm pump while ensuring the life of the silicon wafer, thereby improving the oxidation efficiency.

Description

Technical Field

[0001] The present application relates to the field of photovoltaic technology, and in particular to an oxidation treatment method and a solar cell. Background Art

[0002] TOPCon (Tunnel Oxide Passivated Contact) cells are a new type of high-efficiency solar photovoltaic cells. They are compatible with PERC solar cell production lines during production and have become a new generation of mainstream solar cell technology. When the front of the TOPCon cell uses boron as a doping element to form a local high-doped emitter, the boron diffusion process may cause some damage to the silicon wafer surface, such as dangling bonds and defects. These surface states will cause electron-hole pairs to recombine on the surface, reducing the open circuit voltage and efficiency of the cell. Therefore, oxidation treatment is required to grow a thin oxide layer, which can effectively capture and neutralize dangling bonds and defects on the surface, reduce surface states, and thus reduce the surface recombination rate.

[0003] However, in the process of forming an oxide layer in the prior art, after the oxidation furnace and the diaphragm pump have been working for a long time for oxidation, the precipitated boron element reacts with oxygen to produce boron oxide and diffuses into the diaphragm pump and the tail gas pipe connected to the diaphragm pump, causing a large amount of boron oxide particles to be deposited in the diaphragm pump and the tail gas pipe, thereby reducing the working efficiency and service life of the diaphragm pump and the tail gas pipe. Therefore, the diaphragm pump needs to be cleaned and maintained regularly, but the cleaning process requires the oxidation process to be suspended, which takes a long time, resulting in low overall oxidation efficiency of the silicon wafer. Summary of the invention

[0004] In view of this, the present application provides an oxidation treatment method and a solar cell, which can reduce the cleaning times of the oxidation furnace and the diaphragm pump and improve the oxidation efficiency while ensuring the life of the silicon wafer and the oxidation quality.

[0005] In a first aspect, the present application provides an oxidation treatment method, the oxidation treatment method comprising the following steps:

[0006] Placing a silicon wafer to be oxidized in an oxidation furnace, wherein the silicon wafer to be oxidized comprises a base layer and an emitter region disposed on a surface of the base layer;

[0007] During the heating stage of the oxidation furnace, the surface of the emitter region is subjected to an oxidation treatment using oxygen that has passed through a pure water bath;

[0008] In the constant temperature stage of the oxidation furnace, the surface of the emitter region is subjected to secondary oxidation treatment using oxygen that has passed through a pure water bath;

[0009] During the cooling stage of the oxidation furnace, the surface of the emitter region is subjected to a three-time oxidation treatment using dry oxygen, and an oxide layer is formed on the surface of the emitter region.

[0010] In some embodiments, the temperature rising stage, the constant temperature stage and the temperature falling stage are performed under normal pressure, wherein the pressure of the normal pressure environment is 800 mbar to 1000 mbar.

[0011] In some embodiments, the temperature of the pure water bath is 30°C to 70°C.

[0012] In some embodiments, the oxygen flow rate of the primary oxidation treatment is 1000 sccm to 15000 sccm.

[0013] In some embodiments, the time of the primary oxidation treatment is 3 min to 10 min.

[0014] In some embodiments, the oxygen flow rate of the secondary oxidation treatment is 1000 sccm to 20000 sccm, and / or the time of the secondary oxidation treatment is 10 min to 60 min.

[0015] In some embodiments, the oxygen flow rate of the three oxidation treatments is 5000 sccm to 15000 sccm.

[0016] In some embodiments, the three oxidation treatments are performed for 20 min to 40 min.

[0017] In some embodiments, the temperature of the temperature rising stage is 750°C to 1060°C, the temperature of the constant temperature stage is 1000°C to 1060°C, and the temperature of the temperature falling stage is 800°C to 1060°C.

[0018] In a second aspect, the present application provides a solar cell, wherein the solar cell comprises an oxide layer, and the oxide layer is prepared by the oxidation treatment method according to any one of claims 1 to 10.

[0019] After adopting the technical solution of this application, at least the following beneficial effects are achieved:

[0020] The oxidation treatment method provided by the present application uses oxygen to bring water vapor into the water bath during the heating stage and the constant temperature stage. The water vapor provides a more uniform and stable temperature environment, so that the oxidation reaction can be carried out simultaneously on the entire emitter region surface, thereby accelerating the overall oxidation speed, and the required oxide layer thickness and oxidation efficiency can be obtained more quickly; and the oxidation time of the silicon wafer at high temperature is reduced, the damage to the silicon wafer caused by high temperature is reduced, and the minority carrier life is improved; at the same time, the water vapor can clean the furnace tube and diaphragm pump of the oxidation furnace, take away impurities in the furnace, reduce the impact of impurities in the furnace on the silicon wafer to be oxidized, improve the oxidation quality, and reduce the maintenance times of the oxidation furnace and the diaphragm pump, and increase the service life of both. Furthermore, the use of dry oxygen oxidation in the subsequent cooling stage can improve the oxidation defects caused by wet oxygen oxidation in the heating stage and the constant temperature stage, and thus obtain a higher quality oxide layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A schematic diagram of the structure of a TOPCon battery using an oxidation treatment method provided in this application;

[0022] Figure 2 This is a flow chart of the oxidation treatment method provided in this application.

[0023] Figure ID:

[0024] 1. Crystalline silicon substrate; 2-first emitter region; 3. first passivation layer; 4. first metal electrode; 5. second emitter region; 6. second tunneling dielectric layer; 7. second doping layer; 8. second passivation layer; 9. second metal electrode. DETAILED DESCRIPTION

[0025] In order to better understand the technical solution of the present application, the embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0026] It should be clear that the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0027] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "said" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

[0028] It should be understood that the term "and / or" used in this article is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0029] It should be noted that the directional words such as "upper", "lower", "left", and "right" described in the embodiments of the present application are described at the angles shown in the accompanying drawings and should not be understood as limiting the embodiments of the present application. In addition, in the context, it is also necessary to understand that when it is mentioned that an element is connected to another element "upper" or "lower", it can not only be directly connected to another element "upper" or "lower", but also indirectly connected to another element "upper" or "lower" through an intermediate element.

[0030] TOPCon (Tunnel Oxide Passivated Contact) cells are a new type of high-efficiency solar photovoltaic cells. They are compatible with PERC solar cell production lines during production and have become a new generation of mainstream solar cell technology. Figure 1 The TOPCon cell includes a crystalline silicon substrate 1, which is an N-type single crystal silicon substrate. Electrons are majority carriers, while holes are minority carriers. The single crystal silicon substrate has the characteristics of orderly internal atomic arrangement and continuous and defect-free crystal structure, which can reduce the scattering of electrons and holes during movement and improve the mobility of carriers, thereby improving the photoelectric conversion efficiency of the TOPCon cell.

[0031] The front side of the crystalline silicon substrate 1 usually includes the following layers: a first emitter region, which forms a local high-doped P+ region through boron diffusion or other doping processes, a first passivation layer 3, which is used to increase light absorption and provide a good carrier transmission channel; a first metal electrode 4, which is formed by depositing metal materials (such as silver or aluminum paste) on the first passivation layer 3 using screen printing, laser ablation and other technologies. The first metal electrode 4 is in contact with the emitter and can lead the current generated from the crystalline silicon substrate 11 to the external circuit. It can be understood that the front structure of the TOPCon battery is composed of the first emitter region 2, the first passivation layer 3 and the first metal electrode 4, and the morphology of the front structure is a pyramid velvet structure, which has certain morphological characteristics, thereby reducing reflection losses.

[0032] The back side of the crystalline silicon substrate 11 is sequentially stacked with a second emitter region 5, a second tunnel dielectric layer 6, a second doped layer 7, a second passivation layer 8 and a second metal electrode 9, wherein the second metal electrode 9 is disposed on the second doped layer 7 and at least partially exposed outside the second passivation layer 8. It can be understood that the back side structure of the TOPCon cell is formed by the structure of the second emitter region 5, the second tunnel dielectric layer 6, the second doped layer 7, the second passivation layer 8 and the second metal electrode 9, and the morphology of the back side structure is a polished surface or an etched surface structure.

[0033] When the front side of the TOPCon battery uses boron as a doping element to form a local high-doped emitter, the boron diffusion process may cause some damage to the silicon wafer surface, such as dangling bonds, defects, etc. These surface states will cause electron-hole pairs to recombine on the surface, reducing the open circuit voltage and efficiency of the battery. Therefore, it is necessary to perform oxidation treatment to grow a thin layer of silicon oxide layer, which can effectively capture and neutralize the dangling bonds and defects on the surface, reduce surface states, and thus reduce the surface recombination rate. However, in the process of forming a silicon oxide layer in the prior art, after the oxidation furnace and the diaphragm pump perform long-term oxidation work, the precipitated boron element reacts with oxygen to produce boron oxide and diffuses into the diaphragm pump and the tail gas pipe connected to the diaphragm pump, so that the diaphragm pump and the tail gas pipe are deposited with a large amount of boron oxide particles, which reduces the working efficiency and service life of the diaphragm pump and the tail gas pipe. Therefore, the diaphragm pump needs to be cleaned and maintained regularly, but the cleaning process requires the oxidation process to be suspended, which takes a long time, resulting in low overall oxidation efficiency of the silicon wafer.

[0034] In view of this, the present application provides an oxidation treatment method, please refer to Figure 2 , the oxidation treatment method comprises the following steps:

[0035] Step S10, placing a silicon wafer to be oxidized in an oxidation furnace, wherein the silicon wafer to be oxidized comprises a base layer and an emitter region disposed on a surface of the base layer;

[0036] Step S20, during the temperature rise phase of the oxidation furnace, the surface of the emitter region is subjected to an oxidation treatment using oxygen that has passed through a pure water bath;

[0037] Step S30, performing secondary oxidation treatment on the surface of the emitter region using oxygen that has passed through a pure water bath during the constant temperature stage of the oxidation furnace;

[0038] Step S40, in the cooling stage of the oxidation furnace, the surface of the emitter region is subjected to a three-time oxidation treatment using dry oxygen to form an oxide layer on the surface of the emitter region.

[0039] In the above scheme, the oxidation treatment method provided by the present application uses oxygen to bring water vapor into the water bath during the heating stage and the constant temperature stage. The water vapor provides a more uniform and stable temperature environment, so that the oxidation reaction can be carried out simultaneously on the entire emitter region surface, thereby accelerating the overall oxidation rate, and the required oxide layer thickness and oxidation efficiency can be obtained more quickly; and the oxidation time of the silicon wafer at high temperature is reduced, the damage to the silicon wafer caused by high temperature is reduced, and the minority carrier life is improved; at the same time, water vapor can clean the furnace tube and diaphragm pump of the oxidation furnace, take away impurities in the furnace, reduce the impact of impurities in the furnace on the silicon wafer to be oxidized, improve the oxidation quality, and reduce the maintenance times of the oxidation furnace and diaphragm pump, and increase the service life of both. Furthermore, the use of dry oxygen oxidation in the subsequent cooling stage can improve the oxidation defects caused by wet oxygen oxidation in the heating stage and the constant temperature stage, and thus obtain a higher quality oxide layer.

[0040] The preparation method of the present application is specifically explained below in conjunction with the examples:

[0041] Step S10, placing a silicon wafer to be oxidized in an oxidation furnace, wherein the silicon wafer to be oxidized comprises a base layer and an emitter region disposed on a surface of the base layer;

[0042] The preparation process of the silicon wafer to be oxidized includes: single crystal silicon wafer preparation, texturing, boron diffusion, laser SE, and cleaning.

[0043] In some embodiments, the preparation of single crystal silicon wafers includes purification of polycrystalline silicon raw materials, growth of single crystal silicon rods, silicon rod cutting, edge trimming and chamfering, surface grinding and polishing, cleaning and testing.

[0044] Polysilicon raw material purification and single crystal silicon rod growth refer to placing polysilicon raw materials into a quartz crucible, melting the polysilicon raw materials using a heater in a single crystal furnace, and then inserting a seed crystal fixed on the seed crystal shaft of a lifting device into the surface of the melt. After the seed crystal and the melt are fully melted, the lifting device slowly pulls the seed crystal upward, and the crystal grows at the lower end of the seed crystal, thereby obtaining a single crystal silicon rod.

[0045] Silicon rod cutting refers to fixing the cooled silicon rod on the cutting equipment. The wire pitch of the cutting equipment rotates at high speed and passes through the single crystal silicon rod immersed in the cutting fluid. The abrasive on the wire saw is used to grind the single crystal silicon rod so that the single crystal silicon wafer is cut along the predetermined path. During the cutting process, the wire saw speed, pressure and cutting fluid flow rate must be strictly controlled to ensure the thickness accuracy and flatness of the single crystal silicon wafer and reduce cracks and micro defects caused by cutting.

[0046] Edge cutting and chamfering are due to the irregular edges of the cut monocrystalline silicon wafers. Therefore, the monocrystalline silicon wafers are finely processed by precision cutting equipment, such as laser or mechanical cutting tools, to remove the burrs and bad parts around the monocrystalline silicon wafers, so that the edges around the monocrystalline silicon wafers become flat and accurate in size to ensure the yield and device performance of subsequent processes. Chamfering refers to the bevel treatment of the four corners of the monocrystalline silicon wafer, which changes the original sharp right angles into bevels with a certain angle, so as to reduce the stress concentration caused by collisions during the subsequent cleaning, transmission, packaging and other processes of the silicon wafers, thereby reducing the possibility of breakage of the monocrystalline silicon wafers.

[0047] Surface grinding in surface grinding and polishing is due to the saw marks and unevenness on the front and back surfaces of the single crystal silicon wafer after cutting. Therefore, it is necessary to gradually reduce the thickness of the single crystal silicon wafer and improve its surface flatness through mechanical action. It is usually divided into two stages: coarse grinding and fine grinding. Coarse grinding is mainly used to quickly improve the surface flatness, while fine grinding is used to further improve the surface quality so that the front and back surfaces of the single crystal silicon wafer can meet the required accuracy requirements. Polishing is the process of more refined processing of the front and back surfaces of the single crystal silicon wafer by chemical mechanical polishing and other methods after surface grinding. The purpose is to eliminate the tiny scratches and defects caused by grinding, reduce the surface roughness to the nanometer level, reduce the surface state density, reduce the amount of electrons and holes bound, and then reduce the recombination of electrons and holes, thereby improving the photoelectric conversion efficiency of the single crystal silicon wafer as a solar cell.

[0048] Cleaning in cleaning and testing is to use cleaning agents to remove cutting residues, particulate contaminants, organic matter and other impurities on the surface of the single crystal silicon wafer to ensure the cleanliness of the surface of the single crystal silicon wafer. Testing refers to the use of microscopic equipment to observe the microstructure of the silicon wafer surface to check for scratches, pits, particulate contaminants and other defects to obtain single crystal silicon wafers that meet quality standards.

[0049] After the above steps of polysilicon raw material purification, single crystal silicon rod growth, silicon rod cutting, edge trimming and chamfering, surface grinding and polishing, cleaning and testing, single crystal silicon wafers that meet production needs can be obtained for the subsequent production process of silicon wafers to be oxidized.

[0050] In some embodiments, a texturing process is performed on a single crystal silicon wafer to obtain a base layer with a pyramid structure. The specific texturing steps are: immerse the single crystal silicon wafer in a mixed solution of hydrofluoric acid (HF) and other acids, and use silicon to react with HF to generate gaseous silicon tetrafluoride (SiF4). At the same time, due to the different reaction rates of different crystal faces of silicon, a base layer with a microscopic pyramid structure with a specific directionality is formed. It can be understood that after the microscopic pyramid structure is formed, the reflection of sunlight on the surface of the silicon wafer can be reduced, and the absorption rate of sunlight on the surface of the silicon wafer can be increased, thereby improving the photoelectric conversion efficiency.

[0051] Furthermore, the texturing process also includes a doping process, that is, doping phosphorus elements in the single crystal silicon wafer. After the phosphorus elements replace the positions of silicon atoms in the silicon lattice, they can provide excess electrons, so that the single crystal silicon wafer forms an N-type silicon substrate.

[0052] In some embodiments, boron laser SE refers to forming a local high-concentration boron-doped region on the front side of an N-type silicon substrate by boron diffusion or other doping techniques to create a P+ region, wherein the P+ region has a high concentration of trivalent boron atoms, which can accept electrons from the silicon lattice and leave holes as majority carriers, thereby improving the effective collection of photogenerated carriers.

[0053] After the preparation of the oxidized silicon wafers is completed, the oxidized silicon wafers enter the oxidation furnace, which is the boat entry process. That is, the boat containing the silicon wafers to be processed is sent into the oxidation furnace with pre-set temperature and atmosphere conditions. The temperature set when entering the boat is 750℃~850℃, the time is 400s~1200s, the pressure is 1060 mbar, and it is carried out under a nitrogen atmosphere. Furthermore, after the oxidized silicon wafers enter the oxidation furnace, the sealing of the oxidation furnace is tested by pressure extraction / leakage detection to ensure that the oxidation furnace will not cause a decrease in oxidation efficiency due to oxygen leakage during the subsequent oxidation process.

[0054] Step S20, during the temperature rising stage of the oxidation furnace, an oxidation treatment is performed on the surface of the cleaned emitter region using oxygen that has passed through a pure water bath.

[0055] The pure water used in step S20 is also called deionized water, ultrapure water or high-purity water, which removes all mineral ions, organic matter, microorganisms, particulate matter and other dissolved or suspended impurities in the water, that is, water that is almost completely free of impurities. It can be understood that after the oxygen is bathed in the above-mentioned pure water, the oxygen containing water vapor will not carry other impurities into the oxidation furnace or diaphragm pump, which can reduce the impact of impurities on the oxidation of silicon wafers and improve the oxidation quality.

[0056] A water bath is a process of passing oxygen into a container (such as a sink or thermostat) filled with pure water, and adjusting the temperature of the water to provide or maintain a constant temperature environment. Since water has good heat transfer properties, a water bath can provide a uniform and stable temperature environment for oxygen. At the same time, pure water evaporates when oxygen flows through it, so that oxygen is transported along with water vapor. It can be understood that by using oxygen to bring water vapor into the water bath, water vapor provides a more uniform and stable temperature environment, so that the oxidation reaction can proceed simultaneously on the entire emitter region surface, thereby accelerating the overall oxidation rate, and the desired oxide layer thickness and oxidation efficiency can be obtained more quickly; and the oxidation time of the silicon wafer at high temperature is reduced, the damage to the silicon wafer caused by high temperature is reduced, and the minority carrier lifetime is increased.

[0057] The temperature of the pure water bath is 30°C to 70°C. Optionally, the temperature of the pure water bath can be 30°C, 40°C, 50°C, 60°C, 70°C, etc., or other values ​​within the range. It can be selected according to actual needs and is not limited here. It can be understood that the temperature of the pure water bath within the above range can gently and evenly promote the oxidation reaction and improve the oxidation quality.

[0058] The oxygen flow rate of the primary oxidation treatment is 1000sccm~15000sccm. Optionally, the oxygen flow rate of the primary oxidation treatment can be 1000sccm, 3000sccm, 5000sccm, 7000sccm, 9000sccm, 11000sccm, 13000sccm and 15000sccm, etc., or other values ​​within the range. It can be selected according to actual needs and is not limited here. It can be understood that the oxygen flow rate of the primary oxidation treatment is within the above range, while ensuring the thickness of the oxide layer, the obtained oxide layer has low defect density and good chemical stability.

[0059] The time of the primary oxidation treatment is 3min~10min, and the time of the primary oxidation treatment can be 3min, 4min, 5min, 6min, 7min, 8min, 9min, 10min, etc., or other values ​​within the range, which can be selected according to actual needs and are not limited here. It can be understood that when the time of the primary oxidation treatment is within the above range, the thickness of the obtained oxide layer is moderate, and the defects of the oxide layer, the interface recombination center or the inhomogeneity of the oxide layer caused by long-term oxidation are reduced.

[0060] Step S30, during the constant temperature stage of the oxidation furnace, the surface of the emitter region is subjected to secondary oxidation treatment using oxygen that has passed through a pure water bath.

[0061] In step S30, the oxygen flow rate of the secondary oxidation treatment is 1000sccm~20000sccm. Optionally, the oxygen flow rate of the secondary oxidation treatment can be 1000sccm, 3000sccm, 5000sccm, 7000sccm, 9000sccm, 11000sccm, 13000sccm and 15000sccm, etc., or other values ​​within the range, which can be selected according to actual needs and are not limited here. It can be understood that the oxygen flow rate of the secondary oxidation treatment is within the above range, while ensuring the thickness of the oxide layer, the obtained oxide layer has low defect density and good chemical stability.

[0062] The time of the secondary oxidation treatment is 10min~60min, and the time of the secondary oxidation treatment can be 10min, 20min, 30min, 40min, 50min and 60min, etc., or other values ​​within the range, which can be selected according to actual needs and are not limited here. It can be understood that when the time of the secondary oxidation treatment is within the above range, the thickness of the obtained oxide layer is moderate, and the defects of the oxide layer, the interface recombination center or the inhomogeneity of the oxide layer caused by long-term oxidation are reduced.

[0063] The oxidation method used in the primary oxidation treatment and the secondary oxidation treatment in this application is wet oxidation, which has a high oxidation rate and can form a thicker oxide layer in a shorter time, thereby improving the oxidation efficiency. In addition, the water vapor used in the wet oxidation process has a high reactivity, which can reduce the oxidation temperature and alleviate the thermal stress on the silicon wafer.

[0064] However, impurities or defects may be introduced into the oxide layer generated by wet oxidation, which may lead to uneven thickness and quality of the oxide layer, affecting the quality and performance of the oxide layer. Therefore, a dry oxidation process in step S40 is required.

[0065] Step S40, in the cooling stage of the oxidation furnace, the surface of the emitter region is subjected to a three-time oxidation treatment using dry oxygen to form an oxide layer on the surface of the emitter region.

[0066] In the present application, the oxidation environment of dry oxidation is relatively easier to control, and thus the thickness and uniformity of the quality of the formed oxide layer can be improved by dry oxidation, thereby improving the quality of the oxide layer.

[0067] In step S40, the oxygen feeding amount of the three oxidation treatments is 5000sccm~15000sccm. Optionally, the oxygen feeding amount of the three oxidation treatments can be 5000sccm, 7000sccm, 9000sccm, 11000sccm, 13000sccm and 15000sccm, etc., or other values ​​within the range, which can be selected according to actual needs and are not limited here. It can be understood that the oxygen feeding amount of the three oxidation treatments is within the above range. While ensuring the thickness of the oxide layer, it can better improve the oxidation defects caused by wet oxygen oxidation in the heating stage and the constant temperature stage, thereby obtaining an oxide layer of higher quality.

[0068] The time of the three oxidation treatments is 10min~60min, and the time of the three oxidation treatments can be 10min, 20min, 30min, 40min, 50min and 60min, etc., or other values ​​within the range, which can be selected according to actual needs and are not limited here. It can be understood that when the time of the three oxidation treatments is within the above range, the thickness of the obtained oxide layer is moderate, and the oxidation defects caused by wet oxygen oxidation in the heating stage and the constant temperature stage are better improved, thereby obtaining an oxide layer of higher quality.

[0069] In some embodiments, the temperature rise stage, the constant temperature stage and the temperature drop stage are carried out under normal pressure, that is, the pressure in the oxidation furnace is returned to normal pressure after the pressure is pumped out; wherein, the pressure of the normal pressure environment is 800mbar~1000mbar, and optionally, the pressure of the normal pressure environment can be 800mbar, 820mbar, 840mbar, 860mbar, 880mbar, 900mbar, 920mbar, 940mbar, 960mbar, 980mbar and 1000mbar, etc., or other values ​​within the range, which can be selected according to actual needs and are not limited here. It can be understood that carrying out the oxidation process under normal pressure can better protect the oxidation furnace and the diaphragm pump and extend the service life of the oxidation furnace and the diaphragm pump.

[0070] It should be noted that the temperature in the heating stage of the present application is 750℃~1060℃, the temperature in the constant temperature stage is 1000℃~1060℃, and the temperature in the cooling stage is 800℃~1060℃. Optionally, the temperature in the heating stage can be specifically 750℃, 800℃, 850℃, 900℃, 950℃, 1000℃ and 1060℃, etc., the temperature in the constant temperature stage can be specifically 1000℃, 1010℃, 1020℃, 1030℃, 1040℃, 1050℃ and 1060℃, etc., the temperature in the cooling stage can be specifically 800℃, 850℃, 900℃, 950℃, 1000℃ and 1060℃, etc., or other values ​​within the range can be used. It can be selected according to actual needs and is not limited here.

[0071] In some embodiments, after the three oxidation processes are completed, a clean, inert or specific gas may be used to purge the oxidation furnace, the purge time is 60s to 300s, the purge temperature is 750°C to 900°C, the purge pressure is 800 mbar to 1060 mbar, and the process is performed under a nitrogen atmosphere of 1000sccm to 10000sccm. It is understandable that the purge process can ensure that the internal environment of the oxidation furnace is pure and pollution-free, which is convenient for the next oxidation process.

[0072] In some embodiments, after the purging is completed, the boat containing the oxidized silicon wafers can be sent out of the oxidation furnace, and the temperature set when leaving the boat is 750℃~900℃, the time is 400s~1200s, the pressure is 1060mbar, and it is carried out under a nitrogen atmosphere of 1000sccm~5000sccm. It can be understood that the process parameters of leaving the boat are within the above range, which can avoid deformation, cracking and other problems caused by excessive thermal stress during the rapid cooling process of the silicon wafer; at the same time, it ensures that the microstructure and component distribution formed in the process are stably preserved, such as the distribution of dopants in the silicon wafer.

[0073] Through the above steps S10 to S40, an oxide layer of desired thickness and high quality can be quickly obtained, reducing the damage of high temperature to the silicon wafer and increasing the minority carrier lifetime; at the same time, the maintenance times of the oxidation furnace and the diaphragm pump are reduced, and the oxidation efficiency is improved.

[0074] The following is a further description of the embodiments of the present invention in multiple embodiments. The embodiments of the present invention are not limited to the following specific embodiments. They can be appropriately modified within the scope of the unchanged main rights.

[0075] Example 1

[0076] (1) A boat containing a silicon wafer to be processed is placed into an oxidation furnace, wherein the temperature when entering the boat is set to 800°C, the time is 600 seconds, the pressure is 1060 mbar, and the process is carried out under a nitrogen atmosphere. The silicon wafer to be oxidized includes a base layer and an emitter region disposed on the surface of the base layer.

[0077] (2) The surface of the emitter region is oxidized using oxygen in a pure water bath at a pressure of 900 mbar and a temperature of 1040°C, wherein the oxygen flow rate into the water bath is 8000 sccm, the flow time is 6.5 min, and the temperature of the water bath is 50°C.

[0078] (3) The surface of the emitter region is subjected to secondary oxidation treatment using oxygen passed through a pure water bath at a pressure of 900 mbar and a temperature of 1040°C; the oxygen flow rate into the water bath is 11000 sccm, the flow time is 35 min, and the temperature of the water bath is 50°C.

[0079] (4) The surface of the emitter region is subjected to a three-time oxidation treatment using dry oxygen at a pressure of 900 mbar and a temperature of 900°C, thereby forming an oxide layer on the surface of the emitter region; wherein the amount of dry oxygen introduced is 10,000 sccm, the introduction time is 30 min, and the temperature of the water bath is 50°C.

[0080] (5) The oxidation furnace was purged with nitrogen gas at a flow rate of 5000 sccm, wherein the purging time was 200 s, the purging temperature was 800° C., and the purging pressure was 1060 mbar.

[0081] (6) The boat containing the oxidized silicon wafers is sent out of the oxidation furnace. The temperature set when leaving the boat is 800° C., the time is 600 s, the pressure is 1060 mbar, and the process is carried out in a nitrogen atmosphere of 3000 sccm.

[0082] Example 2

[0083] The difference from Example 1 is that in step (2), the amount of oxygen introduced into the water bath is 15,000 sccm, and the introduction time is 10 min. In step (3), the amount of oxygen introduced into the water bath is 20,000 sccm, and the introduction time is 60 min.

[0084] Example 3

[0085] Different from Example 1, the amount of dry oxygen introduced in step (4) is 5000 sccm and the introduction time is 20 minutes.

[0086] Example 4

[0087] Different from Example 1, the amount of dry oxygen introduced in step (4) is 15000 sccm and the introduction time is 40 minutes.

[0088] Example 5

[0089] Different from Example 1, steps (2), (3), and (4) are carried out at a pressure of 900 mbar.

[0090] Example 6

[0091] Different from Example 1, steps (2), (3), and (4) are carried out at a pressure of 1000 mbar.

[0092] Comparative Example 1

[0093] Different from Example 1, step (4) uses water bath oxygen for oxidation process.

[0094] Comparative Example 2

[0095] Different from Example 1, steps (2) and (3) both use dry oxygen for the oxidation process.

[0096] test:

[0097] (1) Lifetime test: Sinton WCT-120 test instrument is used in transient analysis mode. This instrument can measure the lifetime of semi-finished products. Five pieces are evenly drawn from each group of samples. The lifetime of the four corners and the middle area of ​​each piece is tested. The final average is the average minority carrier lifetime of each group of samples.

[0098] (2) Observe the amount of impurities attached to the diaphragm pump at regular intervals, and clean it when it reaches a certain thickness. The time interval between the cleaning time and the start of the oxidation process is the diaphragm pump cleaning cycle.

[0099] Table 1

[0100]

[0101] Test result analysis:

[0102] It can be seen from the test results of Examples 1 to 6 that the oxidation treatment method provided by the present application uses oxygen to bring water vapor into the water bath during the heating stage and the constant temperature stage. The water vapor provides a more uniform and stable temperature environment, so that the oxidation reaction can be carried out simultaneously on the surface of the entire emitter region, thereby accelerating the overall oxidation rate, and the required oxide layer thickness can be obtained more quickly, and the oxidation efficiency is high; and the oxidation time of the silicon wafer at high temperature is reduced, the damage to the silicon wafer caused by high temperature is reduced, and the minority carrier life is improved; at the same time, water vapor can clean the furnace tube and diaphragm pump of the oxidation furnace, take away impurities in the furnace, reduce the impact of impurities in the furnace on the silicon wafer to be oxidized, improve the oxidation quality, and reduce the maintenance times of the oxidation furnace and the diaphragm pump, and increase the service life of both. Furthermore, the use of dry oxygen oxidation in the subsequent cooling stage can improve the oxidation defects caused by wet oxygen oxidation in the heating stage and the constant temperature stage, and thus obtain a higher quality oxide layer.

[0103] According to the test results of Example 1 and Comparative Example 1, the three oxidation processes in Comparative Example 1 are all wet oxidations, which can achieve a good cleaning effect on the diaphragm pump, but the defect of pure wet oxidation will cause a slight decrease in the carrier lifetime.

[0104] According to the test results of Example 1 and Comparative Example 2, the three oxidation processes in Comparative Example 1 are all dry oxidations, and the oxidation time is long. The long-term high temperature causes the carrier lifetime to be reduced, and the diaphragm pump cannot be cleaned during the oxidation process. The diaphragm pump cleaning cycle is short, that is, the number of cleaning times is increased.

[0105] The above describes in detail the structure, features and effects of the present invention based on the embodiments shown in the drawings. The above is only a preferred embodiment of the present invention, but the present invention is not limited to the scope of implementation shown in the drawings. Any changes made according to the concept of the present invention, or modifications to equivalent embodiments with equivalent changes, which still do not exceed the spirit covered by the description and drawings, should be within the protection scope of the present invention.

Claims

1. An oxidation treatment method, characterized in that: The oxidation treatment method comprises the following steps: Placing a silicon wafer to be oxidized in an oxidation furnace, wherein the silicon wafer to be oxidized comprises a base layer and an emitter region disposed on a surface of the base layer; In the heating stage of the oxidation furnace, the surface of the emitter region is subjected to a primary oxidation treatment using oxygen that has passed through a pure water bath, wherein pure water evaporates when oxygen flows through, so that oxygen carries water vapor to the emitter region together, the temperature of the pure water bath is 30° C. to 70° C., and the primary oxidation treatment lasts for 3 min to 10 min; In the constant temperature stage of the oxidation furnace, the surface of the emitter region is subjected to secondary oxidation treatment using oxygen that has passed through a pure water bath, and the time of the secondary oxidation treatment is 10 minutes to 60 minutes; The water vapor cleans the furnace tube and the diaphragm pump of the oxidation furnace; In the cooling stage of the oxidation furnace, the surface of the emitter region is subjected to a three-time oxidation treatment using dry oxygen to form an oxide layer on the surface of the emitter region. The time for the three-time oxidation treatment is 20 minutes to 40 minutes.

2. The oxidation treatment method according to claim 1, characterized in that: The temperature rising stage, the constant temperature stage and the temperature falling stage are carried out under normal pressure environment, wherein the pressure of the normal pressure environment is 800mbar~1000mbar.

3. The oxidation treatment method according to claim 1, characterized in that: The oxygen flow rate of the primary oxidation treatment is 1000 sccm to 15000 sccm.

4. The oxidation treatment method according to claim 1, characterized in that: The oxygen flow rate of the secondary oxidation treatment is 1000 sccm to 20000 sccm.

5. The oxidation treatment method according to claim 1, characterized in that: The oxygen flow rate of the three oxidation treatments is 5000 sccm to 15000 sccm.

6. The oxidation treatment method according to claim 1, characterized in that: The temperature in the heating stage is 750°C to 1060°C, the temperature in the constant temperature stage is 1000°C to 1060°C, and the temperature in the cooling stage is 800°C to 1060°C.

7. A solar cell, characterized in that: The solar cell comprises an oxide layer, and the oxide layer is prepared by the oxidation treatment method according to any one of claims 1 to 6.

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