A topcon cell masking method

Abstract

A TOPCon cell mask method, comprising: using an SE process to laser dope a silicon wafer; forming an oxidation layer mask in an oxidation furnace; spraying a boric acid solution with a mass concentration of 0.01%-1% on the laser doped surface of the silicon wafer; after the boric acid solution on the surface of the silicon wafer is dried, introducing oxygen into the oxidation furnace at high temperature; before the oxygen enters the oxidation furnace, water bath cooling is performed on the oxygen in a low-temperature pure water bottle, so that the oxygen carries water vapor into the oxidation furnace; under the action of the reaction, a silicon dioxide layer is formed on the surface of the silicon wafer, and an oxidation layer mask is formed in the laser doped area; and the process of spraying boric acid and introducing oxygen carrying water vapor into the oxidation furnace greatly increases the growth speed of the mask silicon dioxide.

Description

Technical Field

[0001] This invention belongs to the field of solar cell technology, and specifically relates to a masking method for alkaline polishing of N-type crystal TOPCon cells. Background Technology

[0002] Currently, N-type TOPCon cells have become an important cell technology in the photovoltaic field, boasting advantages such as high conversion efficiency, high bifaciality, low temperature coefficient, low degradation, and low cost. TOPCon cells are an upgraded product based on PERC cell technology and offer greater compatibility with production lines.

[0003] SE process is an important process for PERC cells. Through SE laser doping, the grid line part of the crystalline silicon cell is laser doped, which allows phosphorus atoms in the N+ layer formed by diffusion in the PERC cell to be doped into the silicon substrate under laser energy. This reduces the contact resistance between the metal grid line part and the silicon wafer, thereby improving efficiency.

[0004] However, in current N-type TOPCon cells, boron diffusion is used to form borosilicate glass on the silicon wafer surface. Due to the low diffusion coefficient of boron, high laser energy is required for laser doping, but this high energy can easily damage the borosilicate glass on the silicon wafer surface. Since subsequent processes require alkaline polishing of the back side, without the protection of the borosilicate glass, the alkaline solution will damage the PN junction in the laser-doped area on the front side, leading to a decrease in cell conversion efficiency. Therefore, it is necessary to generate silicon dioxide as a mask in the SE laser area to protect the PN junction in the laser-doped region. Traditional SE post-chain oxidation masking technology, suitable for PERC processes, involves introducing a certain amount of oxygen to thermally oxidize the silicon wafer at a high temperature of 800-900℃. However, the formation temperature of borosilicate glass in N-type TOPCon cells is much higher, requiring temperatures above 1000℃. Therefore, the growth rate of the masked silicon dioxide from simple high-temperature oxygen oxidation is low and cannot meet the process requirements, thus limiting the applicability of chain oxidation in SE laser doping of TOPCon cells. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a TOPCon battery masking method, which significantly increases the growth rate of masked silicon dioxide by spraying boric acid and using oxygen to carry water vapor into an oxidation furnace.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a TOPCon battery masking method, comprising a silicon wafer laser-doped using SE process, forming an oxide layer mask in an oxidation furnace, spraying a boric acid solution with a mass concentration of 0.01%-1% on the laser-doped surface of the silicon wafer, and after the boric acid solution on the surface of the silicon wafer dries, introducing oxygen into the oxidation furnace at high temperature. Before entering the oxidation furnace, the oxygen passes through a water bath in a low-temperature pure water bottle, allowing the oxygen to carry water vapor into the oxidation furnace. Under the reaction, a silicon dioxide layer is formed on the surface of the silicon wafer, and an oxide layer mask is formed in the laser-doped area.

[0007] Furthermore, the amount of boric acid solution with a mass concentration of 0.01%-1% sprayed on the laser-doped surface is 10-100 ml.

[0008] Furthermore, the boric acid solution is dried using hot air at 60-90℃.

[0009] Furthermore, the furnace temperature when oxygen is introduced into the oxidation furnace is 700-1100℃, the oxygen flow rate is 10-100 slm, and the reaction time is 100-500 seconds.

[0010] Compared with existing technologies, the beneficial effects of this invention are as follows: After spraying boric acid onto the laser-doped silicon wafer, the boric acid decomposes upon heating to form B2O3. In an atmosphere with a certain amount of water vapor, the reaction rate between B2O3 and silicon can be accelerated, thereby accelerating the growth rate of the SiO2 layer and rapidly generating a protective mask for the laser region. Simultaneously, this process can further increase the boron doping concentration in the SE laser-doped region, which is beneficial for reducing the doping concentration in the gate region, thereby reducing contact resistance and improving conversion efficiency, resulting in an overall efficiency improvement of over 0.1%. This solution also has another advantage: secondary boron diffusion in the SE laser-doped region via mask diffusion provides conditions for improving the sheet resistance of boron diffusion and reducing the doping concentration, facilitating further optimization of the boron diffusion process. Furthermore, the secondary doping during mask diffusion also provides conditions for reducing the SE laser power, allowing the use of lower laser power while achieving the desired surface doping concentration after secondary doping. Lower laser power helps reduce laser damage to the top of the silicon wafer pyramid, thus contributing to efficiency improvement and possessing significant economic value. Detailed Implementation

[0011] To further illustrate the present invention, specific embodiments are listed below:

[0012] Step 1: The silicon wafers after SE laser treatment begin to enter the chain oxidation furnace, with the laser-doped surface on top of the rollers;

[0013] Step 2: Spray 10-100ml of boric acid solution with a mass concentration of 0.01%-1% onto the surface;

[0014] Step 3: Use hot air at 60-90℃ to dry the sprayed silicon wafers, so that the boric acid solution on the surface is dry.

[0015] Step 4: At 700-1100℃, 10-100 slm of oxygen is introduced. Before entering the equipment, the oxygen is passed through a pure water bath at 20℃ to ensure that it carries a certain amount of water vapor into the furnace tube. The reaction lasts for 100-500 seconds. Under the combined action of water vapor and oxygen, the reaction Si + O2 = SiO2 occurs, producing a silicon dioxide layer of a certain thickness on the silicon wafer surface. Simultaneously, after spraying boric acid solution onto the surface, the following reactions occur: 2H3BO3 = B2O3 + 3H2O, 2B2O3 + 3Si = 3SiO2 + 4B. The addition of boric acid can significantly increase the formation rate of the oxide layer, thereby forming an oxide layer mask in the SE laser doping region, facilitating the implementation of the alkaline polishing process.

[0016] Obviously, the above embodiments are merely one example of the present invention, and any simple improvements on the principles provided by the present invention are within the scope of protection of the present invention.

Claims

1. A TOPCon cell masking method, comprising forming an oxide layer mask in an oxidation furnace on a silicon wafer laser-doped using SE technology, characterized in that... A boric acid solution with a mass concentration of 0.01%-1% is sprayed onto the laser-doped surface of the silicon wafer. After the boric acid solution on the silicon wafer surface dries, oxygen is introduced into the oxidation furnace at high temperature. Before entering the oxidation furnace, the oxygen passes through a water bath in a low-temperature pure water bottle, allowing the oxygen to carry water vapor into the oxidation furnace. Under the reaction, a silicon dioxide layer is formed on the surface of the silicon wafer, and an oxide layer mask is formed in the laser-doped area.

2. The TOPCon battery masking method according to claim 1, characterized in that... The amount of boric acid solution with a mass concentration of 0.01%-1% sprayed on the laser-doped surface is 10-100 ml.

3. The TOPCon battery masking method according to claim 1, characterized in that... The boric acid solution is dried using hot air at 60-90℃.

4. The TOPCon battery masking method according to claim 1, characterized in that... The furnace temperature when oxygen is introduced into the oxidation furnace is 700-1100℃, the oxygen flow rate is 10-100 slm, and the reaction time is 100-500 seconds.