A PERC cell oxidation process

Abstract

The present invention provides an oxidation process for a PERC battery, comprising the following steps: 1. Open the furnace tube to enter the boat; 2. Pump out the pressure; 3. First oxidation: Cool down and increase the pressure, and introduce a certain amount of nitrogen and oxygen into the oxidation furnace tube to carry out the first oxidation of the oxide layer; 4. Second oxidation: Cool down and increase the pressure on the basis of step 3, and introduce a certain amount of nitrogen and oxygen into the oxidation furnace tube to carry out the second oxidation of the oxide layer; 5. Third oxidation: Cool down and maintain the pressure on the basis of step 4, and introduce a certain amount of nitrogen and oxygen into the oxidation furnace tube to carry out the third oxidation of the oxide layer; 6. Back pressure: maintain the temperature of step 5, and introduce nitrogen to return the pressure to the normal pressure state; 7. Exit the boat. The oxidation is divided into three stages. The oxidation stage continuously cools down to realize the process of cooling and oxidizing, and the low-pressure environment is changed to a slightly negative pressure environment to improve the effect of the oxide layer and reduce the loss burden of the vacuum pump.

Description

Technical Field

[0001] The invention belongs to the field of solar cells, and in particular relates to an oxidation process of a PERC cell. Background Art

[0002] PERC (Passivated Emitter and Rear Cell) solar cells are one of the more popular high-efficiency cells on the market. The preparation method is generally: texturing-diffusion-front laser doping-remove back PSG-alkali polishing-oxidation-back deposition of passivation film-front deposition of anti-reflection film-back laser opening-back electrode, back electric field and positive electrode printing-firing. For the oxidation process, the existing means is to use a low-pressure constant temperature process in a furnace tube, but the cells produced by this process expose many defects during EL testing, such as EL black spots, EL pitting, etc., which seriously affect the qualified rate of the finished battery products. In addition, the low-pressure operating environment will increase the life burden of the oxidation furnace vacuum pump, increase the blade loss, and lead to increased costs. Summary of the invention

[0003] In view of the above, the present invention provides an oxidation process for PERC cells. The oxidation is a process after alkali polishing and before the deposition of a passivation film on the back. The oxidation is divided into three stages. The temperature is continuously lowered during the oxidation stage to achieve the process of oxidation while cooling. The low-pressure environment is changed to a slightly negative pressure environment to improve the effect of the oxide layer, reduce the burden on the vacuum pump, extend the life, and reduce the loss. The specific technical solution of the present invention is as follows.

[0004] A PERC cell oxidation process, characterized in that it is prepared using a tubular oxidation furnace, comprising the following steps:

[0005] Step 1, open the furnace tube and put the boat in: load the alkali-polished silicon wafers into the boat, and after loading, place them on the furnace paddle to prepare for the boat loading process. A certain flow of nitrogen is introduced into the furnace, the furnace door is opened, and the furnace paddle sends the boat into the furnace chamber;

[0006] Step 2, pumping pressure: After the boat is put into the furnace, close the furnace door, increase the temperature and pump out the pressure to make the furnace tube in a low pressure state, and at the same time remove the suspended impurities brought into the furnace tube when entering and leaving the boat;

[0007] Step 3, first oxidation: lowering the temperature and increasing the pressure, introducing a certain amount of nitrogen and oxygen into the oxidation furnace tube to perform the first oxidation of the oxide layer;

[0008] Step 4, second oxidation: based on step 3, the temperature is lowered and the pressure is increased, and a certain amount of nitrogen and oxygen are introduced into the oxidation furnace tube to perform a second oxidation of the oxide layer;

[0009] Step 5, third oxidation: based on step 4, the temperature is lowered, the pressure is maintained, and a certain amount of nitrogen and oxygen are introduced into the oxidation furnace tube to perform the third oxidation of the oxide layer;

[0010] Step 6, back pressure: maintaining the temperature of step 5, introducing nitrogen to return the pressure to normal pressure;

[0011] Step 7, boat out: the furnace door is opened, the furnace paddle pulls the boat out, the process is completed, and the furnace door is closed.

[0012] Furthermore, in step 2, the pumping and pressure extraction is carried out for 220 seconds, the temperature is increased to 720-750°, and the pressure is reduced to 160 mbar.

[0013] Furthermore, the first oxidation temperature was lowered by 10°, and at the same time, an oxygen flow rate of 8000 sccm and a nitrogen flow rate of 1000 sccm were introduced, and the pressure in the furnace tube was slowly increased to 700 mbr for 300 s to form a dense oxide film on the surface of the silicon wafer.

[0014] Furthermore, the second oxidation continued with an oxygen flow rate of 8000sccm and a nitrogen flow rate of 1000sccm, the temperature was reduced by 30°, and the pressure was restored to a slightly negative pressure state of 900mbar, which lasted for 900s to continue to form a dense oxide film on the basis of the first oxidation layer.

[0015] Furthermore, in the third oxidation, an oxygen flow rate of 8000 sccm and a nitrogen flow rate of 1000 sccm were continuously introduced, the temperature was reduced by 30°, and the pressure was maintained at a slightly negative pressure of 900 mbar for 310 s to continue to form a dense oxide film on the basis of the second oxidation layer.

[0016] Furthermore, after the three oxidations were completed, the temperature of the last oxidation was maintained, and nitrogen gas with a flow rate of 10,000 sccm was introduced into the furnace tube to return the pressure to normal pressure.

[0017] The beneficial effects of the present invention are: changing the existing low-pressure constant temperature process, adopting a cooling and micro-pressure oxidation process, forming a dense oxide layer on the surface of the silicon wafer in stages while annealing and gettingtering, the cooling process can increase the surface gettering effect, the second and third oxidations restore the micro-pressure state of 900mbar, which can not only improve the oxidation effect, form a denser oxide film than the prior art, reduce the surface recombination efficiency, reduce the proportion of surface black spots and pitting, improve the hydrophilic diffusion effect of the silicon wafer surface, but also reduce the mechanical damage of the vacuum pump during operation, extend the life of the equipment, thereby improving the overall conversion efficiency of the battery cell and reducing costs.

[0018] Additional aspects and advantages of the present invention will be further given in the following description, and in part will become obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0020] Figure 1 The oxidation process flow chart for this application;

[0021] Figure 2 It is the PID experimental data report;

[0022] Figure 3 It is a line chart of the proportion of black dots and pitting;

[0023] Figure 4 This is a comparison chart of hydrophilic diffusion effects. DETAILED DESCRIPTION

[0024] The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, but should not be construed as limiting the present invention.

[0025] A PERC cell oxidation process is carried out using a tubular oxidation furnace and includes the following steps:

[0026] Step 1, open the furnace tube and put the boat in: load the alkali-polished silicon wafers into the carrier boat, and after loading, place them on the furnace paddle to prepare for the boat loading process. Nitrogen with a flow rate of 10,000 sccm is introduced into the furnace to purge the furnace tube. The furnace door is opened and the furnace paddle sends the carrier boat into the furnace chamber.

[0027] Step 2, depressurization: After the boat is put into the furnace, close the furnace door, increase the temperature and depressurize for 220 seconds, raise the temperature to 720°, and reduce the pressure to 160mbar, so that the furnace tube is in a low-pressure state. At the same time, it can also remove suspended impurities brought into the furnace tube when entering and leaving the boat, and reduce the impact of particles entering and leaving the boat on the battery cells during subsequent oxidation.

[0028] Step 3: First oxidation: Lower the temperature and increase the pressure. When the temperature reaches 710 degrees, introduce 1000sccm of nitrogen and 8000sccm of oxygen into the oxidation furnace tube for the first oxidation of the oxide layer. Slowly increase the pressure in the furnace tube to 700mbr for 300s to form a dense oxide film on the front side of the silicon wafer.

[0029] Step 4, second oxidation: the temperature is reduced to 680°, and an oxygen flow rate of 8000sccm and a nitrogen flow rate of 1000sccm are continuously introduced. The pressure is restored to a slightly negative pressure state of 900mbar and continued for 900s, so that the battery cell forms a dense oxide layer under a slightly negative pressure state while annealing and doping are performed.

[0030] Step 5, third oxidation: the temperature is reduced to 650°, an oxygen flow rate of 8000sccm and a nitrogen flow rate of 1000sccm are continuously introduced, and the pressure is maintained at a slightly negative pressure of 900mbar for 310s to continue to form a dense oxide film on the basis of the second oxide layer.

[0031] Step 6, back pressure: time 100 s, temperature 650°, nitrogen gas with a flow rate of 10000 sccm is introduced into the furnace tube to return the pressure to normal pressure, that is, the pressure is 1060 mbar.

[0032] Step 7, boat out: the furnace door is opened, the furnace paddle pulls the boat out, the process is completed, and the furnace door is closed.

[0033] First, the practicability of this method is tested and verified by PID test data, such as Figure 2 The overall average of PID monitoring is 1.51%, which is lower than the set standard of 3.5%, proving that the PID of the battery cell has not failed after the oxidation formula is modified, and it is determined that it can be put into use. The experimental group is the data or effect obtained by the process of this application, and the comparative group is the data or effect obtained by the existing low-pressure (150-250mbar) constant temperature oxidation process. The following experimental group and comparative group represent the same.

[0034] This method can effectively improve the proportion of black spots and pits in EL, and at the same time improve the efficiency to a certain extent, and can effectively solve the problem of mechanical pump blade loss. The specific efficiency improvement is shown in the following table, and the efficiency is improved by 0.015%-0.023%.

[0035] project Comparison group efficiency Experimental group efficiency Efficiency Difference Data set 1 23.1701% 23.1852% 0.0151% Data set 2 23.2231% 23.2465% 0.0233%

[0036] The proportion of black spots and pits in EL decreased by about 0.2%. Figure 3 .

[0037] In addition, hydrophilicity test comparison, such as Figure 4 The hydrophilicity of the experimental group diffused larger and faster than that of the control group, and the effect was better.

[0038] Although specific embodiments of the present invention have been described in detail with reference to the illustrative embodiments of the present invention, it must be understood that a variety of other modifications and embodiments may be devised by those skilled in the art that will fall within the spirit and scope of the principles of the present invention. Specifically, within the scope of the foregoing disclosure, the accompanying drawings, and the claims, reasonable variations and improvements may be made in the arrangement of the components and / or the dependent combination layout without departing from the spirit of the present invention. Except for variations and improvements in the components and / or layout, the scope is defined by the appended claims and their equivalents.

Claims

1. A PERC cell oxidation process, characterized in that: The preparation is carried out in a tubular oxidation furnace, including the following steps: Step 1, open the furnace tube and put the boat in: load the alkali-polished silicon wafers into the boat, and after loading, place them on the furnace paddle to prepare for the boat loading process. A certain flow of nitrogen is introduced into the furnace, the furnace door is opened, and the furnace paddle sends the boat into the furnace chamber; Step 2, depressurization: After the boat is loaded, close the furnace door, increase the temperature and depressurize, the pressure drops to 160mbar, the furnace tube is in a low pressure state, and the temperature is raised to 720-750℃; Step 3, first oxidation: lower the temperature and increase the pressure, lower the temperature by 10°C, slowly increase the pressure in the furnace tube to 700mbar, introduce a certain amount of nitrogen and oxygen into the oxidation furnace tube for the first oxidation of the oxide layer, and continue for 300s to form a dense oxide film on the surface of the silicon wafer; Step 4, second oxidation: based on step 3, the temperature is lowered and the pressure is increased, the pressure is restored to a slightly negative pressure state of 900 mbar, the temperature is reduced by 30°C, a certain amount of nitrogen and oxygen are introduced into the oxidation furnace tube, and the second oxidation of the oxide layer is carried out for 900 seconds to continue to form a dense oxide film on the basis of the first oxidation layer; Step 5, third oxidation: based on step 4, the temperature is lowered by 30°C, the pressure is maintained at a slightly negative pressure of 900 mbar, a certain amount of nitrogen and oxygen are introduced into the oxidation furnace tube, and the third oxidation of the oxide layer is carried out for 310 seconds to continue to form a dense oxide film on the basis of the second oxide layer; Step 6, back pressure: maintaining the temperature of step 5, introducing nitrogen to return the pressure to normal pressure; Step 7, boat out: the furnace door is opened, the furnace paddle pulls the boat out, the process is completed, and the furnace door is closed.

2. The oxidation process of the PERC cell according to claim 1, characterized in that: Step 2: The pumping time is 220s.

3. The oxidation process of the PERC cell according to claim 2, characterized in that: The first oxidation process has an oxygen flow rate of 8000 sccm and a nitrogen flow rate of 1000 sccm.

4. The oxidation process of the PERC cell according to claim 3, characterized in that: The second oxidation process continuously introduced an oxygen flow rate of 8000 sccm and a nitrogen flow rate of 1000 sccm.

5. The oxidation process of the PERC cell according to claim 4, characterized in that: The third oxidation was conducted with an oxygen flow rate of 8000 sccm and a nitrogen flow rate of 1000 sccm.

6. The oxidation process of the PERC cell according to claim 1 or 5, characterized in that: After the three oxidations were completed, the temperature of the last oxidation was maintained, and nitrogen gas with a flow rate of 10,000 sccm was introduced into the furnace tube to return the pressure to normal pressure.

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