阅读说明：本技术 一种选择性发射极太阳能电池的扩散工艺方法 (Diffusion process method of selective emitter solar cell ) 是由 厉文斌 赵颖 任勇 何悦 于 2020-12-28 设计创作，主要内容包括：本发明提供了一种选择性发射极太阳能电池的扩散工艺方法,所述方法包括：将前处理后的硅片置于扩散设备中,抽真空后升温,通入氧气进行预氧化；然后升温,通入氧气和携磷源载气,沉积磷源；停止通气,继续升温后维持恒温,进行无源推进处理；然后降温,再次通气后沉积磷源；停止通入携磷源载气进行二次氧化,然后通气再次沉积磷源,得到扩散处理后的硅片。本发明通过对硅片扩散工艺的改进,通过对制备PN结前后磷源沉积浓度的控制,优化表面掺杂浓度和结深,改善蓝光响应,减少硅片内部缺陷；所述方法通过二次氧化能够为后续激光掺杂提供磷源,改善硅片表面沉积磷源浓度的一致性,有助于激光掺杂后方阻降幅的提高,从而提升光电转换效率。(The invention provides a diffusion process method of a selective emitter solar cell, which comprises the following steps: placing the pretreated silicon wafer in diffusion equipment, vacuumizing, heating, and introducing oxygen for pre-oxidation; then heating, introducing oxygen and phosphorus source carrying carrier gas, and depositing a phosphorus source; stopping ventilation, continuously heating, maintaining constant temperature, and performing passive propulsion treatment; then cooling, ventilating again and depositing a phosphorus source; stopping introducing the carrier gas carrying the phosphorus source for secondary oxidation, and then introducing gas for depositing the phosphorus source again to obtain the silicon wafer after diffusion treatment. According to the invention, through improvement of a silicon wafer diffusion process and control of phosphorus source deposition concentration before and after preparation of PN junction, surface doping concentration and junction depth are optimized, blue light response is improved, and internal defects of the silicon wafer are reduced; the method can provide a phosphorus source for subsequent laser doping through secondary oxidation, improve the consistency of the concentration of the phosphorus source deposited on the surface of the silicon wafer, and contribute to the improvement of the resistance drop amplitude after laser doping, thereby improving the photoelectric conversion efficiency.)

1. A diffusion process method of a selective emitter solar cell, the method comprising the steps of:

(1) placing the pretreated silicon wafer in diffusion equipment, vacuumizing, heating, and introducing oxygen for pre-oxidation to form a silicon dioxide layer;

(2) after the pre-oxidation in the step (1) is finished, heating, introducing oxygen and phosphorus source carrying carrier gas, and depositing a phosphorus source on the surface of the silicon wafer;

(3) stopping introducing oxygen and phosphorus source-carrying carrier gas, continuously heating, maintaining constant temperature, and performing passive propulsion treatment;

(4) after the step (3) is finished, cooling, introducing oxygen and carrier gas carrying the phosphorus source again, and depositing the phosphorus source;

(5) stopping introducing the phosphorus source carrying carrier gas, carrying out secondary oxidation, simultaneously introducing oxygen and the phosphorus source carrying carrier gas, and depositing the phosphorus source again to obtain the silicon wafer after diffusion treatment.

2. The diffusion process method according to claim 1, wherein the silicon wafer of step (1) is a P-type silicon wafer;

preferably, the pretreatment of the silicon wafer in the step (1) is sequentially a cleaning and texturing process;

preferably, the diffusion device of step (1) comprises a tubular diffusion furnace;

preferably, the silicon wafer in the step (1) is firstly placed in a quartz boat with the front side facing upwards, and is fed into the diffusion equipment together with the quartz boat.

3. The diffusion process of claim 1 or 2, wherein the pressure after the evacuation of step (1) is reduced to less than 100 Pa;

preferably, the temperature of the step (1) is increased to 740-760 ℃;

preferably, the flow rate of the oxygen introduced in the step (1) is 500-1000 sccm;

preferably, the pressure in the furnace is 50-150 mbar during the pre-oxidation in the step (1);

preferably, the pre-oxidation time in the step (1) is 3-6 min.

4. The diffusion process method according to any one of claims 1 to 3, wherein the temperature rise in the step (2) is divided into two stages, wherein the temperature rise in the first stage is 760 to 780 ℃ and the temperature rise in the second stage is 780 to 800 ℃;

preferably, the phosphorus source of step (2) comprises phosphorus oxychloride;

preferably, the carrier gas of step (2) comprises nitrogen and/or an inert gas;

preferably, the deposition in the step (2) comprises a primary deposition and a secondary deposition, wherein the primary deposition is performed after the temperature is raised to a constant temperature in the first stage, and the secondary deposition is performed from the temperature raised in the second stage;

preferably, during the primary deposition, the introduction flow rate of the phosphorus source-carrying carrier gas is 200-800 sccm, and the introduction flow rate of the oxygen is 100-1000 sccm;

preferably, during the secondary deposition, the introduction flow rate of the phosphorus source-carrying carrier gas is 600-1200 sccm, and the introduction flow rate of the oxygen is 100-1000 sccm;

preferably, the pressure in the furnace is independently 50-150 mbar during the primary deposition and the secondary deposition;

preferably, carrier gas is additionally introduced during the primary deposition and the secondary deposition to maintain the pressure, and the introduction flow rate is independently 0-1000 sccm;

preferably, the time of the primary deposition and the time of the secondary deposition are independently 2-4 min.

5. The diffusion process method according to any one of claims 1 to 4, wherein the temperature of the step (3) is raised to 850 to 870 ℃, and then the temperature is maintained at a constant temperature;

preferably, in the passive propulsion treatment process in the step (3), carrier gas is independently introduced to maintain the pressure at 50-150 mbar;

preferably, the introduction flow rate of the carrier gas is 1000-2000 sccm;

preferably, the passive propulsion treatment in the step (3) comprises two stages of temperature rising and constant temperature, and the total time is 10-25 min.

6. The diffusion process method according to any one of claims 1 to 5, wherein the temperature after the temperature reduction in the step (4) is 760 ℃ to 790 ℃;

preferably, the introduction flow rate of the phosphorus source-carrying carrier gas in the step (4) is 100-600 sccm, and the introduction flow rate of the oxygen is 100-600 sccm;

preferably, during the deposition in the step (4), the pressure in the furnace is 50-150 mbar;

preferably, in the step (4), carrier gas is additionally introduced to maintain the pressure, and the introduction flow is 0-1000 sccm;

preferably, the deposition time in the step (4) is 2-4 min.

7. The diffusion process method according to any one of claims 1 to 6, wherein the temperature of the secondary oxidation in the step (5) is 760 to 780 ℃;

preferably, the flow rate of the oxygen gas introduced during the secondary oxidation in the step (5) is 100-1000 sccm;

preferably, carrier gas is also introduced during the secondary oxidation in the step (5) to maintain the pressure in the furnace to be 50-150 mbar, and the introduction flow rate of the carrier gas is 0-1000 sccm;

preferably, the time of the secondary oxidation in the step (5) is 5-10 min.

8. The diffusion process method according to any one of claims 1 to 7, wherein the temperature of the deposition in the step (5) is 760 to 780 ℃;

preferably, the introduction flow rate of the phosphorus source-carrying carrier gas in the step (5) is 800-1200 sccm, and the introduction flow rate of the oxygen is 500-1000 sccm;

preferably, during the deposition in the step (5), the pressure in the furnace is 50-150 mbar;

preferably, in the step (5), carrier gas is additionally introduced to maintain the pressure, and the introduction flow is 0-1000 sccm;

preferably, the deposition time in the step (5) is 5-10 min.

9. The diffusion process method according to any one of claims 1 to 8, wherein after the deposition in step (5) is completed, the introduction of the carrier gas carrying the phosphorus source and the oxygen is stopped, the temperature is reduced, the carrier gas is introduced for pressurization, the quartz boat is taken out, and the silicon wafer is unloaded.

10. The diffusion process of any one of claims 1-9, wherein the process comprises the steps of:

(1) placing the cleaned and felted P-type silicon wafer with the right side facing upwards in a quartz boat, feeding the quartz boat and the P-type silicon wafer into a tubular diffusion furnace together, vacuumizing until the pressure is below 100Pa, then heating to 740-760 ℃, introducing oxygen with the flow rate of 500-1000 sccm for pre-oxidation, wherein the pressure in the furnace is 50-150 mbar, and the pre-oxidation time is 3-6 min, so as to form a silicon dioxide layer;

(2) after the pre-oxidation in the step (1) is finished, heating to 760-780 ℃, performing constant temperature primary deposition, introducing oxygen with the flow rate of 100-1000 sccm and phosphorus-carrying source carrier gas with the flow rate of 200-800 sccm, depositing a phosphorus source on the surface of the silicon wafer, then continuously heating to 780-800 ℃, starting secondary deposition from the heating, introducing oxygen with the flow rate of 100-1000 sccm and phosphorus-carrying source carrier gas with the flow rate of 600-1200 sccm, wherein the pressure in the furnace during the primary deposition and the secondary deposition is independently 50-150 mbar, additionally introducing carrier gas with the flow rate of 0-1000 sccm to maintain the pressure, and the time of the primary deposition and the time of the secondary deposition are independently 2-4 min;

(3) stopping introducing oxygen and phosphorus source-carrying carrier gas, continuously heating to 850-870 ℃, maintaining constant temperature, and performing passive propulsion treatment in the heating and constant temperature stages, wherein the carrier gas with the flow of 1000-2000 sccm is introduced to maintain the pressure of 50-150 mbar, and the total time of the passive propulsion treatment is 10-25 min;

(4) after the step (3) is finished, cooling to 760-790 ℃, introducing oxygen with the flow rate of 100-600 sccm and phosphorus source carrying carrier gas with the flow rate of 100-600 sccm again, introducing the carrier gas with the flow rate of 0-1000 sccm additionally to maintain the pressure in the furnace to be 50-150 mbar, and depositing a phosphorus source for 2-4 min;

(5) stopping introducing the carrier gas carrying the phosphorus source, introducing oxygen with the flow rate of 100-1000 sccm for secondary oxidation, wherein the temperature of the secondary oxidation is 760-780 ℃, and during the secondary oxidation, the carrier gas with the flow rate of 0-1000 sccm is also introduced to maintain the pressure in the furnace to be 50-150 mbar, and the time of the secondary oxidation is 5-10 min;

and then simultaneously introducing oxygen with the flow rate of 500-1000 sccm and carrier gas with the flow rate of 800-1200 sccm for depositing the phosphorus source again, wherein the deposition temperature is 760-780 ℃, further introducing the carrier gas with the flow rate of 0-1000 sccm for maintaining the pressure in the furnace to be 50-150 mbar, and the deposition time is 5-10 min, then stopping introducing the oxygen and the carrier gas with the phosphorus source, cooling, introducing the carrier gas for pressurizing, taking out the quartz boat, and unloading the silicon wafer to obtain the silicon wafer after diffusion treatment.

Technical Field

The invention belongs to the technical field of solar cells, and relates to a diffusion process method of a selective emitter solar cell.

Background

With the rapid development of the photovoltaic industry, the application of the solar photovoltaic market will present a wide-field and diversified trend, photovoltaic products adapted to various requirements will be continuously published, the cost of the solar cell and the photovoltaic system will be continuously reduced, the solar cell and the photovoltaic system will still be the subject and driving force of the development of the photovoltaic industry, the silicon material, the module, the matching component and the like will face the market pressure of rapid price reduction, and the solar cell will be continuously developed towards high efficiency and low cost.

In recent years, with the development of solar cell technology, new cells such as SE cells, PERC + SE cells and the like are continuously developed, compared with conventional solar cells, the process flow of the SE cells is that a laser doping process is added after a diffusion process, a phosphorus source generated in the diffusion process is used as a doping source, a silicon wafer is locally fused by using the thermal effect of laser, and the phosphorus source outside a PN junction is injected into the surface layer of the silicon wafer by using high temperature, so that a high-doping area is locally formed, therefore, the diffusion process is used as a pre-process of the laser doping process and also provides a necessary phosphorus source for selective doping.

CN 102270701a discloses a one-time diffusion process of a selective emitter crystalline silicon solar cell, which comprises the steps of printing silicon ink on a silicon wafer; introducing oxygen into a diffusion furnace to form silicon dioxide layers on the surfaces of the silicon wafer and the silicon ink; and introducing phosphorus oxychloride into the diffusion furnace for diffusion, so that a heavily doped region is formed in the region printed with the silicon ink, and a shallow doped region is formed in the region not printed with the silicon ink on the silicon chip. The diffusion process has different diffusion degrees on different regions of a silicon wafer, but does not consider the requirement of a phosphorus source in subsequent laser doping, only depends on the phosphorus source diffused before for doping, easily causes inconsistent doping concentration of an emitter region, easily generates internal defects and causes carrier combination loss.

CN 103050581A disclosesA diffusion process for laser doping a selective emitter junction, comprising the steps of: cleaning the surface of a silicon wafer and texturing the surface of the silicon wafer; heating the diffusion furnace to 750-800 ℃, and putting the silicon wafer on a quartz boat and pushing the quartz boat into the diffusion furnace; oxidizing the surface of the silicon wafer, and introducing carried POCl₃The nitrogen is used for depositing a phosphorus source, and the deposition time is 10-40 min; stopping carrying POCl₃Introducing nitrogen, raising the temperature in the diffusion furnace to 800-900 ℃, and performing passive propulsion treatment on the silicon wafer; introducing carried POCl into the diffusion furnace again₃The nitrogen gas is used for depositing a phosphorus source; stopping carrying POCl₃Introducing nitrogen, and performing nitrogen purging on the silicon wafer; and taking out the silicon wafer after diffusion is finished. Although the method can reduce the doping concentration on the surface of the silicon wafer to a certain extent and reduce the surface recombination, the concentration of the phosphorus source on the surface of the silicon wafer is still inconsistent, and the phosphorus source deposited after passive propulsion can aggravate the concentration of the phosphorus source on the surface of the silicon wafer and influence the uniformity of sheet resistance.

In summary, for the preparation of the laser-doped selective emitter cell, it is necessary to improve the diffusion process thereof to meet the need of the phosphorus source during laser doping, so that the sheet resistance reduction amplitude of the selective emitter after laser doping is more consistent.

Disclosure of Invention

Aiming at the problems in the prior art, the invention aims to provide a diffusion process method of a selective emitter solar cell, which improves the silicon wafer diffusion process steps, forms an oxide layer again after a PN junction is prepared and deposits a phosphorus source, can provide the phosphorus source for subsequent laser doping, optimizes the surface doping concentration and the PN junction depth of the silicon wafer, improves the consistency of resistance reduction amplitude after laser doping, and improves the photoelectric conversion efficiency of the solar cell.

In order to achieve the purpose, the invention adopts the following technical scheme:

the invention provides a diffusion process method of a selective emitter solar cell, which comprises the following steps:

(1) placing the pretreated silicon wafer in diffusion equipment, vacuumizing, heating, and introducing oxygen for pre-oxidation to form a silicon dioxide layer;

(2) after the pre-oxidation in the step (1) is finished, heating, introducing oxygen and phosphorus source carrying carrier gas, and depositing a phosphorus source on the surface of the silicon wafer;

(3) stopping introducing oxygen and phosphorus source-carrying carrier gas, continuously heating, maintaining constant temperature, and performing passive propulsion treatment;

(4) after the step (3) is finished, cooling, introducing oxygen and carrier gas carrying the phosphorus source again, and depositing the phosphorus source;

(5) stopping introducing the phosphorus source carrying carrier gas, carrying out secondary oxidation, simultaneously introducing oxygen and the phosphorus source carrying carrier gas, and depositing the phosphorus source again to obtain the silicon wafer after diffusion treatment.

In the invention, for the preparation of the solar cell, the diffusion process mainly forms PN junction with the primary silicon wafer through phosphorus source deposition and diffusion, which is the core unit of the cell work, for the selective emitter cell, laser doping is carried out on the basis of a diffusion process to realize local heavy doping, therefore, after the silicon wafer is subjected to phosphorus source deposition and diffusion to form a uniform diffusion layer, the surface oxidation and phosphorus source deposition are carried out again, the silicon-phosphorus glass layer can be formed by the phosphorus source and the oxide layer deposited subsequently, the phosphorus source and the oxide layer are prevented from entering the silicon wafer to influence the uniformity of the diffusion layer, a doping source can be provided for subsequent laser doping, the uniformity of high sheet resistance after diffusion is improved, the consistency of the descending amplitude of the sheet resistance after laser doping is better, the surface doping concentration and junction depth are optimized, the compounding of the surface of the silicon wafer is reduced, and the conversion efficiency of the solar cell is improved.

The following technical solutions are preferred technical solutions of the present invention, but not limited to the technical solutions provided by the present invention, and technical objects and advantageous effects of the present invention can be better achieved and achieved by the following technical solutions.

As a preferable technical scheme of the invention, the silicon wafer in the step (1) is a P-type silicon wafer.

Preferably, the pretreatment of the silicon wafer in the step (1) is sequentially a cleaning and texturing process.

Preferably, the diffusion device in step (1) comprises a tubular diffusion furnace.

Preferably, the silicon wafer in the step (1) is firstly placed in a quartz boat with the front side facing upwards, and is fed into the diffusion equipment together with the quartz boat.

In a preferred embodiment of the present invention, the pressure after the evacuation in step (1) is reduced to 100Pa or less, for example, 100Pa, 80Pa, 60Pa, 50Pa, 30Pa, 10Pa or 1Pa, but the present invention is not limited to the above-mentioned values, and other values not shown in the above-mentioned range are also applicable.

Preferably, the temperature in step (1) is increased to 740 to 760 ℃, for example 740 ℃, 745 ℃, 750 ℃, 755 ℃, or 760 ℃, but is not limited to the recited values, and other values not recited within the range of values are also applicable.

Preferably, the oxygen gas is introduced into the reactor in step (1) at a flow rate of 500-1000 sccm, such as 500sccm, 600sccm, 700sccm, 800sccm, 900sccm, or 1000sccm, but not limited to the above-mentioned values, and other values not listed in the above-mentioned range are also applicable.

Preferably, the pressure in the furnace during the pre-oxidation in step (1) is 50-150 mbar, such as 50mbar, 60mbar, 80mbar, 100mbar, 120mbar, 140mbar or 150mbar, but not limited to the recited values, and other values not recited in the range of the recited values are also applicable.

In the invention, oxygen is introduced into the furnace in the oxidation step to maximize the concentration of the oxygen, accelerate the oxidation speed, reduce the time required by the oxidation, and ensure the stability of the pressure in the furnace through the stability of the gas flow.

Preferably, the pre-oxidation time in step (1) is 3-6 min, such as 3min, 3.5min, 4min, 4.5min, 5min, 5.5min or 6min, but not limited to the recited values, and other values not recited in the range of the recited values are also applicable.

In the invention, the surface of the silicon wafer is pre-oxidized before the phosphorus source is deposited to form a silicon dioxide layer, and the formed silicon dioxide layer can slow down the phosphorus deposition speed and lead the phosphorus to be diffused more uniformly because the diffusion coefficient of phosphorus in the silicon dioxide layer is smaller than that in silicon; by controlling the pre-oxidation temperature and the oxygen concentration, the deposited silicon dioxide layer is more uniform, and the consistency of the diffusion coefficients of the phosphorus sources in all areas on the surface of the silicon wafer is better.

In a preferred embodiment of the present invention, the temperature increase in the step (2) is divided into two stages, and the first stage is increased to 760 to 780 ℃, for example, 760 ℃, 765 ℃, 770 ℃, 775 ℃, 780 ℃ or the like, but not limited to the values listed, and other values not listed within the range of the values are also applicable; the temperature in the second stage is raised to 780 to 800 ℃, for example 780 ℃, 785 ℃, 790 ℃, 795 ℃ or 800 ℃, but the temperature is not limited to the values listed, and other values not listed in the numerical range are also applicable.

Preferably, the phosphorus source of step (2) comprises phosphorus oxychloride.

Preferably, the carrier gas of step (2) comprises nitrogen and/or an inert gas.

Preferably, the deposition in step (2) includes a primary deposition and a secondary deposition, the primary deposition is performed after the temperature of the first stage is raised to a constant temperature, and the secondary deposition is performed after the temperature of the second stage is raised.

Preferably, in the first deposition, the flow rate of the carrier gas carrying the phosphorus source is 200 to 800sccm, such as 200sccm, 300sccm, 400sccm, 500sccm, 600sccm, 700sccm, or 800sccm, but is not limited to the recited values, and other values in the range of the recited values are also applicable; the flow rate of the oxygen gas is 100 to 1000sccm, such as 100sccm, 200sccm, 300sccm, 500sccm, 600sccm, 800sccm, or 1000sccm, but is not limited to the above-mentioned values, and other values not shown in the above-mentioned range are also applicable.

Preferably, during the second deposition, the flow rate of the carrier gas carrying the phosphorus source is 600 to 1200sccm, such as 600sccm, 700sccm, 800sccm, 900sccm, 1000sccm, 1100sccm, or 1200sccm, but is not limited to the recited values, and other values in the range of the recited values are also applicable; the flow rate of the oxygen gas is 100 to 1000sccm, such as 100sccm, 200sccm, 300sccm, 500sccm, 600sccm, 800sccm, or 1000sccm, but is not limited to the above-mentioned values, and other values not shown in the above-mentioned range are also applicable.

Preferably, the pressure in the furnace is independently 50 to 150mbar, such as 50mbar, 60mbar, 80mbar, 100mbar, 120mbar, 140mbar or 150mbar, etc., for the primary deposition and the secondary deposition, but is not limited to the recited values, and other values not recited in the range of the values are also applicable.

Preferably, the first deposition and the second deposition are additionally carried out with a carrier gas to maintain the pressure, and the flow rate is independently 0-1000 sccm, such as 0sccm, 100sccm, 200sccm, 300sccm, 500sccm, 600sccm, 800sccm, or 1000sccm, but not limited to the above values, and other values not listed in the above range are also applicable.

Preferably, the time of the first deposition and the time of the second deposition are independently 2 to 4min, such as 2min, 2.5min, 3min, 3.5min or 4min, but not limited to the recited values, and other values not recited in the range of the values are also applicable.

In the invention, the phosphorus source is deposited twice, the first deposition is carried out at a relatively low temperature, the concentration of phosphorus generated by reaction is relatively low, a layer of phosphorus source (phosphorosilicate glass layer) with good uniformity is mainly deposited on an oxide layer, the earlier stage phosphorus propulsion is more uniform, the second deposition is higher than the first deposition, and the phosphorus source with relatively high concentration is deposited on the phosphorosilicate glass deposited for the first time to prepare for subsequent high-temperature propulsion.

As a preferable embodiment of the present invention, the temperature after the temperature rise in the step (3) is 850 to 870 ℃ such as 850 ℃, 855 ℃, 860 ℃, 865 ℃ or 870 ℃, but not limited to the above-mentioned values, and other values not shown in the above-mentioned range are also applicable, and then the temperature is maintained at a constant temperature.

Preferably, the carrier gas is introduced separately during the passive propulsion process in step (3) to maintain a pressure of 50 to 150mbar, such as 50mbar, 60mbar, 80mbar, 100mbar, 120mbar, 140mbar or 150mbar, but not limited to the recited values, and other values not recited in the range of values are also applicable.

Preferably, the carrier gas is introduced at a flow rate of 1000 to 2000sccm, such as 1000sccm, 1200sccm, 1400sccm, 1600sccm, 1800sccm, or 2000sccm, but not limited to the recited values, and other unrecited values within the range of values are also applicable.

Preferably, the passive propulsion process of step (3) includes two stages of temperature rising and constant temperature, and the total time is 10-25 min, such as 10min, 12min, 15min, 18min, 20min, 22min or 25min, but not limited to the recited values, and other values not recited in the range of the recited values are also applicable.

In the invention, the passive propulsion process is mainly to diffuse the phosphorus source to the silicon wafer to form a PN junction on the surface layer of the silicon wafer.

In a preferred embodiment of the present invention, the temperature after the temperature reduction in the step (4) is 760 to 790 ℃, for example, 760 ℃, 765 ℃, 770 ℃, 775 ℃, 780 ℃, 785 ℃ or 790 ℃, but the temperature is not limited to the above-mentioned values, and other values not shown in the above-mentioned range are also applicable.

Preferably, the flow rate of the phosphorus source-carrying carrier gas in step (4) is 100 to 600sccm, such as 100sccm, 200sccm, 300sccm, 400sccm, 500sccm, or 600sccm, but not limited to the recited values, and other unrecited values within the range of the recited values are also applicable; the flow rate of the oxygen gas is 100 to 600sccm, such as 100sccm, 200sccm, 300sccm, 400sccm, 500sccm, or 600sccm, but is not limited to the above-mentioned values, and other values not shown in the above-mentioned range are also applicable.

Preferably, the pressure in the furnace during the deposition in step (4) is 50-150 mbar, such as 50mbar, 60mbar, 80mbar, 100mbar, 120mbar, 140mbar or 150mbar, but not limited to the recited values, and other values not recited in the range of the recited values are also applicable.

Preferably, in step (4), the carrier gas is additionally introduced to maintain the pressure, and the flow rate is 0-1000 sccm, such as 0sccm, 100sccm, 200sccm, 300sccm, 500sccm, 600sccm, 800sccm, or 1000sccm, but not limited to the recited values, and other unrecited values within the range of the recited values are also applicable.

Preferably, the deposition time in step (4) is 2-4 min, such as 2min, 2.5min, 3min, 3.5min or 4min, but not limited to the recited values, and other values not recited in the range of values are also applicable.

In a preferred embodiment of the present invention, the temperature of the secondary oxidation in the step (5) is 760 to 780 ℃, for example, 760 ℃, 765 ℃, 770 ℃, 775 ℃ or 780 ℃, but the temperature is not limited to the above-mentioned values, and other values not shown in the above-mentioned range are also applicable.

Preferably, the flow rate of the oxygen gas during the secondary oxidation in step (5) is 100 to 1000sccm, such as 100sccm, 200sccm, 300sccm, 500sccm, 600sccm, 800sccm, or 1000sccm, but not limited to the recited values, and other unrecited values within the range of the recited values are also applicable.

Preferably, the secondary oxidation in step (5) is performed by introducing carrier gas to maintain the pressure in the furnace at 50-150 mbar, such as 50mbar, 60mbar, 80mbar, 100mbar, 120mbar, 140mbar or 150mbar, but not limited to the cited values, and other values in the range of values are also applicable, and the flow rate of the carrier gas is 0-1000 sccm, such as 0sccm, 100sccm, 200sccm, 300sccm, 500sccm, 600sccm, 800sccm or 1000sccm, but not limited to the cited values, and other values in the range of values are also applicable.

Preferably, the time of the secondary oxidation in step (5) is 5-10 min, such as 5min, 6min, 7min, 8min, 9min or 10min, but not limited to the recited values, and other values not recited in the range of the values are also applicable.

In the invention, the secondary oxidation can be carried out to form a silicon dioxide layer on the basis of the original silicon dioxide layer and the deposited phosphorus source, so that the phosphorus source and the silicon dioxide basically form a phosphorosilicate glass layer during the secondary deposition, the phosphorus source and the silicon dioxide are not easy to diffuse into a silicon wafer, and the condition that the stability of sheet resistance is influenced due to the non-uniform deposited layer is avoided; the newly formed oxide layer blocks the phosphorus source to the outside, providing a sufficient doping source for laser doping.

In the invention, after the PN junction is prepared, a layer of low-concentration phosphorus source is firstly deposited, and then secondary oxidation is carried out, namely, primary phosphorus source deposition is carried out before and after secondary oxidation, so that the subsequent SE process laser propulsion can be easier, the deposition temperature is relatively low, the phosphorus diffusion capability is weak, and the PN junction is not influenced basically.

In a preferred embodiment of the present invention, the deposition temperature in step (5) is 760 to 780 ℃, for example, 760 ℃, 765 ℃, 770 ℃, 775 ℃ or 780 ℃, but the deposition temperature is not limited to the above-mentioned values, and other values not shown in the above-mentioned range are also applicable.

Preferably, the flow rate of the phosphorus source-carrying carrier gas in the step (5) is 800-1200 sccm, such as 800sccm, 900sccm, 1000sccm, 1100sccm, or 1200sccm, but is not limited to the recited values, and other unrecited values within the range of the recited values are also applicable; the flow rate of the oxygen gas is 500 to 1000sccm, such as 500sccm, 600sccm, 700sccm, 800sccm, 900sccm, or 1000sccm, but is not limited to the values listed, and other values not listed in the numerical range are also applicable.

Preferably, the pressure in the furnace during the deposition in step (5) is 50-150 mbar, such as 50mbar, 60mbar, 80mbar, 100mbar, 120mbar, 140mbar or 150mbar, but not limited to the recited values, and other values not recited in the range of the recited values are also applicable.

Preferably, in step (5), a carrier gas is additionally introduced to maintain the pressure, and the flow rate is 0-1000 sccm, such as 0sccm, 100sccm, 200sccm, 300sccm, 500sccm, 600sccm, 800sccm, or 1000sccm, but not limited to the recited values, and other unrecited values within the range of the recited values are also applicable.

Preferably, the deposition time in step (5) is 5-10 min, such as 5min, 6min, 7min, 8min, 9min or 10min, but not limited to the recited values, and other values not recited in the range of values are also applicable.

In the invention, the pressure in the furnace is maintained the same without strictly controlling the flow of the introduced gas to be consistent, the reaction requirement is satisfied if the gas is good, the tail part of the furnace tube can be provided with a vacuumizing device, and the pressure of the furnace tube is maintained to be basically consistent by adjusting the vacuumizing frequency.

As the preferable technical scheme of the invention, after the deposition in the step (5) is finished, the introduction of the phosphorus source-carrying carrier gas and the oxygen is stopped, the temperature is reduced, the carrier gas is introduced for pressurizing, the quartz boat is taken out, and the silicon wafer is unloaded.

As a preferred technical scheme of the invention, the method comprises the following steps:

(1) placing the cleaned and felted P-type silicon wafer with the right side facing upwards in a quartz boat, feeding the quartz boat and the P-type silicon wafer into a tubular diffusion furnace together, vacuumizing until the pressure is below 100Pa, then heating to 740-760 ℃, introducing oxygen with the flow rate of 500-1000 sccm for pre-oxidation, wherein the pressure in the furnace is 50-150 mbar, and the pre-oxidation time is 3-6 min, so as to form a silicon dioxide layer;

(2) after the pre-oxidation in the step (1) is finished, raising the temperature to 760-780 ℃, then carrying out primary deposition at a constant temperature, introducing oxygen with the flow rate of 100-1000 sccm and phosphorus-carrying source carrier gas with the flow rate of 200-800 sccm, depositing a phosphorus source on the surface of the silicon wafer, then continuing raising the temperature to 780-800 ℃, starting secondary deposition from the raised temperature, introducing oxygen with the flow rate of 100-1000 sccm and phosphorus-carrying source carrier gas with the flow rate of 600-1200 sccm, wherein the pressure in the furnace during the primary deposition and the secondary deposition is independently 50-150 mbar, the pressure is maintained by additionally introducing carrier gas with the flow rate of 0-1000 sccm, and the time of the primary deposition and the time of the secondary deposition are independently 2-4 min;

(3) stopping introducing oxygen and phosphorus source-carrying carrier gas, continuously heating to 850-870 ℃, maintaining constant temperature, and performing passive propulsion treatment in the heating and constant temperature stages, wherein the carrier gas with the flow of 1000-2000 sccm is introduced to maintain the pressure of 50-150 mbar, and the total time of the passive propulsion treatment is 10-25 min;

(4) after the step (3) is finished, cooling to 760-790 ℃, introducing oxygen with the flow rate of 100-600 sccm and phosphorus source carrying carrier gas with the flow rate of 100-600 sccm again, introducing the carrier gas with the flow rate of 0-1000 sccm additionally to maintain the pressure in the furnace to be 50-150 mbar, and depositing a phosphorus source for 2-4 min;

(5) stopping introducing the carrier gas carrying the phosphorus source, introducing oxygen with the flow rate of 100-1000 sccm for secondary oxidation, wherein the temperature of the secondary oxidation is 760-780 ℃, and during the secondary oxidation, the carrier gas with the flow rate of 0-1000 sccm is also introduced to maintain the pressure in the furnace to be 50-150 mbar, and the time of the secondary oxidation is 5-10 min;

and then simultaneously introducing oxygen with the flow rate of 500-1000 sccm and carrier gas with the flow rate of 800-1200 sccm for depositing the phosphorus source again, wherein the deposition temperature is 760-780 ℃, further introducing the carrier gas with the flow rate of 0-1000 sccm for maintaining the pressure in the furnace to be 50-150 mbar, and the deposition time is 5-10 min, then stopping introducing the oxygen and the carrier gas with the phosphorus source, cooling, introducing the carrier gas for pressurizing, taking out the quartz boat, and unloading the silicon wafer to obtain the silicon wafer after diffusion treatment.

Compared with the prior art, the invention has the following beneficial effects:

(1) according to the method, through improvement of the diffusion process step of the silicon wafer, an oxide layer is formed again after the PN junction is prepared, a phosphorus source is deposited, the surface doping concentration and the junction depth are optimized through control of the deposition concentration of the phosphorus source before and after the PN junction is prepared, the blue light response is improved, and the internal defects of the silicon wafer are reduced;

(2) according to the method, a phosphorus source can be provided for subsequent laser doping through secondary oxidation, the concentration and the surface consistency of the phosphorus source deposited on the surface of the silicon wafer after diffusion are improved, and the resistance reduction amplitude and the consistency of the resistance reduction amplitude after subsequent laser doping are improved, so that the process range of a sintering curve in the silk-screen metallization process is enlarged, and the photoelectric conversion efficiency and the high-quality product rate of a battery are improved;

(3) the method disclosed by the invention is simple in improvement mode, obvious in effect, easy to operate and beneficial to wide application.

Drawings

Fig. 1 is a flowchart of a diffusion process method of a selective emitter solar cell according to embodiment 1 of the present invention.

Detailed Description

In order to better illustrate the present invention and facilitate the understanding of the technical solutions of the present invention, the present invention is further described in detail below. However, the following examples are only simple examples of the present invention and do not represent or limit the scope of the present invention, which is defined by the claims.

The invention provides a diffusion process method of a selective emitter solar cell, which comprises the following steps:

(1) placing the pretreated silicon wafer in diffusion equipment, vacuumizing, heating, and introducing oxygen for pre-oxidation to form a silicon dioxide layer;

(2) after the pre-oxidation in the step (1) is finished, heating, introducing oxygen and phosphorus source carrying carrier gas, and depositing a phosphorus source on the surface of the silicon wafer;

(3) stopping introducing oxygen and phosphorus source-carrying carrier gas, continuously heating, maintaining constant temperature, and performing passive propulsion treatment;

(4) after the step (3) is finished, cooling, introducing oxygen and carrier gas carrying the phosphorus source again, and depositing the phosphorus source;

(5) stopping introducing the phosphorus source carrying carrier gas, carrying out secondary oxidation, simultaneously introducing oxygen and the phosphorus source carrying carrier gas, and depositing the phosphorus source again to obtain the silicon wafer after diffusion treatment.

The following are typical but non-limiting examples of the invention:

example 1:

the embodiment provides a diffusion process method of a selective emitter solar cell, and a flow chart of the method is shown in fig. 1, and the method comprises the following steps:

(1) placing the cleaned and processed P-type silicon wafer with the right side facing upwards in a quartz boat, feeding the cleaned and processed P-type silicon wafer and the quartz boat into a tubular diffusion furnace together, vacuumizing until the pressure is 100Pa, then heating to 750 ℃, introducing oxygen with the flow rate of 500sccm for pre-oxidation, controlling the pressure in the furnace to be 100mbar, and controlling the pre-oxidation time to be 3min to form a silicon dioxide layer;

(2) after the pre-oxidation in the step (1) is finished, heating to 770 ℃, performing primary deposition at a constant temperature, introducing oxygen with the flow rate of 400sccm and nitrogen with the phosphorus source with the flow rate of 500sccm, depositing the phosphorus source on the surface of the silicon wafer, then continuously heating to 790 ℃, starting secondary deposition from the temperature rise, introducing oxygen with the flow rate of 600sccm and nitrogen with the phosphorus source with the flow rate of 700sccm, controlling the pressure in the furnace to be 100mbar during the primary deposition and the secondary deposition, additionally introducing nitrogen with the flow rate of 400sccm, wherein the time of the primary deposition and the time of the secondary deposition are both 3 min;

(3) stopping introducing oxygen and nitrogen carrying a phosphorus source, continuously heating to 860 ℃, maintaining constant temperature, and performing passive propulsion treatment in the stages of heating and constant temperature, wherein the nitrogen with the flow rate of 1500sccm is introduced to maintain the pressure at 100mbar, and the total time of the passive propulsion treatment is 15 min;

(4) after the step (3) is finished, cooling to 770 ℃, introducing oxygen with the flow rate of 400sccm and phosphorus-carrying source nitrogen with the flow rate of 400sccm again, introducing nitrogen with the flow rate of 400sccm additionally, controlling the pressure in the furnace to be 100mbar, and performing deposition for three times for 2 min;

(5) stopping introducing nitrogen carrying a phosphorus source, introducing oxygen with the flow rate of 500sccm to perform secondary oxidation, wherein the temperature of the secondary oxidation is 770 ℃, introducing nitrogen with the flow rate of 400sccm during the secondary oxidation, controlling the pressure in the furnace to be 100mbar, and controlling the time of the secondary oxidation to be 8 min;

and then simultaneously introducing oxygen with the flow rate of 500sccm and nitrogen with a phosphorus source with the flow rate of 800sccm, depositing for four times, wherein the deposition temperature is 770 ℃, introducing nitrogen with the flow rate of 400sccm, controlling the pressure in the furnace to be 100mbar, depositing for 5min, stopping introducing the oxygen and the nitrogen with the phosphorus source, cooling, introducing the nitrogen, pressurizing, taking out the quartz boat, unloading the silicon wafer, and obtaining the silicon wafer after diffusion treatment.

Example 2:

the embodiment provides a diffusion process method of a selective emitter solar cell, which comprises the following steps:

(1) placing the cleaned and processed P-type silicon wafer with the right side facing upwards in a quartz boat, feeding the cleaned and processed P-type silicon wafer and the quartz boat into a tubular diffusion furnace together, vacuumizing until the pressure is 80Pa, then heating to 760 ℃, introducing oxygen with the flow of 800sccm for pre-oxidation, controlling the pressure in the furnace to be 150mbar, and controlling the pre-oxidation time to be 4min to form a silicon dioxide layer;

(2) after the pre-oxidation in the step (1) is completed, heating to 780 ℃, performing primary deposition at a constant temperature, introducing oxygen with the flow of 750sccm and nitrogen with the flow of 800sccm and a phosphorus source, depositing a phosphorus source on the surface of a silicon wafer, then continuing heating to 800 ℃, starting secondary deposition from the temperature rise, introducing oxygen with the flow of 1000sccm and nitrogen with the flow of 1200sccm, controlling the pressure in the furnace to be 150mbar during the primary deposition and the secondary deposition, additionally introducing nitrogen with the flow of 100sccm, wherein the time of the primary deposition and the time of the secondary deposition are both 4 min;

(3) stopping introducing oxygen and nitrogen carrying a phosphorus source, continuously heating to 870 ℃, maintaining the constant temperature, performing passive propulsion treatment in the stages of heating and constant temperature, introducing nitrogen with the flow of 1000sccm, controlling the pressure to 80mbar, and controlling the total time of the passive propulsion treatment to be 20 min;

(4) after the step (3) is finished, cooling to 790 ℃, introducing oxygen with the flow rate of 250sccm and nitrogen with the phosphorus source with the flow rate of 500sccm again, introducing nitrogen with the flow rate of 600sccm additionally, controlling the pressure in the furnace to be 150mbar, and performing deposition for three times for 3 min;

(5) stopping introducing nitrogen carrying a phosphorus source, introducing oxygen with the flow rate of 800sccm for secondary oxidation, wherein the temperature of the secondary oxidation is 780 ℃, introducing nitrogen with the flow rate of 600sccm during the secondary oxidation, controlling the pressure in the furnace to be 150mbar, and controlling the time of the secondary oxidation to be 5 min;

and then simultaneously introducing oxygen with the flow rate of 750sccm and nitrogen with a phosphorus source with the flow rate of 1000sccm, depositing for four times, wherein the deposition temperature is 780 ℃, introducing nitrogen with the flow rate of 300sccm to maintain the pressure in the furnace to be 150mbar, and the deposition time is 8min, then stopping introducing the oxygen and the nitrogen with the phosphorus source, cooling, introducing the nitrogen for pressurizing, taking out the quartz boat, and unloading the silicon wafer to obtain the silicon wafer after diffusion treatment.

Example 3:

the embodiment provides a diffusion process method of a selective emitter solar cell, which comprises the following steps:

(1) placing the cleaned and processed P-type silicon wafer with the right side facing upwards in a quartz boat, feeding the cleaned and processed P-type silicon wafer and the quartz boat into a tubular diffusion furnace together, vacuumizing until the pressure is 50Pa, then heating to 740 ℃, introducing oxygen with the flow rate of 1000sccm for pre-oxidation, controlling the pressure in the furnace to be 150mbar, and controlling the pre-oxidation time to be 6min to form a silicon dioxide layer;

(2) after the pre-oxidation in the step (1) is completed, firstly heating to 760 ℃, then carrying out constant temperature primary deposition, introducing oxygen with the flow rate of 100sccm and argon carrying a phosphorus source with the flow rate of 200sccm, depositing the phosphorus source on the surface of the silicon wafer, then continuously heating to 780 ℃, starting secondary deposition from the temperature rise, introducing oxygen with the flow rate of 300sccm and argon carrying a phosphorus source with the flow rate of 600sccm, controlling the pressure in the furnace to be 50mbar during the primary deposition and the secondary deposition, additionally introducing argon with the flow rate of 500sccm, wherein the time of the primary deposition and the time of the secondary deposition are both 2 min;

(3) stopping introducing oxygen and argon carrying a phosphorus source, continuously heating to 850 ℃, maintaining constant temperature, performing passive propulsion treatment in the stages of heating and constant temperature, introducing argon with the flow of 2000sccm, maintaining the pressure at 150mbar, and performing the total time of the passive propulsion treatment at 10 min;

(4) after the step (3) is finished, cooling to 760 ℃, introducing oxygen with the flow rate of 600sccm and argon with a phosphorus source with the flow rate of 600sccm again, introducing argon with the flow rate of 200sccm additionally, controlling the pressure in the furnace to be 50mbar, and performing deposition for three times for 4 min;

(5) stopping introducing argon carrying a phosphorus source, introducing oxygen with the flow rate of 200sccm for secondary oxidation, wherein the temperature of the secondary oxidation is 760 ℃, introducing argon with the flow rate of 1000sccm during the secondary oxidation, controlling the pressure in the furnace to be 50mbar, and controlling the time of the secondary oxidation to be 10 min;

and then simultaneously introducing oxygen with the flow of 1000sccm and argon with a phosphorus source with the flow of 1200sccm, depositing for four times, wherein the deposition temperature is 760 ℃, the pressure in the furnace is controlled to be 50mbar, the deposition time is 10min, then stopping introducing the oxygen and the argon with the phosphorus source, cooling, introducing the argon for pressurizing, taking out the quartz boat, and unloading the silicon wafer to obtain the silicon wafer after diffusion treatment.

Example 4:

the embodiment provides a diffusion process method of a selective emitter solar cell, which comprises the following steps:

(1) placing the cleaned and processed P-type silicon wafer with the right side facing upwards in a quartz boat, feeding the cleaned and processed P-type silicon wafer and the quartz boat into a tubular diffusion furnace together, vacuumizing until the pressure is 90Pa, then heating to 745 ℃, introducing oxygen with the flow of 700sccm for pre-oxidation, controlling the pressure in the furnace to be 120mbar, and controlling the pre-oxidation time to be 5min to form a silicon dioxide layer;

(2) after the pre-oxidation in the step (1) is completed, heating to 775 ℃, performing constant temperature primary deposition, introducing oxygen with the flow of 600sccm and nitrogen with the phosphorus source with the flow of 500sccm, depositing the phosphorus source on the surface of the silicon wafer, then continuously heating to 795 ℃, starting secondary deposition from the temperature rise, introducing oxygen with the flow of 800sccm and nitrogen with the phosphorus source with the flow of 900sccm, wherein the furnace pressure during the primary deposition and the secondary deposition is 120mbar, additionally introducing nitrogen with the flow of 250sccm to maintain the pressure, and the time of the primary deposition and the secondary deposition is 2.5 min;

(3) stopping introducing oxygen and nitrogen carrying a phosphorus source, continuously heating to 855 ℃, maintaining constant temperature, performing passive propulsion treatment in the heating and constant temperature stages, introducing nitrogen with the flow of 1600sccm, maintaining the pressure at 120mbar, and keeping the total time of the passive propulsion treatment at 25 min;

(4) after the step (3) is finished, cooling to 780 ℃, introducing oxygen with the flow rate of 100sccm and nitrogen with the phosphorus source with the flow rate of 150sccm again, introducing the nitrogen with the flow rate of 1000sccm additionally to maintain the pressure in the furnace at 120mbar, and performing deposition for three times, wherein the deposition time is 3.5 min;

(5) stopping introducing nitrogen carrying a phosphorus source, introducing oxygen with the flow rate of 1000sccm for secondary oxidation, wherein the temperature of the secondary oxidation is 765 ℃, introducing nitrogen with the flow rate of 300sccm during the secondary oxidation to maintain the pressure in the furnace at 120mbar, and the time of the secondary oxidation is 7 min;

and then simultaneously introducing oxygen with the flow rate of 900sccm and nitrogen with a phosphorus source with the flow rate of 1100sccm, carrying out deposition for four times, wherein the deposition temperature is 765 ℃, introducing nitrogen with the flow rate of 250sccm, maintaining the pressure in the furnace at 120mbar, and the deposition time is 7.5min, then stopping introducing the oxygen and the nitrogen with the phosphorus source, cooling, introducing the nitrogen for pressurizing, taking out the quartz boat, and unloading the silicon wafer to obtain the silicon wafer after diffusion treatment.

Comparative example 1:

this comparative example provides a diffusion process for a selective emitter solar cell, which is referred to the process in example 1, except that: and (3) not including the third deposition in the step (4) and the second oxidation and the fourth deposition in the step (5), namely, pressurizing and cooling are carried out after the step (3) is finished.

Comparative example 2:

this comparative example provides a diffusion process for a selective emitter solar cell, which is referred to the process in example 4, except that: the secondary oxidation and the four-time deposition in the step (5) are not included.

Comparative example 3:

this comparative example provides a diffusion process for a selective emitter solar cell, which is referred to the process in example 4, except that: the three depositions of step (4) are not included.

The sheet resistance of the silicon wafers after diffusion treatment obtained in examples 1 to 4 and comparative examples 1 to 3 was measured, and further laser doping was performed under the same conditions, and the sheet resistance data at this time was measured, and the result data is shown in table 1; after the silicon wafer is further prepared into a selective emitter cell, the electrical properties of the silicon wafer are measured, and the results are shown in table 2.

TABLE 1 changes in sheet resistance of diffusion-treated and laser-doped silicon wafers as described in examples 1-4 and comparative examples 1-3

From the data in table 1, the sheet resistance reduction of the examples from the diffusion-treated silicon wafer to the laser-doped silicon wafer is 41.6 in examples 1 and 2, 53.4 in example 3, 59.6 in example 4, 26.4 in comparative example 1, 43.2 in comparative example 2, and 50.2 in comparative example 3, and the comparison of the data of the comparative examples and the corresponding examples shows that the sheet resistance reduction in the comparative examples is significantly reduced, and the larger the sheet resistance reduction, the better the laser doping effect, the more advantageous the filling factor of the cell after metallization, and the higher the conversion efficiency.

Table 2 performance of the silicon wafers described in examples 1-4 and comparative examples 1-3 after fabrication into selective emitter cells

As can be seen from the data in table 2, the improvement of the electrode sheet performance in the embodiment mainly lies in the performance aspects of the fill factor and the conversion efficiency, which contributes to the improvement of the overall performance of the battery through the improvement of the present invention.

It can be seen from the above examples and comparative examples that the method of the present invention forms an oxide layer and deposits a phosphorus source again after the preparation of the PN junction by improving the diffusion process steps of the silicon wafer, optimizes the surface doping concentration and junction depth by controlling the deposition concentration of the phosphorus source before and after the preparation of the PN junction, improves the blue light response, and reduces the internal defects of the silicon wafer; the method can provide a phosphorus source for subsequent laser doping through secondary oxidation, improve the concentration and surface consistency of the phosphorus source deposited on the surface of the silicon wafer after diffusion, and contribute to the improvement of the resistance reduction amplitude and consistency thereof after subsequent laser doping, so that the process range of a sintering curve in the silk-screen metallization process is improved, and the photoelectric conversion efficiency and the high-quality product rate of a battery are improved; the method has the advantages of simple improvement mode, obvious effect, easy operation and contribution to wide application.

The applicant states that the present invention is illustrated in detail by the above examples, but the present invention is not limited to the above detailed methods, i.e. it is not meant that the present invention must rely on the above detailed methods for its implementation. It will be apparent to those skilled in the art that any modifications to the present invention, equivalents of the method of the present invention and additions of ancillary steps, selection of specific means, etc., are within the scope and disclosure of the present invention.