Chain-type getter phosphorus source, preparation method and application thereof

Abstract

The application discloses a phosphorus source for chain type gettering, and mass percentage of each component is as follows: 2-10% of phosphorus source precursor, 1-20% of polyethylene glycol, 1-5% of citric acid, 1-10% of organic solvent, and the rest is water. The application also provides a preparation method and application of the phosphorus source. The phosphorus source can be well matched with the existing chain type diffusion gettering equipment, and can avoid or improve the problem of residual of metaphosphoric acid and pyrophosphoric acid generated by the existing phosphorus source chain type high temperature diffusion gettering. By adjusting the phosphorus source formula, the temperature, time, atmosphere and other parameters of the chain type phosphorus diffusion gettering are optimized, and the diffusion uniformity and junction depth of the phosphorus diffusion are improved compared with the conventional phosphoric acid mixed solution. The phosphorus source prepared by the application, combined with the chain type equipment for rapid phosphorus diffusion, can reach the same diffusion level as the traditional tube type diffusion in a short time, so that the industrial application of the chain type diffusion is realized, and the problems of the current tube type diffusion equipment and expensive automation are solved.

Description

Technical Field

[0001] This invention relates to the photovoltaic field, specifically to a chain-type getter phosphorus source, its preparation method, and its application. Background Technology

[0002] Phosphorus (P) removal from impurities in crystalline silicon is a well-known and conventional method. By capturing impurities with P, the overall minority carrier lifetime is extended, thereby improving cell performance. Heavily doped P impurity layers can provide numerous gettering mechanisms, such as segregation and stress-induced gettering. Currently, in the fabrication of conventional PERC and TOPCon cells, the excellent gettering effect of pn junctions prepared by phosphorus diffusion is utilized.

[0003] In the field of solar cells, phosphorus diffusion mainly uses POCl3 as a precursor in tubular high-temperature diffusion. However, diffusion equipment and automation are expensive, and the precursor POCl3 is highly toxic and corrosive. When applied to gettering processes, achieving better double-sided gettering results results in significant production capacity loss. Furthermore, with the increasing demand for thinner wafers, the high fragmentation risk of tubular gettering has become increasingly prominent. Therefore, chain gettering has emerged as a solution.

[0004] Similar to chain diffusion, chain gettering currently relies primarily on simple phosphoric acid mixtures and imported phosphoric acid sources developed by companies such as Filmtronics and Honeywell. Simple phosphoric acid mixtures inevitably generate difficult-to-remove metaphosphoric acid and pyrophosphoric acid during high-temperature processes, resulting in uneven diffusion, a thick surface dead layer, poor PN junction quality, and shallow junction depth, thus hindering improved gettering performance. Furthermore, the high cost of phosphoric acid sources developed by companies like Filmtronics and Honeywell restricts their industrial research and application.

[0005] Therefore, it is crucial to develop a low-cost phosphorus source suitable for chain getter applications, enabling it to achieve superior performance compared to tubular getter applications in chain equipment. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a chain-type getter phosphorus source, wherein the mass percentage of each component is as follows: phosphorus source precursor 2%–10%, polyethylene glycol 1%–20%, citric acid 1%–5%, organic solvent 1%–10%, and the balance is water.

[0007] Preferably, the phosphorus source precursor is selected from one or more of phosphoric acid, P2O5, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, polyphosphoric acid, and phosphate esters.

[0008] Preferably, the phosphate ester is selected from one or more of pyrophosphate esters, polyphosphate esters, phosphate polyesters, phosphites, diphosphate esters, triethyl phosphate, 2-ethylhexyl phosphate, and hypophosphite.

[0009] Preferably, the organic solvent is selected from one or more of ester organic solvents, alcohol organic solvents, and amide organic solvents.

[0010] Preferably, the ester organic solvent is selected from one or more of formate organic solvents, acetate organic solvents, glycerol ester organic solvents, phosphate ester organic solvents, phospholipid organic solvents, and silicate organic solvents.

[0011] Preferably, the alcoholic organic solvent is selected from one or more of methanol, ethanol, and isopropanol.

[0012] The present invention also provides a method for preparing the above-mentioned chain-type getter phosphorus source, comprising the following steps: adding 2% to 10% by mass of phosphorus source precursor, 1% to 20% of polyethylene glycol, 1% to 5% of citric acid, 1% to 10% of organic solvent and the balance of water into a reactor, reacting at 25 to 150°C for 2 to 48 hours, and filtering to obtain the phosphorus source.

[0013] The present invention also provides a chain-type gettering method, in which phosphorus diffusion and gettering (phosphorus source diffusion and phosphorus gettering) are performed on a silicon wafer with the above-mentioned phosphorus source deposited on its surface in a chain diffusion device.

[0014] Preferably, the phosphorus source is deposited by spin coating, spray coating or roll coating.

[0015] Preferably, the phosphorus source deposition thickness is 1–2 μm; the phosphorus diffusion and gettering process conditions are: temperature 200–900℃, time 10–200 s, and atmosphere is nitrogen or oxygen.

[0016] The advantages and beneficial effects of this invention are as follows: The phosphorus source of the present invention can be well matched with existing chain diffusion gettering equipment. The phosphorus source of the present invention can avoid or improve the problem of residual metaphosphoric acid and pyrophosphoric acid generated by existing phosphorus source (phosphoric acid mixture) chain high temperature diffusion gettering.

[0017] Existing phosphorus sources are mainly composed of phosphoric acid. Phosphoric acid dehydrates at around 200℃ to form pyrophosphoric acid, and at 300℃ to form metaphosphoric acid. With further heating, metaphosphoric acid dehydrates to form phosphorus pentoxide, which has a diffusion effect. Existing phosphorus sources with phosphoric acid as the main component (mainly used in chain diffusion fields) require a high concentration of phosphoric acid, above 10%, to obtain better diffusion or gettering effects. During the high-temperature process, phosphoric acid dehydrates, forming a large amount of metaphosphoric acid solid, which accumulates at the furnace mouth and is difficult to remove by simple cleaning methods, affecting the appearance and use of the equipment.

[0018] This invention abandons the traditional phosphoric acid as the main phosphorus source and uses a mixture of P2O5, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, polyphosphoric acid, phosphate esters and other substances to form a composite phosphorus source, which greatly reduces the phosphoric acid content in the solution and reduces the residue of metaphosphoric acid, pyrophosphoric acid and other substances, and significantly improves the problem of metaphosphoric acid solid precipitation at the furnace mouth.

[0019] This invention improves the uniformity and bonding depth of phosphorus diffusion compared to conventional phosphoric acid mixtures by adjusting the phosphorus source formulation and optimizing parameters such as temperature, time, and atmosphere in chain-type phosphorus diffusion and gettering, and achieves the same level as tubular diffusion.

[0020] Adding citric acid to the phosphorus source can reduce the interaction between the active component and the carrier, thereby improving the dispersion of active phosphorus atoms on the silicon wafer surface, making the phosphorus more uniformly dispersed on the silicon wafer surface, and obtaining better diffusion uniformity.

[0021] A composite phosphorus source is used, which includes components such as ammonium dihydrogen phosphate and diammonium hydrogen phosphate. The large number of ammonium ions generated in the solution form a large number of holes in the silicon wafer during the diffusion process. These holes assist the diffusion of the phosphorus source, enabling the active phosphorus atoms to achieve a deeper diffusion depth.

[0022] The phosphorus source of this invention is low in toxicity, and the raw materials are readily available and inexpensive.

[0023] The phosphorus source prepared using this invention, combined with a chain-type device for rapid phosphorus diffusion, can achieve the same diffusion level as traditional tubular diffusion in a short time, enabling the industrial application of chain diffusion and solving the problem of high cost of current tubular diffusion equipment and automation. Detailed Implementation

[0024] The specific embodiments of the present invention will be further described below with reference to examples. These examples are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention.

[0025] This invention provides a chain-type getter method, comprising the following steps: 1) Preparation of phosphorus source for chain gettering: 2%–10% (w / w) of phosphorus source precursor, 1%–20% of polyethylene glycol, 1%–5% of citric acid, 1%–10% of organic solvent, and the balance water are added to a reactor and reacted at 25–150℃ for 2–48 h. The phosphorus source is obtained by filtration. Wherein: The phosphorus source precursor is selected from one or more of phosphoric acid, P2O5, diammonium dihydrogen phosphate, diammonium hydrogen phosphate, polyphosphoric acid, and phosphate esters. Specifically, the phosphate ester is selected from one or more of the following: pyrophosphate ester, polyphosphate ester, phosphate polyester, phosphite ester, diphosphate ester, triethyl phosphate ester, 2-ethylhexyl phosphate ester, and hypophosphite ester. The organic solvent is selected from one or more of ester organic solvents, alcohol organic solvents, and amide organic solvents; Specifically, the ester organic solvent is selected from one or more of the following: formate organic solvents, acetate organic solvents, glycerol ester organic solvents, phosphate ester organic solvents, phospholipid organic solvents, and silicate organic solvents; Specifically, the alcoholic organic solvent is selected from one or more of methanol, ethanol, and isopropanol; 2) Phosphorus diffusion and gettering (i.e., phosphorus source diffusion and phosphorus gettering) are performed on silicon wafers with the above-mentioned phosphorus source deposited on their surface in a chain diffusion device; specifically: Phosphorus sources are deposited on the surface of silicon wafers using spin coating, spray coating, or roller coating methods, with a deposition thickness of 1–2 μm. The process conditions for phosphorus diffusion and gettering in a chain diffusion device are: temperature 200–900℃, time 10–200s, and atmosphere of nitrogen or oxygen.

[0026] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A chain-type gettering method, characterized in that, Phosphorus diffusion and gettering are performed on silicon wafers with phosphorus source deposited on the surface in a chain equipment. The phosphorus source is deposited by spin coating, spray coating or roll coating. The deposition thickness of the phosphorus source is 1 to 2 μm. The process conditions for phosphorus diffusion and gettering are: temperature 200 to 900℃, time 10 to 200s, and atmosphere is nitrogen or oxygen. The phosphorus source is prepared by the following steps: 2% to 10% by mass of phosphorus source precursor, 1% to 20% by mass of polyethylene glycol, 1% to 5% by mass of citric acid, 1% to 10% by mass of organic solvent and the balance of water are added to a reactor and reacted at 25 to 150°C for 2 to 48 hours, and then filtered to obtain the phosphorus source. The phosphorus source precursor is selected from several of P2O5, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and polyphosphoric acid. The organic solvent is selected from one or two of ester organic solvents and amide organic solvents; The ester organic solvent is selected from one or more of the following: formate organic solvents, acetate organic solvents, glycerol ester organic solvents, phospholipid organic solvents, and silicate organic solvents.