Method for reducing metal impurities in polysilicon

Abstract

The invention relates to the technical field of preparation of polysilicon for solar cells and particularly relates to a method for reducing metal impurities in polysilicon. The method comprises the following steps of: 1) rinsing: immersing a primary silicon chip into an RCA (ricinus communis agglutinin) I solution and an RCA II solution in succession for rinsing; 2) drying; 3) fast heat treatment: placing the silicon chip after drying into a fast heat treatment furnace for performing fast heat treatment under a nitrogen atmosphere; and 4) impurity absorption: placing the silicon chip in a diffusion furnace for performing single-side phosphorus diffusion, performing vapor deposition of aluminum on the surface without the phosphorus diffusion of the silicon chip after the phosphorus diffusion in a vacuum film plating machine, and then performing phosphorus and aluminum co-impurity absorption treatment under the nitrogen atmosphere; cleaning: soaking the silicon chip in an HCl solution and a mixed acid solution of HF and HNO3 in succession; and drying. The method has the beneficial effects that: after PECVD (plasma enhanced chemical vapor deposition) passivation treatment of the silicon chip treated through the method according to the invention, the mu-PCD (microwave photoconductive decay) method is utilized for performing minority carrier lifetime testing, and the result finds that the minority carrier lifetime is obviously prolonged.

Description

technical field [0001] The invention relates to the technical field of polysilicon preparation for solar cells, in particular to a method for reducing metal impurities in polysilicon. Background technique [0002] Since the 1970s, in view of the limited supply of conventional energy sources and the increasing pressure on environmental protection, many countries in the world have set off an upsurge in the development and utilization of solar energy. Crystalline silicon solar cells have become the main variety of solar cells and dominate the photovoltaic market because of their high reliability, long life, and ability to withstand various environmental changes. Ingot polycrystalline silicon has the advantages of simple manufacturing process, low cost, and high production efficiency. At present, it has gradually replaced Czochralski monocrystalline silicon as the main production raw material for crystalline silicon solar cells. However, compared with Czochralski monocrystalline...

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Problems solved by technology

As the most common transition metal, iron has a solubility of up to 10 in silicon at 1000°C. 15 cm -3 , with a diffusion coefficient of up to 10 -6 cm 2 / s, the temperature in the silicon ingot production process is around 1420°C, so iron elements can easily enter the silicon crystal and affect the crystal quality. Research by Reiss et al. shows that if the Czochralski monocrystalline silicon solar cell material contains about 5×10 11 cm -3 Fe impurities, then the conversion efficiency of the solar cell will be reduced by 3%-4%

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