A method for producing polycrystalline silicon diffused twice

The present invention discloses a method for manufacturing a PN junction made of polycrystalline silicon diffusion twice, the method comprising: a constant source diffusion step S1, step S2 defined heating source diffusion, a constant source diffusion step S3. In the present invention, since the constant source diffusion step S3, it increases the deposition of the polysilicon wafer surface impurities phosphorous. Thus, in step S1, the phosphorus impurities can be correspondingly reduced once deposited, thus avoiding excessive deposition of phosphorus impurities. Then, step S3 is at a high temperature, polycrystalline silicon at this time to increase solubility phosphorus atom, phosphorus impurities deposited no further forward, to control the amount of dissolved phosphorus impurities in polycrystalline silicon is deposited by controlling the amount of phosphorus impurity, to avoid due to excessive deposition and advanced again to produce "dead zone" exists. The method for producing polycrystalline silicon PN junction made of two diffusion provided by the invention can be implemented to solve the surface of the "dead layer" problem after polysilicon wafers manufactured by the PN junction is present purposes.