Abstract: In the production of polysilicon by application of modified Siemens process , all the energy for polysilicon chemical vapor deposition is supplied by the heat generation on silicon rods which are heated up by the passage of current .The coupling model of thermal and electromagnetic field for the silicon rods located in a 24-rod polysilicon reduction furnace was developed by coupling joule heating equation controlled by frequency and heat dissipation ( radiation and convection ) .Furthermore , the results were evaluated to be valid by comparing with industrial data .The influences of rod radius , AC frequency and wall emissivity on temperature and current density profile within rod were studied .The interesting results show that the skin effect begins to appear when the radius of the silicon rods increases to the value of skin depth.High frequency current sources can generate an even temperature profile and a higher deposition radius of rods can be obtained .The temperature difference between the center temperature and surface temperature of rods increases for a low AC frequency with increasing wall emissivity while the temperature difference has a weak influence on the temperature profile at a high AC frequency .

Key words: In the production of polysilicon by application of modified Siemens process , all the energy for polysilicon chemical vapor deposition is supplied by the heat generation on silicon rods which are heated up by the passage of current .The coupling model of thermal and electromagnetic field for the silicon rods located in a 24-rod polysilicon reduction furnace was developed by coupling joule heating equation controlled by frequency and heat dissipation ( radiation and convection ) .Furthermore , the results were evaluated to be valid by comparing with industrial data .The influences of rod radius , AC frequency and wall emissivity on temperature and current density profile within rod were studied .The interesting results show that the skin effect begins to appear when the radius of the silicon rods increases to the value of skin depth.High frequency current sources can generate an even temperature profile and a higher deposition radius of rods can be obtained .The temperature difference between the center temperature and surface temperature of rods increases for a low AC frequency with increasing wall emissivity while the temperature difference has a weak influence on the temperature profile at a high AC frequency .