Electrical characterization of heavily doped polycrystalline silicon for high-frequency bipolar transistor application

Electrical conduction data from heavily doped p-type polysilicon thin films at room temperature and above are presented. Specifically, the sheet resistance, in the range from 1 kΩ/□ to 100 Ω/□ for a doping level of 10¹⁹cm^-3to 10²⁰cm^-3, is characterized over temperatures from 300 to 450 K. It is shown that the polysilicon resistivity, larger than the corresponding crystalline value by a factor ∼ 10, is flat over the entire temperature range used for measurement. This large resistivity is correlated to the degree of dopant activation and the mobility in polysiUcon. The measured mobility varying from 8 to 20 cm²/V . s is shown to be smaller than the crystalline mobility at the same doping level by a factor 7 ∼ 3. These data are comprehensively discussed and quantified, based on a distributed resistivity model.