Effect of Nitrogen on Boron doped Polysilicon Thin Films Properties

In this paper we discuss the influence of the chemical interaction between boron and nitrogen introduced in polysilicon thin layers by using two different doping modes, on electrical and structural properties of boron and nitrogen codoped polysilicon thin films. The in-situ nitrogen doped silicon samples are obtained by LPCVD at low temperature (465degC) by a mixture of disilane (Si₂H₆) and ammonia (NH₃). This stage of deposit is followed by boron ionic implantation. The B-N pairs are identified by FTIR spectroscopy analysis. Results show an increase on the peak surface when the nitrogen concentration increases. The electrical and structural investigations show that, after thermal annealing, both resistivity and crystallinity of films strongly depend on nitrogen doping level. It has been observed that higher nitrogen doping tends to increase resistivity and decrease crystallinity of thin films. These results can be explained by a reduction of the boron density electrically active and thus, an inhibition of the crystalline growth caused by the B-N complex formation