Characterization by SEM and FTIR of B-LPCVD polysilicon films after thermal oxidation

The aim of this work is the study and analysis of the properties of polycrystalline silicon thin films that have been deposited on oxidized monocrystalline silicon for a use as MOS structures gates. The polysilicon films were elaborated by chemical vapour deposition at low pressure (LPCVD) from silane (SiH₄) and boron trichloride (BCl₃) gas mixture, at temperature 605 °C. They have been subjected to thermal annealing in dry oxidizing atmosphere at temperatures ranged between 850 and 1100°C. The analysis of the specific behavior of such a structure towards oxidation, was based on two methods of investigation namely scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The SEM images show an increase in grain size and crystallinity when the doping level and temperature of oxidation increase. FTIR results analysis highlights the various chemical bonds existing in films such as SiH and Si-O-Si and reveals the breaking of some bonds at high oxidation temperature, which gives rise to more trapping states.