OXYGEN-ADSORPTION AND ELECTRICAL BEHAVIOR OF THIN, VERY-LOW-PRESSURE CHEMICAL-VAPOR-DEPOSITED POLYSILICON FILMS

We report here the results of experiments on the influence of oxygen adsorption on the conductivity of very-low-pressure chemically-deposited polysilicon thin films of various thicknesses obtained by plasma reactive etching a 600 nm initial film. It is observed that oxygen acts as an acceptor on the unintentionally-doped as on the lightly-doped polysilicon films, provided they are adequately annealed. Oxygen adsorptions made over 2 min at atmospheric pressure increase the film resistance variation by up to 2 decades; this variation depends on adsorption temperature and film thickness. Temperature-programmed desorptions at 3 K/min and 0.1 mPa up to 650 K always restore the films to their initial resistivity value. The DELTA-R-TPD curves are nearly independent of adsorption temperature. Deduced from a simple model, the desorption energy values are 0.31 +/- 0.05 eV for unetched films and 0.64 +/- 0.05 eV for etched films of thickness below 500 nm. Associated frequency factor values confirm that no isothermal oxygen desorption is observed even at 433 K.