STRESSES IN THIN POLYCRYSTALLINE SILICON FILMS

The mechanisms of generation and relaxation of stress have been studied in thin polycrystalline silicon (p-Si) films prepared by low pressure chemical vapor deposition (LPCVD) from silane in a horizontal reactor at residual pressures of 0.2-0.6 Pa and deposition temperatures of 853-943 K. The films were deposited onto silicon wafers overgrown preliminarily with an SiO2 film 40-45 nm thick or an Si3N4 film 0.1-0.2 μm thick. It has been found that the basic contribution to the stress level is from an intrinsic compressive stress arising in the p-Si films because of their oxidation during deposition. Relaxation of stress occurs via the low temperature (grain boundary) dislocation climb mechanism. Minimum levels of stress are found when the growth of the LPCVD p-Si films occurs mainly as a result of a heterogeneous reaction at maximum temperature and minimum pressure of the residual gases.