Eliipsometric Study of Rapid Thermal Annealed PECVD SiN Films

Abstract

ABSTRACTA conventional parallel plate plasma enhanced chemical vapor deposition system using SiH4-NH3-N2 at 13.56MHz and 300°C was used to deposit SiN films on silicon substrates. Special care was used to assure an oxide free surface before deposition. The silane flow was varied to obtain stoichiometric Si3 N4 and silicon-rich films. Rapid thermal anneal (RTA) was performed for 30 sec at temperatures in the range 600°C — 900°C. Spectroscopic ellipsometry was used to characterize the films. Data was taken for 44 wavelengths (3200–7500Å range) at three angles of incidence on each sample. The structural and optical properties were obtained using several structural models of the film. The models assumed an effective medium approximation for the following three combinations of film constituents: Si3N4 and voids; Si3N4 and amorphous silicon (a-Si); Si3N4, voids and a-Si. In general, the three constituent model gave the best fits to the experimental data. In all films, we observed a decrease in the film thickness and void fraction as the RTA temperature increased. The a-Si percentage did not change vs. the RTA temperature. The reduction in void fraction for the silicon-rich samples was larger than for the Si3N4 film. The results are comparable to those measured by other methods on regular furnace annealed SiN films, i.e. annealing times of 30 minutes or more.