POLYCRYSTALLINE SILICON ON TUNGSTEN SUBSTRATES

Thin films of electron-beam-vaporized silicon were deposited on fine-grained tungsten substrates under a pressure of similar 1 multiplied by 10** minus **1**0 Torr. Mass spectra from a quadrapole residual gas analyzer were used to determine the partial pressure of 13 residual gases during each processing step. During separate silicon depositions, the atomically clean substrates were maintained at various temperatures between 400 degree and 780 degree C and deposition rates were between 20 and 630 Amin** minus **1. Surface contamination and interdiffusion wer monitored by in situ Auger electron spectrometry before and after cleaning, deposition, and annealing. Auger depth profiling, x-ray analysis, and SEM in the topographic and channeling modes, were utilized to characterize the samples with respect to silicon-metal interface, interdiffusion, silicide formation, and grain size of silicon. The onset of silicide formation was found to occur at approximately 625 degree C. Above this temperature tungsten silicides were formed at a rate faster than the silicon deposition. Fine-grain silicon films were obtained at lower temperatures.