LPCVD SILICON-RICH SILICON-NITRIDE FILMS FOR APPLICATIONS IN MICROMECHANICS, STUDIED WITH STATISTICAL EXPERIMENTAL-DESIGN

A systematic investigation of the influence of the process parameters temperature, pressure, total gas flow, and SiH2Cl2:NH3 gas flow ratio on the residual stress, the refractive index, and its nonuniformity ac ross a wafer, the growth rate, the film thickness nonuniformity across a wafer, and the Si/N incorporation ratio of low pressure chemical va por deposition SixNy films has been performed. As a tool for complete characterization of the property-deposition parameter relations, a ful l factorial experimental design was used to determine the dominant pro cess parameters and their interactions. From this study it could be co ncluded that, in decreasing order of importance, the gas flow ratio of Si and N containing precursors, temperature, and pressure are the mos t relevant parameters determining the mechanical and optical propertie s of the films and the deposition rate and nonuniformity in film prope rties across a wafer. The established relations between properties and deposition parameters were fitted with physical-chemical models, incl uding a film growth model based on a Freundlich adsorption isotherm. T he optimal deposition conditions for films to be used in micromechanic al devices will be discussed. (C) 1996 American Vacuum Society.