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 across a wafer, the growth rate, the film thickness nonuniformity across a wafer, and the Si/N incorporation ratio of low pressure chemical vapor deposition SixNy films has been performed. As a tool for complete characterization of the property-deposition parameter relations, a full factorial experimental design was used to determine the dominant process parameters and their interactions. From this study it could be concluded that, in decreasing order of importance, the gas flow ratio of Si and N containing precursors, temperature, and pressure are the most relevant parameters determining the mechanical and optical properties of the films and the deposition rate and nonuniformity in film properties across a wafer. The established relations between properties and deposition parameters were fitted with physical–chemical models, including a film growth model based on a Freundlich adsorption isotherm. The optimal deposition conditions for films to be used in micromechanical devices will be discussed.