Statistical approach to parameter study of stress in multilayer films of phosphosilicate glass and silicon nitride

Abstract

Mechanical stress in chemical vapor deposited phosphosilicate (APCVD-PSG), plasma deposited PSG (P-PSG), plasma deposited SiN (P-SiN) and a combination of APCVD-PSG and P-SiN films has been characterized through the use of screening and modeling experimental designs. Total stress in these films was determined by measuring the changes in the radius of curvature of silicon substrate. As deposited APCVD-PSG exhibits tensile stress at room temperature. This stress decreases with increase in phosphorus content. The total stress in P-PSG films was compressive. Of the seven process factors studied in the screening experiment, only three factors (phosphorus content, silane and argon flow rates) had statistical significant effect on stress. Over the process domain covered, no factor–factor interactions were observed. P-SiN films showed high compressive stress levels. Modeling study resulted in a parametric model relating room temperature stress to deposition temperature and ammonia flow rate. For dual films, APCVD-PSG and P-SiN, the total stress was a function of nitride film thickness and phosphorus content in PSG. Parametric models were developed for stress after deposition, sinter and aging. In all cases studied, the total stress changed from tensile to compressive with additional processing. The general trend tends to support the direction observed in previous single factor studies for single dielectric films. The current experiments extend these studies for single films and their combinations, by quantifying the various process factor interactions.