Structural and gas barrier properties of hydrogenated silicon nitride thin films prepared by roll-to-roll microwave plasma-enhanced chemical vapor deposition

Hydrogenated amorphous silicon nitride films (a-SiNx:H) have attracted attention as barrier layers to prevent the diffusion of water vapor and other gases into electronic devices. Herein, the chemical composition and physical properties of a-SiNx:H films prepared using a roll-to-roll microwave plasma-enhanced chemical vapor deposition (MW-PECVD) process at low temperatures and variable NH3/SiH4 flow-rate ratios (R) were analyzed. This study was performed to identify the factors affecting the gas permeability of these films as represented by their water vapor transmission rate (WVTR) values. The films fabricated under SiH4-rich conditions (R < 2.75) were oxidized during storage in air to produce silicon oxynitride (SiOxNy), whose properties differed from those of silicon nitride (SiNx). It was found that gas barrier properties were affected by both the film and the Si-H bond densities. Under optimal conditions, the WVTR of a 100-nm-thick SiNx single layer was as low as 7 x 10(-3) g m(-2) d(-1), and the Si-H bond density was 6.71 x 10(21) cm(-3). The compressive and tensile stresses of the SiNx:H films depended on the values of R, with excellent mechanical stability and moisture barrier properties having been obtained for R = 2.75-3.00.