Deposition of SiO₂ by Plasma Enhanced Chemical Vapor Deposition as the Diffusion Barrier to Polymer Substrates

SiO₂ thin films were deposited at the temperatures <150°C by plasma enhanced chemical vapor deposition (PECVD) using a tetraethylorthosilicate (TEOS)/N₂/O₂ gas mixture, and the physical and chemical characteristics as well as the characteristics as a transparent diffusion barrier to H₂O were investigated. Using a gas combination of TEOS(40 sccm)/O₂(500 sccm)/N₂(100 sccm) at source power of 500 W and dc bias voltage of -350 V, SiO₂ with a stoichometric composition of SiO₂ and a smooth surface similar to the substrate could be deposited. When a multilayer diffusion barrier composed of parylene(800 nm)/SiO₂(100 nm)/parylene(800 nm)/SiO₂(100 nm)/parylene(800 nm) was formed on a polyethersulfone (PES) substrate, the water vapor transmission rate (WVTR) of the substrate was decreased from 54.1 to 0.3 gm/(m²·day).