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 degrees C by plasma enhanced chemical vapor deposition (PECVD) using a tetraethylorthosilicate (TEOS)/N-2/O-2 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)/O-2(500 sccm)/N-2(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 0.3gm/(m(2.)day).