Characteristics of SiO_xN_y films deposited by inductively coupled plasma enhanced chemical vapor deposition using HMDS/NH₃/O₂/Ar for water vapor diffusion barrier

SiO_xN_y thin films were deposited by inductively coupled plasma enhanced chemical vapor deposition (ICP-PECVD) using hexamethyldisilazane (HMDS, 99.9%)/NH₃/O₂/Ar at a low temperature, and examined for use as a water vapor diffusion barrier. The film characteristics were investigated as a function of the O₂:NH₃ ratio. An increase in the O₂:NH₃ ratio decreased the level of impurities such as -CH_x, N-H in the film through a reaction with oxygen. Thereby, a more transparent and harder film was obtained. In addition, an increase in the O₂:NH₃ ratio decreased the nitrogen content in the film resulting in a more SiO₂-like SiO_xN_y film. Using SiO_xN_y fabricated with an O₂:NH₃ ratio of 1:1, a multilayer thin film consisting of multiple layers of SiO_xN_y/parylene layers was formed on a polyethersulfone (PES, 200 μm) substrate, and its water vapor transmittance rate (WVTR) was investigated. A WVTR < 0.005 g/(m² day) applicable to organic thin film transistors or organic light emitting diodes was obtained using a multilayer composed of SiO_xN_y (260 nm)/parylene (< 1.2 μm) on the PES.