Improvement in the moisture barrier properties and flexibility by reducing hydrogen dangling bonds in SiNx thin films with plasma surface treatment

In this study, silicon nitride (SiNx) thin films were deposited by inductively coupled plasma chemical vapor deposition using trisilylamine (TSA, N(SiH3)3) and ammonia (NH3) plasma, and their moisture barrier properties were improved by plasma post-treatment. Ar, N2, and O2 plasmas were applied to the SiNx films after deposition. After O2 plasma treatment, the reduction of hydrogen in -NHx was confirmed by FT-IR analysis. Mass spectroscopic results showed a distinct hydrogen peak in the O2 plasma processes. Hydrogen was speculated to be removed from the SiNx surface, and the reduced hydrogen on the surface was attributed to the densification of the SiNx thin films. The increased film density reduced the moisture permeability of the SiNx thin films. The water vapor transmission rate (WVTR) of 120-nm thick single SiNx thin films was reduced by 77% to 3.0 × 10−3 g/m2-day from 1.3 × 10−2 g/m2-day with O2 plasma treatment. The increase of WVTR evaluated using a bending test was adopted to estimate flexibility. The increase of WVTR reduced to 71% in O2-plasma treated SiNx single layers from 88% with untreated SiNx single layers after bending the film at a bending radius of 1.5 cm. Multilayer moisture barrier films were fabricated using the O2-plasma treated SiNx layers and hydrocarbon plasma polymer layers made of cyclohexane plasma to further improve the moisture barrier properties and flexibility. The increase of WVTR reduced by approximately five times in the multilayer structure with O2 plasma treated SiNx/hydrocarbon plasma polymer after the bending test. A WVTR of 7.6 × 10−4 g/m2-day was obtained with an alternating nine-layer structure. In this study, we demonstrated that plasma post-treatment processes can improve the moisture barrier properties and flexibility by reducing the hydrogen dangling bonds and hydrogen concentration inside SiNx thin films.