Effect of the RF power on the characteristic properties of high-performance silicon nitride single-layer permeation barriers

Permeation barriers for organic devices and packaging on flexible substrates are realized by using a simple single-layered silicon nitride (SiNx) film deposited via radio frequency (RF) plasma-enhanced chemical vapor deposition (PECVD) at a low temperature (~70 °C) with plasma and radical control. Several operation parameters like RF power and treatment time duration were changed to study the impact of plasma parameters (electron excitation temperature, atomic N radical and N+ ions) on the barrier films. Optical emission spectroscopy (OES) diagnostic is used to explore the deposition conditions to improve the quality and the properties of the permeation barriers deposited on a polyethylene terephthalate (PET) substrate. OES measurements revealed that the minimum electron excitation temperature and high intensity of the N+ ion observed by an 870.2 nm emission line were the crucial parameters to achieve the minimum water vapor transmission rate (WVTR) by changing the film microstructure factor with all other operation parameters remained fixed. By incorporating plasma and radical treatment at different RF powers, a minimum WVTR of 1.8 × 10−2 g/m2/day, measured at room temperature was achieved relevant to the condition of the maximum N+ ion emission intensity. The decrease in permeability is attributed to the rearrangement of the atoms at the interfaces when the average transferred ion energy to the substrate exceeds the threshold of displacement energy = electron excitation temperature ~ electron temperature. Also, this work reports on the correlations between the plasma chemistry and the chemical, mechanical, barrier, and optical properties of the deposited films.