Evaluation of plasma process-induced mechanical property change in SiN films using a cyclic nanoindentation technique

Abstract

Recently, plasma process-induced damage (PID) has garnered significant interest in the design of thin dielectric films implemented in semiconductor devices. Silicon nitride (SiN) films, a material of interest in strain engineering, are found to suffer from PID because they are exposed to various plasmas during device manufacturing processes. Only a limited amount of experimental evidence is available at present regarding plasma-induced mechanical property changes of SiN films. In this study, we investigated the mechanical property change in SiN and SiO₂ films using a cyclic nanoindentation technique. We focused on the contact stiffness (S) as the principal mechanical property parameter. Firstly, a single loading/unloading test confirmed an increase in S after Ar and He plasma exposures. Subsequently, we examined the time-dependent features of damaged SiN and SiO₂ films under cyclic loading/unloading. From the cyclic test, an increase in S was seen with the number of loading/unloading cycles (N) for both SiN and SiO₂ films. A larger increase in S was observed for the damaged SiN, while no significant increase was seen for the damaged SiO₂ films. The observed increase in S and its time dependence are attributed to the strain developed by the created defects (e.g. interstitial species) and the reconstruction and stabilization of plasma-damaged Si–N networks with created defects, respectively. The time-dependent S analysis under cyclic loading/unloading is useful for evaluating the effects of PID on the mechanical properties of thin films.