Monitoring the chemical and structural changes during progressive aqueous alteration of silica thin films deposited by CVD process: accurate thickness loss rates measurements

This study investigates the alteration behaviour in aqueous KOH solution (pH 4) of CVD amorphous silica thin films exhibiting different network qualities. The hydrolysis of the networks was elucidated through ERDA (Elastic Recoil Detection Analysis) hydrogen depth profiles acquired throughout the alteration process. Thickness loss rates were successfully calculated showing remarkably low initial rates ranging from 2.5 to 4.8 nm/day, directly correlated with the initial network quality. A minimal rate as low as 0.5 nm/day, comparable to bulk silica performances, was recorded indicating the limited hydration and hydrolysis mechanisms leading to the release of H₄SiO₄. These phenomena are occurring with a cyclic hydrolysis–dissolution process. These findings represent the first available dataset on dissolution rates of CVD-deposited silica films. This comprehensive investigation has facilitated the accurate correlation of CVD deposition temperature and, therefore, the network quality of silica films to the chemical and mechanical response to aqueous alteration.