Material loss of silicon nitride thin films in a simulated ocular environment

The dissolution behavior of silicon nitride in a simulated eye environment is studied as a function of temperature and ion concentration. Thin films of silicon nitride were manufactured using plasma-enhanced chemical vapor deposition (PECVD) and low-pressure chemical vapor deposition (LPCVD), respectively. The thickness of the films was measured as a function of time under various conditions. The experimental results showed that the films dissolve in saline solution over time. For the case of a thin membrane of 500 µm diameter and 200 nm thickness, typical dissolution rates are 1 nm/day for PECVD and 0.3 nm/day for LPCVD films. Dissolution of silicon nitride was found to be reduced using sputtered titanium oxide as protective overcoat.