Wet etching studies of silicon nitride thin films deposited by electron cyclotron resonance (ECR) plasma enhanced chemical vapor deposition

Silicon nitride films of various compositions have been deposited on silicon substrate by electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECR-PECVD) technique from mixtures of Ar, N2 and SiH4 as precursors. Film composition and refractive index as a function of deposition parameters like gas flow ratio and pressure were studied. Wet etching studies were conducted using diluted phosphoric acid and buffered oxide etch (BOE) solutions of various concentrations. The etching studies using phosphoric acid were conducted in the temperature range of 70-90 °C. For BOE the temperature range was 25-55 °C. The etch rate with BOE solution is much higher than with phosphoric acid. The results indicate that the mechanism of etching with phosphoric acid is different from that with BOE solution.