Reactive Ion Etching of PECVD Amorphous Silicon and Silicon Nitride Thin Films with Fluorocarbon Gases

Abstract

Plasma-enhanced chemical vapor deposited (PECVD) amorphous silicon (α-Si:H) and silicon nitride films have been reactive ion etched with fluorocarbon gases. Process parameters such as power, pressure, and gas flow rate have tremendous effects on etch rates and the etch selectivity. The film etch rate increases with the increase of the power under various pressure and flow rate conditions. Etching mechanisms of three gases (CF4, C2F6, and CHF3) are different. With the same gas and etching condition, etching mechanisms of α-Si:H and nitride are also different. For the CF4 plasma, both the plasma-phase chemistry and the self-bias voltage control the etch rate and the etch selectivity of nitride to α-Si:H. For the C2F6 plasma, the self-bias voltage dominates the etch rate and the etch selectivity. For the CHF3 plasma, a self-bias voltage higher than a threshold voltage is required before the film can be etched. The etch selectivity of nitride to α-Si:H is greater than one with all etching conditions. An etch selectivity as high as 25 has been obtained with CF4 or CHF3. ESCA spectra show that the CF4 etched surface is clean, the C2F6 etched surface is probably covered with a carbonaceous layer, and the CHF3 etched surface is coated with the fluorocarbon polymer. © 1990, The Electrochemical Society, Inc. All rights reserved.