Etching of Ag and Au films in CH4-based plasmas at low temperature

Abstract

Plasma-assisted Ag and Au subtractive etching was investigated in CH4 plasmas at 10 °C. The etch rate of Ag (29 ± 2 nm/min) was higher than that observed for Cu (17 nm/min), while the Au etch rate (12 nm/min) was lower than that for both Ag and Cu. Etch rates of Ag and Au due to pressure variation decreased as pressure increased, analogous to Cu etch results. However, the specific plasma conditions under which hydrocarbon formation occurred on Cu, Ag, and Au depended upon the metal being etched as a result of variation in surface chemical reactivities. Comparison of etch results using glass slides and Si wafers as etch masks, confirmed the formation of volatile etch products for Cu and Au. Etch product removal for Au and Cu was enhanced by UV photons, while Ag etching showed no effect at wavelengths > 300 nm. These studies demonstrated that in CH4 plasmas, chemical components in the etch process are most important for Cu while Ag and Au etching is more dependent upon physical sputtering.