Plasma etching properties of various transparent ceramics

The etching properties of four types of transparent ceramics: sapphire (a single crystalline α-Al₂O₃), γ-AlON (γ-aluminum oxynitride), Mg-spinel (MgAl₂O₄), and Y₂O₃, as well as a polycrystalline opaque Al₂O₃ were examined using an inductively coupled plasma etcher under an incident plasma power of 2,000 W for up to 3 h. The transparent γ-AlON and opaque Al₂O₃ showed significant surface morphological changes, whereas sapphire, Mg-spinel, and Y₂O₃ revealed a relatively smooth surface upon etching. However, direct correlation between the surface morphological change and the degree of etching could not be drawn because sapphire showed a uniform surface etching despite its significant mass loss. Even though Y₂O₃ was found to be more plasma-resistant than Al₂O₃, overall, Mg-spinel was the most feasible transparent material for monitoring window application in a semiconductor processing chamber because of its minimal degree of erosion (≤0.4g/m²) and the transmittance change (≤2%) upon 3 h of fluorocarbon (CF₄) plasma etching.