Plasma etching properties of various transparent ceramics

The etching properties of four types of transparent ceramics: sapphire (a single crystalline alpha-Al2O3), gamma-AlON (gamma-aluminum oxynitride), Mg-spinet (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 gamma-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/m(2)) and the transmittance change (<= 2%) upon 3 h of fluorocarbon (CF4) plasma etching.