Defect enhanced ultraviolet etching of amorphous insulators

We have studied the photoablation of thin films of SiO2, SiO1.5 and Si3N4 using pulses of ultraviolet laser light (λ=248 nm). Photon energy densities used were orders of magnitude smaller than those normally found for macroscopic damage creation. Whereas SiO1.5 ablates readily, a cumulative process occurs for SiO2 which we argue involves defect creation leading to the formation of unstable, substoichiometric superficial layers. Mechanisms of defect creation involving electron-hole pair formation are discussed in the light of recent studies on hot electron transport in SiO2.