Silicon suboxide (SiOx): laser processing and applications

Abstract

Substoichiometric silicon oxide SiOx with x < 2 in form of evaporated or sputtered thin films offers a versatile material basis for laser ablation techniques such as film patterning, laser-induced forward transfer, or laser-induced backside dry etching. Applications in the field of (micro-) optics are favoured strongly by the fact that SiOx can be oxidised to UV-transparent SiO2 by thermal treatment (furnace or laser annealing). On the other hand, with x a parts per thousand 1, SiOx exhibits an absorption coefficient of > 10(5) cm(-1) in the deep UV below 250 nm, comparable to strongly absorbing polymers such as polyimide. This enables precise ablation with, e.g., excimer lasers at moderate fluences. For example, UV-transparent diffractive elements or phase masks are made by laser patterning of an appropriate SiOx film and subsequent oxidation to SiO2. Modifications of the basic film ablation process lead to novel surface topographies such as blister or cup arrays with potential non-optical applications, e.g., in micro-/nanofluidics.