Effect of oxygen on fluorine-based remote plasma etching of silicon and silicon dioxide

Abstract

The addition of oxygen to a fluorine-containing gas in a remote microwave discharge significantly affects the etch rates of SiO2 and Si, and the selectivity of the etching. For a F2/He etchant mixture, the addition of O2 drops the etch ratio to 1:1, from a value of 40:1 without O2. For CF4, the ratio is reversed to less than 1:3, from an initial 10:1. A mechanism for this behavior is proposed, based on simultaneous etching and oxidation of the silicon surface by atomic F and O, respectively. When CF4 or C2F6 is the source of F, the selective deposition of a fluorocarbon polymer on Si strongly affects the etching behavior. Auger and x-ray photoelectron spectroscopy analysis supports these interpretations. The control of selectivity may be useful for an isotropic deglaze process.