Patent ID: 8801952

Claim:
A method of etching silicon oxide from the walls of a trench on a surface of a patterned substrate in a substrate processing region of a substrate processing chamber, the method comprising at least four sequential steps comprising: (i) exposing the patterned substrate to hydrogen by flowing a hydrogen-containing precursor into the substrate processing region, (ii) removing process effluents including unadsorbed hydrogen-containing precursor from the substrate processing region, (iii) exposing the patterned substrate to fluorine by flowing a fluorine-containing precursor into the substrate processing region to form solid by-products on the patterned substrate, and (iv) removing process effluents including unreacted fluorine-containing precursor from the substrate processing region; and further comprising a sublimation operation of raising a temperature of the substrate above a sublimation temperature to remove the solid by-products, wherein the sublimation operation occurs after the step of exposing the patterned substrate to fluorine, and wherein the at least four sequential steps in combination with the sublimation operation are referred to collectively as an etch cycle.