Modification of plasma-etched profiles by sputtering

Abstract

Two-dimensional etch profiles are modeled for plasma etching. The etch rate dependence on the angle of incidence of the bombarding ions on the etched surface has a sputtering-type yield. The etch profile is advanced in time by an evolution equation for an etch rate proportional to the modified ion energy flux. Approximate analytical expressions for the etch rates are derived as a product of the etch rates in the absence of the sputtering-type yield and a weighting factor that depends on the angle the ion drift velocity makes with the normal to the wafer surface. The weighting factor is determined from experimental measurements of the angular dependence of ion beam etching by sputtering. These etch rates are valid when the ratio of the ion drift speed to the ion thermal speed is large compared to one. The etching is modeled in the ion flux-limited regime for simplicity. The modifications of the shape of etch profiles of a long rectangular trench and a waveguide structure or strip are treated.