Patent ID: 8765574

Claim:
A method of etching material from a high aspect ratio trench on a patterned substrate, the method comprising the sequential steps of: providing a patterned substrate having a conformal liner layer on walls of the high aspect ratio trench; forming an inhomogeneous passivation layer over the conformal liner layer in the high aspect ratio trench, wherein the inhomogeneous passivation layer has an outer passivation thickness near the opening of the high aspect ratio trench and an inner passivation thickness deep within the high aspect ratio trench, and wherein the outer passivation thickness is greater than the inner passivation thickness; gas phase etching the conformal liner layer, wherein the gas phase etching process selectively removes material from the conformal liner layer faster than material from the inhomogeneous passivation layer; removing the remainder of the inhomogeneous passivation layer to leave a remainder of the conformal liner layer, wherein the remainder of the conformal liner layer has an outer remaining conformal liner thickness near the opening of the high aspect ratio trench and an inner remaining conformal liner thickness deep within the high aspect ratio trench, and wherein the outer remaining conformal liner thickness is greater than the inner remaining conformal liner thickness; gas phase etching the remainder of the conformal liner layer to leave nearly vertical walls on the sides of the high aspect ratio trench.