DRY ETCH PROCESS
A method for conformal dry etch of a liner material in a high aspect ratio trench is achieved by depositing or forming an inhomogeneous passivation layer which is thicker near the opening of a trench but thinner deep within the trench. The methods described herein use a selective etch following formation of the inhomogeneous passivation layer. The selective etch etches liner material faster than the passivation material. The inhomogeneous passivation layer suppresses the etch rate of the selective etch near the top of the trench (where it would otherwise be fastest) and gives the etch a head start deeper in the trench (where it would otherwise be slowest). This method may also find utility in removing bulk material uniformly from within a trench.