Embodiments described herein relate to methods for etching a substrate. Patterning processes, such as double patterning and quadruple patterning processes, may benefit from the embodiments described herein which include performing an inert plasma treatment to implant ions into a spacer material, performing an etching process on an implanted region of the spacer material, and repeating the inert plasma treatment and the etching process to form a predominantly flat top spacer profile. The inert plasma treatment process may be a biased process and the etching process may be an unbiased process. Various processing parameters, such as pressure, may be controlled to influence a desired spacer profile.