Methods of producing V-shaped trenches in crystalline substrates are described. The methods involve processing a patterned substrate with etch masking materials defining each side of exposed silicon (100). The exposed silicon (100) is exposed to remotely-excited halogen-containing precursor including chlorine or bromine. The plasma effluents formed from the halogen-containing precursor preferentially remove silicon from all exposed facets other than silicon (111). Etching the crystalline substrates with the plasma effluents produce at least two silicon (111) facets between two adjacent masking elements. Forming the silicon (111) facets may be accelerated by pretreating the crystalline substrates using a halogen-containing precursor locally excited in a biased plasma to initiate the generation of the trench.