A method for processing a substrate includes receiving the substrate including a patterned mask disposed over a layer stack including a second layer disposed over a first layer, the patterned mask including a feature pattern, and etching the substrate to transfer the feature pattern to the second layer and form first openings that expose the first layer. The method further includes exposing a first sidewall of the first openings to a first focused beam at a first processing angle to extend the first openings in a first direction and form second openings, and etching the substrate to transfer the second openings through the first layer and form third openings. And the method further includes exposing the first sidewall of the third openings to a second focused beam at a second processing angle to form fourth openings.