A method of treating a substrate includes directing ions to the substrate along at least one non-zero angle with respect to a perpendicular to a substrate surface in a presence of a reactive ambient containing a reactive species where the substrate includes a surface feature. At least one surface of the surface feature is etched using the ions in combination with the reactive ambient at a first etch rate that is greater than a second etch rate when the ions are directed to the substrate without the reactive ambient and greater than a third etch rate when the reactive ambient is provided to the substrate without the ions.