US Patent 11158487 Diagonal compound mill

Ion beams are directed to a substrate surface to expose a tapered, tilted surface in the substrate. The ion beams and the substrate are situated so that a first ion beam is incident along a first axis at a glancing angle, and a second ion beam is incident along a second axis in a plane defined by the glancing angle and at an angle with respect to the first axis. Exposure to the second ion beam tends to produced superior quality in the exposed surface such as by reducing curtain artifacts.