The method described here uses gray scale lithography to form curve surfaces in photoresist. These surfaces can be of arbitrary shape since the remaining resist following exposure and develop is dependent on the exposure dose, which is controlled precisely by the opacity of the photo-mask. The process may include a silicon etch step, followed by a photoresist etch step to form an etching cycle. Each etch cycle may form a pair of substantially orthogonal stepped surfaces, with a characteristic “rise” and “run.”