A method of forming gratings, comprising: depositing a resist material on a grating material disposed over a substrate, the resist material having a first device area and second device area; patterning the resist material into a patterned resist layer, the patterned resist layer having: a first portion of pattern features formed over the first device area, the first portion of pattern features having a first slant angle; a second portion of pattern features formed over the second device area, the second portion of pattern features having a second slant angle; projecting a first ion beam to the first device area for a first period of time to form a first plurality of gratings in the grating material, the first ion beam having a first beam angle to a surface of the substrate, the first ion beam having a first ion beam profile, wherein the first slant angle is about equal to the first beam angle of the first ion beam while the second portion of pattern features have the second slant angle such that the ion beam having the first beam angle does not form gratings on the second device area of the substrate; and projecting a second ion beam to the second device area for a second period of time to form a second plurality of gratings in the grating material, the second ion beam having a second beam angle to the surface of the substrate, the second ion beam having a second ion beam profile, wherein the first portion of pattern features have the first slant angle, such that the ion beam having the second beam angle does not form gratings on the first device area of the substrate; wherein at least one of the first ion beam profile and the second ion beam profile is not uniform. depositing a resist material on a grating material disposed over a substrate, the resist material having a first device area and second device area; patterning the resist material into a patterned resist layer, the patterned resist layer having: a first portion of pattern features formed over the first device area, the first portion of pattern features having a first slant angle; a second portion of pattern features formed over the second device area, the second portion of pattern features having a second slant angle; projecting a first ion beam to the first device area for a first period of time to form a first plurality of gratings in the grating material, the first ion beam having a first beam angle to a surface of the substrate, the first ion beam having a first ion beam profile, wherein the first slant angle is about equal to the first beam angle of the first ion beam while the second portion of pattern features have the second slant angle such that the ion beam having the first beam angle does not form gratings on the second device area of the substrate; and projecting a second ion beam to the second device area for a second period of time to form a second plurality of gratings in the grating material, the second ion beam having a second beam angle to the surface of the substrate, the second ion beam having a second ion beam profile, wherein the first portion of pattern features have the first slant angle, such that the ion beam having the second beam angle does not form gratings on the first device area of the substrate; wherein at least one of the first ion beam profile and the second ion beam profile is not uniform. a first portion of pattern features formed over the first device area, the first portion of pattern features having a first slant angle; a second portion of pattern features formed over the second device area, the second portion of pattern features having a second slant angle; projecting a first ion beam to the first device area for a first period of time to form a first plurality of gratings in the grating material, the first ion beam having a first beam angle to a surface of the substrate, the first ion beam having a first ion beam profile, wherein the first slant angle is about equal to the first beam angle of the first ion beam while the second portion of pattern features have the second slant angle such that the ion beam having the first beam angle does not form gratings on the second device area of the substrate; and projecting a second ion beam to the second device area for a second period of time to form a second plurality of gratings in the grating material, the second ion beam having a second beam angle to the surface of the substrate, the second ion beam having a second ion beam profile, wherein the first portion of pattern features have the first slant angle, such that the ion beam having the second beam angle does not form gratings on the first device area of the substrate; wherein at least one of the first ion beam profile and the second ion beam profile is not uniform.