Fabrication of multi-level relief patterns in a substrate

Claim 1

In the method of making a multi-level straight walled square wave diffration grating having a periodicity of less than 5 microns on the surface of a substrate which comprises: coating said substrate with a photoresist, exposing said photoresist through a mask and developing said photoresist so as to provide a first surface relief pattern, etching said pattern into said substrate to a first depth corresponding to a predetermined primary color, recoating said etched substrate with photoresist, exposing said photoresist through a mask and developing said photoresist so as to provide a superposed second surface relief pattern, and etching said pattern into said substrate to a second depth corresponding to another predetermined primary color, the improvement which comprises carrying out said etching steps by sputter etching at a rate of about 200-400 angstroms per minute in the presence of a reactive gas at a pressure of from 2-20 millitorr, which gas has the formula CX n F 4-n wherein X is hydrogen or chlorine and n is an integer from 0-4 which forms volatile byproducts with the sputtered material and removing said byproducts.