Diffractive optical elements and methods of making the same are described.
In one aspect, a diffractive optical element is made by forming a multilayer structure
comprising multiple amorphous silicon phase shift layers having respective thicknesses
selected so that the diffractive optical element is operable to phase shift infrared
light within an operative wavelength range. The amorphous silicon phase shift layers
are separated by respective silicon dioxide etch stop layers having respective
thicknesses of about 5 nm or less. Layers of the multilayer structure are serially
masked and etched to form a multi-step optical structure. In another aspect, a
diffractive optical element is made by forming a multilayer structure comprising
multiple etch layers separated by respective etch stop layers selectively etchable
with respect to the etch layers. One or more of the etch and etch stop layers are
substantially opaque to light within an operative wavelength range. Opaque layers
are converted into substances substantially transparent to light within the operative
wavelength range. Layers of the multilayer structure are serially masked and etched
to form a multi-step optical structure.
