US Patent 7145721 Anti-reflective structures

An anti-reflective structure is formed on a surface to transmit incident light with minimal losses. The anti-reflective surface has a plurality of protrusions having a feature size smaller than the wavelength of incident light. The protrusions increase in height in either a sloped linear manner or in a curvilinear manner, and the protrusions repeat across the surface in at least one dimension to transmit the incident light. Gray scale lithography may be used to produce these patterns of protrusions in photoresist layers. High fidelity transfer of the protrusion patterns into the surfaces is accomplished by utilizing, for example, an electron cyclotron resonance plasma. Transmission values at such patterned surfaces maybe as high as 99.3%.