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Evolution of a microlens surface under etching conditions

This paper discusses the effects of an etching process on the optical figure of a microlens transferred from photoresist to an underlying substrate. I state a general equation for the evolution of a surface under etching conditions. I then show how isotropic and anisotropic etching conditions behave within this surface evolution theory. I demonstrate how ion milling is not an anisotropic process when eroding 3-D surfaces. Finally, I show that this behavior leads to aberrations in microlenses when subjected to ion milling as a pattern transfer technique.