Optical EngineeringEtching selectivity control during resist pattern transfer into silica for the fabrication of microlenses with reduced spherical aberrations
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An effective technique for the fabrication of refractive microlens arrays in silica wafers relies on the transfer by reactive ion etching (RIE) of melted photoresist microlenses. Anisotropic RIE allows the modification of the transferred profile by changing the relative etch rate of silica and photoresist, accomplished through continuous adjustment of the etching-gas composition. Material etch rates may spontaneously vary during the transfer process although operative parameters are held unchanged. An accurate survey of the etching process has been carried out to observe the principal responses of etch-parameter variations and to elaborate a procedure to adapt microlens shaping to the most severe requirements.