<title>Fabrication of microlens arrays by reactive ion milling</title>

Abstract

Fabrication of refractive microlens arrays on several infrared (IR) transmissive materials was studied. The fabrication process consists of forming photoresist microlenses by thermal reflow of photoresist islands, and transferring this pattern into the IR substrate by ion milling. Microlens arrays having a wide range of F-numbers (F/0.3 - F/12) and sizes were fabricated using a modified ion milling process, where background oxygen and ion energy were used to control the photoresist and substrate erosion rates, respectively. This approach enabled a large range of milling selectivity (e.g. 0.6 - 12 for CdTe) and hence accurate control of lens sag heights. This is important since photoresist microlenses can be successfully fabricated only within a limited range of F-numbers. The etch selectivity also enabled fabrication of nonspherical shapes, starting from spherical photoresist preforms, by judicious control of sputter selectivity during the milling process. Microlens arrays were fabricated in several IR materials, including CdTe, ZnS, Ge, Si, GaAs, InP, GaP and Al2O3. Among these materials GaP and ZnS are also attractive visible and near IR wavelength microlens materials, where their high refractive index results in much lower sag heights than quartz lenses of comparable F-number.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.