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.

Date Published: 8 March 1996
PDF: 6 pages
Proc. SPIE 2687, Miniaturized Systems with Micro-Optics and Micromechanics, (8 March 1996); doi: 10.1117/12.234628

Published in SPIE Proceedings Vol. 2687:
Miniaturized Systems with Micro-Optics and Micromechanics
M. Edward Motamedi, Editor(s)