Three-dimensional micro-structuring for optical applications

The fabrication of 3D-microstructures with well-defined curved surface contours is of great interest for various mechanical, optical and electronic devices. Obviously in the micro-optic domain, there is a great demand to produce surface topographies for refractive or diffractive optical elements. This paper describes two micromachining techniques for the fabrication of micro optical elements. First a short overview on graytone lithography based on subresolution pixeled chromium glass masks is given. Using graytone lithography infrared diffractive optical elements have been fabricated in silicon using an 1:1 dry etching process. For low cost application in the visible wavelength region a replication technique in polycarbonat by injection moulding has been used. In a second approach microlenses and -arrays have been directly processed into borosilicate glasses (especially bondabel glasses like BOROFLOAT(R)33 [1]) using an viscous flow of the glass at higher temperatures. Beside the possibility for the replication of any available silicon structures into the borosilicate glass substrate this technique allows the fabrication of optical micro lens arrays with high aspect ratios in a contactless mode.