Abstract
Advances in micro and nano fabrication technologies for MEMS require high-level measurement techniques with regard
to sampling and sensitivity. For this purpose at the Institute of Microtechnology (IMT) highly sensitive piezoresistive 3D
force sensors based on SU-8 polymer have been developed. In this paper we present an improved micro fabrication
process for a double-sided micro structured design. The sensors are produced by multilayer processing techniques such
as UV lithography and coating methods. The double-sided micro structured design demands a photoresist application
method which simultaneously features a top side structuring and a casting from a mold. We use a new micro molding
process to meet the demands. The micro fabrication technology is described, focusing on the development of the
molding structure for shaping of the bottom side and a capable release process for the detachment of the molded
structures.
The fabrication process of the SU-8 mold layer is optimized to fabricate molding structures with heights from a few μm
up to 350 μm. Therefore different SU-8 formulations, namely with classification numbers 5, 25, 50, and 100, have been
used. The fundamental limitations for the mold design result from the lithography process, which defines the smallest
lateral resolution, and from the characteristics of a molding process, e. g. the impossibility to realize an undercut. To
allow for reliable release, the molding structures have to be coated with a sacrificial layer. A silicon nitride is deposited
onto the substrate with an accompanying monitoring of the deposition temperature during the PECVD process.
