MICROMECHANICS VIA X-RAY ASSISTED PROCESSING

The application potential of micromechanics is very large and falls into very-large-scale-integration-like markets such as magnetic recording and electromechanical components and application specific markets such as surgery tools and sensors. Many of these markets cannot now be addressed because cost effective fabrication technology is not now available to fabricate the required highly complex devices. Idealized fabrication tools must address three dimensional processing with tolerances in the 100 ppm range and must extend over a large material base. They must do that with some integrated circuit-cofabrication compatibility in a cost effective manner. There is a premium for tools which can handle large structural heights with small critical dimensions. X-ray assisted processing can satisfy some of the requirements of the idealized tool. X-ray assisted processing started with the basic LIGA process in Germany. This process can be extended by merging it with surface micromachining and assembly. The current versions of LIGA and LIGA-like processing are restricted in performance by photoresist strain which is typically found in thick photoresist processes. Photoresist strain can and has been reduced significantly by introducing solvent bonded photoresist application procedures which are followed by precision milling and polishing. This extends allowed photoresist thicknesses to heights in the centimeter range. Exposure via synchrotron generated x-ray fluxes and subsequent developing has produced structures with structural heights to 1 cm. This implies that x-ray assisted processing does not only play a major role in micromechanical fabrication but also in precision engineering. This statement is further supported by results that indicate that multiple x-ray mask processes are feasible and that plastic parts can be fabricated by direct x-ray exposure over large surface areas without injection molding. Test vehicles for x-ray assisted processing at the University of Wisconsin fall into two categories: modular micromechanical building blocks such as gear boxes and novel sensors such as high speed magnetic micromotors.