High precision mask fabrication for deep X-ray lithography using 40-kV shaped electron beam lithography

Deep X-ray lithography is the primary process step of the LIGA technique, by means of which high volume production of micro-mechanical, micro-optical and micro-fluidic components becomes possible. In order to produce appropriate masks for deep X-ray lithography, several fabrication schemes can be taken into account. The most accurate and efficient fabrication process for LIGA masks is the structure transfer with soft X-ray lithography from an intermediate mask pattern which is produced by direct electron beam writing. We report on a new approach where the direct patterning of an intermediate mask has been performed by an upgraded Leica ZBA shaped electron beam writer at 40 kV in order to achieve ultimate high throughput combined with superior resolution. Optimised development and exposure processes as well as the use of proximity correction methods allowed to produce feature sizes down to a 0.4 –2 μm resist layer. The results obtained so far have been analysed via a statistical ‘design of experiment’ method which is incorporated into a fully identified set of process parameters. Embedding this novel intermediate mask fabrication in the well established LIGA process, a cost effective process environment meeting today’s pattern transfer requirements is provided.