THERMOELASTIC DEFORMATIONS OF MASKS FOR DEEP X-RAY-LITHOGRAPHY

Deep x-ray lithography (DXRL) with synchrotron radiation is a key technology in the LIGA process which is used to fabricate precise components for micro mechanics, micro fluidics and micro optics [1,2]. For high throughput a large flux intensity is required, which leads to temperature changes and a corresponding image blur as well as pattern displacement on the mask. Thermoelastic deformations of x-ray masks are negligible in normal x-ray lithography (XRL) performed at a storage ring, where resist layers up to 1 mum thick are used. However, in DXRL the precision of the structure transfer can suffer substantially due to thermoelastic deformations. In order to identify the most suitable mask membrane material and exposure conditions a three dimensional, time dependent finite element analysis of the thermoelastic mask deformations during exposures has been performed. Measurements of the mask temperature were made to check the calculations. Two methods have been identified to limit the distortions below 0.2 mum for an irradiation at a high flux synchrontron radiation source like the DCI storage ring in Orsay/France: use of thick beryllium mask blanks which have a large thermal inertia to lower the temperature transients when the exposure is done with a high scan velocity of several cm/s, use of diamond mask membranes which are thicker than the Au absorber structures.