Self-Aligned 3D Shadow-Mask Technique For Patterning Deeply Recessed Surfaces of MEMS Devices

We present a 3D shadow-mask technique for patterned modification of an area that is recessed from the top surface because of a large topographical step. The silicon shadow mask is micromachined and fits self-aligned into the removed area of the device wafer. For a 500-um-deep topography, the gap between the aperture and the surface is reduced to less than 100 um, yielding a much higher resolution than achievable with conventional approaches. The use of this technique is demonstrated for direct evaporation of metal patterns 10x50 um2 in size on the backside of a membrane of a bimorph-actuated device. The same pattern dimensions were achieved by exposing a spray-coated resist layer through the shadow-mask aperture. Full-wafer processing with the reusable shadow mask is demonstrated.