Three-dimensional integration of heterogeneous silicon micro-structures by liftoff and stamping transfer

We propose a method of integrating heterogeneous silicon microstructures (typical scale of 10-100 νm) into a single silicon substrate to fabricate MEMS structures. It includes adhesion-based liftoff and stamping transfer (LIST) processes using poly-(dimethylsiloxane) (PDMS) sheets. Silicon microstructures fabricated on different wafers are lifted onto the PDMS sheets by breaking the narrow columns supporting the microstructures by applying a vertical load to the PDMS sheet, and then transferred onto the silicon substrate with high yield (more than 90%) and superior positioning accuracy (within 0.3 νm on average in a 2 × 3 mm area). Multiple heterogeneous silicon structures are integrated into a single silicon substrate by repeating this LIST process. We fabricated two-dimensional arrays, three-dimensional pyramidal structures and overhanging bridge microstructures with our method, which proved that the LIST process could be used to integrate heterogeneous MEMS structures into a single wafer.