Stiction (adhesion of suspended structures and the underlying surface) is a considerable problem for batch fabricated MEMS devices. MEMS devices are often released through wet etching. As the wafer is removed from the wet etch liquid is trapped between the small space separating the MEMS device and the substrate. This liquid, through capillary forces, pulls the cantilevered MEMS device down to the substrate where it remains. The purpose of this study was repair the stiction by using a laser-induced stress wave.

Numerous techniques have been explored to resolve this problem. However, most require significant trade-offs e.g. non-standard silicon processing, additional design structures, long release process times, etc.

Cantilevered beams were fabricated using a standard MEMS process with the exception of the special release process used after the final isopropyl rinse. The stiction-failed beams varied from 100 –1000 microns in length, with their intended substrate separation (after release) of 2 or 4.5 microns. A Nd:YAG laser pulse was focused to a 3mm diameter spot on the backside of the Si substrate whose front surface had the MEMS structures, including the stiction-failed cantilevered beams. The cantilever beams were examined before and after each laser exposure under an optical microscope to spot for the released structures. Cantilevered beams were released starting at 7kJ/m2 and additional beams were released as the laser energy was increased. It was confirmed that no adjoining structures were damaged by the stress wave. The whole process of stiction repair is accomplished literally in few seconds. This technology can thus be used to substantially increase the yield of MEMS devices during fabrication, and also to repair in-use stiction.

The invention has been tested and fully demonstrated on actual MEMS chips that had several cantilevers failed due to stiction.

Because the process is very simple, quick (takes few seconds at most) and can be implemented on-line during batch processing of MEMS structures, operates at very safe low laser energy densities, and does not involve direct contact with the MEMS features. A United States Patent is pending for this technology.