BACKGROUND:  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. 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.

INNOVATION:  A non-contact process has been developed to over come the MEMS stiction problem. Laser spallation is an innovative technology for de-adhering and measuring adhesion strength of film and multilayer film interfaces. Typically, a nanosecond duration pulse from a Nd:YAG laser is used to launch a compressive stress wave into the substrate. This compressive stress wave travels through the substrate and film. Upon reaching the free surface it is reflected as a tensile wave. It is this tensile wave, that upon reaching the thin film interface, releases the film from the substrate. A similar methodology can be used to free stiction-failed MEMS devices.

DEVELOPMENT TO DATE:  Cantilevered beams were fabricated using a standard MEMS process with the exception of the special release process used after the final isopropyl rinse. The beam length varied from 100 -1000 um and the substrate separation was 2 or 4.5 um. A Nd:YAG laser was focused to a 3mm diameter spot on the back of the substrate to generate the stress wave. Cantilevered beams were released starting at 7kJ/m^2 and additional beams were released as the beam energy was increased. Typical beam release times were a few seconds of laser exposure.

Reference: UCLA Case No. 2004-003

US Patent Application: 11/511,858