In-line adhesion monitoring and the effects of process variations on adhesion in MEMS

Capacitive microinstruments with compliant electrodes for accurate determination of small adhesion force between polycrystalline silicon surfaces are presented. The test structures can determine the adhesion force as low as 60nN. Using these devices, the effects of fabrication and release variations on the adhesion force are investigated. The measurement results show that the adhesion force does not depend on the apparent contact area over the range of parameters examined. Moreover, a distinct difference between adhesion force values measured on wafers with different fabrication processes is observed that is attributed to different surface topography. The distribution of adhesion force in 8" wafers is also studied and is found not uniform throughout a single wafer.