Self-assembled fluorocarbon films for enhanced stiction reduction

We have developed a fluorinated self-assembled monolayer (SAM) coating process for stiction reduction in polysilicon MEMS that does not use chlorinated solvents. Using this process, cantilever beams up to 2 mm in length emerge from the final water rinse dry and released. Beam arrays fabricated from two types of polysilicon were used to characterize in-use stiction. In the first set of structures (poly A, rms roughness ≈12 nm), all beams out to the maximum length of 1 mm remained unstuck following actuation, giving an adhesion energy per apparent contact area of less than 2.4 μJ/m². Poly B structures (rms roughness ≈3 nm) gave an apparent adhesion energy of 5.2 μJ/m² compared to 23 μJ/m² for the OTS SAM coating. The fluorinated SAMs survive heat treatment in both air and N₂ at 400°C for 5 minutes and are thus compatible with several MEMS packaging processes