Chemical vapor deposition of fluoroalkylsilane monolayer films for adhesion control in microelectromechanical systems

We have developed a new process for applying a hydrophobic, low adhesion en ergy coating to microelectromechanical (MEMS) devices. Monolayer films are synthesized from tridecafluoro-1,1,2,2- tetrahydrooctyltrichlorosilane (FOT S) and water vapor in a low-pressure chemical vapor deposition process at r oom temperature. Film thickness is self-limiting by virtue of the inability of precursors to stick to the fluorocarbon surface of the film once it has formed. We have measured film densities of similar to3 molecules nm(2) and film thickness of similar to1 nm. Films are hydrophobic, with a water cont act angle >110 degrees. We have also incorporated an in situ downstream mic rowave plasma cleaning process, which provides a clean, reproducible oxide surface prior to film deposition. Adhesion tests on coated and uncoated MEM S test structures demonstrate superior performance of the FOTS coatings. Cl eaned, uncoated cantilever beam structures exhibit high adhesion energies i n a high humidity environment. An adhesion energy of 100 mJ m(-2) is observ ed after exposure to >90% relative humidity. Fluoroalkylsilane coated beams exhibit negligible adhesion at low humidity and less than or equal to 20 m uJ m(-2) adhesion energy at >90% relative humidity. No obvious film degrada tion was observed for films exposed to >90% relative humidity at room tempe rature for similar to 24 h. (C) 2000 American Vacuum Society. [S0734-211X(0 0)00705-8].