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Gas phase hydrophobisation of MEMS silicon structures with self-assembling monolayers for avoiding in-use sticking

: Knieling, T.; Lang, W.; Benecke, W.


Sensors and Actuators. B 126 (2007), Nr.1, S.13-17
ISSN: 0925-4005
Fraunhofer IPMS ()

During MEMS fabrication several techniques like dry etching with HF gas, sublimation or supercrit. drying, etc., for avoiding the liq./air phase transition below released structures are employed. However, these procedures do not prevent them from sticking during exposition in humid environments. For minimizing chem. and time consumption, a gas phase and industry-suited batch process was developed for hydrophobisation instead of coating in liq. solns. In this 2 step procedure the silicon-contg. surfaces are terminated with OH groups in water plasma or in a heavy oxidizing liq. soln. contg. H2O2. Afterwards a satd. atm. contg. of silanes (FDTS, FOTS) is created where they form a self-assembled monolayer on the substrate with a low energy surface. The SAM's were characterized by contact angle (q) measurements, where also surface energies (gamma ) were detd. Here FDTS and FOTS produced best results with q = 115.5 Deg, gamma = 11.0 mJ/m2 and q = 113.3 Deg, gamma = 12.4 mJ/m2 on.