Surface Engineering for MEMS Reliability


The integration of miniaturized mechanical components with microelectronic components has spawned a new technology known as microelectromechanical systems (MEMS). This technology extends the benefits of microelectronic fabrication to sensing and actuating functions. Examples of MEMS devices that have been commercially produced include relatively simple mechanisms such as accelerometers, pressure sensors and digital mirror projectors.

 Despite recent progress in micromachining capability, the realization of more complex commercial and specialized use of MEMS is challenged due to plaguing reliability issues. Barriers to the widespread commercialization and development of MEMS technologies are steep and require engineering at the molecular level. Reliability issues which commonly limit MEMS to the research level include (but are not limited to) adhesion (also referred to as "stiction") and wear.

 The goal of this work is to improve MEMS reliability by developing new processes and techniques that allow the study of adhesion and wear, that are industrially favorable and that are process compatible with MEMS fabrication schemes. A "tribology chip" has been developed which employs a variety of standard micromechanical test instruments as well as new devices. Also, a liquid based anti-adhesion coating process for MEMS which utilizes non-chlorosilane chemistry is developed. This octadecene based coating process is simpler than the standard chlorosilane processes, and circumvents a number of limitations imposed by chlorosilane chemistry.

 In order to provide a manufacturable anti-adhesion process, a new vapor phase coating method has been developed. This method is based on chlorosilane chemistry, specifically dichlorodimethylsilane, and has been shown to be effective at reducing adhesion in fully packaged devices at the wafer scale.

 To address the issue of wear, novel methods of producing films of silicon carbide as coatings for existing polysilicon micromachines have been investigated. One method is based on the selective reaction of the buckminsterfullerene, C60, with silicon. Another utilizes a pyrolysis reaction of a single source precursor, 1,3-disilabutane (DSB). While the C60 based method has proven to be cumbersome, the DSB method shows great promise as a wear resistant coating for micromachines.

Publication date: 
May 31, 2003
Publication type: 
Ph.D. Dissertation
Ashurst, W. R. (2003). Surface Engineering for MEMS Reliability. United States: University of California, Berkeley.

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