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Diamond-Like Carbon Films for Silicon Passivation in Microelectromechanical Devices

Published online by Cambridge University Press:  15 February 2011

M. R. Houston ,
R. T. Howe ,
K Komvopoulos  and
R. Maboudian
M. R. Houston
Affiliation:
Department of Chemical Engineering, Berkeley Sensor and Actuator Center, University of California, Berkeley, California 94720
R. T. Howe
Affiliation:
Department of Electrical Engineering and Computer Sciences, Berkeley Sensor and Actuator Center, University of California, Berkeley, California 94720
K Komvopoulos
Affiliation:
Department of Mechanical Engineering, Berkeley Sensor and Actuator Center, University of California, Berkeley, California 94720, California 94720
R. Maboudian
Affiliation:
Department of Chemical Engineering, Berkeley Sensor and Actuator Center, University of California, Berkeley, California 94720
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Abstract

The surface properties of diamond-like carbon (DLC) films deposited by a vacuum arc technique on smooth silicon wafers are presented with specific emphasis given to stiction reduction in microelectromechanical systems (MEMS). The low deposition temperatures afforded by the vacuum arc technique should allow for easy integration of the DLC films into the current fabrication process of typical surface micromachines by means of a standard lift-off processing technique. Using X-ray photoelectron spectroscopy (XPS), contact angle analysis, and atomic force microscopy (AFM), the surface chemistry, microroughness, hydrophobicity, and adhesion forces of DLC-coated Si(100) surfaces were measured and correlated to the measured water contact angles. DLC films were found to be extremely smooth and possess a water contact angle of 87°, which roughly corresponds to a surface energy of 22 mJ/m2. It is shown that the pull-off forces measured by AFM correlate well with the predicted capillary forces. Pull-off forces are reduced on DLC surfaces by about a factor of five compared to 10 nN pull-off forces measured on the RCA-cleaned silicon surfaces. In the absence of meniscus forces, the overall adhesion force is expected to decrease by over an order of magnitude to the van der Waals attractive force present between two DLC-coated surfaces- To further improve the surface properties of DLC, films were exposed to a fluorine plasma which increased the contact angle to 99° and lowered the pull-off force by approximately 20% over that obtained with as-deposited DLC. The significance of these results is discussed with respect to stiction reduction in micromachines.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 383: Symposium I – Mechanical Behavior of Diamond and Other Forms of Carbon , 1995 , 391
Copyright
Copyright © Materials Research Society 1995

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