A study of the surface chemistry, morphology and wear of silicon based MEMS

Abstract

AbstractPolysilicon microelectromechanical systems (MEMS) are the subject of intense research activity. This paper reports on the surface chemistry, topography and nanowear properties of a MEMS test structure fabricated at Sandia National Laboratories, studied using XPS and atomic force microscopy (AFM). XPS C 1s and Si 2p spectra from the polysilicon components, silicon nitride substrate and a reference Si wafer are compared. The results confirm the presence of a self‐assembled monolayer (SAM) on the MEMS surface. An island‐like morphology is found on both polysilicon and silicon nitride surfaces of the MEMS. The islands take the form of caps, being up to 0.5 µm in diameter and 20 nm in height. It is concluded that a dual columnar and equiaxed microstructure develops during growth of these low pressure chemical vapour deposition (LPCVD) layers and the islands are caps to the columnar structures. A 35 µN load applied to the AFM diamond tip leads to a wear depth of 1.4 ± 0.13 nm and 2.1 ± 0.06 nm on the polysilicon and silicon nitride MEMS equiaxed surfaces, respectively. Under the same load, greater wear of the columnar caps on both surfaces is observed. The results suggest that the morphology present on the polysilicon surface will be worn flat during operation and will not adversely affect the wear properties of the polysilicon components. Copyright © 2004 John Wiley & Sons, Ltd.