Structural and mechanical properties of polycrystalline silicon germanium for micromachining applications

Sherif Sedky, Paolo Fiorini, Matty Caymax, Stefano Loreti, Kris Baert, Lou Hermans, Robert Mertens

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Abstract

In this paper, we propose polycrystalline silicon germanium (poly SiGe) as a material suitable for MEMS applications. Films are prepared by chemical vapor deposition (CVD) at atmospheric pressure (AP) or reduced pressure (RP). The structure of the films is investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM) for different deposition and annealing conditions. The stress in the as-grown and annealed layers is measured, and the correlation between stress and structural properties is discussed. It is demonstrated that by adjusting the deposition conditions, the stress of the as-grown material can be varied from -145 to +60 MPa. Examples of poly SiGe micromachined devices, prepared at 650°C, are presented. It is shown that by using as-grown poly SiGe, it is possible to realize surface-micromachined suspended membranes having 0.6-μm-wide and 50-μm-long supports. The effect of the average stress and stress gradient on the mechanical stability of surface-micromachined structures is illustrated. Finally, the strain in poly SiGe is measured, and it is found to vary, according to the deposition conditions from -6.88 × 10-4to 3.6 × 10-4. These values are compared to those measured for APCVD poly Si. [358].
Original languageEnglish
Pages (from-to)365 - 372
Number of pages8
JournalJournal of Microelectromechanical Systems
Volume7
Issue number4
DOIs
Publication statusPublished - Dec 1998
Externally publishedYes

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All Science Journal Classification (ASJC) codes

  • Mechanical Engineering
  • Electrical and Electronic Engineering

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