S. Sedky et al., Structural and mechanical properties of polycrystalline silicon germanium for micromachining applications, J MICROEL S, 7(4), 1998, pp. 365-372
In this paper, we propose polycrystalline silicon germanium (poly SiGe) as
a material suitable for MEMS applications. Films are prepared by chemical v
apor 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 anneal
ing 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 p
oly Sice micromachined devices, prepared at 650 degrees C, are presented. I
t is shown that by using as-grown poly SiGe, it is possible to realize surf
ace-micromachined suspended membranes having 0.6-mu m-wide and 50-mu m-long
supports. The effect of the average stress and stress gradient on the mech
anical stability of surface-micromachined structures is illustrated. Finall
y, the strain in poly SiGe is measured, and it is found to vary, according
to the deposition conditions from -6.88 x 10(-4) to 3.6 x 10(-4). These val
ues are compared to those measured for APCVD poly Si. [358].