Fabrication of beam resonators from hot-wall chemical vapour deposited SiC
Introduction
Silicon carbide (SiC) micro electromechanical systems (MEMS) are promising devices for high efficiency radio frequency (RF) applications [1], [2]. Among the unique material properties of SiC, the high value of Young’s Modulus and the relatively low mass density permit SiC to achieve higher resonant frequencies compared to other materials [3]. In addition, the mechanical strength, high thermal conductivity and the high sublimation point of SiC make it an extremely robust material suitable for harsh environment applications. In the past decade, significant progress has been made in the growth of SiC wafers, however, the epitaxial growth on silicon (Si) and dry etching techniques need still further developments to improve the quality and reliability of SiC MEMS [4].
In this work, single crystal and polycrystalline 3C–SiC have been grown on Si wafers. X-ray diffraction has been employed to characterise the epi-layers. In addition, the grown SiC films have been used to fabricate cantilever resonators with different beam lengths. The resonators have been actuated mechanically and Young’s Modulus has been calculated for both epi-layers from the measured resonant frequencies.
Section snippets
Growth of the 3C–SiC films
Both single crystal and polycrystalline 3C–SiC films have been grown in a hot-wall chemical vapour deposition reactor (CVD) [5] on 100 mm diameter p-type boron-doped (1 0 0) Si wafer without rotation of the wafer. Hydrogen purified through heated palladium cells, mixed with 2% of Ar has been used as carrier gas while silane (SiH4) and propane (C3H8) have been used as precursor gases. The Si/H2 ratio has been fixed at 0.024% and the C/Si ratio between 0.8 and 1. Prior the SiC growth, before and
Characterisation of the 3C–SiC films
After the growth process, the epi-layers have been assessed with a Nomarski optical microscope in reflection mode. The nucleation of the single crystal layer has been observed to be more homogeneous compared to the polycrystalline one. Furthermore, by reflectance technique in the visible range, an average epi-thickness of 1.4 and 2.3 μm have been measured for the polycrystalline and single crystal layers, respectively, leading to a typical growth rate in a 3–4 μm/h range.
The crystal structure of
Summary
Single crystal and polycrystalline 3C–SiC films have been grown in a hot-wall CVD reactor. The films structure has been investigated by XRD analysis showing a high crystal quality for the single crystal film. Both SiC epi-layers have been used to fabricate cantilever resonators with different lengths. The resonators have been actuated mechanically and the measured natural resonant frequencies have been used to calculate Young’s Modulus E of both materials. For the single crystal and the
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