Measurement of Residual Stress and Young’s Modulus on Micromachined Monocrystalline 3C-SiC Layers Grown on <111> and <100> Silicon

Abstract

3C-SiC is an emerging material for MEMS systems thanks to its outstanding mechanical properties (high Young’s modulus and low density) that allow the device to be operated for a given geometry at higher frequency. The mechanical properties of this material depend strongly on the material quality, the defect density, and the stress. For this reason, the use of SiC in Si-based microelectromechanical system (MEMS) fabrication techniques has been very limited. In this work, the complete characterization of Young’s modulus and residual stress of monocrystalline 3C-SiC layers with different doping types grown on &lt;100&gt; and &lt;111&gt; oriented silicon substrates is reported, using a combination of resonance frequency of double clamped beams and strain gauge. In this way, both the residual stress and the residual strain can be measured independently, and Young’s modulus can be obtained by Hooke’s law. From these measurements, it has been observed that Young’s modulus depends on the thickness of the layer, the orientation, the doping, and the stress. Very good values of Young’s modulus were obtained in this work, even for very thin layers (thinner than 1 mm), and this can give the opportunity to realize very sensitive strain sensors.

Fabrication of Wafer-Level Vacuum-Packaged 3C-SiC Resonators with Q-Factor above 250,000

“…A hetero-epitaxial, non-intentionally doped 0.8 µm thick 3C-SiC thin film was grown on 500 µm thick <100> p-type silicon substrates using chemical vapor deposition, as described in [3]. The process flow adopted to fabricate the wafer-level vacuum-packaged SiC double-clamped beams is shown in Figure 1.…”

Emerging SiC Applications beyond Power Electronic Devices

“…Nevertheless, it is crucial to notice that the mechanical properties of SiC, such as its high Young’s modulus or the layer internal stresses, are in such cases largely affected, and may negatively impact vibrating MEMS structures. Indeed, the Young’s modulus (E) values obtained, through MEMS (clamped beams, membranes) structures, clearly indicate that E strongly depends on a crystalline structure or orientation, thicknesses and doping type and level (by at least a factor of 3, from 120 to 500 GPa) [ 21 , 24 , 142 , 143 , 144 , 145 , 146 , 147 ]. In particular, a strong dependence of the Young’s modulus from both point defects [ 24 ] and stacking faults [ 142 ] has been reported.…”

“…This has always been a problem for using monocrystalline SiC layers in MEMS devices. Such layers certainly provide even better mechanical properties than polycrystalline ones [ 145 , 152 ], but cannot be grown directly on insulating materials such as SiO 2 . Instead, they need to be grown on single-crystal silicon substrates at relatively high temperatures (typically above 1300 °C), to achieve the best crystalline quality and consequently the most outstanding mechanical properties.…”

“…SMM generally consist of multilayer stacks, where some of the layers are used as a sacrificial layer and are etched in particular areas to form the structures. When one wishes to take full advantage of the exceptional mechanical properties of SiC (such as a high Young’s modulus, allowing an increase in the vibration frequencies of the systems compared to Si with an identical design) or to add electronic functions close to the MEMS, single crystal 3C-SiC is the material of choice [ 145 , 170 , 171 , 172 ]. Furthermore, it has been shown that it is possible to grow multi-layers of 3C-SiC/Si monocrystalline [ 173 , 174 ].…”

3C-SiC/Si heterostructure for self-powered multiband (UV-VIS) photodetection applications

“…The main problems in epitaxial growth of 3C-SiC on Si substrates are large lattice (∼20%) and thermal expansion coefficient (∼8%) mismatches between the substrate and the film. The large lattice mismatch creates stacking faults in SiC layer resulting in a high residual stress in the film [34]. Another issue rises with the outdiffusion of Si into the SiC at the interface, which results in pits and voids at the Si/SiC interlayer [29].…”