Papers by Author: Thierry Chassagne

Abstract: First objective of present contribution is to supply a compact description of two thickness-dependent characteristics of state of the art as-grown 3C-SiC/Si templates: structural quality and surface morphology. Second objective is to point out the benefits of surface planarization and indicate the temperature limits of thermal treatment that can be applied to polished 3C-SiC/Si templates without deterioration of planarization results. We believe that this kind of overview, based on our long term experience in fabrication of 3C-SiC/Si templates, may be useful for the scientific community working on future applications of cubic silicon carbide polytype.

Abstract: The silicon carbide cubic polytype (3C-SiC) is perfectly appropriate to fabricate microelectromechanical systems. However, for such applications, the stress can largely influence both the fabrication of 3C‑SiC‑based microsystems and their related mechanical properties. Accordingly, in this study, we investigated the influence of strong aluminum incorporation towards the mechanical properties of 3C-SiC epilayers grown on silicon substrates.

Abstract: Comparative study of p-type 4H-SiC epitaxial layers grown simultaneously on two different 4H-SiC substrates, namely n-type and semi-insulating have been done by different structural, optical and electrical experimental techniques.

Abstract: After presenting an exhaustive experimental study of aluminum incorporation in epitaxial 4H-SiC and 3CSiC films grown by chemical vapor deposition (CVD), we focalize once more on what is called site competition effects. We observed that the influence of C/Si ratio on dopant (Al, N) incorporation in SiC was qualitatively different depending on whether the growth experiments were performed in “low temperature” (LT) or “high temperature” (HT) regime. Partial explanation of observed phenomena basing on thermal evolution of carbon coverage of SiC surface is proposed.

Abstract: In this study we report the growth of graphene on different silicon carbide substrates by chemical vapor deposition (CVD) in order to understand the influence of the substrate offcut on the graphene layers. For this purpose, graphene was grown on substrates with different offcuts, under hydrogen-argon atmosphere, and analyzed using AFM, LEED and Raman spectroscopy. We discuss the morphology and strain in graphene, and finally the ideal offcut for graphene growth.

Abstract: The aim of this paper is to review the recent developments conducted for the achievement of 3C-SiC‑based heterostructures compatible with MEMS applications. Indeed, the research activities engaged since years permitted to demonstrate that the defect density has an impact towards the Young’s modulus of sub-micron 3C‑SiC epilayers. We also gained knowledge about the stress relaxation mechanisms, targeting to master the stress gradient, as stress is a key parameter to consider MEMS applications.Based on these results, we investigated the elaboration of microstructures using 3C‑SiC/Si/3C‑SiC stacks on silicon substrates. Our first noticeable result was the elaboration of a (110)-oriented 3C‑SiC membrane on a 3C‑SiC pseudo-substrate, using the silicon epilayer as a sacrificial one. But the surface of the 3C‑SiC membrane was facetted and rough, which could hamper its use for the development of new MEMS devices. Then, with further improvements, we succeeded to master the growth of a (111)‑oriented 3C‑SiC epilayer. This feature led to a drastic reduction of the roughness in comparison with the (110) orientation. Actually, using the same experimental protocol than previously, we succeeded to complete a (111)‑oriented 3C‑SiC membrane with a RMS roughness limited to 9nm. Such an optimized structure could be the starting point for the achievement of new MEMS devices operating in harsh environment or for medical applications benefiting of the 3C‑SiC biocompatibility

Abstract: In the range 80 K-900 K, we have investigated the electrical properties of heavily aluminum in-situ doped, 4H-SiC samples. The temperature dependence of the hole concentration and Hall mobility was analyzed in the model taking into account heavy and light holes. The modelisation parameters were compared with experimental values of Secondary Ion Mass Spectroscopy (SIMS) and Capacitance-Voltage (CV) measurements.

Abstract: Exhaustive experimental study of aluminum incorporation in epitaxial 4H-SiC and 3C‑SiC films grown by chemical vapor deposition (CVD) was performed. The influence of polytype and substrate orientation was verified. Role of principal process conditions (growth temperature and pressure, deposition rate, chemical environment) was investigated in details. Finally, the evolution of optical properties of resulting SiC films with Al content was examined.

Abstract: In this work, the electrical properties of SiO₂/SiC interfaces onto a 2°-off axis 4H-SiC layer were studied and validated through the processing and characterization of metal-oxide-semiconductor (MOS) capacitors. The electrical analyses on the MOS capacitors gave an interface state density in the low 1×10¹² eV^-1cm^-2 range, which results comparable to the standard 4°-off-axis 4H-SiC, currently used for device fabrication. From Fowler-Nordheim analysis and breakdown measurements, a barrier height of 2.9 eV and an oxide breakdown of 10.3 MV/cm were determined. The results demonstrate the maturity of the 2°-off axis material and pave the way for the fabrication of 4H-SiC MOSFET devices on this misorientation angle.

Abstract: We evaluate the influence of the growth parameters on the crystal quality of Si films grown by chemical vapor deposition on 3C-SiC(001)/Si (001) epilayers. It is shown that the pressure plays a major role on the final quality of the films, with two distinct growth regimes. The defects in the films were found to be antiphase boundaries and μ-twins. The influence of the growth parameters as well as the 3CSiC structural properties on these defects are discussed. The impact of a subsequent thermal annealing, under different gas environments, is also investigated and reveals some noticeable differences according to the gas environment used in the annealing process.