Date of Award

5-2014

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Materials Science and Engineering

Major Professor

Gerd Duscher

Committee Members

Kurt E. Sickafus, Yanwen Zhang, Gong Gu, John R. Dunlap

Abstract

The interface between silicon carbide (SiC) and silicon dioxide (SiO­2) is generally considered to be the cause for the reduced electron mobility of SiC power devices. Previous studies showed an inverse relationship between the mobility and the transition layer width at SiC/SiO2 interface. In this research the transition region at the interface was investigated with atomic resolution transmission electron microscopy (TEM) and electron energy-loss spectroscopy (EELS).

From a tilting series of high resolution TEM imaging and a through focal series of Z-contrast imaging, the 3D atomic structure of the SiC/SiO2 vicinal interface was constructed. The vicinal interface was revealed to consist of atomic steps and facets deviating from the ideal off-axis cut plane, which caused the atomic scale roughness of the interface. This is in strict contrast to previous studies that concluded on a chemical composition change.

During the Z-contrast imaging, simultaneous EELS spectra were collected at the interface. A new model based method was developed to quantify these EELS spectra more precisely. Composition profiles of Si, C and O across the interface were extracted from the spectra. Composition profiles showed that the transition region was due to the vicinal interface and its atomic scale roughness but minimal stoichiometric change. Compositions calculated with a chemometrics approach conformed that the interface was stoichiometric. The transition layer width had an intrinsic value of ~2 nm viewed from the step edge-on direction. In addition, the interface of oxide layers grown on an on-axis cut substrate was examined with the same method mentioned above. The results showed the on-axis cut interface had the same composition fluctuation region as the off-axis cut interface viewing from the step edge-on direction.

The roughness is directly correlated with processing conditions and the material system may have an intrinsic local roughness. This atomic scale roughness of the interface is limiting the electron mobility and reliability of SiC based devices.

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