Profiling of the SiO 2 - SiC Interface Using X-ray Photoelectron Spectroscopy
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Profiling of the SiO2 - SiC Interface Using X-ray Photoelectron Spectroscopy 1 1 1 2 2 R. N. Ghosh , S. Ezhilvalavan , B. Golding , S. M. Mukhopadhyay , N. Mahadev , P. 2 3 4 Joshi , M. K. Das and J. A. Cooper, Jr. 1 Center for Sensor Materials, Michigan State Univ., E. Lansing, MI 48864 2 Dept. of Mechanical & Materials Engineering, Wright State Univ., Dayton, OH 45435 3 Cree Inc., 4600 Silicon Dr., Durham, NC 27703 4 School of Electrical & Computer Engineering, Purdue Univ., W. Lafayette, IN 47907
ABSTRACT
The implementation of SiC based sensors and electronics for operation in chemically harsh, high temperature environments depends on understanding the SiO 2/SiC interface in field effect devices. We have developed a technique to fabricate wedge polished samples (angle ~ -4 1x10 rad) that provides access to the SiO2/SiC interface via a surface sensitive probe such as xray photoelectron spectroscopy (XPS). Lateral scanning along the wedge is equivalent to depth profiling. Spatially resolved XPS images of the O 1s and Si 2p core levels were obtained of the interfacial region. Samples consist of device-quality thermally grown oxides on 4H-SiC single crystal substrates. The C 1s spectrum suggests the presence of a graphitic layer on the nominally bare SiC surface following thermal oxidation.
INTRODUCTION
Recent advances in silicon carbide device technology have enabled the implementation of SiC based sensors and electronics for operation in chemically harsh, high temperature environments that are beyond the reach of Si based technology. Despite their initial promise, the performance of SiC field effect devices is limited by the low mobility, compared to the bulk, of electrons in a two dimensional electron gas at the SiO2/SiC interface. There are a number of mechanisms responsible for short range non-uniformities in the electrostatic potential at the SiO2/SiC interface that contribute to additional scattering of the confined electrons. These may include: a) interface roughness, i. e., spatial inhomogeneities of the SiO 2/SiC interface b) random distribution of excess charge in the oxide or close to the interface c) structural disorder of the SiC lattice at the interface, which may create a transitional layer in both the oxide and the silicon carbide. Both theoretical and experimental studies of the of the oxidation of SiC [1, 2] suggest the presence of carbon dangling bonds at the interface and/or small carbon precipitates remaining in the SiC following oxidation. Our interest is the chemical disorder of the SiO 2/SiC system and how it results in electron scattering by fluctuations in the electrostatic potential at the interface between the two materials. A number of different experimental techniques have been utilized to study this problem. Atomic
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resolution Z-contrast microscopy, combined with spatially resolved electron energy loss spectroscopy, have revealed a 1.5-6 nm thick layer with a monotonically decaying C concentration at the interface [3, 4]. X-ray photoelectron spectroscopy (XPS) together wit
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