Intrinsic Surface defects on 4H SiC substrates
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1246-B03-03
Intrinsic Surface defects on 4H SiC substrates M.E. Zvanut, S.A. Thomas, and J. Dashdorj Department of Physics, University of Alabama at Birmingham 1300 University Blvd., Birmingham, AL 35299-1170, U.S.A.
ABSTRACT We have investigated a point defect, common to all SiC substrates, that is thought to be a broken carbon bond. Electron paramagnetic resonance spectroscopy performed in combination with three different etching methods using p-type, n-type, and semi-insulating substrates demonstrate that the center lies near the surface of a wafer. The results suggest that on the order of 1013 cm-2 defects are removed within the first micron of the surface of a wafer. INTRODUCTION One of the most important attributes of almost any semiconductor is the surface, where most devices are built. This is particularly true for SiC because it has attractive characteristics for high voltage, high current device applications due to the large thermal conductivity and electrical breakdown voltage [1,2]. Most device structures are epitaxially deposited on the Siface of a specially prepared SiC wafer using a variety of preparation techniques. As shown in several recent studies, the structural quality of this surface is critical to future applications of many proposed electronic devices [3]. While electrical studies can highlight the significance of these centers, they cannot directly chemically identify the defect structure. This work utilizes electron paramagnetic resonance (EPR) spectroscopy to identify and count point defects that are shown to be located within the first micron of a 4H SiC substrate surface. Many techniques exist for characterizing the surface of semiconductors, including atomic force microscopy, x-ray photoemission spectroscopy, and scanning electron microscopy. The tool used here, EPR spectroscopy, has successfully revealed several important features of a variety of semiconductor systems [4-8]. For example, Brodsky and Title studied amorphous SiC and others have addressed the technologically significant Si/SiO2 interface [4,7]. The success of EPR in these instances is somewhat surprising because the technique is not surface specific, nor can it directly measure the depth distribution of defects. However, EPR can provide the total number of centers and their chemical identity. When combined with an etching process, the technique can be used to determine the location of the defects.
EXPERIMENTAL DETAILS Three types of 4H SiC substrates grown by physical vapor transport were measured by EPR before and after etching. The bare substrate pieces were cut from a 3 -cm single-side polished p-type wafer, a 5-10 -cm double-side polished n-type wafer, or vanadium-doped double side polished high resistivity wafer. All samples were examined before and after a 900 o C dry (
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