Lateral/vertical Homoepitaxial Growth on 4H-SiC Surfaces Controlled by Dislocations
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Lateral/vertical Homoepitaxial Growth on 4H-SiC Surfaces Controlled by Dislocations Yoosuf N. Picard1, Andrew J. Trunek2, Philip G. Neudeck3, and Mark E. Twigg1 1 Electronics Science and Technology, Naval Research Lab, Code 6812, 4555 Overlook Ave. SW, Washington, DC, 20375 2 Ohio Aerospace Institute, 21000 Brookpark Rd., Cleveland, OH, 44135 3 NASA Glenn Research Center, 21000 Brookpark Rd., Cleveland, OH, 44135 ABSTRACT This paper reports the influence of screw dislocations on the lateral/vertical growth behavior of chemical vapor deposited (CVD) on-axis homoepitaxial 4H-SiC films grown on patterned mesas. Electron channeling contrast imaging (ECCI) was utilized to image both atomic steps and dislocations while the film structure/orientation was determined using electron backscatter diffraction (EBSD). The presence and position of screw dislocations within the mesa impacted the resultant film thickness, lateral shape, and atomic step morphology. Mesa side walls that incline inwards due to faceting during screw-dislocation driven vertical film growth can intersect with the dislocation step sources near the side walls. If this occurs for all screw dislocations on a mesa, we observe a transition towards laterally dominated growth that produces webbed structures and films surfaces exhibiting significantly lower step densities. Transition from vertical to lateral dominated growth is consistent with ECCI imaged dislocation very near a mesa side wall. INTRODUCTION Homoepitaxial growth of 4H-SiC by chemical vapor deposition (CVD) is a critical processing step for both fabricating devices and producing high quality substrate surfaces. Many process parameters during CVD growth influence nucleation behavior, step-flow dynamics, and growth rates, but dislocations intrinsic to the original wafer substrate can also play a key role. For example, efforts to fabricate step-free 4H-SiC surfaces using patterned mesa structures show film nucleation, growth, and step morphology can be strongly affected by the presence of dislocations [1]. The influence of dislocations on the resulting morphology of on-axis homoepitaxial films grown on patterned mesas is investigated in this work using electron backscattering detection (EBSD) and electron channeling contrast imaging (ECCI). These combined analysis techniques allow structural/orientation determination of the epitaxial film [2] and dislocation/atomic step imaging of the film surfaces [2,3]. Various films grown on individual, isolated mesa structures are analyzed to correlate dislocations and atomic step morphologies to the observed vertical and lateral growth behavior. EXPERIMENT Isolated mesa structures were fabricated on 4H-SiC (0001) on-axis wafer surfaces prior to step-flow homoepitaxial growth by CVD. Specific mesa shapes were formed by photolithographic patterning followed by reactive ion etching [1] for two separate specimens, Sample A and B. Sample A consisted of mesas spanning up to 500 µm wide with a variety of
complex shapes in order to encourage webbed formatio
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