Recent Developments in SiC Homoepitaxy using Dichlorosilane for High Power Devices
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1246-B04-06
Recent Developments in SiC Homoepitaxy using Dichlorosilane for High Power Devices Iftekhar Chowdhury1, MVS Chandrasekhar1, Paul B Klein2, Joshua D. Caldwell2 & Tangali Sudarshan1. 1 University of South Carolina, Electrical Engineering, Columbia, SC 29208 2 Naval Research Laboratory, Washington D.C ABSTRACT Thick and high quality 4H-SiC epilayers have been grown in a vertical hot-wall chemical vapor deposition system at a high growth rate on (0001) 80 off-axis substrates. We discuss the use of dichlorosilane as the Si-precursor for 4H-SiC epitaxial growth as it provides the most direct decomposition route into SiCl2, which is the predominant growth species in chlorinated chemistries. The RMS roughness of the films ranged from 0.5-2.0 nm with very few morphological defects (carrots, triangular defects, etc.) being introduced, while enabling growth rates of 30-100 µm/hr, 5-15 times higher than most conventional growths. A specular surface morphology was attained by limiting the hydrogen etch rate until the system was equilibrated at the desired growth temperature. Site-competition epitaxy was observed over a wide range of C/Si ratios, with doping concentrations as low as 2x1014 cm-3 being recorded. X-ray rocking curves indicated that the epilayers were of high crystallinity, with linewidths as narrow as 7.8 arcsec being observed, while microwave photoconductive decay (µPCD) measurements indicated that these films had high injection (ambipolar) carrier lifetimes in the range of 2 µs. These films also appeared to be free of polytype inclusions. INTRODUCTION Silicon carbide is a desirable material for high power and high frequency devices due to its wide band gap, high break-down field and high thermal conductivity compared to silicon. Furthermore, the higher junction operating temperatures possible with SiC (~400°C), in comparison to silicon (~170°C - 200°C), reduces the cooling requirements of SiC-based power systems, allowing compact, high performance modules to be realized. In recent years, there has been strong interest in high-power devices with blocking voltages in excess 10 kV. Several papers have been published on power DMOSFETs [1], implanted VJFETs [2], PiN diodes [3], and Schottky diodes [4]. In all these devices, an epitaxial layer of 80-100 µm is required to achieve large blocking voltages. To obtain such thicknesses with standard silane-based chemical vapor deposition (CVD) processes, which have typical growth rates of 6-7 um/hr [5], process times would exceed ten hours, leading to a significant increase in the manufacturing cost. Therefore, the development of SiC epitaxy with growth rates exceeding 50 µm/hr is highly desired. SiC CVD processes typically use silane and light hydrocarbons, such as propane or ethylene, diluted in hydrogen as a carrier gas. Growth rate increment by increasing precursor flow leads to the homogeneous nucleation of liquid silicon droplets [6]. These SiC-coated droplets eventually decrease the efficiency of precursor use and degrade crystal quality. Recent results [7
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