Single crystal growth of SiC and electronic devices

Abstract

Single crystal growth of silicon carbide (Sic) and application to electronic devices are reviewed. In the crystal growth, bulk and homoepitaxial growth are picked up, and crystal quality and electrical properties are described. For electronic devices, various device processes are argued. Power devices based on Sic are stressed in this review. Bulk single crystals of SiC can be grown by a sublimation method, and large-area 6H-SiC and 4H-SiC single crystals are obtained. The occurrence of SiC polytypes is affected by the growth condition, and can be controlled successfully by optimizing these conditions. 6H-SiC is grown on 6H-SiC (0001) Si-faces, and 4H-SiC on 6H-SiC (0001) C-faces. The crystallinity of bulk crystals is investigated by reflection high-energy electron diffraction (RHEED) and X-ray analysis, and characterization is carried out in detail by optical and electrical measurement. Successful homoepitaxial vapor phase growth of SiC can be realized using off-axis (0001) substrates prepared by a sublimation method called “step-controlled epitaxy”. Since the crystallinity of epilayers is improved during the step-controlled epitaxy, this growth technique is a key for getting high-quality crystal surfaces. Impurity doping is controlled during homoepitaxial growth by employing impurity gases, such as N2, trimethylaluminum (TMA), and B2H6. A wide-range of carrier concentrations of 5 × 1013∼3 × 1018 cm−3 for n-type and 5 × 1016∼3 × 1020 cm−3 for p-type are realized. The impurity-incorporation mechanism in the step-controlled epitaxy is discussed based on the C/Si ratio dependence of impurity doping. Electrical properties of SiC grown by step-controlled epitaxy are determined precisely. A high electron mobility of 720 cm2/Vs is obtained in an undoped 4H-SiC epilayer with an electron concentration of 2.5 × 10l6 cm−3 at 300 K. This electron mobility is about two times higher than that of 6H-Sic (∼380 cm2/Vs). High breakdown fields of 1∼5 × 106 V/cm are obtained for both 6H- and 4H-SiC, one order of magnitude higher than those for Si. A high saturation electron drift velocity of 1.6 × 107 cm/s is obtained in 4H-Sic, which may make possible high performance of high-frequency 4H-SiC power devices. Impurity levels and deep levels are investigated by Hall effect, admittance spectroscopy, and DLTS measurement. Metal/4H-SiC Schottky barrier heights are characterized and a strong dependence on metal work function without strong “pinning” is elucidated. Device processes are described for ion implantation. Interface properties of SiO2/SiC are characterized in detail using metal-oxide-semicond.