Silicon carbide epitaxial growth for power device applications

Basic material properties make SiC an interesting semiconductor for devices operating at high temperature and high power. The controlled growth of high-quality epilayers is a key issue in the realization of SiC electronics. This thesis focuses on the studies of epitaxial growth of SiC with an aim to improve the epilayer quality, growth reproducibility and doping controllability. A new chemical vapor deposition (CVD) system was designed and custom-built for this purpose, and the system was characterized by growing undoped films under various growth conditions. Process conditions were developed to grow undoped film with background doping concentration less than 1015 cm −3 with specular surface morphology. P-type films with trimethylaluminum as the precursor were grown with the hole concentrations in the range 10 15 to 1018 cm−3. These films were characterized by atomic force microscopy, double crystal x-ray diffraction, Capacitance-Voltage measurements and variable temperature Hall measurements.; Detailed investigation on the various in-situ etching processes was carried out and the results show that etching SiC in pure H₂ results in the formation of Si-droplets due to the low removal rate of Si compared to that of hydrocarbons. Adding C₃H₈ to H₂ flow is effective in inhibiting the formation of Si-droplets, but reduces the etch rate. While this process with low etch rate is routinely used in cleaning commercially available substrates, it is not suitable for cleaning susceptors or for etching substrates with deep surface damage. Two new processes, H ₂/O₂ etching and H₂/sublimation etching have been developed to overcome the low etch rate problem. Etching using H₂/O ₂ can increase the etch-rate and yet prevent the formation of Si droplets. The new sublimation method can etch SiC much faster (∼100μm/hr) at relatively low temperature (<1600°C). This later method is particularly useful for cleaning the susceptors after growth. Use of this method prior to every growth has improved the growth reproducibility as well as increased the lifetime of susceptors.; Another key contribution of this thesis is a detailed study on the in-situ doping using phosphorous. The doping behavior of phosphorous is investigated and compared with that of nitrogen. Compared to nitrogen, phosphorous incorporation shows a weaker dependence on the precursor flow and shows a limited site competition effect. Also, phosphorous incorporation for a given precursor flow decreases with temperature while that of nitrogen increases. The phosphorous-doped epilayers are characterized by variable temperature Hall measurements, from which two energy levels for both 4H-SiC and 6H-SiC are extracted. These are the first available data on the ionization energy of phosphorous in epitaxial SiC.