Papers by Author: Huang De Lin

Abstract: In this work, nitrogen doping was investigated during the low-temperature halo-carbon epitaxial growth of 4H-SiC on Si- and C-faces. The dependencies of nitrogen incorporation on nitrogen flow rate, Si/C ratio, growth rate, and temperature were investigated. It was established that the efficiency of nitrogen incorporation for the C-face growth at 1300 °C is higher than that for the Si-face for a wide range of the growth conditions. Seeming deviation of the Si/C ratio dependence from the “site-competition” trend confirmed the critical role of the silicon vapor condensation during the low-temperature epitaxy. Opposite trends for the nitrogen doping dependence on the growth rate were observed on the Si- and C-faces. Finally, a complex temperature dependence of the nitrogen doping in the temperature range from 1300 to 1450 0C was observed.

Abstract: Previously reported CVD epitaxial growth of 4H-SiC at temperatures down to and below 13000C using CH3Cl precursor offered a promise of new device applications that could benefit from lower-temperature growth process. In this work, selective epitaxial growth (SEG) of 4H-SiC mesas using conventional SiO2 low temperature mask is reported. Virtually no nucleation on the mask could be observed after SEG at 13000C. The mask could be easily removed after the growth, with no degradation of the surface of SiC substrate under the mask. For the growth conditions that normally resulted in growth rate of 2 /m/hr and defect-free epilayer morphology during regular full-wafer (non-SEG) epitaxy, the epilayer morphology during SEG was significantly degraded by the appearance of oriented triangular defects, while the growth rate increased more than three times in comparison to the blanket epitaxial growth due to the loading effect. The growth at optimized growth conditions and lower growth rate resulted in significant reduction of the surface defects, making this approach promising for obtaining device-quality mesas. The crystal quality of the mesas, defects at the mesa walls, formation of facets during SEG, and other effects are reported.

Abstract: Low-temperature epitaxial growth of 4H-SiC with CH3Cl carbon precursor was further developed. In-situ doping with nitrogen and aluminum was investigated. The nitrogen concentration in epitaxial layers grown on the C face was almost two orders of magnitude higher than that in the Si-face epilayers grown in the same growth run at 13000C. The opposite trend was observed for intentional aluminum doping, with more than an order of magnitude higher aluminum concentration incorporated in Si-face epilayers. High values of nitrogen and aluminum doping well in excess of 1020 cm-3 without any obvious epilayer morphology degradation can be achieved on C-face and Siface respectively. Addition of HCl during halo-carbon growth at 13000C resulted in drastic improvement of the surface morphology. Also, a significant increase of the growth rate took place confirming that the improvement in the epilayer morphology during HCl-assisted growth is predominantly related to silicon cluster etching by additional Cl-containing vapor species.

Abstract: In this work, the mechanism of the epitaxial growth of 4H SiC using CH3Cl as the carbon source gas was investigated. The experiments were conducted with a H2 carrier gas flow rate reduced in comparison to the standard conditions used for device-quality, full-wafer C3H8 growth. Low-H2 conditions have been found favorable for investigating the differences between the two gas systems. A non-linear trend of the growth rate dependence on CH3Cl flow was observed. This dependence was quantitatively different for C3H8 growth, which serves as an indication of different kinetics of CH3Cl and C3H8 precursor decomposition, as well as differences in Si droplet formation and dissociation. The maximum growth rate that we were able to achieve was by a factor of two higher for the CH3Cl precursor than for the C3H8 precursor at the same temperature and flow conditions. The growth on lower off-axis angle substrates produced surface morphology degradation similar for both CH3Cl and C3H8 precursor systems.

Abstract: The advantages of the CH3Cl carbon precursor were investigated in order to achieve good-quality homoepitaxial layers of the 4H-SiC polytype at temperatures lower than what was considered practical (or even possible) with C3H8-based growth. It was observed that the process window for good epilayer morphology becomes narrower when the growth temperature is decreased. Successful growth experiments have been conducted in this work down to a temperature of 1290-13000C, with the growth rate in excess of 2 +m/hr and a mirror-like defect-free epilayer surface morphology. Growth on a 2” substrate produced promising growth rate homogeneity. The dependence of the growth rate on SiH4 flow followed a clear exponential dependence. This trend is tentatively attributed to Si vapor condensation. Photoluminescence results suggest that the crystalline quality of the epilayers grown at 13000C is comparable to that of 17000C growth.

Abstract: The results of the initial experiments with halogenated carbon precursor chloromethane (CH3Cl) for epitaxial growth of 4H-SiC are presented. The growth rate for mirror-like morphology was easily increased up to about 7 µm/hr at C-rich conditions without detectable surface morphology degradation. Further increase of the silane flow resulted in island formation. The growth with the traditional silane-propane system at the same conditions (and optimized Si/C ratio) produced a very different result, with the growth rate decreasing from upstream to downstream, and morphology degradation taking place for much lower growth rate than in CH3Cl growth. Consequently, the epitaxial growth with chloromethane appears to have significantly different kinetics of the gas-phase precursor decomposition and different mechanisms of the surface reactions, which favors the step-flow growth. In addition, these preliminary data indicated that the maximum achievable growth rate corresponding to the good surface morphology may be noticeably larger for the CH3Cl+SiH4+H2 growth system.