Materials Science Forum Vols. 483-485

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.

Abstract: 4H-SiC layers have been homoepitaxially grown on off-axis 4H-SiC(000-1) under various conditions by horizontal hot-wall CVD. Improvement of surface morphology and reduction of background doping concentration have been achieved. Surface morphology grown on the (000-1) C face strongly depends on the C/Si ratio at 1500 °C, and hillock-like surface defects can be eliminate by increasing growth temperature to 1600 °C. Site-competition behavior is clearly observed under low-pressure growth conditions even on the (000-1) C face. The lowest doping concentration has been determined to be 6.0x1014 cm-3. A trial of high-speed growth on the (000-1) C face and deep level analysis are also discussed.

Abstract: Chemical vapor deposition of 4H-SiC on (0001) substrates with various off-angles from 1o to 45o has been investigated. On large-off-angled (15o-45o) substrates, very smooth surface morphology is obtained in the wide range of C/Si ratio. The micropipe dissociation during epitaxial growth is observed on 4o-45o off-angled substrates with a low C/Si ratio. The incorporation of nitrogen was dramatically suppressed by increasing C/Si ratio irrespective of substrate’s off-angle.

Abstract: Homoepitaxial growth was carried out on 4H-SiC on-axis substrate by horizontal hot wall chemical vapor deposition. By using carbon face substrate, specular surface morphology of a wide area of up to 80% of a 2-inch epitaxial wafer was obtained at a low C/Si ratio growth condition of 0.6. The Micropipe in on-axis substrate was indicated to be filled with spiral growth and to be dissociated into screw dislocations during epitaxial growth. It was found that the appearance of basal plane dislocations on the epitaxial layer surface can be prevented by using an on-axis substrate.

Abstract: In this paper, we investigated the density of basal plane dislocations (BPDs) in 4H-SiC epilayers grown on (0001) and (000-1). Re-polishing of the substrate surface, in-situ H2 etching and off-cut angle were found to influence the propagation of BPDs into the epilayers. The epitaxial growth on (000-1) substrates yields a relatively low density of BPDs compared to growth on (0001). The electrical characteristics of pn diodes were also investigated, and the suppressed forward degradation and high-voltage blocking performance were obtained in the use of the (000-1) epilayers.

Abstract: The phosphorus incorporation into SiC epilayer is studied when varying the CVD process growth parameters and the results are compared with thermodynamical calculations. Photoluminescence spectra are also presented.

Abstract: Mechanisms and consequences of silicon vapor condensation during SiC epitaxial growth or implant annealing with silane overpressure were investigated. The model for the silicon liquid droplets formation in the gas phase and their deposition on the surface of the SiC substrate was developed. The droplet formation dependence on the silane flow rate, temperature profile in the reactor, and the local temperature variations introduced by the wafer carrier and SiC substrate were investigated.

Abstract: Growth of 4H-SiC epitaxial layers has been performed in a horizontal hot-wall CVD (chemical vapor deposition) reactor using the silane-propane-hydrogen system. Two inch 4H-SiC, C-face wafers with an off-cut angle of about 7° towards <11 2 0> direction have been used as substrates. Micropipe dissociation has been investigated by varying the carbon-silicon (C/Si) ratio in the source gas atmosphere. Depending on the C/Si ratio the micropipes propagate into the layer without changing their image (C/Si > 1) or they dissociate in separate dislocations leaving a scar like formed surface region (C/Si £ 1). The substrates including epitaxial layers of reduced micropipe density were used as seeds for bulk crystal growth. If a micropipe is once closed in an epilayer grown at a low C/Si ratio, it is not opened in the subsequent growth process at high temperature.

Abstract: Thick epilayers up to 60 µm have been grown on ) 0 2 11 ( face SiC substrates at a growth rate of 15 µm/hr by chemical vapor deposition (CVD). The epilayer surface is extremely smooth with a RMS roughness of 0.6 nm for a 20µm×20µm area. Threading screw and edge dislocations parallel to the c-axis are present in the ) 0 2 11 ( substrate; however, they do not propagate into the epilayer. The I-V characteristics of the Schottky diodes on this face were studied. Basal plane (0001) dislocations with a density of ~105 cm-2 were found in the ) 0 2 11 ( epilayers by molten KOH etching and electron beam induced current (EBIC) mode of the scanning electron microscope (SEM).

Abstract: We report an experimental investigation of the residual (n-type) and intentional (p-type) doping level of <11-20> epitaxial layers grown on a-cut 4H-SiC substrates. Using SIMS, C(V) measurements, low temperature photoluminescence and Hall effect investigations, we show that nitrogen incorporates 3 times more than usually found for <0001> surfaces. Conversely, aluminum incorporates 8 times less. Altogether, this is in excellent agreement with previous results from stepcontrolled epitaxy.