Papers by Author: M.F. Brady

Abstract: Availability of high-quality, large diameter SiC wafers in quantity has bolstered the commercial application of and interest in both SiC- and nitride-based device technologies. Successful development of SiC devices requires low defect densities, which have been achieved only through significant advances in substrate and epitaxial layer quality. Cree has established viable materials technologies to attain these qualities on production wafers and further developments are imminent. Zero micropipe (ZMP) 100 mm 4HN-SiC substrates are commercially available and 1c dislocations densities were reduced to values as low as 175 cm-2. On these low defect substrates we have achieved repeatable production of thick epitaxial layers with defect densities of less than 1 cm-2 and as low as 0.2 cm-2. These accomplishments rely on precise monitoring of both material and manufacturing induced defects. Selective etch techniques and an optical surface analyzer is used to inspect these defects on our wafers. Results were verified by optical microscopy and x-ray topography.

Abstract: Recent advances in PVT c-axis growth process have shown a path for eliminating micropipes in 4HN-SiC, leading to the demonstration of zero micropipe density 100 mm 4HN-SiC wafers. Combined techniques of KOH etching and cross-polarizer inspections were used to confirm the absence of micropipes. Crystal growth studies for 3-inch material with similar processes have demonstrated a 1c screw dislocation median density of 175 cm-2, compared to typical densities of 2x103 to 4x103 cm-2 in current production wafers. These values were obtained through optical scanning analyzer methods and verified by x-ray topography.

Abstract: Experimental results are presented for SiC epitaxial layer growth employing a large-area, up to 8x100-mm, warm-wall planetary SiC-VPE reactor. This high-throughput reactor has been optimized for the growth of uniform 0.01 to 80-micron thick, specular, device-quality SiC epitaxial layers with low background doping concentrations of <1x1014 cm-3 and intentional p- and n-type doping from ~1x1015 cm-3 to >1x1019 cm-3. Intrawafer layer thickness and n-type doping uniformity (σ/mean) of ~2% and ~8% have been achieved to date in the 8x100-mm configuration. The total range of the average intrawafer thickness and doping within a run are approximately ±1% and ±6% respectively.

Abstract: Experimental results are presented for SiC epitaxial layer growths employing a largearea, 7x3-inch, warm-wall planetary SiC-VPE reactor. This high-throughput reactor has been optimized for the growth of uniform 0.01 to 30-micron thick, specular, device-quality SiC epitaxial layers with background doping concentrations of <1x1014 cm-3. Multi-layer device profiles such as Schottky, MESFETs, SITs, and BJTs with n-type doping from ~1x1015 cm-3 to >1x1019 cm-3, p-type doping from ~3x1015 cm-3 to >1x1020 cm-3, and abrupt doping transitions (~1 decade/nm) are regularly grown in continuous growth runs. Intrawafer layer thickness and n-type doping uniformities of <1% and <5% s/mean have been achieved. Within a run, wafer-to-wafer thickness and doping variation are ~±1% and ~±5% respectively. Long term run-to-run variations while under process control are approximately ~3% s/mean for thickness and ~5% s/mean for doping. Latest results from an even larger 6x4-inch (100-mm) reactor are also presented.