III-Nitride Epitaxial Material on Large-Diameter Semi-Insulating SiC Substrates for High Power RF Transistors
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III-Nitride Epitaxial Material on Large Diameter Semi-Insulating SiC Substrates for High-Power RF Transistors Adam W. Saxler1, Edward L. Hutchins1, Jason Jenny1, and Austin Blew2 1 Cree, Inc., 4600 Silicon Drive, Durham, NC 27703, U.S.A. 2 Lehighton Electronics, Inc., P.O. Box 328, Lehighton, PA 18235-0328, U.S.A. ABSTRACT Metalorganic chemical vapor deposition was employed to deposit high quality, highly uniform III-Nitride transistor structures on 100 mm diameter semi-insulating 4H-SiC substrates. Electron mobility was over 2000 cm2/Vs at room temperature. Sheet resistivity uniformity was as low as 0.75%. Typical standard deviations were about 1% in most properties including sheet resistivity, carrier concentration, mobility, and AlGaN composition. Additionally, wafers maintained their flat shape after deposition of these structures. Wafer bow and warp were typically less than 20 µm for optimized structures and 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 0 0 0 0 0 0 0 0 0 0 0 0
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AlN Barrier GaN Channel Buffer Layer SiC Substrate
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Figure 1. (a) Micropipe map for a 100-mm high-purity semi-insulating 4H-SiC substrate. The micropipe density is 26 cm-2 and 77% of the squares are micropipe free. (b) Schematic drawing of the epi layer structure.
Electrical measurements were performed using Lehighton instruments. A model 1600 instrument at Lehighton was used to measure mobility and carrier concentration, at five points approximately one inch in diameter as shown in Figure 2. The mobility was 2070 cm2/Vs with a standard deviation of only 0.4 %. The sheet carrier concentration was 8.9 x 1012 cm-2 with a standard deviation of 1.0 %. Combined, this gives a sheet resistivity of 340 Ω/square with a standard deviation of 0.8 %.
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Figure 2. Room temperature mobility (a) and sheet carrier concentration (b) maps of a 100 mm HEMT wafer on HPSI 4H-SiC.
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A Lehighton model 1510 located at Cree was used to measure resistivity at 61 points with a 14 mm diameter head. The edge of the head came within 2 mm of the wafer edge during the mapping process. A map of a III-Nitride HEMT with an average sheet resistivity of 305 Ω/square and a standard deviation of only 0.75% is shown in Figure 3. Statistics for 19 wafers are shown in Figure 4 with a median sheet resistivity standard deviation of only 1.1%.
Figure 3. Sheet resistivity map of a III-Nitride HEMT on a 100 mm HPSI 4H-SiC substrate showing excellent uniformity with only 2 mm edge exclusion.
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100mm Wafer Count
Quantiles 100.0% maximum 99.5% 97.5% 90.0% quartile 75.0% median 50.0% quartile 25.0% 10.0% 2.5% 0.5% minimum 0.0%
59.790 59.790 59.790 3.370 1.410 1.110 0.870 0.750 0.750 0.750 0.750
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Sheet Resistivity Standard Deviation (%)
Figure 4. Statistics for sheet resistivity uniformity on 19 wafers with a median of only 1.1%.
The compo
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