Papers by Author: Carl Hoff

Abstract: 4H Silicon Carbide (4H-SiC) has a great potential for low-loss power devices due to its superior electrical properties. However, the increase in demand for the power devices requires high quality SiC substrates and epitaxial layers. Mercury probe Capacitance Voltage (Hg CV) measurement is a well known procedure to characterize epi layers grown on SiC substrates, due to its non-destructive technique. However, careful calibration of the tool is very important for repeatable and accurate measurements. Here we present very close repeatability of Hg CV within 2.4% (standard deviation 0.7%), between different Solid State Measurements (SSM) setups compared with Ni Schottky (NiS) CV. In addition to growing uniformly doped epi layers, high surface quality of the epi layer is also needed for improved device performance. Improved process conditions resulted in a smooth epi with a surface roughness Ra 1.2 nm for a 6 µm thick epi layer. Molten Potassium Hydroxide (KOH) etching analysis also revealed a significant correlation between the surface roughness and epi defects.

Abstract: In this paper we present highly uniform SiC epitaxy in a horizontal hot-wall CVD reactor with wafer rotation. Epilayers with excellent thickness uniformity of better than 1% and doping uniformity better than 5% are obtained on 3-in, 4° off-axis substrates. The same growth conditions for uniform epitaxy also generate smooth surface morphology for the 4° epiwafers. Well controlled doping for both n- and p-type epilayers is obtained. Abrupt interface transition between n- and pdoped layers in a wide doping range is demonstrated. Tight process control for both thickness and doping is evidenced by the data collected from the epi operations. The average deviation from target is 2.5% for thickness and 6% for doping. PiN diodes fabricated on a standard 3-in, 4° epiwafer have shown impressive performance. More than half of the 1 mm2 devices block 1 kV (2.3 MV/cm) with a low leakage current of 1 μA.

Abstract: This paper presents SiC CVD epitaxy for MESFET fabrication in a horizontal hot-wall reactor with gas foil rotation. Excellent uniformity of < 2% for thickness and < 10% for doping has been routinely obtained for both 3x2-in. and 1x3-in. growth. The highly uniform epitaxy is maintained for the growth of a large range of doping concentrations (less than 5x1015 to greater than 1.5x1019 cm-3) and thicknesses (0.25 – 60 μm). MESFET buffer/channel structure has been characterized with SIMS measurement showing sharp interface transition. Pinch-off voltages are extracted from CV measurements over a full 2-in. wafer.