Papers by Author: Swapna G. Sunkari

Abstract: In this work we present the epitaxial growth of 4H-SiC on 100mm 4° off-axis substrates grown in a multi-wafer CVD planetary reactor. Highly uniform epitaxial layers having thickness and doping uniformities of 1.7% and 1.4% respectively were grown in the production reactor with optimized process conditions at 8µm/hr and 30µm/hr growth rates. Process optimizations resulted in epitaxial layers with surface roughness (RMS) of 0.32nm. Epitaxial layers with a thickness of 53µm grown with a 30µm/hr growth process had minimal degradation in surface roughness (RMS of 0.39nm).

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: Epitaxial growth of 3-in, 4° off-axis 4H SiC with addition of HCl has been presented. Good surface morphology with a low defect density has been obtained, even for epi thickness of 38 µm. Comprehensive characterization techniques conducted on the epi material obtained in this process have independently confirmed the high purity and low density of crystalline imperfections. Low temperature PL displays clear free exciton I77 recombination while no L1 line is discernable. DLTS measurements have confirmed a low concentration of Z1/2 and EH6/7 below or in the range of 1011 cm-3. Time resolved PL at room temperature performed on a 38 µm thick epi wafer gives long carrier lifetime in the range of 1.5 to above 5 µsec. PiN diodes with diode area up to 25 mm2 have demonstrated blocking voltages above 900V, with a max electric field of above 2.5 MV/cm.

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: Room temperature Fourier Transform Infrared Reflection Spectroscopy (FTIR) was used to investigate the thickness and Free Carrier Concentration (FCC) of heavily and lightly doped 4H and 6H-SiC epitaxial films. Multiple epitaxial layer stacks typical of lateral devices such as the MESFET were grown on 6H-SiC semi-insulating substrates. The estimation of thickness and FCC of the n-channel epi layer is improved by studying the Longitudinal Optical Phonon Plasmon Coupled Modes (LPP). A modelbased analysis of the experimental reflectance spectra from these samples is performed using a dielectric function that accounts for the phonon-photon coupling and plasmonphoton coupling. The value of the LPP+ mode frequency estimated from the reflectance spectrum in the range 600-1200 cm-1 is observed to increase in direct correlation with the electron free-carrier concentration.