Papers by Author: Jody Fronheiser

Abstract: We describe fabrication of Van der Pauw (VDP) structures for characterization of gate oxides grown on 4H SiC epi surfaces. Implementation of sub-resolvable features (SRF) as a corner compensation mechanism is analyzed with challenges and advantages presented. Results of on-wafer screening tests suggest that implementation of SRFs widens tolerance for misalignment, producing similar yield between uncompensated VDPs with 0.2 micron overlap and compensated VDPs with 0.1 micron overlap for structures with best alignment. Optimization of SRFs for SiC could be an attractive option for extending lithographic capability in advanced devices.

Abstract: The quality of the SiC/SiO₂ interface is critical to the stability and performance of MOS-based SiC power devices. Charge pumping is a flexible interface characterization technique. In this work, a significant portion of the total traps are found to be located in the near-interface oxide using frequency-dependent charge pumping. Oxide trap tunneling mechanisms are discussed, and trap profile as a function of depth is calculated. The trap density is shown to increase exponentially as it gets closer to the interface.

Abstract: The gate oxide reliability and channel mobility of carbon face (000-1) 4H Silicon Carbide (SiC) MOSFETs are investigated. Several gate oxidation processes including dry oxygen, pyrogenic steam, and nitrided oxides were investigated utilizing MOS capacitors for time dependent dielectric breakdown (TDDB), dielectric field strength, and MOSFETs for inversion layer mobility measurements. The results show the C-face can achieve reliability similar to the Si-face, however this is highly dependent on the gate oxide process. The reliability is inversely related to the field effect mobility where other research groups report that pyrogenic steam yields the highest electron mobility while this work shows it has weakest oxide in terms of dielectric strength and shortest time to failure.

Abstract: We have extended a magnetic resonance based study of MOS devices to include electrically detected magnetic resonance (EDMR) measurements of fully processed MOSFETs from three facilities as well as conventional electron paramagnetic resonance (EPR) resonance measurements on simple SiC/SiO2 structures. We find close similarity between the conventional EPR and the EDMR spectra.

Abstract: We explain the role of nitrogen in simultaneously increasing the inversion channel mobility and reducing the threshold voltage of SiC MOSFET. A variety of computational techniques have been used to compute the atomic scale configuration of a nitridated SiC/SiO2 interface, and the corresponding change in Fermi level, inversion channel mobility, and threshold voltage. X-ray photoelectron spectroscopy (XPS) has been used to investigate the SiC/SiO2 interface to determine the nitrogen concentrations and chemical bonding. We elucidate the physics behind improved channel mobility due to NO anneal and demonstrate that the trade-off between threshold voltage and inversion channel mobility can be correlated to the extent of nitridation.

Abstract: 4H-SiC single photon avalanche diodes are reported. A separate absorption and multiplication non-reach through device structure was optimized for operation in Geiger mode. An estimated dark current at a gain of 1000 was ranging between 0.4 pA (0.75 nA/cm2) and 20nA (38 A/cm2) on devices with an effective mesa diameter of 260 m. The electron beam induced current technique was used to image defects in the active region of studied devices. Increased reverse bias leakage current and increased Geiger mode dark count probability were correlated with the presence of large number of defects. Single photon detection efficiencies of up to 11% were measured at a wavelength of 266 nm in Geiger mode.

Abstract: In this work, solar-blind UV 4H-SiC avalanche photodetectors were fabricated and tested in linear and Geiger modes. APDs with both PIN and separate absorption and multiplication (SAM) structures were investigated. PIN structures demonstrated higher quantum efficiencies while the SAM structure exhibit lower leakage currents. Deposition of a thin film optical filter on top of the devices was used to provide a high photon rejection ratio of (Stas add value here). However, an external filter showed a better photon rejection ratio compared to the deposited one by about one order of magnitude.

Abstract: We report on the fabrication and testing of SiC p-i-n avalanche photodiodes. APDs of 0.25 mm2 area on a-plane (1120) 6H-SiC as well as off-axis Si face 6H and 4H-SiC were successfully fabricated. A beveled mesa was used as edge termination. Recessed windows were formed using reactive ion etching to enhance low-wavelength UV performance. We performed current-voltage tests with and without UV illumination to determine dark current, photocurrent, and gain on selected devices. Dark current was less than 1 pA at 0.5Vbr on multiple devices. Quantum efficiency of 40% or greater was observed for all orientations and polytypes.

Abstract: In this work, avalanche photodiodes (APDs) were fabricated using a-plane 6H- and 4H-SiC materials to investigate their electrical and optical properties. Temperature dependence of avalanche breakdown was measured. The diode structures were fabricated with positive angle beveling and oxide passivation to ensure a uniform breakdown across the device area. Despite the apparent presence of micro-plasmas, we observed that the breakdown voltage of a-plane 6H-SiC APDs increased with temperature suggesting a positive temperature coefficient.

Abstract: The effect of using different orientations of 4H-SiC substrates on the performance of 4H-SiC MOSFETs has been evaluated. Three sets of samples with (0001), (000-1) and (11-20) oriented SiC substrates were used to fabricate the MOSFETs, with a gate oxide process consisting of a low- temperature deposited oxide followed by NO anneal at 1175°C for 2hrs. Various device parameters, particularly threshold voltage, subthreshold slope, field-effect mobility, inversion sheet carrier concentration and Hall mobility have been extracted. Temperature characterization up to 225°C was also performed.