Materials Science Forum Vols. 778-780

Abstract: Low frequency noise in 4H-SiC lateral p-channel metal oxide semiconductor field effect transistors (PMOSFETs) in the frequency range from 1 Hz to 100 kHz has been used to investigate the relationship between gate dielectric fabrication techniques and the resulting density of interface traps at the semiconductor-dielectric interface in order to examine the impact on device performance. The results show that the low frequency noise characteristics in p-channel 4H-SiC MOSFETs in weak inversion are in agreement with the McWhorter model and are dominated by the interaction of channel carriers with interface traps at the gate dielectric/semiconductor interface.

Abstract: We evaluated the carrier lifetime to estimate surface recombination velocities for 4H-SiC whose surfaces were treated by various processes. We found that the reactive ion etching (RIE) increased the surface recombination velocity, and we considered that point defects introduced by RIE influence the surface recombination velocity.

Abstract: The electrically active deep levels in a graphene / silicon carbide field effect transistor (FET) were investigated by drain-current deep level transient spectroscopy (I_D-DLTS). An evaluation procedure for I_D-DLTS is developed in order to obtain the activation energy, the capture cross section and the trap concentration. We observed three defect centers corresponding to the intrinsic defects E₁/E₂, E_i and Z₁/Z₂ in n-type 6H-SiC. The determined parameters have been verified by conventional capacitance DLTS.

Abstract: The leakage currents through the gate oxide of MOS capacitors fabricated on n-type 4H-Silicon Carbide (SiC) was measured under accumulation bias conditions with heavy-ion irradiation. The Linear Energy Transfer (LET) dependence of the critical electric field (E_cr) at which dielectric breakdown occurred in these capacitors with two different oxide thicknesses was evaluated. The MOS capacitors with thin gate oxide showed higher E_cr values than those with thick gate oxide. The linear relationship between the reciprocal E_cr and LET was observed for both MOS capacitors. The slope of LET dependence of 1/E_cr for SiC MOS capacitors was smaller than that for Si, suggesting that SiC MOS devices are less susceptible to single-event gate rupture (SEGR) than Si MOS devices.

Abstract: 3C-SiC(111) was grown on Si (111) in a thickness range between 20 and 600 nm by low pressure chemical vapour deposition. The mechanical properties and the residual stress were determined using cantilevers and beams. The Youngs modulus of the 3C-SiC(111) decreases with decreasing thickness of the epitaxial layer.

Abstract: We examined the warpage structure in epitaxial 4H-SiC wafers subjected to phosphorus-ion (P⁺) implantation and post-annealing with varying implantation and annealing temperatures, using glazing-incidence monochromatic synchrotron X-ray topography. Using Raman spectroscopy, we then studied the relationship between the warpage of the crystal plane in the underlying epilayer and the recovery of lattice disorder in the implanted layer. We determined that the warpage structure of the underlying SiC epilayer was closely correlated with the recovery of lattice disorder in the implanted layer.

Abstract: The room temperature residual stress of 4H-SiC wafers has been investigated using a precise X-ray diffraction method. A large strain was observed for the circumferential direction of wafers, more than ten times larger than those measured along the principal plane direction and the radial direction. Optimizing the lateral temperature distribution in growing crystals leads to reduction of residual stress of wafers with high crystal quality.

Abstract: The aim of this work is to develop the bulge test technique combined with the micro-Raman analysis and a refined load-deflection model for high quality 3C-SiC squared-membranes. By the minimization of the total elastic energy, starting from the isotropic relation between the stress tensor and the strain tensor, it is possible to calculate the relationship between the maximum deflection and the applied pressure, in both regime of small and large deflection. Furthermore, the relationship between the measured shift of Raman Transverse Optical (TO) phonon modes and the total residual strain (Δa/a) within the epitaxial 3C-SiC layer was found and in order to understand the stress distribution within the membrane, TO Raman shift maps were performed along the corner and the border of the membrane.

Abstract: Impact ionization coefficients of 4H-SiC were measured at room temperature and at elevated temperatures up to 200°C. Photomultiplication measurement was done in two complementary photodiodes to measure the multiplication factors of holes (M_p) and electrons (M_n), and ionization coefficients were extracted. Calculated breakdown voltage using the obtained ionization coefficients showed good agreement with the measured values in this study, and also in other reported PiN diodes and MOSFETs. In high-temperature measurement, breakdown voltage exhibited a positive temperature coefficient and multiplication factors showed a negative temperature coefficient. Therefore, extracted ionization coefficient has decreased which can be explained by the increase of phonon scattering. The calculated temperature dependence of breakdown voltage agreed well with the measured values not only for the diodes in this study, but also in PiN diode in other literature.

Abstract: A new power law is approximated for effective impact ionization in 4H-SiC, which is then used to generate one-dimensional equations for critical electric field, avalanche breakdown voltage, and depletion layer width that match both simulation and published device results better than previous published equations.