Carrier Trap Density Reduction at SiO2/4H-Silicon Carbide Interface with Annealing Processes in Phosphoryl Chloride and Nitride Oxide Atmospheres.

The electrical and physical properties of the SiC/SiO2 interfaces are critical for the reliability and performance of SiC-based MOSFETs. Optimizing the oxidation and post-oxidation processes is the most promising method of improving oxide quality, channel mobility, and thus the series resistance of the MOSFET. In this work, we analyze the effects of the POCl3 annealing and NO annealing processes on the electrical properties of metal-oxide-semiconductor (MOS) devices formed on 4H-SiC (0001). It is shown that combined annealing processes can result in both low interface trap density (Dit), which is crucial for oxide application in SiC power electronics, and high dielectric breakdown voltage comparable with those obtained via thermal oxidation in pure O2. Comparative results of non-annealed, NO-annealed, and POCl3-annealed oxide-semiconductor structures are shown. POCl3 annealing reduces the interface state density more effectively than the well-established NO annealing processes. The result of 2 × 1011 cm-2 for the interface trap density was attained for a sequence of the two-step annealing process in POCl3 and next in NO atmospheres. The obtained values Dit are comparable to the best results for the SiO2/4H-SiC structures recognized in the literature, while the dielectric critical field was measured at a level ≥9 MVcm-1 with low leakage currents at high fields. Dielectrics, which were developed in this study, have been used to fabricate the 4H-SiC MOSFET transistors successfully.

Microscopic investigations of morphology and thermal properties of ZnO thin films grown by atomic layer deposition method.

This work presents the study of morphology and thermal properties of thin ZnO films fabricated by atomic layer deposition. The layers were deposited on n-Si(100) wafers at 200 °C. X-ray diffraction measurements showed the polycrystalline structure of the thin films with preferred (100) orientation. The thinner ZnO layers were fine grained, while the thicker films were formed with larger, elongated grains. Surface morphology parameters and the thermal conductivities were obtained from microscopic measurements. Thermal properties correlated with surface roughness of the ZnO thin films. Variations in thermal conductivity followed the changes in morphology of the layers. The mean surface roughness depended on the number of deposition cycles and varied from 1.1-2.6 nm. Thermal conductivity varied from 0.28 to 4.29 Wm-1K-1 and increased also with an increase of average crystallite size. The possible correlations between electrical conductivity and thermal conductivity were also analyzed. The phonon contribution to total thermal conductivity dominates over the electron thermal conductivity.