Nam-Kyun Kim

Current conduction mechanisms in atomic-layer-deposited HfO2/nitrided SiO2 stacked gate on 4H silicon carbide

In this paper, current conduction mechanisms of an atomic-layer-deposited HfO2 gate stacked on different thicknesses of thermally nitrided SiO2 based on n-type 4H SiC have been investigated and analyzed. Current-voltage and high-frequency capacitance-voltage measurements conducted at various temperatures (25−140u2009°C) were performed in metal-oxide-semiconductor test structures with 13 nm thick HfO2 stacked on 0-, 2-, 4-, or 6 nm thick nitrided SiO2. Various conduction mechanisms, such as Schottky emission, Fowler-Nordheim tunneling, Poole-Frenkel emission, and space-charge-limited conduction, have been systematically evaluated. The mechanisms of the current conducted through the oxides were affected by the thickness of the nitrided oxide and the electric field applied. Finally, current conduction mechanisms that contributed to hard and soft dielectric breakdown have been proposed.

Effects of thermal nitrided gate-oxide thickness on 4H silicon-carbide-based metal-oxide-semiconductor characteristics

The effects of thermal nitrided gate-oxide thickness on n-type 4H silicon-carbide-based metal-oxide-semiconductor characteristics have been reported. Seven different thicknesses of oxide (tox), ranging from 2to20nm, have been investigated. It has been shown that effective oxide charge (Qeff) and total interface-trap density (Nit) have demonstrated a cyclic trend as tox is increased. These observations have been explained in the letter. Correlations of Qeff and Nit with oxide breakdown field and current transport mechanism in these oxides have also been established and explained.

Analysis of current conduction mechanisms in atomic-layer-deposited Al2O3 gate on 4H silicon carbide

Current conduction mechanisms of an atomic-layer-deposited Al2O3 gate on n-type 4H SiC have been systematically investigated, analyzed, and reported in this letter. It has been revealed that space charge limited, Poole-Frenkel (PF) emission, combination of PF emission and Fowler-Nordheim tunneling are the dominate current conduction mechanisms in the dielectric. Besides, Schottky emission has also been proposed as a possible leakage path at temperature beyond the investigated range. A relationship among the conduction mechanism, temperature, and applied electric field has been presented.

Current conduction mechanisms in post-nitridation rapid-thermal-annealed gate oxides on 4H silicon carbide

In this letter we report current-conduction mechanisms in nitrided gate oxides on n-type 4H SiC subjected to various rapid-thermal-annealing temperatures. The experimental results show that by increasing SiC-SiO2 interface trap density, current conduction in the oxide is increased. Fowler-Nordheim (FN) tunneling which is assisted by SiC-SiO2 interface trap is responsible to the current conduction. In contrast, the current conduction through the oxide is significantly reduced when the oxide is having a multiple discrete energy level of electron trap center. This center enables trapping of electrons that are injected from SiC substrate via FN tunneling, causing a reduction in leakage current and an improvement in oxide breakdown strength. Based on the results, a model has been hypothesized and reasons for these observations have been presented.

Effect of Postoxidation Annealing on High Temperature Grown SiO2 / 4H-SiC Interfaces

SiO 2 was grown by dry (O 2 ) thermal oxidation (at 1175, 1300, or 1400°C) on n-type 4H-SiC substrates. The samples were prepared by subsequently exposing the grown Si0 2 film on 4H-SiC to postoxidation annealing (POA) treatment using nitric oxide (NO) gas. The SiC-Si0 2 interfaces were characterized by high frequency capacitance-voltage measurements, X-ray photoelectron spectroscopy (XPS), and ellipsometry. The interface trap density of the dry oxide grown at 1300°C was much lower than others. At a higher grown temperature (1400°C), the electrical and physical properties of the oxide were not improved compared to those oxides grown at 1175°C. The XPS measurements provided evidence for the presence of intermediate oxidation states of Si oxycarbide in all samples. The areal densities of the intermediate oxidation states affected the interface trap density. The NO POA treatment significantly improved the interface trap density, the near-interface trap density, and the effective oxide charge density of the oxides grown at 1175 and 1300°C. But, this improvement was not observed for the oxide grown at 1400°C. The electrical properties of the metal-oxide-semiconductor devices fabricated using these oxides have also been discussed in terms of the oxide chemical compositions, which were determined by XPS and an oxide etching test.

Anti-reflective nano- and micro-structures on 4H-SiC for photodiodes

In this study, nano-scale honeycomb-shaped structures with anti-reflection properties were successfully formed on SiC. The surface of 4H-SiC wafer after a conventional photolithography process was etched by inductively coupled plasma. We demonstrate that the reflection characteristic of the fabricated photodiodes has significantly reduced by 55% compared with the reference devices. As a result, the optical response Iillumination/Idark of the 4H-SiC photodiodes were enhanced up to 178%, which can be ascribed primarily to the improved light trapping in the proposed nano-scale texturing.

Effects of thermally oxidized-SiN gate oxide on 4H-SiC substrate

We have investigated and reported the results on oxidized-SiN gate oxides on n-type 4H-SiC. The quality of this oxide has been compared with thermal nitrided and dry oxides. In the oxidized-SiC sample, a significant improvement in oxide deposition/growth rate has been obtained while the metal-oxide-semiconductor characteristics of the oxide are comparable to the thermal-nitrided oxide and much better than dry oxide. This achievement has been explained using a proposed chemical model.

Effects of wet-oxidized 4H-SiC annealed in HNO3/H2O vapour

Purpose – The high density of defects mainly attributed to the presence of silicon oxycarbides, residual C clusters, Si- and C-dangling bonds at or near the SiO2/SiC interface degrades the performance of metal-oxide-semiconductor (MOS) devices. In the effort of further improving the quality and enhancement of the SiC oxides thickness, post-oxidation annealed by a combination of nitric acid (HNO3) and water (H2O) vapor technique on thermally grown wet-oxides is introduced in this work. The paper aims to discuss these issues. Design/methodology/approach – A new technique of post-oxidation annealing (POA) on wet-oxidized n-type 4H-SiC in a combination of HNO3 and H2O vapor at various heating temperatures (70°C, 90°C and 110°C) of HNO3 solution has been introduced in this work. Findings – It has been revealed that the samples annealed in HNO3 +u2009H2O vapour ambient by various heating temperatures of HNO3 solution; particularly at 110°C is able to produce oxide with lower interface-state density and higher break...

Fabrication of a 600-V/20-A 4H-SiC schottky barrier diode

In this study, 600-V/20-A 4H-SiC Schottky barrier diodes (SBDs) were fabricated to investigate the effect of key processing steps, especially before and after the formation of a Schottky contact, on the electrical performances of SBDs and on their long-term reliabilities. The results show that 4H-SiC SBDs that had been subjected to a hydrogen-ambient annealing at 470 °C for 10 min and sacrificial treatment right after ion activation exhibited a lower forward voltage drop (VF) at a rated current of 20 A, a higher blocking voltage of 800 V, and a very short reverse recovery time of 17.5 ns. Despite the harsh reverse bias condition and temperature, a long-term reliability test showed that changes in the forward voltage drop and the reverse leakage current (IR) were 0.7% and 8.9% and that the blocking voltage was enhanced. This is attributed to the presence of a stabilized interface between the passivation layer and the SiC due to aging.

Effects of rapid thermal annealing on Al2O3/SiN reaction barrier layer/thermal-nitrided SiO2 stacking gate dielectrics on n-type 4H-SiC

In this letter, we have reported electrical and physical properties of rapid thermal annealed (RTA) Al2O3 stacking dielectric on n-type 4H-SiC. The effects of SiN-reaction barrier layer (RBL) between Al2O3 and thermal-nitrided SiO2 on SiC-based metal-oxide-semiconductor characteristics have been investigated and compared. A significant reduction in oxide-semiconductor interface-trap density (Dit), improvement in dielectric breakdown field and reliability has been observed after the SiN-RBL has been introduced between Al2O3 and SiO2. High-resolution transmission electron microscope and Auger electron spectroscopy analyses reveal that the SiN-RBL suppresses Al diffusion into the nitrided SiO2 during RTA process.