Wook Bahng

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 (25−140 °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.

Electronic properties of atomic-layer-deposited Al2O3/thermal -nitrided SiO2 stacking dielectric on 4H SiC

We report the first electronic-property results on atomic-layer deposited Al 2 O 3 /thermal-nitrided SiO 2 stacking dielectric on n-type 4H SiC. The effects of the ultrathin thermal-nitrided SiO 2 (2, 4. and 6 nm) on the SiC-based metal oxide semiconductor (MOS) characteristics have also been investigated, compared, and explained. A significant improvement in dielectric reliability and dielectric breakdown field has been observed after an ultrathin nitrided oxide has been introduced between Al 2 O 3 and SiC. The best reported results were obtained from Al 2 O 3 stacked with the thickest nitrided oxide (6 nm).

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.

Improved Electronic Performance of

The MOS characteristics of an atomic layer-deposited HfO2/N2O-nitrided SiO2 stacking gate dielectric on n-type 4H SiC (0001) has been investigated. Three different thicknesses of nitrided SiO2 (2, 4, and 6 nm) have been sandwiched between HfO2 and SiC. The electronic performance of the stacking dielectric depends on the thickness of the nitrided SiO2. Among the stacking dielectrics, the lowest effective oxide charge and interface-trap density as well as the most reliable dielectric has been demonstrated by a sample with the thickest nitrided . The reason for this observation is proposed.

\hbox{HfO}_{2}/ \hbox{SiO}_{2}

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.

Stacking Gate Dielectric on 4H SiC

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.

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

We have investigated the electrical properties of metal-oxide-semiconductor (MOS) capacitors with atomic-layer-deposited La2O3, thermal-nitrided SiO2, and atomic-layer-deposited La2O3/thermal-nitrided SiO2 on n-type 4H-SiC. A significant reduction in leakage current density has been observed in La2O3 structure when a 6-nm thick thermal nitrided SiO2 has been sandwiched between the La2O3 and SiC. However, this reduction is still considered high if compared to sample having thermal-nitrided SiO2 alone. The reasons for this have been explained in this paper.

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

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.

Electrical Properties of Atomic-Layer-Deposited La2O3/Thermal-Nitrided SiO2 Stacking Dielectric on 4H-SiC(0001)

The numerical simulation and in-situ X-ray topography were applied to observe the phenomena inside a crucible. Numerical simulation pointed out that macroscopic grown crystal quality such as grown crystal shape strongly depends on the temperature distribution inside a crucible. In-situ X-ray topography revealed that when the defects were generated, and how the defects were propagated. Most of defects were generated at the initial growth stage. It is important to control the initial stage in order to obtain a high quality SiC single crystal. Numerical simulation also suggested that it is important reduce the residual stress in a grown crystal in order to avoid the dislocation occurrence. From these results based on numerical simulation and experiment, SiC sublimation growth was controlled actively, and the large and high quality SiC single crystal have been grown. Introduction Silicon carbide single crystal is usually grown by sublimation (modified Lely method). Since the first report of modified Lely method [1], more than 20 years has passed. However, there is a lot of remaining issues that should be solved. The main reason of this situation is that sublimation process is a black box process inside a closed carbon crucible above 2000 K. It is so difficult to know what going on inside a crucible, that it is much difficult to control the sublimation process actively. In order to overcome this point, the authors have applied the numerical simulation to see the phenomena inside a furnace [2,3,4,5]. The authors also developed the in-situ X-ray topography system to observe the crystal growth features inside a closed carbon crucible [6,7]. By using these observation tools, the SiC sublimation growth could be understand more detail [7,8,9,10], and could be controlled actively [3,11,12]. In this paper, the observation results and the example active control of SiC sublimation growth are described. Simulation The configuration of numerical modeling was based on the conventional RF induction-heating furnace that we used in experiments. Electromagnetic and thermal fields were analyzed by the commercial software, Flux-Expert [13,14], and CFD-ACE+[15]. Since convective heat transfer could be neglected in our experiments, the equation for momentum transfer was not analyzed. From the thermal fields, the concentration distribution of sublimated species was analyzed according to the LTCE model [13]. The residual stress in a grown crystal was also analyzed. Materials Science Forum Online: 2004-06-15 ISSN: 1662-9752, Vols. 457-460, pp 29-34 doi:10.4028/www.scientific.net/MSF.457-460.29

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

The atomic force microscopy-based local oxidation (AFM-LO) of silicon carbide (SiC) is extremely difficult in general, mainly due to their physical hardness and chemical inactivity. Herein, we report the strongly enhanced AFM-LO of 4H-SiC at room temperature without the heating, chemicals or photoillumination. It is demonstrated that the increased tip loading force (∼>100 nN) on the highly doped SiC can produce a high enough electric field (∼8×106 V/cm) under the cathode tip for transporting oxyanions, thereby leading to direct oxide growth on 4H-SiC. The doping concentration and electric field profile of the tip-SiC sample structures were further examined by two-dimensional numerical simulations.