Yasuto Hijikata

Composition analysis of SiO2/SiC interfaces by electron spectroscopic measurements using slope-shaped oxide films

We have characterized SiO2/SiC interfaces by X-ray photoelectron spectroscopy in terms of composition and bonds to clarify the reasons for the problems in silicon carbide metal-oxide-semiconductor field-effect-transistor and MOS structures. The oxide films on 6H–SiC were shaped into slopes by HF chemical etching to obtain the depth profile of the composition and the bondings. An interface layer was found near the SiO2/SiC boundary, where SiO2 stoichiometry is collapsed and there exists the bondings other than Si–O2 and Si–C. Also, we revealed the differences in the interface properties for different oxidation processes.

Oxide Growth Rate Enhancement of Silicon Carbide (0001) Si-Faces in Thin Oxide Regime

Thermal oxidation process of silicon carbide (SiC) has been studied by performing in-situ spectroscopic ellipsometry. In our previous work, we, for the first time, found that the growth rates of SiC(0001) C-face at oxidation thicknesses less than around 20 nm are much higher than those given by the Deal–Grove (D–G) model. In this report, we show that such a growth rate enhancement occurs also in the oxidation of SiC(0001) Si-face. By applying the empirical equation proposed by Massoud et al. [J. Electrochem. Soc. 132 (1985) 2685] to the oxidation of SiC Si-face and comparing the temperature and oxygen partial pressure dependences of oxidation rate parameters obtained with those for C-face, we discuss the difference in oxidation mechanism between SiC Si- and C-faces.

Growth Rate Enhancement of (0001)-Face Silicon–Carbide Oxidation in Thin Oxide Regime

The thermal oxidation of silicon carbide (SiC) has been studied by performing in-situ ellipsometry. We have found that the oxidation rates at the oxidation thickness of approximately less than around 20 nm are much larger than those given using the Deal–Grove (D–G) model, suggesting that the oxidation time dependence of the oxide thickness cannot be explained using the D–G model, i.e., a simple linear-parabolic model, in the initial oxidation stage. By using the empirical relation, which has been proposed for Si oxidation, i.e., adding an exponential term to the D–G equation, the origin of the growth rate enhancement in SiC oxidation has been discussed.

Photoluminescence Study on Temperature Dependence of Band Gap Energy of GaAsN Alloys

We have studied the temperature dependence of photoluminescence (PL) spectra of GaAsN alloys. The PL peak energy shift due to the temperature change decreases with increasing N concentration of GaAsN alloys. The localized state emission partly contributes to the decrease in the PL peak energy shift. In addition, the small PL peak energy shift at high temperatures is due to the reduction in the temperature dependence of the band gap energy. From the analysis using the Bose-Einstein statistical expression, the average phonon energy is much larger than that expected from the linear interpolation between GaAs and GaN, indicating that the interaction between electrons and phonons localized at N atoms plays an important role in the reduction of the temperature dependence of the band gap energy of GaAsN alloys.

Differences in SiC thermal oxidation process between crystalline surface orientations observed by in-situ spectroscopic ellipsometry

For a better understanding of the SiC oxidation mechanism, we investigated differences in the oxidation process for surfaces with different crystal orientations. Real-time observations of oxidation processes for (0001) Si-face, (11 2¯0) a-face, and (000 1¯) C-face substrates at various oxidation temperatures were performed using in-situ spectroscopic ellipsometry. Massouds empirical equation, which is composed of the classical Deal-Grove equation added by an exponential term, was applied to the observed growth rates and the oxidation rate parameters were extracted by curve fitting. The SiC oxidation mechanism is discussed in terms of the oxidation temperature dependence and surface orientation dependence of the oxidation rate parameters.

Characterization of oxide films on 4H-SiC epitaxial (0001¯) faces by high-energy-resolution photoemission spectroscopy: Comparison between wet and dry oxidation

Wet and dry oxide films-4H-SiC epitaxial (0001¯) C-face interfaces have been characterized by capacitance-voltage (C-V) measurements and soft x-ray excited photoemission spectroscopy (SX-PES) and hard x-ray excited photoemission spectroscopy (HX-PES) using synchrotron radiation. The interface state density for wet oxidation is much smaller than that for dry oxidation at any energy level. In the PES measurements, intermediate oxidation states such as Si1+ and Si3+ were observed. In addition, the areal densities of these states were found to be in a good correspondence with those of the interface states. The reasons for the good electrical characteristics of metal-oxide-semiconductor devices fabricated by wet oxidation are discussed in terms of the depth profiles of oxide films derived from the SX-PES and HX-PES results.

Effect of Ar post-oxidation annealing on oxide–4H-SiC interfaces studied by capacitance to voltage measurements and photoemission spectroscopy

The effect of post-oxidation annealing in Ar atmosphere (Ar POA) on 4H-SiC–oxide interfaces has been studied by capacitance to gate-bias voltage (C–V) measurements and photoemission spectroscopy (PES). It was found from the C–V measurements that the shift of the C–V curve disappears when the Ar POA temperature is higher than 600 °C. On the other hand, angle-resolved x-ray photoelectron spectroscopy measurements revealed that the thickness of the intermediate layers containing Si1+ oxidation states observed at the interfaces decreases abruptly when the Ar POA temperature exceeds 500 °C. In ultraviolet photoelectron spectra, O2p peaks were changed by Ar POA at temperatures higher than 600 °C, which is the temperature where the shift of the C–V curve disappears in C–V measurements. This shows that the change in O2p bonding by Ar POA is the origin of the shift observed in C–V characteristics. A model of structural changes in the interfaces by Ar POA has been proposed based on the results of PES measurements and those of C–V measurements.The effect of post-oxidation annealing in Ar atmosphere (Ar POA) on 4H-SiC–oxide interfaces has been studied by capacitance to gate-bias voltage (C–V) measurements and photoemission spectroscopy (PES). It was found from the C–V measurements that the shift of the C–V curve disappears when the Ar POA temperature is higher than 600 °C. On the other hand, angle-resolved x-ray photoelectron spectroscopy measurements revealed that the thickness of the intermediate layers containing Si1+ oxidation states observed at the interfaces decreases abruptly when the Ar POA temperature exceeds 500 °C. In ultraviolet photoelectron spectra, O2p peaks were changed by Ar POA at temperatures higher than 600 °C, which is the temperature where the shift of the C–V curve disappears in C–V measurements. This shows that the change in O2p bonding by Ar POA is the origin of the shift observed in C–V characteristics. A model of structural changes in the interfaces by Ar POA has been proposed based on the results of PES measurements a...

Oxygen partial pressure dependence of the SiC oxidation process studied by in-situ spectroscopic ellipsometry

The oxygen partial pressure dependence of the Silicon carbide (SiC) oxidation process was investigated using in-situ spectroscopic ellipsometry at oxygen partial pressures between 1 and 0.02 atm for 4 H-SiC (0001) Si- and (000−1) C-faces. Analyses of the interface structure between the oxide and SiC indicate that the interface layer has a modified SiC-like structure around 1 nm thick accompanied by oxide growth; the structure and thickness do not change after an oxide growth of about 7 nm. The oxide thickness dependence of the growth rate at sub-atmospheric oxygen pressures is similar to that at 1 atm pressure, that is, just after oxidation starts, the growth rate rapidly decreases as the oxidation proceeds. After an oxide growth of about 7 nm thick, the deceleration of the growth rate suddenly changes to a gentle slope. The thickness at which deceleration changes depends slightly on both the oxygen partial pressure and surface polarity of the SiC substrate. The origins of these two deceleration stages, i...

Real Time Observation of SiC Oxidation Using an In Situ Ellipsometer

Real time observation of SiC oxidation was performed using an in-situ ellipsometer over the temperature range from 900°C to 1150°C. The relations between oxide thickness and oxidation time were obtained precisely by virtue of the real time measurements. We analyzed the relations between oxide thickness and oxidation time by applying the Deal and Grove model to obtain the linear and parabolic rate constants. Taking advantage of in-situ measurements, we successfully obtained the oxidation rate constants with high accuracy.

Characterization of Carrier Concentration and Mobility in n-type SiC Wafers Using Infrared Reflectance Spectroscopy

We have estimated the free-carrier concentration and drift mobility in n-type 6H-SiC wafers in the carrier concentration range of 1017–1019 cm-3 from far- and mid-infrared (30–2000 cm-1) reflectance spectra obtained at room temperature. A modified classical dielectric function model was employed for the analysis. We found good agreement between the electrical properties derived from infrared reflectance spectroscopy and those derived from Hall effect measurements. We have demonstrated the spatial mapping of carrier concentration and mobility for commercially produced 2 inch SiC wafers.