Rinpei Hayashibe

Characterization of Nitride Layer on 6H-SiC Prepared by High-Temperature Nitridation in NH3

The nitride layers were prepared by direct thermal nitridation of 6H-SiC substrates at 1200–1570°C in a NH3 atmosphere. The layer was characterized by using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and Raman scattering spectroscopy. The thickness of the nitride layers prepared at lower than 1400°C was estimated to be less than 10 nm. The higher nitridation temperature resulted in the formation of a thicker surface layer. XPS measurement showed that the surface layer was composed of N, Si, C and O. Peaks corresponding to α-Si3N4 were detected in the Raman spectra and the XRD patterns of the sample prepared at higher than 1500°C, indicating the crystallization of the nitrided layer.

Characterization of Metal–Insulator–Semicomductor Capacitors with Insulating Nitride Films Grown on 4H-SiC

Nitrided layers were grown on a 4H-SiC(0001) by plasma nitridation method using NH3. Nitridation was enhanced with increasing RF power and with decreasing growth pressure. However, the exact capacitance–voltage (C–V) properties of the nitride layer/SiC interface could not be determined because of the leakage current. The SiO2 film was deposited on the nitrided layer by thermal chemical vapor deposition method using tetraethoxysilane (TEOS) omit obtain an insulating film with sufficient thickness and an exact interface property. The interface state density Dit was evaluated from C–V characteristics by the Terman method. It was indicated that Dit near the mid gap of the TEOS oxide/nitride layer structure was higher than those of the TEOS–SiO2 films and thermal oxide film. The Dit of the oxide/nitride layer successfully decreased by post NH3 annealing.

Preparation of Carbon Films by Hot-Filament-Assisted Sputtering for Field Emission Cathode

Carbon thin films on a silicon substrate were prepared by DC magnetron sputtering method with a tungsten hot filament. In order to investigate the effects of the hot filament on film properties, the carbon thin films were characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and electron emission measurements. The tungsten atoms were evaporated from the hot filament and incorporated in the carbon film. The field emission measurement showed that the incorporation of tungsten was effective in reducing the turn-on voltage. The value of the turn-on voltage was 3.0 V/µm for the sample prepared with a tungsten filament heated at the temperature of 2000°C. The intentional insertion of a tungsten layer between the carbon film and the substrate was effective in obtaining a carbon film with a low turn-on voltage for the field emission.

Growth and Characterization of SiC Films by Hot-Wire Chemical Vapor Deposition at Low Substrate Temperature Using SiF4/CH4/H2 Mixture

Microcrystalline SiC films were grown by hot-wire chemical vapor deposition (HW-CVD) at a low substrate temperature using a SiF4/CH4/H2 mixture, and their structural properties were characterized. Low growth pressure resulted in a narrow full width at half maximum (FWHM) of the Si–C peak in Fourier transform infrared absorption spectroscopy (FT-IR) spectra. The deposition rate and the FWHM value increased with increasing filament temperature. This seemed to be caused by change of the concentration ratio of precursors on the growth surface with increasing filament temperature. Also, the film crystallinity depended on the CH4/SiF4 flow rate ratio, and µc-3C-SiC(111) films were successfully obtained at low substrate temperature of 250 °C.

Characterization of Al-Based Insulating Films Fabricated by Physical Vapor Deposition

A novel submount substrate with high thermal conductivity for optoelectronic devices is proposed. The substrate is fabricated by depositing an Al-based insulating film on a copper substrate. AlN films were deposited by RF reactive sputtering using an Al target (5N) in a gas mixture of Ar and N2. Al2O3 films were deposited by oxygen-ion-assisted electron beam (EB) evaporation. Many conductive paths were detected in the AlN films. These defects were introduced in the AlN film during a photolithography process for fabricating electrode patterns because the alkaline developer dissolved the film. An Al–OH peak in Fourier transform infrared spectroscopy (FT-IR) spectra suggested that the Al(OH)3 formation was one of the reasons for the presence of conductive paths in the AlN film. In the case of Al2O3 films, no conducting path was detected in electrical measurements, and no marked change in surface morphology was observed in scanning electron microscopy (SEM) images, after treatment with the alkaline developer. The Al2O3/Cu structure is a candidate for the novel submount substrate with high thermal conductivity.

X-Ray Photoelectron Spectroscopy of Nitride Layer on SiC by Thermal Nitridation Using NH3

Nitride layers were grown on a SiC surface by thermal nitridation using a mixed gas of NH3 and N2. The thermal nitridation was carried out at 1000°C and 1090 °C under the atmospheric pressure. X-ray photoelectron spectroscopy (XPS) was used to characterize the surface layer. The peaks from Si2p, C1s, N1s and O1s were observed in the XPS spectra. These peaks showed that the surface layer consisted of Si, N, C and O. The thickness of the surface layer was estimated at less than 10 nm. Introduction Because of its electrical and physical properties, silicon carbide (SiC) is a very attractive semiconductor for high-temperature, high-power and high-frequency devices [1]. The thermal oxides on SiC also give its significant advantage over other compound semiconductors [2]. However, the generation of CO2 during oxidization is one of the reasons for the poor interface characteristics of SiO2/SiC structure. Employing a nitridation could keep the SiC surface away from this problem. In addition, the products formed by the SiC nitridation are silicon nitride (Si3N4) and carbon nitride (C3N4), which are both excellent insulators. The nitridation of the gate oxide is effective to improve the quality of the SiO2/SiC interface [3]. It is also reported that the silicon nitride layer was grown directly on the Si surface by thermal nitridation [4] [5]. However, no paper has been reported about the direct thermal nitridation of the SiC surface for applying to MIS devices. In this work, the nitride layer was grown on the SiC surface by direct thermal nitridation using a mixed gas of NH3 and N2. Experimental The nitride layer was formed on n-type 6H-SiC (CREE Research, one-sided mirror, 0.32 Ωcm) by direct thermal nitridation. The thermal nitridation was carried out at temperatures from 1000 to 1090 °C using NH3 in a quartz tube. The NH3 gas was diluted to 10% with N2, and the purity of the gas was higher than 99.999%. The gas flow rate was 100 sccm. Before the nitridation, the quartz tube was evacuated by an oil rotary pump to reduce the residual oxygen. Argon gas was flowed through the tube until the furnace temperature increased to the set point. The values of the temperatures shown in this paper were the measured temperatures of the resistance furnace. In order to obtain the flat and clean surface of the SiC substrate, the substrates were thermally oxidized for 2 hours at 1000 °C in wet oxygen and were etched in a hydrofluoric acid as pretreatment. X-ray photoelectron spectroscopy (XPS: Shimazu ESCA850, Mg (Kα)) was used to characterize the nitride layer. The cross-sectional image of the layer was observed by the high resolution transmission electron microscopy (HRTEM: JEOL JEM2010). Materials Science Forum Online: 2004-06-15 ISSN: 1662-9752, Vols. 457-460, pp 1549-1552 doi:10.4028/www.scientific.net/MSF.457-460.1549

Preparation and Characterization of Deposited Tetraethylorthosilicate-SiO2/SiC MIS Structure

The SiO2 layer was deposited on the 4H-SiC Si face by the thermal decomposition of tetraethylorthosilicate(TEOS) in N2 atmosphere to from MIS diodes. The post deposition annealing was effective to improve the interface properties. The interface state density of the deposited SiO2/SiC MIS structure was estimated to be the order of 1011 cm-2eV-1 by Terman method. The direct nitridation of SiC surface prior to the deposition of the SiO2 layer was effective to reduce the interface state density.

Effect of series resistance on field emission characteristics of nano-carbon cathode

To estimate the effects of series resistance on the field emission current associated with an array of carbon nanotubes (CNTs) and nanowalls (CNWs), the model of the floating spheres or lines between anode and cathode plates was proposed. An approximate formula for the field enhancement factor was derived, showing that the series resistance of a CNT array critically affects the field emission of vertically aligned carbon nanotube cathode, and the effect of the series resistance was not the limiting factor to the emission current in the arrayed CNWs cold cathode.

Field emission from the cold cathode using CNTs dispersed in insulating layer

The field emission cathode was fabricated using mized compound of carbon nanotube and insulator. High field enhancement factor ß can be obtained by using distributed carbon nanotubes in the insulating mateial. The turn on field of lower than 5 V/μm was detected for the sample prepared by using sol-gel method.

Effect of Direct Nitridation of 4H-SiC Surface on MOS Interface States

A nitride layer was formed on a SiC surface by direct nitridation in pure N2 or in NH3 diluted with N2. The SiO2 layer was deposited by the thermal decomposition of tetraethylorthosilicate (TEOS) on the nitride layer to form an MIS diode. The XPS analysis showed that the nitride layer was oxidized during the deposition process of SiO2. The direct nitridation was effective to reduce the interface state density between the insulating layer and 4H-SiC