[Show abstract][Hide abstract] ABSTRACT: The effects of the oxidation atmosphere and crystal faces on the
interface-trap density was examined by using constant-capacitance deep-level
transient spectroscopy to clarify the origin of them. By comparing the DLTS
spectra of the low-mobility interfaces oxidized in a N$_2$O atmosphere with
those of the high-mobility interfaces on C-face oxidized in a wet atmosphere,
it was found that a high density of traps are commonly observed around the
energy of 0.16 eV from the edge of the conduction band ($C1$ traps) in
low-mobility interfaces irrespective of crystal faces. It was also found that
the generation and elimination of traps specific to crystal faces: (1) the $C1$
traps can be eliminated by wet oxidation only on the C-face, and (2) the $O2$
traps (0.37 eV) can be observed in the SiC/SiO$_2$ interface only on the
Si-face. The generation of $O2$ traps on the Si-face and the elimination of
$C1$ traps on the C-face by wet oxidation may be caused by the oxidation
reaction specific to the crystal faces.
[Show abstract][Hide abstract] ABSTRACT: Using the fine control of an electron beam (e-beam) in scanning electron microscopy with the capabilities of both electrical and optical imaging, the stacking fault (SF) formation together with its tuning of carrier lifetime was in situ monitored and investigated in p-type 4H-SiC homoepitaxial films. The SFs were formed through engineering basal plane dislocations with the energy supplied by the e-beam. The e-beam intensity required for the SF formation in the p-type films was ∼100 times higher than that in the n-type ones. The SFs reduced the minority-carrier lifetime in the p-type films, which was opposite to that observed in the n-type case. The reason for the peculiar SF behavior in the p-type 4H-SiC is discussed with the cathodoluminescence results.
[Show abstract][Hide abstract] ABSTRACT: To examine the effect of the device structure on the on-state voltage (Von), several types of ultrahigh-voltage 4H-SiC p-channel insulated-gate bipolar transistors (IGBTs) were fabricated. A p-channel IGBT with a retrograde charge storage layer (CSL) and an additional JFET ion implantation region exhibited the lowest Von at 200 °C. To obtain a blocking voltage (BV) greater than 13 kV, a junction termination extension (JTE)-dose dependence of the BV was also investigated. Furthermore, ampere-class p-channel IGBTs with optimized device structures were fabricated for the evaluation of the switching loss (5 kV/1 A). Although the turn-off loss increased with an increase in the temperature, the loss remained as low as less than 10 mJ up to 250 °C. This performance renders the ultrahigh-voltage 4H-SiC p-channel IGBTs suitable for high-temperature and high-power applications.
2014 IEEE 26th International Symposium on Power Semiconductor Devices & IC's (ISPSD); 06/2014
[Show abstract][Hide abstract] ABSTRACT: We have found undiscovered defects on a 4H-SiC epitaxial layer, the shape of which resembles a scraper in images taken by confocal differential interference contrast optical microscopy. The surface morphological structure and formation mechanism of the scraper-shaped defects were investigated by atomic force microscopy and grazing incidence monochromatic synchrotron X-ray topography, respectively. The scraper-shaped defects were surface morphological defects consisting of surface asperity and were caused by the migration of interfacial dislocations. The evaluation of the thermal oxide reliability of metal–oxide–semiconductor capacitors fabricated on these defects was performed by time-dependent dielectric breakdown measurement. The degradation of thermal oxide occurred only on the downstream line of the scraper-shaped defects. The thickness of the oxide layer on these defects was also investigated using cross-sectional transmission electron microscopy.
Japanese Journal of Applied Physics 04/2014; 53(5):051301. · 1.06 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The effect of Fe impurity on the dissociation and motion behavior of basal plane dislocations (BPDs) in 4H-SiC homoepitaxial layers was investigated by electron-beam-induced current (EBIC) and cathodoluminescence (CL) techniques. Under the electron-beam irradiation, the BPDs dissociated to C- and Si-core partials, and these two partials were connected by another partial termed as X in this study. Stacking faults (SFs) were formed among these partials. The recombination activities of the BPDs and partials were enhanced with the existence of Fe impurity. The SFs near the surface region showed obvious dark contrast in EBIC, which was different from that observed in the clean samples. The X partial kept moving with sustained electron-beam irradiation whereas this partial in the clean samples stopped motion when it was connected to the sample surface. The dark contrast of the SFs and the peculiar motion behavior of the X partial are discussed with the CL results.
Japanese Journal of Applied Physics 03/2014; 53(5S1):05FG01. · 1.06 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We investigated the effects of DIT at the interface between SiO2 and Si-, C-, and a-face 4H-SiC in n-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) that were subjected to dry/nitridation and pyrogenic/hydrotreatment processes. DIT at EC − ET = 0.2 eV was evaluated by the C − ψS method using MOS capacitors and was accurately reflected in the subthreshold slope of the MOSFETs. The peak field-effect mobility was inversely proportional to DIT. The mobility for the a-face MOSFETs was 1.5 times or more higher than the other faces mobilities, indicating that mobility limiting factors other than DIT(0.2 eV) may exist for the Si- and C-face interfaces.
[Show abstract][Hide abstract] ABSTRACT: The Al memory effect during the growth of Al-doped 4H-SiC by the hot-wall chemical vapor phase epitaxy method was investigated. To suppress unintentional incorporation of Al impurities during succeeding growth, a technique was developed by employing HCl-assisted "site-competition" growth. Three methods of introducing HCl, namely, HCl flushing before growth, HCl addition during growth, and the combination of the two preceding methods, have been performed and the Al suppression effects corresponding to the input C/Si ratio were studied separately. It is found that lowering the C/Si ratio reduces Al incorporation for all methods of introducing HCl and using the combination of HCl flushing and HCl addition is highly effective. Optimizing growth rate, temperature, and pressure can further improve Al suppression efficiency; thus, a highly abrupt change in Al distribution between Al-doped and undoped epilayers with Al concentration differences of more than five orders of magnitude was obtained, e.g., a steep change from 1020 to 1014 cm−3.
Japanese Journal of Applied Physics 02/2014; 53(4S):04EP07. · 1.06 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We have investigated key factors for controlling the polytype and surface morphology of 4H-SiC homoepitaxial growth on less than 4o off-axis substrates. In addition, we characterized the crystal quality and surface quality of the epitaxial layer of an entire 3-inch vicinal off angled substrate. The results suggested that the control of surface free energy, control of the vicinal off angle itself, and high temperature growth, is highly important in controlling the surface morphology and polytype stability of the epitaxial layer grown on a vicinal off angled substrate. We also obtained a high-quality epitaxial layer grown on a 3-inch vicinal off angle substrate, which was comparable to those on 4o off-axis substrates.
[Show abstract][Hide abstract] ABSTRACT: We successfully fabricated 13-kV, 20-A, 8 mm × 8 mm, drift-free 4H-SiC PiN diodes. The fabricated diodes exhibited breakdown voltages that exceeded 13 kV, a forward voltage drop of 4.9–5.3 V, and an on-resistance (RonAactive) of 12 mW·cm2. The blocking yield at 10 kV on a 3-in wafer exceeded 90%. We investigated failed devices using Candela defect maps and light-emission images and found that a few devices failed because of large defects on the chip. We also demonstrated that the fabricated diodes can be used in conducting high-voltage and high-current switching tests.
[Show abstract][Hide abstract] ABSTRACT: The conduction mechanism of the leakage current in thermal oxide on 4H-SiC was identified. The carrier separation current-voltage method clarified that electrons are the dominant carriers of the leakage current. The temperature dependence of the currentvoltage characteristics indicated that the conduction mechanism of the leakage current involved not only Fowler-Nordheim tunneling (FN) but also Poole-Frenkel (PF) emission. The PF emission current due to the existence of defects in the oxide increased with temperature.
[Show abstract][Hide abstract] ABSTRACT: 4H-SiC(000-1) C-face was oxidized in H2O and H2 mixture gas (H2 rich wet ambient) for the first time. H2 rich wet ambient was formed by the catalytic water vapor generator (WVG) system, where the catalytic action instantaneously enhances the reactivity between H2 and O2 to produce H2O. The dependence of SiC oxidation rate on the H2O partial pressure was investigated. We fabricated 4H-SiC C-face MOS capacitor and MOSFET by the H2 rich wet re-oxidation following the dry O2 oxidation. The density of interface traps was reduced and the channel mobility was improved in comparison with the conventional O2 rich wet oxidation.
[Show abstract][Hide abstract] ABSTRACT: Reliability of gate oxide for trench-gate MOSFET was improved by deposited oxide film with uniform thickness and high-temperature annealing after trench etching. Optimum wafer orientation and trench direction for the trench gate was investigated, and the gate oxide on (11-20) plane of carbon face exhibited the longest lifetime. Influences by the roughness of sidewall and the radius of trench corner are discussed.
[Show abstract][Hide abstract] ABSTRACT: We have investigated a conversion of basal plane dislocation (BPD) to threading edge dislocation (TED) in growth of epitaxial layers (epi-layers) on 4H-SiC vicinal substrates with an off-angle of 0.85° at low C/Si ratio of 0.7 by using deep KOH etching and X-ray topography observations. Deep KOH etching indicated that BPDs in the substrates converted to TEDs in the epi-layers. X-ray topography observations suggested that the conversion occurred during epitaxial growth when the thickness of epi-layers was less than 1.5 μm. We found that the conversion ratio obtained from counting deep KOH etch pits was over 99%.
[Show abstract][Hide abstract] ABSTRACT: Heavily Al-doped 4H-SiC thick epilayers (˜90 μm) were grown on
3-in n+ 4H-SiC wafers by using the hot-wall CVD method. On
the purpose of enhancing incorporated Al-dopant concentration, the
growth condition dependence of the Al incorporation behavior in the
heavy doping range near Al solubility limit in 4H-SiC was investigated
by varying the growth parameters, i.e., growth rate, pressure,
temperature and Al-dopant source flow rate. A series of thick epilayers
possessing Al-dopant concentration from 9.6×1019 to
4.7×1020 cm-3 were obtained. Among them, the
epilayer with Al-dopant concentration of 3.5×1020
cm-3 demonstrates a comparably low resistivity of 16.5
mΩ cm as that of commercial n+ 4H-SiC wafer. The
incorporated Al-dopant concentration dependences on surface morphology,
crystalline quality and crystal structures of the heavily Al-doped thick
epilayers on n+ 4H-SiC substrates were characterized and
Journal of Crystal Growth 10/2013; · 1.69 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Epitaxial layers on a 150-mm-diameter silicon carbide wafer have been
grown using a horizontal hot-wall chemical vapor deposition system for
three 150-mm-diameter wafers. We investigated the surface morphology and
surface defects such as shallow pits and triangular defects of the grown
epitaxial layers, as well as the thickness and carrier concentration
uniformities. The shallow pit and triangular defect densities were 4.6
cm‑2 and 1.6 cm‑2, respectively, and
the thickness and the carrier concentration uniformities were 3.9% and
47%, respectively. We focused on improving the carrier concentration
distribution for practical use and concluded that the cause of the
distribution was the distribution in the effective C/Si ratio in the
direction of the gas flow.
Journal of Crystal Growth 10/2013; · 1.69 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The effect of a thin AlN/GaN superlattice structure (SLs) interlayer on
the strain properties in GaN films grown on Si(110) substrates is
investigated. By comparing the strain states in GaN films without the
interlayer, it is found that the strain in GaN films can be modulated by
the SLs interlayer, which can be converted from a tensile state to a
compressive one. The realization of the compressive strain state in the
GaN film results in the suppression of the crack generation in the thick
GaN growth, which is a general problem in the GaN growth on Si
substrates. Using this simple technique, we successfully grow a
crack-free continuous GaN film exceeding 4 μm thick. Therefore, the
SLs interlayer is a promising structure in growing crack-free thick GaN
on the Si substrate for optic and electronic device applications.
Japanese Journal of Applied Physics 08/2013; 52(8). · 1.06 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Screening of Si-based flux materials for solution growth of SiC single crystals was demonstrated using a thin film composition-spread technique. The reactivity and diffusion of carbon in a composition spread of the flux was investigated by secondary ion mass spectroscopy depth profiling of the annealed flux thin film spread on a graphite substrate. The composition dependence of the chemical interaction between a seed crystal and flux materials was revealed by high-temperature thermal behavior observation of the flux and the subsequent morphological study of the surface after removing the flux using atomic force microscopy. Our new screening approach is shown to be an efficient process for understanding flux materials for SiC solution growth.