Papers by Author: Isaho Kamata

Abstract: Frank-type defects on the basal plane in thick 4H-SiC epitaxial layers converted from threading screw dislocation (TSD) have been characterized by photoluminescence (PL) spectroscopy and PL imaging microscopy. PL emission from the stacking fault (SF) and the Frank partial of the defect was obtained at ~457 nm and >700 nm at room temperature, respectively. The PL emission peaks of two other kinds of Frank-type defects were obtained, and a correspondence between the optical properties and the microscopic structures of the three kinds of defects was clarified.

Abstract: Burgers vector directions of threading edge dislocations (TEDs) in 4H-SiC epitaxial layer are distinguished by grazing incidence high resolution topography. Based on comparison between appearance of KOH etch pits and direction of TED Burgers vector, the size difference of the TED etch pits is found to be dependent on their Burgers vector directions. Examining TEDs in the epilayer by topography, the Burgers vector direction of basal plane dislocations (BPDs) in the substrate is identified. Correspondence between the topography contrast and the sense of a BPD is also investigated.

Abstract: Fast and thick 4H-SiC epitaxial growth is demonstrated in a vertical-type reactor under a low system pressure within the range 13-40 mbar. A very fast growth rate of up to 250 m/h is obtained. The material quality of the epilayers grown in the reactor is evaluated by low-temperature photoluminescence, deep level transient spectroscopy, microwave photoconductive decay, synchrotron topography and room temperature PL imaging. The carrier lifetime of thick epilayers with or without the application of the C+-implantation/annealing method and extended defects in the epilayers grown on 8º and 4º off substrates are discussed.

Abstract: The transfer and generation of extended defects in 4H-SiC epitaxial growth at a high growth rate are examined. An epilayer with virtually no basal plane dislocations (BPDs) is obtained using 4º off Si-face substrates, although the formation of 3C-polytype inclusions is occasionally observed. The behavior of BPDs and threading screw dislocations (TSDs) in epitaxial growth is also investigated by X-ray topography and transmission electron microscopy, and the propagation of BPDs and conversion and generation of TSDs in the epilayers are discussed.

Abstract: Threading edge dislocations (TEDs) in a 4H-SiC epitaxial layer are investigated using high-resolution synchrotron topography. Six types of TED image are confirmed to correspond to the Burgers vector directions by a comparison of computer simulated images and observed topography images in crystal boundaries. Using a mapping method, a wide spatial distribution of the six types of TED is examined in a quarter section of a 2-inch wafer.

Abstract: Defect formation in 4H-SiC(0001) and (000-1) epitaxy is investigated by grazing incidence synchrotron reflection X-ray topography and transmission electron microscopy. Frank-type faults, which are terminated by four Frank partials with a 1/4[0001] type Burgers vector with the same sign on four different basal planes, are confirmed to be formed by conversion of a 1c threading edge dislocation (TSD) in the substrate as well as simultaneous generation of a 1c TSD during epitaxy. The collation between the topography appearance and the microscopic structure and the variety of Frank faults are shown. Formation of carrot defects and threading dislocation clusters are also investigated.

Abstract: Synchrotron reflection X-ray topography and KOH etching were applied to investigate the effects of the ion implantation/annealing process on the existing dislocations in the 4H-SiC epilayers and second epitaxial growth on the ion implanted layer. No systematic generation of dislocations or stacking faults caused by the second epitaxial growth on the implanted layer was observed, while BPDs were confirmed to migrate in the epilayer during the implantation/annealing process. The BPDs bend markedly near the bottom of the implanted layer and tend to lie along the <1-100> (perpendicular to the off-cut direction) after the implantation/annealing process. The lattice mismatch strain created by the implantation is a possible driving force of the glide motion of the BPDs.

Abstract: We investigated the location of the nuclei of Shockley-type stacking faults (SSFs) in the 4H-SiC pin diodes, using electroluminescence (EL) imaging. The nuclei of SSFs were identified as three types, located (i) on the mesa edge, (ii) in the surface region, and (iii) inside the epilayer. We compared the frequency of the nuclei according to these three locations for the (0001) and (000-1) pin diodes. The number of SSFs originated from the nuclei inside the epilayer in the (000-1) pin diodes was much less (<4 cm-2) than that in the (0001) pin diodes. However, the numbers of SSF nuclei (0.3 ~ 0.8 per device) located on the mesa wall and the surface region in the (000-1) pin diodes were comparable to the (0001) pin diodes. We also investigated the process responsible for generating the SSF nuclei.

Abstract: A vertical hot-wall type reactor, with a unique structure designed for controlling both gas flow behavior and thermal gradient (
T/mm) on the susceptor surface, was developed. The simulation results indicate that depending on the height of the epitaxy room (h), the
T/mm can be changed from a negative to a positive value. Preliminary epitaxial growth experiments resulted in a maximum growth rate of 51 μm/h, 4-inch area uniformity of σ/mean=1.7% for growth rate and σ/mean=21.5 % for doping concentration, and Z1/2 trap concentration of 9×1012 cm-3 at a growth rate of 43 μm/h.

Abstract: We compared the electrical characteristics of 4H-SiC(0001) and (000-1) Schottky barrier diodes (SBDs), and derived the Schottky barrier heights (Hbs) of Ta, W, Mo, and Pd on {0001}. We investigated the annealing temperature dependence of Hbs in Mo and the W Schottky contacts for (0001) and (000-1). The Hbs are increased by annealing, except for the W Schottky contact on (0001). The yields of 0.25 cm2 as-deposited Mo-SBDs were 93.3% for (0001) and 71.1% for (000-1), respectively. We also demonstrated over 1 cm2 (0001) as-deposited Mo-SBD with a low leakage current, an excellent ideality factor, and no excess current, encouraging the enlargement of the active area in the SBD.