Katsunori Danno

High-Speed Growth of High-Quality 4H-SiC Bulk by Solution Growth Using Si-Cr Based Melt

High-speed solution growth using Si-Cr based melt has been performed on on-axis 4H-SiC(0001) at a high temperature of about 2000°C. The maximum growth rate for one-hour growth reaches to 1120 m/h, while the typical growth rate of growth for 2h is about 500 m/h. A large crystal that is about 25 mm in diameter and 1650 m in thickness can be obtained by growth for 5h. The crystal quality is confirmed to be homogeneous by X-ray diffraction and X-ray topography, because FWHM is less than 30 arcsec. Etch pit density of the threading dislocations in the grown crystal is 103-104 cm-2, and that of basal plane dislocation is 2×102-3×103 cm-2. Resistivity of the crystals grown by the solution growth is comparable to those of crystals grown by physical vapor transport technique.

Transmission Electron Microscopy Analysis of a Threading Dislocation with c+a Burgers Vector in 4H-SiC

A threading dislocation (TD) in 4H-SiC, which was interpreted as a right-handed threading screw dislocation (TSD) by synchrotron monochromatic-beam X-ray topography (SMBXT) and molten KOH etching with Na2O2 additive (KN etching), was characterized by large-angle convergent-beam electron diffraction (LACBED) and weak-beam dark-field methods. It was found that this TD was a so-called c+a dislocation with Burgers vector of b=[0001]+(1/3)[2110], which is often misinterpreted as TSD (c-dislocation) by SMBXT and KN etching. The rotation direction of the screw component within the c+a TD determined by LACBED agreed with the SMBXT observation.

Molten KOH Etching with Na2O2 Additive for Dislocation Revelation in 4H-SiC Epilayers and Substrates

A novel etching solution using molten KOH with Na2O2 additive (KN etching) for dislocation revelation in 4H-SiC epilayers and substrates has been proposed. Threading screw and edge dislocations (TSDs and TEDs) have been clearly revealed as hexagonal etch pits differing in pit size, and basal plane dislocations (BPDs) as seashell-shaped pits. KN etching has provided a solution to the problem that KOH etching is not effective for dislocation identification in n+-4H-SiC. The influences of SiC off-axis angles, carrier concentrations, and growth techniques on the effectiveness of KN etching have also been investigated. It has been shown that KN etching is applicable to SiC epilayers and substrates with any off-axis angle from 0 to 8° and electron concentrations from 1015 to 1019 cm-3.

Complete Micropipe Dissociation in 4H-SiC(03-38) Epitaxial Growth and its Impact on Reverse Characteristics of Schottky Barrier Diodes

Micropipe dissociation has been investigated in homoepitaxial growth of 4H-SiC(03 3 8) by chemical vapor deposition. Almost complete (~100%) closing of micr opipes was realized, although some of very large (> 3 μm) micropipes were threading into epilayers. Based on KOH etching experiments on various epilayers, the authors propose a model of micropipe dissociation in 4H-SiC(03 38) epitaxial growth. The reverse characteristics of Ni/4H-SiC (03 38) Schottky barrier diodes were significantly improved by micropipe closing. Introduction Recent progress in SiC growth and processing technologies has accel er ted the development of high-voltage SiC diodes and FETs [1]. To scale up the current handling c apability of SiC power devices, however, micropipes (hollow cores associated with superscrew dislocations) have to be eliminated [2]. Furthermore, 4H-SiC(0001) MOSFETs have suffered from unacceptably low channel mobility, which has significantly limited the MOSFET perf ormance [3]. To overcome these problems, the authors have proposed a novel crystal face, 4H-SiC(03 38), which is inclined by 54.7 from (0001) toward [01 10] and is semi-equivalent to (001) in the cubic structure [4]. The quality of SiO2/4H-SiC(03 38) interface may be potentially superior, compared with the conventional (0001) [5]. In this paper, complete dissociation (closing) of mi cropipes in 4HSiC(03 38) epitaxial growth is presented. The improved reverse characteris ti s of 2~3 kV Schottky barrier diodes are demonstrated. Epitaxial Growth of 4H-SiC(03 38) Homoepitaxial growth was performed by either horizontal hot-wall CV D at 1550C [6] or chimneytype vertical CVD at 1700 C [7] in a SiH4-C3H8-H2 system on 4H-SiC(0338) substrates. 4HSiC(03 38) substrates were prepared by slicing of 4H-SiC boules grown on (000 1) seed crystals at SiXON. The typical size of substrates was about 40 x 2 mm. The C/Si ratio during CVD was 1.5~1.8 for horizontal hot-wall CVD and 0.7~0.8 for chimney-type CVD. The typic al growth rate was 5 μm/h for horizontal CVD and 20 μm/h for chimney-type CVD. The epilayers were 15~110 μm thick and were unintentionally doped with nitrogen to 7 x10~2x10 cm. Specular surface morphology was obtained with a rms roughness of 0.18~0.22 nm in a 10 μm x 10 μm area. No macrostep bunching was observed, owing to the lack of intentional off-angle . Details of 4HSiC(03 38) growth are described elsewhere [8]. Micropipe Dissociation during 4H-SiC(03 38) Epitaxial Growth Materials Science Forum Online: 2003-09-15 ISSN: 1662-9752, Vols. 433-436, pp 197-200 doi:10.4028/www.scientific.net/MSF.433-436.197

Top-seeded solution growth of 3 inch diameter 4H-SiC bulk crystal using metal solvents

We performed top-seeded solution growth of 4H-SiC for obtaining longer length crystal. Si-Cr and Si-Ti melts were used as solvents. Meniscus formation technique was applied to the present study. Special attention was paid to improve the process stability during long-term growth. One of major technological problems in the solution growth is that the precipitation of polycrystalline SiC which hiders the stable single crystal growth. Another problem is the fluctuation of supersaturation at the growth interface during the growth. Through the optimization of growth process conditions, we have successfully grown 4H-SiC single crystals up to 14 mm long with three-inch-diameter, and evaluated their crystalline quality.

Characterization of Surface Defects of Highly N-Doped 4H-SiC Substrates that Produce Dislocations in the Epitaxial Layer

The structures of defects that form different types of etch pits on highly N-doped 4H-SiC substrates, that were produced by a sublimation method, after molten KOH etching were characterized. It was found that most of the dislocations in the epitaxial layer originated from defects at the surface of substrate whose etch pit structures were clearly different from the conventional structures. The etch pits were classified into drop, oval, round and caterpillar pits. The drop and oval pits were concluded to be formed by the deformation of conventional etch pits. Round pits were concluded to originate from half loop dislocations and were transformed to complex dislocations by epitaxial growth. Analysis by transmission electron microscopy measurement indicates that slipped edge dislocations (or screw dislocations) on the basal plane form caterpillar pits.

Deep Levels in Electron-Irradiated n- and p-type 4H-SiC Investigated by Deep Level Transient Spectroscopy

The authors have investigated deep levels in electron-irradiated n- and p-type 4H-SiC epilayers by deep level transient spectroscopy (DLTS). By low-energy electron irradiation at 116 keV, the Z1/2 and EH6/7 concentrations are increased in n-type samples, and the concentrations are almost unchanged after annealing at 950°C for 30 min. In p-type samples, the unknown centers, namely EP1 and EP2, are introduced by irradiation. By annealing at 950°C, the unknown centers are annealed out. The HK4 center (EV + 1.44 eV) is increased by the electron irradiation and subsequent annealing at 950°C. The dependence of increase in the trap concentrations by irradiation (NT) on the electron fluence reveals that NT for the Z1/2 and EH6/7 centers is in proportional to the 0.7 power of electron fluence, while the slope of the plot is 0.5 for the HK4 center. The Z1/2 and EH6/7 centers show similar annealing stage and are thermally stable up to 1500-1600°C, while the HK4 center is annealed out at about 1350°C. The Z1/2 and EH6/7 centers may be derived from a same origin (single carbon vacancy: VC) but different charge state. The HK4 center may be a complex including VC.

Dislocation Revelation from (0001) Carbon-face of 4H-SiC by Using Vaporized KOH at High Temperature

A novel etching technique using vaporized KOH to reveal various types of dislocations from the C-face of 4H-SiC has been proposed. Three different pit geometries have been observed, which can be attributed to three dislocation types commonly found in 4H-SiC. Pit positions on the Si-face and C-face have been compared to study the dislocation propagation behaviors across the sample thickness. Activation energy EA=49 kcal/mol has been obtained, indicating a surface-reaction-dominant process. This etching technique has provided an effective and inexpensive method of making inch-scale mapping of dislocation distribution for C-face epitaxial and bulky 4H-SiC.

Dislocation Revelation in Highly Doped N-Type 4H-SiC by Molten KOH Etching with Na2O2 Additive

We have proposed a new wet etching recipe using molten KOH and Na2O2 as the etchant (“KN etching”) for dislocation revelation in highly doped n-type 4H-SiC (n+-4H-SiC). Threading screw dislocations (TSDs) and threading edge dislocations (TEDs) have been clearly revealed as hexagonal etch pits differing in pit sizes, and basal plane dislocations (BPDs) as seashell-shaped pits. This new etching recipe has provided a solution to the problem that conventional KOH etching is not effective for dislocation identification in 4H-SiC if the electron concentration is high (>mid-1018 cm-3). We have investigated the effect of SiC off-cut angle on KN etching and it has been shown that the “KN etching” is applicable for the n+-SiC substrate with off-angle from 0o to 8o.

Thermal Stability of Defect Centers in n- and p-Type 4H-SiC Epilayers Generated by Irradiation with High-Energy Electrons

This paper comprises a systematic study of the thermal stability of defect centers observed in n- and p-type 4H-SiC by deep level transient spectroscopy (DLTS); the defects are generated by irradiation with high-energy electrons of 170 keV or 1 MeV.