Tomohiro Kawase - Academia.edu (original) (raw)

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Papers by Tomohiro Kawase

Cost reduction is the top priority of device manufacturers to overcome keen competition and obtai... more Cost reduction is the top priority of device manufacturers to overcome keen competition and obtain larger market share. The 6-inch process is the key technology in achieving the cost reduction goal. However, the larger temperature difference in a 6-inch wafer in comparison to a 4-inch wafer increases the possibility of slip-dislocation generation and wafer breakage during high temperature processes. This prevents device manufacturers from succeeding with the 6-inch process. Enlarging the diameter from 4 inches to 6 inches also causes the increase of dislocation density and residual strain as well as difficulty in obtaining good reproducibility of the crystals. Growth of 6-inch GaAs single crystals by LEC[1], VCZ[2] and VGF[3] methods have been reported and the manufacturing efforts continue. The 6-inch wafer production by the LEC method was reported at the GaAs MANTECH Conference in 1998[4]. We have successfully developed the Vertical Boat (VB) method for mass production of GaAs sub...

Materials Science in Semiconductor Processing, 2006

In order to assess macroscopic and microscopic profiles of carrier concentration in n-type InP su... more In order to assess macroscopic and microscopic profiles of carrier concentration in n-type InP substrates, near-infrared (NIR) transmittance has been measured and quantitatively converted into the term of carrier concentration with the calibration curve determined experimentally in the range from 1 Â 10 18 to 6.4 Â 10 18 cm À3. The InP substrate assessed here was a 4-in S-doped substrate grown by the vapor-pressure-controlled Czochralski (VCZ) technique. It was found that the radial profile of carrier concentration was macroscopically concave. An elliptical striation pattern due to microscopic fluctuation of carrier concentration was observed, which seemed to be originating from unwanted asymmetry in the VCZ growth process. The macroscopic and microscopic profiles of carrier concentration may provide very important information about the crystal growth situations such as the shape of solid-liquid interface and the stability of crystal growth.

Transactions of the Japan Institute of Metals, 1986

A structure analysis of Ti5Si3D0 .9 has been carried out to determine the deuterium trap sites by... more A structure analysis of Ti5Si3D0 .9 has been carried out to determine the deuterium trap sites by neutron powder diffraction with the Rietveld profile analysis. It is revealed that the deuterium atoms are located at octahedral (2b) sites surrounded by six Ti atoms in the crystal structure of Ti5Si3D0 .9, space group P63/mcm. Local vibration spectrum of hydrogen in Ti5Si3H0.83 measured by neutron inelastic scattering supports this result; the energy eigenvalue of the primary vibration mode is found at 7.53 kJ/mol (78 meV). The hole radius and the spring constant of the Ti-H(D) bond are discussed.

Low-dislocation-density large-diameter GaAs single crystals with low-residual-strain have been st... more Low-dislocation-density large-diameter GaAs single crystals with low-residual-strain have been strongly required. We have developed dislocation-free 3-inch Si doped GaAs crystals for photonic devices, and low-dislocation-density low-residual-strain 4-inch to 6-inch semi-insulating GaAs crystals for electronic devices by Vertical Bridgman(VB) technique. We confirmed that VB substrates with low-residual-strain have higher resistance against slip-line generation during MBE process. VB-GaAs single crystals show uniform radial profile of resistivity reflecting to the flat solid-liquid interface during the crystal growth. Uniformity of micro-resistivity of VB-GaAs substrate is much better than of the LEC-GaAs substrate, which is due to the low-dislocation-density of VB-GaAs single crystals.

Semiconductors and Semimetals, 1990

Publisher Summary This chapter presents a discussion on the production and quality control of ind... more Publisher Summary This chapter presents a discussion on the production and quality control of indium phosphide (InP) substrates. It describes the techniques related to InP single crystal materials and their characterization. The applications of InP crystals and the requirements for their quality is described in the chapter. The chapter reviews the details of crystal growth techniques, including recent developments obtained in laboratories. The techniques used in the evaluation, quality control, and wafer processing are also described in the chapter. InP single crystals have been used exclusively as conductive substrates for infrared optical devices. They are also under development as semi-insulating substrates usable in higher frequency microwave devices, such as metal–insulator–semiconductor field-effect transistor (MISFETs) and optoelectronic integrated circuits. There is a great demand for the development of higher quality indium phosphide single crystals. For this purpose, the technologies reviewed in the chapter, especially those concerning both the crystal growth and the processing of this material, are very important for future developments. Etch-pit density (EPD) is one of the best indicators of the quality of II–-V semiconductor crystals.

SPIE Proceedings, 1989

Low-dislocation-density InP single crystals have been successfully grown under the low axial temp... more Low-dislocation-density InP single crystals have been successfully grown under the low axial temperature gradient of dT/dZ = 30°C/cm by the VCZ method, which is an LEC method with phosphorus vapor pressure applied over the liquid encapsulant during growth. The average EPD is about 2,000 cm-2 in the 2-inch diameter crystals doped with Fe or Sn. The slip-free and dislocation-free crystals have been obtained by doping S of 2 x 1018cm-3 at the seed end. The InP crystals have uniform distributions of electrical properties with variations of less than 2%. The photoluminescence measurements of Sn-doped crystal have revealed no deep level due to phosphorus vacancy. The VPE InGaAs layer grown on the S-doped VCZ substrate exhibits few propagated dislocations and a very low leak current.

physica status solidi c, 2007

The light absorption mechanisms below the fundamental energy gap in undoped and Si-doped GaAs cry... more The light absorption mechanisms below the fundamental energy gap in undoped and Si-doped GaAs crystals have been investigated to assess EL2 defects and the carrier concentration distribution in III-V compound semiconductor substrates. It is demonstrated, that the near-infrared transmittance mapping equipment consisting of a high-brigthness LED, a high-sensitivity CCD camera, and a digital image processing system is capable to reveal surface scratches and local crystal imperfections such as inclusions, voids, and twining inside the substrate, besides EL2 defects and the carrier concentration distribution. Hence, the homogeneity of III-V compound semiconductor substrates with diameter up to 6 inches can be assessed in less than several seconds with high spatial resolution of 640×480 pixels.

physica status solidi (a), 2007

The light absorption below the fundamental energy gap in n-type GaAs has been investigated precis... more The light absorption below the fundamental energy gap in n-type GaAs has been investigated precisely. It is experimentally confirmed that there are the three different mechanisms: (a) the enhancement of fundamental absoption due to the shrinkage of energy gap and band filling by doping Si atoms, (b) deep-level (EL2) absorption, and (c) free-carrier absorption. It is found that the transmittance measurement at the wavelength longer than about 1000 nm in the free-carrier absorption region is more useful and direct, compared with that near the fundamental absorption region from 900 nm to 950 nm, precisely to determine the carrier concentration in n-type GaAs. The two-dimensional profile of carrier concentration in a VB-grown 3 φ GaAs substrate is measured in high spatial resolution with the short time less than 5 seconds by using a sophisticated near-infrared transmittance-measuring equipment. The absolute amount and homogeneity of carrier concentration can be assessed in the range from 0.3 to 3 × 10 18 cm-3 .

Journal of Crystal Growth, 2007

ABSTRACT AlN single crystals with thicknesses from 3μm to 4mm were grown on SiC substrates by the... more ABSTRACT AlN single crystals with thicknesses from 3μm to 4mm were grown on SiC substrates by the sublimation method. Evaluations of crystalline quality were performed by X-ray diffraction (XRD), transmission electron microscope (TEM) and etch pit density (EPD) measurement. The FWHM of the XRD rocking curve for AlN (101¯0) reflection was as small as 26arcsec for the sample of 4mm thickness, and the dislocation density was estimated to be less than 106cm−2 by EPD measurement in spite of the large lattice mismatch of 1% between AlN and SiC. TEM observation was conducted to investigate the mechanism of the improvement of the crystalline quality. We observed the significant reduction of dislocations above the interface, allowing growth of 3μm–4mm thick AlN with high crystalline quality. These results show that the commercial production of large-sized, high-quality substrates of AlN single crystal is possible using the sublimation technique.

24th Annual Technical Digest Gallium Arsenide Integrated Circuit (GaAs IC) Symposiu

Macroscopic and microscopic uniformity in 4-inch InP substrates has been significantly improved b... more Macroscopic and microscopic uniformity in 4-inch InP substrates has been significantly improved by new developments in SEI's Vertical Boat (VB) technique. In this paper, we report improvements, in etch-pit density (EPD) distribution, micro-resistivity profiles, and photoluminescence (intensity and 4.2K spectra), for 4-inch InP VB in comparison to both VCZ (SEI proprietary Vapor pressure controlled Chockralski) and commercially available VGF substrates.