The rapid growth method for water-soluble crystals is reviewed. In the preparation stage of the growth solution, an excess energy such as thermal and sonic one was applied to the solution that would be effective to decompose the clusters of molecules. The highest supersaturation achieved was over 120%. The growth rate of 54 mm/day was achieved in the growth of dKDP crystal. This technology was applied to the crystals for power-photonics application resulting in the 10 times rapider growth than the conventional method. The evaluation of the grown crystals in various properties are discussed for KDP, dLATGS and KAP.
New unidirectionally solidified eutectic ceramics such as Al_2O_3/YAG or Al_2O_3/GdAlO_3 has recently been fabricated by controlling accurately the unidirectional solidification. The eutectic composite has a new microstructure, in which single crystal Al_2O_3 and single crystal complex oxide compounds (YAG or GdAlO_3) are three-dimensionally and continuously connected and finely entangled without grain boundaries. The eutectic composite fabricated is thermally stable and has the following properties: l) the flexural strength at room temperature can be maintained up to just below melting point (about 2040〜2150 K), 2) it shows neither weight gain nor grain growth, even upon heating at 1973 K in an air atmosphere for 1000 hours (in cases of Al_2O_3/YAG). Consequently, several useful applications can be considered: for example, new aero gas turbine and power generation system with non-cooled turbine blades at ultrahigh temperature above 1773 K.
Understandings and control of solid-phase reaction at metal/Si interfaces become more and more important in realizing future ULSI devices. In this paper, we have summarized the general formation process of silicide at metal/Si interfaces and discussed the interfacial reaction in Co/Si (001) and Ti/SiGe/Si (001) systems from a viewpoint of ULSI applications. In the case of epitaxial growth of thin CoSi2 films, surface morphology is strongly affected by defects and adsorbed-oxygen atoms on Si surfaces, which means that the control of Si surfaces is essential to grow high-quality epitaxial CoSi2 films. At the Ti/SiGe interfaces, Ti atoms preferentially react with Ge atoms and Ge-rich SiGe layers are formed as a result of solid-phase reaction. It can be concluded that SiGe/Si heterostructures are one of candidates in realizing low resistivity contacts.
A computer code is developed for simulation of the dislocation density in a bulk single crystal during the Czochralski (CZ) growth process. In this computer code, the shape of crystal-melt interface and the temperature in a crystal at an arbitrary time are determined by linear interpolation of the discrete results that are obtained by heat conduction analysis of a CZ single crystal growth system. A dislocation kinetics model called the Haasen-Sumino model is used as the constitutive equation. In this model, the creep strain rate is related to the dislocation density, and this model extended to the multiaxial stress state is incorporated into a finite element elastic creep analysis program for axisymmetric bodies. Dislocation density analyses are per-formed using this computer code for Si, InP and GaAs bulk single crystal. The present analyses indicate a W-type dislocation density distribution across the diameter in InP and GaAs single crystals that can be observed in actual CZ growth of InP and GaAs.
The effect of hydrogen anneal is summarized in concerning to improvement of CZ silicon crystal quality. By applying the hydrogen anneal at 1200℃ to the CZ silicon wafer, both grownin defects and OSF's (oxidation induced stacking faults) were perfectly eliminated in the surface and sub-surface. The BMD (bulk micro defect) can be controlled during the device manufacture process. In addition, the gate oxide formed on the hydrogen annealed wafer has superior properties comparing to that on the CZ wafer. The elimination mechanism of grown-in defect was discussed. That was due to surface reconstruction of the grown-in defect by surface atom migration. The surface atom migration strongly depends on the oxide film covered on the grownin defect surface. The covered oxide was reduced by hydrogen and perfectly disappeared in the region with under-saturated oxygen during hydrogen annealing.
Behavior of bubbles in silica glass for growing silicon crystals as crucibles was investigated. The silica glass was heated at 1500℃ for 2-10h under 5-100 Torr of Ar atmosphere. Bubbles scarcely move in the silica glass. This finding is consistent with the calculated data. The bubbles are expanded with the holding time at 1500℃. The extent of expansion is estimated by the observed density of silica glass. The rising velocity of the bubbles in molten silicon is also suggested.