Papers by Keyword: Hot Zone

Abstract: At the high growth temperatures of the PVT method, thermal radiation from the graphite crucible surface to the seed region is the dominant mode of heat transfer. In this study, we propose a newly designed crucible structure with a thinner graphite wall compared to the conventional design for SiC crystal growth. The SiC ingot grown using the conventional crucible exhibited the smallest thickness variation (flat top surface) between the center and the edge of the ingot, accompanied by polytype inclusions, which led to an increase in defect density. In contrast, SiC ingots grown using the newly designed crucibles (Design A and Design B) showed a convex top surface and a significantly lower defect density due to the improved heat transfer efficiency. Thinning the graphite crucible wall helps maintain a relatively higher temperature at the seed edge region, thereby effectively enhancing thermal radiation in the radial direction inside the crucible. These results indicate that thermal radiation in the radial direction can be achieved through appropriate optimization of the graphite wall thickness.

Abstract: The hot-zone design using an air-pocket was adopted to produce uniform temperature gradient in horizontal direction. In order to investigate the change of temperature gradient toward horizontal direction with growth time, the front shape of SiC growing crystal was measured with different growth stages such as initial, growing and finished stage. While SiC ingot grown in conventional hot-zone design exhibited inhomogeneous growth front in the initial stage of growth and multi facet formation in final stage, which could result in increased defect density, a homogeneous temperature gradient and improved crystal quality was obtained in the modified hot-zone design. Based on the mapping measurement of FWHM (Full width at half maximum) value in X-ray rocking curve, the crystal quality of SiC crystals grown with the modified hot-zone design was observed to be definitely better than conventional design.

Abstract: Single crystal of LiNbO₃ has been successfully grown by the Czochralski method in an air atmosphere with a r.f heating crystal growth system namely Automatic Diameter Control Crystal Growth System (ADC-CGS). This paper reports on the effect of new thermal insulation on the growth process of LiNbO₃ single crystal. The effect of hot zone thermal insulation design was investigated. The conditions required to grow high quality LiNbO₃ single crystals are described. A set of crystal growth processes were conducted with the rotation rate of the seed at 15 rpm and the pulling rate at 2.0 mm/hr kept constant. All of the runs were grown along <104> orientation. To control the diameter of the crystal, we have to alter the thermal environment inside the hot zone. In other words, during the crystal growth we have to increase the control power to get smaller diameter and decrease the control power to get larger diameter.

Abstract: The numerical modeling of melt flow, heat transfer and impurity (phosphorus) diffusion in the double crucible of "Redmet-90M" Cz puller was carried out in an application to a 200 mm diameter Si single crystal growth. The double crucible consists of two coaxial crucibles having different sizes: 490 mm (external) and 300 mm (internal) inner diameters. The bottom of internal crucible has a central hole of Do = 6 and 12 mm diameter for melt inflow from the external crucible. During crystal pulling the granulated Si was added in the external crucible and a melt of the internal crucible was doped by phosphorus. Three-dimensional features of a rotating melt flow affecting on heat transfer and impurity diffusion in the internal crucible were analyzed. In particular, the melt precession and thermal asymmetry near the liquid-solid interface (LSI) in the internal crucible are discussed. It is shown that a significant phosphorus losses caused by its evaporation from a melt surface may be compensated by additional phosphorus doping in the internal crucible.

Abstract: In an application to large diameter Czochralski (CZ) silicon (Si) single crystal growing the influence on crystal temperature field of various thermal shield assemblies located near to its surface is discussed. By means of mathematical modeling the computer model of thermal processes in an application to a hot zone of "Redmet-90" puller [1], intended for 200 and 300 mm diameter Si single crystal growth is developed. The role of the ring shield and the shield assembly, consisting of two shields (an internal cone and an external one is repeating the crucible shape) and being as a basis of some patents, is investigated. On the basis of the carried out calculations the new thermal shield assembly for "Redmet-90" puller was offered. Its influence on formation of the characteristic thermal zones in growing single crystal, corresponding to defect formation processes in dislocation-free Si crystals (the recombination of intrinsic point defect – IPD, and the formation of their agglomerates) is discussed. The influence of a melt flow on the liquid/solid interface (LSI) shape and thermal stability of crystal growing process is analyzed.

Abstract: The modeling of extrusion of various Al alloys and their particulate metal matrix composites was conducted by DEFORM™ finite element analysis to develop strain rate, stress and temperature distributions through the peak load and into steady state following development of the hot zone. The hot strength and ductility, constitutive constants and microstructural evolution had been determined by hot torsion. The relative load-stroke curves were determined for several billet temperatures, extrusion ratios and ram speeds. The grid distortion and distributions of important internal parameters define the evolution of microstructure. The extrudability was estimated on the basis of load, ductility and the potential for modeling the microstructure developed.

Abstract: The features of microdefect formation during dislocation-free Si single crystals are considered in connection with the specific thermal CZ growing conditions. For this purpose the thermal crystal growth histories are calculated by means of a global thermal mathematical model and then on their basis the intrinsic point defect recombination and microdefect formation are modeled numerically. Difficulty of such integrated approach is explained by of the complicated and conjugated thermal modeling and a presence of various temperature zones in growing single crystal, answering to various defect formation mechanisms.