Boule Shape Dependence of Shear and von-Mises Stress Distributions in Bulk SiC during Sublimation Growth
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1246-B01-03
Boule Shape Dependence of Shear and von-Mises Stress Distributions in Bulk SiC during Sublimation Growth
Roman V. Drachev, Darren M. Hansen and M. J. Loboda Compound Semiconductor Solutions, Dow Corning Corp, Auburn, MI, 48611
ABSTRACT An analytical study of the dependence of shear and von-Mises stress distributions, which develop during PVT (Physical Vapor Transport) growth of 4H-SiC, has been executed. The key parameters investigated include thermal conditions of the crystal growth and parameters of the growing boule geometry. The evaluation was conducted via a 24 full factorial DOE (Design of Experiments). Parameters of the growing boule geometry, i.e. seed diameter, growth front height, inclination angle and height of the side surface were set as the DOE factors, while responses were calculated using numerical simulations. It is found that unique SiC boule growth conditions, which simultaneously minimize both the shear stress and von Mises stress magnitudes, cannot be achieved. Optimization of the shear stress distribution favors longer SiC boules with small seed diameters, small expansion angles and flat growth fronts. Alternatively, optimization of vonMises stress favors short crystals with small seed diameters and small expansion angles but with curved growth fronts. Consequently, optimization of stress components in SiC crystals involves careful investigation of the interaction and compromise of the reaction cell geometry and growth conditions.
INTRODUCTION Shear and von-Mises stress magnitudes and their spatial distributions within PVT growing boules of SiC are among the most critical factors that influence quality and fabrication processes of SiC substrates. In fact, generation of dislocations, their movement in the growing crystal, formation of micropipes and probability of ingot cracking are directly related to the subject of interest [1–3]. Eventually these stress related phenomena determine production yields of SiC wafers and material characteristics such as dislocation and micropipe densities, mosaisity, radius of lattice curvature, resistivity and its uniformity, which are critical to commercial success [2,4,5]. Magnitudes of the stress distributions and their uniformities depend on the temperature distribution within the growing boule, method of the boule suspension inside the reaction cell, thermo-mechanical properties of the materials that are in direct contact with the crystal during the process of growth and crystallographic orientation of the growing monocrystal. These stress characteristics also depend on the shape factors of the growing boule such as seed diameter, growth front shape, height and inclination angle of the crystal side surface. This is why dependence of the shear and von-Mises stress magnitudes and their spatial distributions on the shape factors of the growing boule is the subject of this study.
PROBLEM DEFINITION AND INVESTIGATION APPROACH The simplified configuration shown in Fig.1 has been chosen as a simulation model for the shear and von-Mises stress stud
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