Thermal stress as the major factor of defect generation in SiC during PVT growth

Abstract

Numerical simulations of the thermal stress distribution in a SiC boule 2” in diameter and 1” long grown by conventional PVT technique were performed based on the temperature field distribution in a resistively heated growth reactor that was simulated using the GAMBIT-2.0.4/FIDAP-8.6.2 software package. Analysis of the simulation results revealed the existence of a thermal stress, which was excessively nonuniform in distribution and whose magnitude exceeded the value of the critical resolved shear stress of 1.0 MPa by a factor of 2. The high stress initiated plastic deformation and the high temperature provoked the intense self-diffusion processes. The combination of these factors alters the mechanism of plastic deformation, significantly affecting the structural quality of the growing crystal. The influence of self-diffusion processes initiating the formation of interstitial atoms and vacancies; stacking fault formation as a result of the nonconservative motion of the basal plane dislocations; and micropipe formation from the dislocation groups piled up at silicon and carbon second phase inclusions are also discussed.

Growth of Silicon Carbide

“…Furthermore, a nonuniform temperature distribution in the crystal, as a result of heat dissipation, will induce thermal stress, and as a consequence, defect generation in the crystal volume. Defect generation becomes significant when the induced thermal stress τ (r, θ, z) exceeds the value of critically resolved shear stress τ C (1.0 MPa) at the high SiC growth temperature [16,45].…”

“…As noted in Section 15.4.2, if the thermal stress generated during crystal growth exceeds the critically resolved sheer stress by a factor of two, intense plastic flow occurs, resulting in high-density dislocation generation. Since solid deformation at high temperatures is tightly entwined with the phenomena of self-diffusion, the movement of dislocations is essentially nonconservative and results in the formation of very complicated defect structures [45].…”

“…15.4). Several mechanisms of micropipe formation have been proposed [10,45,57,58]. Micropipes are generally considered to be empty-core screw dislocations with a large strain energy (large Burger's vector).…”

Bulk growth of single crystal silicon carbide

“…Screw dislocations originate mostly from the seed crystal and partially produced by imperfect nucleation. Threading edge and basal plane dislocations also partially propagate from the seed crystal; however thermal stresses during growth, causing plastic deformation, are considered to be the dominant mechanism for their generation [11]. The typical density of threading closed core screw and edge dislocations in good quality substrates is 10 3 -10 4 per cm 2 , but these defect types are not as detrimental for device performance as micropipes [12].…”

Control of the temperature field by double induction coils for growth of large-sized SiC single crystals via the physical vapor transport technique

“…Therefore, controlling the radial temperature distribution and gradient are critical in growing high-quality SiC single crystals with a large size and low thermal stress. 7,8 Yang et al simulated and calculated the impact of temperature distribution on the quality of the grown SiC ingot. Their simulated results showed that a concave temperature distribution along the radial direction is better than a convex temperature distribution along the radial direction in terms of lessening the thermal stress in the obtained SiC ingot.…”