Turbulent melt convection and its implication on large diameter silicon Czochralski crystal growth

Turbulent convection was studied in silicon melts during the Czochralski growth of crystals with large diameters (up to 300 mm) by measuring the temperature distribution in the melt and analyzing the occuring temperature fluctuations for various parameter settings. It was found that the flow in the central region of a large Czochralski silicon melt is dominated by buoyancy convection showing features of a transition state from soft to hard turbulence. In the periphery regions, towards the walls of the rotating crucible and also directly below the rotating crystal interface, the dominating forced convection stabilizes the melt Bow and keeps it in the beginning of a soft turbulence state. The measured temperature distributions were also used to determine the turbulent heat transfer through large scale silicon Czochralski melts in terms of the dimensionless Nusselt number Nu. A scaling law was found for Nu which is used to improve the global thermal numerical simulation of the silicon Czochralski process.