INTERFACE SHAPE, HEAT-TRANSFER AND FLUID-FLOW IN THE FLOATING-ZONE GROWTH OF LARGE SILICON-CRYSTALS WITH THE NEEDLE-EYE TECHNIQUE

A computer simulation is carried out to study the interface shape, hea t transfer and fluid flow in the floating zone (FZ) growth of large(> 100 mm) Si crystals with the needle-eye technique and with feed/crysta l rotation. Natural convection, thermocapillary convection, electromag netic (EM) forces and rotation in the melt are considered. The unknown shape of the molten zone is calculated as a coupled thermal-electroma gnetic-hydrodynamic problem and compared with that observed during exp eriments. The effects of the growth rate and the process stage on the shape of the interface are demonstrated. It was observed that natural convection and rotation dominate over thermocapillary and EM convectio n, at least for conditions corresponding to the industrial FZ Si produ ction with the needle-eye technique. It is shown that under these cond itions the rotation destabilizes the flow and only unsteady flows exis t in the molten zone. The calculated distributions of the oscillation amplitude of the tangential velocity at the growing interface correspo nd to the radial resistivity distributions measured in the single crys tal by the photo-scanning method.