Numerical investigation of the effect of rotation on the oscillatory thermocapillary convection and dopant transport in a silicon liquid bridge

Abstract

As a crucible-free method, the floating zone method can provide suitable conditions for growing high purity silicon single crystals for semiconductor devices. For doped crystals, the three-dimensional and oscillatory thermocapillary convection during growth always lead to undesirable macro-segregation and dopant striations. Three-dimensional numerical transient simulations are carried out for a laterally heated silicon liquid bridge to study the oscillatory thermocapillary convection and dopant transport. A small temperature variation can induce the periodic oscillatory flow in the liquid bridge which leads to a non-axisymmetric and periodic dopant distribution at the growth interface. Effect of rotation on the oscillatory thermocapillary convection and time-dependent dopant distribution at the growth interface is investigated. Sufficient crystal rotation is helpful to increase azimuthal uniformity and reduce concentration variation at the growth interface. The iso-rotation of crystal and feed is favorable for eliminating the oscillations of thermocapillary convection and concentration. However, for the same rotation rate, the stronger forced convections in the cases of single-rotation of crystal and conter-rotation of crystal and feed are more efficient in reducing concentration variation at the growth interface, and the concentration oscillation can be reduced by increasing rotation rate in both cases.