Comparison of the effect of ug and magnetic fields on the crystal growth of floating zone silicon

Abstract

The growth process of silicon crystals grown with the float- zone method is strongly influenced by convection in the melt zone. Crystal growth under microgravity (μg)offers the advantage to reduce the buoyancy related convection. The size restriction which we have under terrestrial conditions due to the hydrostatic pressure is also avoided. But due to the low Prandtl number of silicon (Pr=0.02) and the comparatively high temperature dependence of surface tension (δy/δT=-.28x10-3 N/mK) even small free melt zones exhibit time-dependent thermocapillary (Marangoni) convection. Thus irregular dopant inhomogeneities occurred in doped crystals grown under 1g conditions as well as in crystals grown under (mu) g. Attempts to enhance the dopant distribution by applying static magnetic fields resulted in most cases in either a reduced radial homogeneity, or in time-dependent thermoelectromagnetic convection (TEMC). A promising alternative are transverse rotating magnetic fields: the time-dependent thermocapillary convection is not damped as in the case of static fields, but a 2D-axisymmetric, azimuthal flow is superimposed. Several experiments performed under 1g demonstrated the positive effect of rotating magnetic fields on the microscopic dopant distribution as well as on the radial dopant profile homogeneity.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.