Comparison of floating-zone Si crystals grown under μg and in an axial magnetic field

Abstract

The influence of buoyancy and thermocapillary (Marangoni) convection on the segregation in Si floating-zone (FZ) crystals grown under microgravity (μg) is compared against that of crystals grown under 1g and with an axial magnetic field of up to 0.5T. In the absence of RF heating both thermocapillary and buoyancy convection contribute to macrosegregation, but only thermocapillary convection is time-dependent due to the small critical Marangoni number of Si and leads to dopant striations. Consequently, floating-zone growth under μg is not capable of suppressing the formation of striations, but due to the reduced mixing of the melt the striation intensity is modestly decreased and the axial macrosegregation is changed. The application of an axial magnetic field up to 0.5T under terrestrial growth conditions allows a suppression of striations together with a change in the axial macrosegregation. It is, however, detrimental to the radial uniformity of the dopant concentration by producing a non-facet “core” in the crystal, with the core diameter depending on the magnetic induction.