Silicon crystal growth in a cusp magnetic field

Abstract

Czochralski silicon crystal growth in the presence of an axially symmetric cusp magnetic field is reported for the first time. The free surface of the melt is centered between two superconducting coils. Oxygen concentration in the crystal is shown to be successfully controlled from 1X10 18 to 2X10 17 atoms/cm 3 by increasing the cusp magnetic field strength up to 3500 Oe at the center of the bottom melt-silica crucible interface, while keeping the crystal rotation constant at 30 rpm and keeping the crucible rotation constant at −10 rpm. Both oxygen and dopant distributions are homogenized by the magnetic field. The controllability of oxygen concentration is due to the advantageous characteristics of the cusp magnetic field to realize localized control of thermal convection at the melt-crucible interface, independent of that at the melt free surface. The good crystal homogeneity results because there is no need to change the crystal and crucible rotations adequately to control the oxygen concentration, in contrast to the previous use of a transverse or vertical magnetic field in which extreme changes in the crucible or crystal rotation rate are required.