EDDY-CURRENT MEASUREMENT OF CRYSTAL AXIAL THERMAL PROFILES DURING CZOCHRALSKI SILICON CRYSTAL-GROWTH

The axial thermal profiles of silicon crystals during the Czochralsi crystal growth process were measured experimentally by using an eddy current technology. The intrinsic conductivity changes in the crystal resulting from cooling were measured in terms of the eddy current amplitude and phase responses, and the axial thermal profiles of the growing crystal were subsequently derived from the results. The experimental results indicate that the axial thermal profile in the region is nearly linear and quite transient during the initial phase of body growth. As the crystal gets longer, the increasing heat loss by radiation from the crystal surface causes the overall profile to shift downward. When the crystal reaches 200-250 mm in length, a steady state condition is achieved, and the overall axial thermal profile stays nearly invariant for the remainder of the growth. The steady state axial thermal gradient in the region is estimated to be about 4-6 degree C/mm.