Growth of High Purity Oxygen-Free Silicon by Cold Crucible Techniques.

Abstract : This work includes a detailed evaluation of previous research on cold crucible technology, the design and construction of a cold crucible assembly and the investigation of the growth of single crystals of high purity silicon using the water-cooled cold crucible. In parallel with the experimental work, a theoretical analysis is being carried out on the thermodynamics and heat flow characteristics within the melt confined in the cold crucible in an effort to develop a better understanding of the crystal growth process. Results to date have been encouraging. A water-cooled copper cold crucible (73 mm I.D.) which incorporates a bottom-feeding mechanism, has been designed, constructed and tested. Silicon melts (weighing 750 grams) can be routinely melted using low frequency induction heating (approx. 250-300 Khz) and confined within the cold crucible for extended periods without contamination. Seeding techniques have been developed to permit the Cz growth of single crystals of silicon with lengths up to 100 mm and diameters in excess of 25 mm. The preliminary characterization data on the single crystals produced are inconclusive. However, it appears that the purity levels (including oxygen content) of single crystals produced to date are equal to or in most cases, better than, the purity level of the polycrystalline feed material.