Design of a Zone Refiner for Optimization Studies

Abstract

Many of the physical properties of semiconductor materials depend on the presence of imperfections. A significant source of lattice imperfections is the inclusion of foreign atoms, or impurities. Since most semiconductor devices require accurate and repeatable results, highly pure materials are desired. In order to obtain high purity semiconductor metals, zone purification is commonly utilized as the final purification stage. The University of Victoria Crystal Growth Lab (CGL) Group is carrying out an optimization study of the zone refining process. To provide the required experimental platform for this study, a zone refining test bench (``CGL zone refiner'') was developed. The apparatus will be used to study the effects of zone geometry and mixing on the efficiency of the zone refining process. It also has the capability of zone refining, under an applied rotating magnetic field and an electric current, in order to examine their effect. A series of preliminary experiments were carried out with the CGL zone refiner prior to optimization testing. Samples were removed from the processed ingots and sent for glow discharge mass spectrometry (GDMS) analysis. The GDMS results indicated that the system operates efficiently and that, even with as few as three zone passes, the CGL zone refiner purified the material. A numerical thermal analysis for the zone refining of Te is also presented. In general, the numerical results were in agreement with experimental observations; the solid/liquid interface was convex(toward liquid) for small liquid zones, concave for large liquid zones and the system was thermally stable.