Development of a horizontal zone refiner for optimization studies

Date

2006

Authors

Haas, Jordan

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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. Due to the demand for increasing purity in an extremely competitive industry. producers must increase process efficiency and reduce production costs. The University of Victoria Crystal Growth Lab Group (CGL) is participating in a project aimed at increasing the efficiency of a commercial zone refining system. The project is composed of two parts: a numerical analysis intended to simulate the process. and an experimental study intended to verify the numerical model and conduct optimization experiments. A zone refiner was designed and developed in the lab for the experimental portion of the project. This thesis details the experimental portion of the project. The CGL zone refiner will be used to study the effects of zone geometry and mixing on the efficiency of the process. In order to achieve the most efficient possible combination. the zone refiner was constructed with the capability to adjust all of the typical process variables such as zone speed, zone spacing, and number of zone passes. as well as to accommodate specific methods aimed at increasing mixing in the melt such as applying an electric current or a rotating magnetic field. Once the CGL zone refiner system was complete, several experiments were carried out to prove and characterize the system. Samples were removed from the purified ingots and sent for glow discharge mass spectrometry (GDMS) analysis. The GDMS results indicated that the CGL zone refiner purified the ingot as desired and that there were no external sources of contamination from the process: in general, a reduction in concentration was seen for the impurities tested. During both the initial thermal testing and the subsequent full process experiments, the zone refiner performed as expected and without difficulty. The entire process was qualified and determined to be stable and easily controlled. The experiments conducted to date have shown that the system is a capable zone refiner for all of the planned studies.

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Keywords

semiconductors, zone melting, purification

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