Floating zone crystal growth
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Floating zone crystal growth is a method of growing cylindrical boules of very high purity single crystal Silicon for use in the semiconductor industry. It is arguably one of the most enabling techniques developed in the information era, pioneered by Siemens AG to allow integrated circuits to be mass produced on smaller scales.
Similar to zone refining, the principle is that since the segregation coefficient k (the ratio of an impurity in the solid phase to that in the liquid phase) of most impurities in Silicon is less than one, in situations where molten liquid Silicon is in contact with solid Silicon the impurity atoms will diffuse to the liquid region since they prefer to sit in the liquid phase. Thus, by passing a boule of silicon through a thin section of furnace very slowly such that only a small region of the boule is molten at any time, the impurities will collect in the molten region and migrate with it as the boule is moved through the heat zone. Because of the lack of impurities in the leftover regions which solidify, the boule can grow as a perfect single crystal if a seed crystal is placed at the base to initiate a chosen direction of crystal growth.
[edit] References
- [1]
- Porter and Easterling, Phase Transformations in Metals and Alloys.
