Silicon melt crystal growth

Czochralski seeded single-crystal growth from semiconductors stable as melts, which yields the meters-large single crystals of ultra-high purity silicon used in nearly all technological applications. 

The primary application for floating-zone melting is crystal growth rather than purification. Semiconductor-grade sflicon is not purified by zone refining silicon chlorides are distilled and then reduced with hydrogen. 

T. Yoshikawa, K. Morita, Refining of silicon during its solidification from a Si-A1 melt. The 4th Asian Conference on Crystal Growth and Crytsal Technology. Sendai, Japan, 2008... 

Another attempt to make feed rods for FZ crystal growth from cheap starting material is to melt solar (or lower) grade raw silicon in a quartz crucible and pull a rod of the desired diameter after the CZ method, not necessarily a single crystal. A lot of impurities can be removed by segregation and in the subsequent FZ step, almost all oxygen and most of the other impurities can be removed, too. However, the actual costs of such an approach must be carefully considered, but it is still an option to overcome the diameter limitations of the Siemens process. 

Obviously, the circumstances during crystal growth have a major impact on the crystal structure and on the chemical, electrical and mechanical properties of the silicon ribbon. Silicon-melt preparation and especially the dissolution of impurities from the crucible material and the wafer cooling procedure are also crucial. 

In general, crystal growth is more complex than the system outlined above due to the behaviour of the To (temperature at the bottom of the solidified wafer), which in general is not constant, the temperature dependence of the material characteristics, and the often turbulent flow in the liquid silicon melt. The variable growth speed results in thickness dependent material characteristics due to processes like velocity dependent effective segregation of metallic impurities. 

The equilibrium distribution coefficient close to the melting point is also known as the partition coefficient. Since the partition coefficient controls the incorporation of impurities in the crystal during crystal growth and zone refining, it is one of the most important parameters that can be obtained from the thermochemical database. It is worth noting that the distribution coefficient determined by the ratio of volume concentrations, cm 3, can be related to the distribution coefficient by introducing the density ratio of liquid and solid silicon ... 

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