Solar Grade-Silicon, Ingot, Wafer Technology and ... - Displaybank

Solar Grade-Silicon, Ingot, Wafer Technology and Market Trend (2008~2012)
3.2.2 Floating Zone Method (FZ)
Floating zone method was developed by Keck and others in 1952. It manufactures
silicon with the highest purity. Its basic principle includes partially melting long bar to
produce liquid phase region. It moves the region following after the bar to grow
monocrystal. Most impurities within silicon usually have equilibrium distribution
coefficient less than 1 that the impurities are separated in the liquid phase region with
CO/K concentration. The liquid phase region is cornered to move impurities towards
the end of the bar simultaneously.
Figure 3.2.3. Floating Zone Method Equipment
SAMPLE
As shown in the figure, the FZ method has no parts in contact with silicon
liquid unlike the CZ method that it can fundamentally prevent pollutions from
crucibles and obtain silicon with high quality. On the other hand, it requires a
liquid phase to remain in-between solid phases as a surface tension that it has
a limitation in a diameter of ingot to be manufactured. The method is generally
used to manufacture silicon bars of several tens of mm. The maximum
diameter of ingot using the currently developed floating zone method is about
150 mm. Therefore, the FZ method is improper to be used commercially due
to low productivity. Instead, it is used in special occasions when silicon with
high purity is needed.
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Jan’09