Floating Zone Method

Fig. 8 illustrates the floating zone crystal pulling method.

· When extremely high purity silicon is required the growth technique of choice is float-zone method.

· The basic feature of this growth technique is that the molten part of the sample is supported by the solid part. There is no need for a crucible and so there is lower melt contamination, especially oxygen and carbon.

· A rod of high purity polycrystalline material is held in a chuck while a metal coil is driven by a high power radio frequency signal is slowly passed along the length. The molten silicon at the seed end starts to freeze, forming the same crystal orientation as the seed crystal.

· After the heating coils move over the whole polysilicon rod, it converts to a single crystal silicon ingot.

Fig. 8 Schematic of a float zone refining system.[4]