Zone Refining

High purity (99.999% (5N) or more) metals play a key role in current high-tech industrial field, such as special electronics, integrate circuits, photovoltaic systems, optical elements, chemical applications, etc., as in these areas even low concentrations of impurities could completely deactivate the desirable function.

Zone refining is the most important of the zone-melting techniques. It is being widely used in the semiconductor industry for refining of germanium and silicon to purity levels of 9N and above (i.e. >=99.9999999%).

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The Induction Zone Refining technique involves melting a narrow zone of a long ingot of the material to be processed. This molten zone is then slowly moved by moving the Induction Coil gradually along the length of the ingot in one direction. This process is repeated multiple times till the required purity level is reached. In this process difference between solubility of impurities in the molten and solid phases is used to concentrate impurities at the end section of the ingots.

Induction heating is ideal for this process since heat is rapidly generated inside the material forming a sharp narrow molten zone. Also, the temperatures that can be attained are much higher than those of conventional heaters.

Application area

• It is widely used in the semiconductor industry for refining of germanium and silicon to purity levels of 9N and above (i.e. ³99.9999999%).
• Ultra-purification (99.999% and above) of materials which have sharp