Contamination‐Free High Temperature Treatment of Silicon or Other Materials

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Abstract
It has been shown that the contamination picked up during high temperature treatments of silicon stems from the diffusion of impurities from the outside of the quartz furnace tube and into the material being heat‐treated. This contamination can be prevented by placing the quartz tube into a protective atmosphere of in dry oxygen, i.e., by passing a dry mixture through the annulus of a double‐walled quartz tube. Silicon wafers oxidized in such a tube at 1000°C were found to be uncontaminated at the sensitivity afforded by neutron activation analysis. It is suggested that many transition group metals diffuse preferentially along incipient grain boundaries in vitreous quartz at high temperatures, the grain boundaries in turn stemming from the devitrifying action of sodium vapors in the furnace. The double‐wall tube arrangement thus not only prevents transition group metals from diffusing into and through the quartz of the inner wall, but also prevents sodium from initiating the devitrification process thus rendering the quartz more opaque to transition group metal diffusion.

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