External Gettering Research Articles

Purification of Vanadium by External Gettering

Vanadium metal has been purified with respect to carbon, oxygen and nitrogen by allowing these impurities to diffuse to and react with a surface layer rich in titanium. The nitrogen concentration was reduced from 100 ppm to less than 1 ppm, the carbon concentration was reduced from 240 ppm to less than 2 ppm and the oxygen concentration was reduced from 290 ppm to 6 ppm. The resistance ratio was increased from 52 to more than 685, a value that would indicate a total interstitial impurity concentration of 11 ppm. The diamond pyramid hardness was between 44 and 50 after purification. The internal friction peaks due to these interstitial solutes had almost completely disappeared in the purified metal. The purification can be done at any temperature at which the interstitial solutes are able to diffuse rapidly enough. Both 1000 and 1200 °C were found to be satisfactory with somewhat higher purity obtained at 1000 °C. This method is quite versatile and can be applied to specimens more than one cm thick if sufficient time is allowed for diffusion.

(Invited) Advances in Silicon Crystal Properties

The defect situations as they are presented in different categories of silicon material are briefly described. It is stated that oxygen or carbon are predominant factors in forming localized defects. After a brief introduction into lattice kinetics of gettering, different aspects of defect engineering are discussed. For dislocation-free crystals, this article mainly concentrates on the kinetics of two types of defects: oxygen swirl and haze. Substantial efforts to prevent their formation in the surface region of the wafer by applying either internal or external gettering methods have been made more recently. The special nature of polycrystal-line silicon solidified from the molten state, finally represents a different system of internal gettering.