THE IMPACT OF GRAPHITE-FURNACE PARTS ON RADIAL IMPURITY DISTRIBUTION IN CZOCHRALSKI-GROWN SINGLE-CRYSTAL SILICON

The origins of metal impurities in Czochralski-grown single-crystal si licon were investigated in order to develop crystals with improved rad ial impurity homogeneity. The radial metallic impurity distribution in silicon crystals was evaluated by means of minority carrier recombina tion lifetime. The crystal circumference was found to be an area of de graded lifetime. A quantitative analysis of radial impurity distributi on in silicon was carried out using deep level transient spectroscopy techniques. Iron was the predominant impurity detected on the circumfe rence of the crystal. The radial distribution of iron impurity concent ration showed good correlation with calculated results. An experimenta l technique was developed which allowed us to isolate the influence of the graphite parts of the Czochralski furnace as a contamination sour ce during high-temperature processing; Commercially available graphite materials of different purity levels, both with and without silicon c arbide coatings, were evaluated. It was confirmed that the graphite fu rnace parts play a role in determining the radial impurity distributio n profile.