Impurity Incorporation in Czochralski Silicon Grown for VLSI

Tight control of oxygen concentration (within ±0.3 ppma) is attained with a new method in the Czochralski growth of large-diameter silicon (86 to 125 mm). Programmed variation in growth parameters is employed during growth to compensate for the normal decrease in oxygen concentration otherwise present. The presence of A1 and B impurities in vendor-supplied silica crucibles (up to 100 and 1 ppm by weight, respectively) is shown to significantly alter the apparent dopant segregation coefficient. The nondetection limits of various other metallic impurities, such as Mo, V, Ti, etc., being large (∼5 ppm by weight) in the silica crucibles, the concentrations of these impurities can easily exceed undesirable levels in the crystal (up to 10¹² atoms/cm³). Fluctuations in growth parameters can raise the concentrations of these impurities further (by approximately two times) over microscopic regions of growth.