MORPHOLOGY OF OXIDE PRECIPITATES IN CZOCHRALSKI SILICON DEGENERATELY DOPED WITH BORON

The morphology of oxide precipitates in Czochralski-grown silicon degenerately doped with boron to the concentration of 10(19) atoms/cm3 was studied after a two-step anneal using the transmission electron microscope. In addition to square-shaped precipitate platelets having {100}-type habit planes commonly observed in lightly doped silicon, it was found that the oxide precipitates in degenerately doped silicon also exhibited a disk-shaped morphology with both {110}- and {111}-type habit planes. Based upon the result from the calculation of the elastic stress field around the precipitate disk, it is hypothesized that the formation of the disk-shaped precipitates on the planes other than the {100}-type planes could be facilitated by localized reduction in the elastic moduli of silicon resulting from degenerately doping with boron. This finding is significant for understanding the fundamental differences in the oxygen precipitation mechanisms between silicon lightly and degenerately doped with boron.