MECHANICAL STRENGTH OF CZOCHRALSKI SILICON-CRYSTALS WITH CARBON CONCENTRATIONS AT AND BELOW 10(15) CM(-3)

Using a tensile strength test at 900-degrees-C, we study the mechanical strength of Czochralski silicon crystals with a low carbon concentration (3.5 X 10(14) cm-3), and a typical carbon concentration (1.8 X 10(15) cm-3). After heat treatment of these crystals at 700-degrees-C, we find that low carbon content Si crystals are more resistant to oxygen precipitation and that the upper yield stress is higher than in typical carbon content Si crystals. Observations using a transmission electron microscope reveal that the precipitate density in the low carbon content Si crystals are nearly one-fifth that of the typical carbon content crystals. Also, the precipitates in both types of Si crystals act as dislocation generation sources during the deformation. Our model is compatible with the observations that less dislocations are generated in the lower carbon content Si crystals during the deformation, resulting in higher strength compared to conventional carbon content Si crystals.