THE 900-DEGREES-C UPPER YIELD STRESS OF CZOCHRALSKI SILICON SINGLE-CRYSTALS WITH CARBON CONCENTRATIONS OF 4.0X10(14) AND 3.5X10(15) CM(-3)

In order to investigate the influence of carbon on the high-temperature strength of Czochralski silicon single crystals, we measured the 900-degrees-C upper yield stress of crystals containing carbon at concentrations of 4.0 X 10(14) cm-3 (''low C'') and 3.5 X 10(15) cm-3 (''standard C''). Prior to testing, all crystals were beat treated for 20 h at 700-degrees-C. They were then annealed at 1000-degrees-C for periods between 1.5-7 h. During the longest anneal, the interstitial oxygen content fell from 2.0 X 10(18) to 1.0 X 10(18) cm-3 in low C crystals and from 1.9 X 10(18) to 7 X 10(17) cm-3 in ''standard C'' crystals. The 900-degrees-C upper yield stress of 7 h annealed low C crystals is 13 MPa, which is 30-40% higher than that measured in standard C crystals. The precipitate density, measured optically, is 4 X 10(5) cm-2 in low C samples and 9 X 10(5) cm-2 in standard C crystals. In all cases, the precipitates punched out dislocations. A model that assumes that the higher interstitial oxygen content retained by the low C crystals results in higher locking stresses for glide dislocations can quantitatively account for these observations.