The maximum phosphorus concentration that can be incorporated in a silicon crystal using the Czochralski crystal growth method was investigated. The value was found to be related to the hot-zone configuration and is about 1.11 x 10(20) atom/cm(3) for 100 mm (111)crystals grown from a short tank grower with an 18 kg charge size. This doping concentration corresponds to a resistivity value of 0.00071 Omega-cm. When the tang-end of a growing crystal reached this doping concentration, dislocations were generated at the center of the crystal about 50 mm above the solid/melt interface. The dislocations propagated down to the solid/melt interface and resulted in growing a dislocated crystal from that point on. Dislocation loop clusters were observed in the centers of the rang end crystals where the resistivity was lower than 0.00092 Omega-cm (8.19 x 10(19) arom/cm(3)). These clusters most likely were the slip dislocation sources.