We examine the origins of metal impurities in Czochralski (Cz) single-crystal silicon in order to develop improved crystal purification techniques. We calculate the mass of metal impurities incorporated into molten silicon from each origin during crystal growth and estimate the concentration of impurities in the molten silicon and single-crystal silicon. To confirm these results, we analyze a sample of the residual melt after crystal growth. By comparing the calculated and experimental results, it is shown that the main origins of Al and Ni are probably the quartz crucible and polysilicon, respectively, while Fe originates from both. The calculated concentration of Fe and Ni in single-crystal silicon is 10 8 -10 9 cm - 3 , and that of Al is 10 1 1 -10 1 2 cm - 3 . We confirm that the concentrations of Fe and Ni can be reduced by using high-purity silicon as a raw material.