The control of oxygen concentration in 200 mm-diameter Si single crystals is studied in the cusp-magnetic Czochralski method, and the effects of zero-Gauss plane (ZGP), ZGP shape, which is due to magnetic ratio (MR) of the lower to upper current densities in the configurations of the cusp-magnetic field, and magnetic intensity (MI) on the oxygen concentration and its distribution in the crystal are experimentally investigated. The shape of ZGP is not only flat but also parabolic due to MR. The oxygen concentration depends on MR, ZGP and MI. The oxygen concentration decreases with increasing MR. As ZGP decreases, which is moved from the crucible bottom toward the free surface, the oxygen concentration decreases. There is no significant influence of ZGP on the radial distribution of the oxygen concentration. With increasing melt-charge size, oxygen concentration increases because the contact-area between crucible wall and silicon melt increases and convection in the larger amount of the melt is much stronger. The experimental results are compared with other studies. (c) 2006 Elsevier B.V. All rights reserved.