An improved furnace was designed to reduce the carbon impurity of multicrystalline silicon at unidirectional solidification process. Global simulations of oxygen and carbon transport in the improved furnace showed that the carbon concentration in the crystal can be reduced to a negligible value in the order of 10(14) atom/cm(3); simultaneously, the oxygen concentration in the crystal can also be reduced by at least 30%. Therefore, the present design can markedly reduce the back transfer of CO from graphite components of the furnace. (C) 2010 Elsevier B.V. All rights reserved.