The shape of the melt/crystal interface in Czochralski grown silicon crystal is a result of the interaction of several phenomena. In particular, melt convection plays a key role as it affects the heat and mass transfer inside the melt. Depending on the growth conditions and heat transfer in the melt, the interface shape can evolve from a purely concave or convex shape to a W-shape. The aim of this study is to explore the heat transfer conditions and melt flow patterns leading to the formation of W-shape interfaces. The 2D simulations are performed for 6 in. diameter silicon in order to identify conditions leading to W-shape formation. The numerical results show that the formation and development of W-shape interfaces is associated with growth conditions favoring the appearance of a vortex underneath the crystal. This vortex significantly influences the thermal field within the crystallization zone and locally alters the interface deflection. This study suggests that the formation of the W-shape interfaces influences significantly the grown-in defects and crystal quality. (C) 2011 Elsevier B.V. All rights reserved.