To understand and control the mechanism of defect generation is a fundamental aspect of crystal growth. The formation of grown in defects like misoriented regions respectively micropipes may be correlated with second phase inclusions such as silicon droplets or carbon particles. Inclusions could be identified as carbon particles by SEM and EELS. Their distribution along the growth direction and at the phase boundary were investigated by Optical Microscopy. It was found that their density varies in axial as well as radial direction. The dependence of the carbon particle concentration on growth parameters such as temperature stability, time and the distance between source and seed is shown. A concentration model will be discussed. Therefore any change of the vapour phase composition, characterised by the, loss of silicon and caused by changing of a growth parameter, may result in a drastic local increase of the carbon particle concentration. The lattice information of the substrate is lost and defects may be formed if a critical value is exceeded.