The influence of substrate surface scratches on the quality of CVD grown 4H-SiC homo-epitaxial layers has been studied using a combination of post-growth Monochromatic Synchrotron X-ray Topography (MSXT) and KOH etching. MSXT observations suggest that the scratches on the substrate surface act as dislocation nucleation centers during the growth. When the scratch is along the off-cut direction, only TED-TED pairs are generated. As the inclination of the scratch to the off-cut direction increases, an increasing number of TED-BPD pairs are generated. A model is presented for a possible mechanism for the nucleation of dislocations at scratches.