Damaged layers, which are introduced during chemo-mechanical polishing (CMP) underneath the 4°off-cut 4H-SiC wafer surface and cause surface defects formations after epitaxial films growth, are investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM observations show presence of small scratches on wafer surfaces after CMP process. The widths of such scratches are submicron meters, thus it is hard to detect them by optical microscopy. TEM observations show that high-density regions of dislocation loops exist below scratches and the widths of such dislocation loops are much wider than the morphological width. Details of the dislocation structure are also analyzed. It is shown that the high-density dislocation loops cause local surface roughening on the surface of the epitaxial film.