Micro-scratches on 4H-SiC wafers can transform into dislocations, stacking fault and other type of defects during homoepitaxial process, leading to reduce yield of epitaxial wafers. These micro-scratches are challenging to detect using non-destructive optical characterization methods due to their ultra-thin line width, which is beyond the resolution of current optical technology. A novel method has been developed to reveal these micro-scratches, which are typically invisible under optical microscopy, on SiC wafers after chemo-mechanical polishing (CMP) treatment. This method is based on the classical nucleation theory, and KCl crystals preferentially nucleate on high-index crystallographic facets with high surface energy during the KCl solution drying process. The experimental results show that the KCl crystals could embed in the ravines of the micro-scratches at a KCl solution concentration of 0.013 mol/L, allowing for their indirect detection by optical microscopy. When the concentration of KCl solution is greater than 0.013 mol/L, lots of KCl crystals crystallize on the areas without micro-scratches and interfere with the characterization of micro-scratches. KCl crystals formed by this method can be removed from the surface through the RCA cleaning process without impacting the subsequent wafer processing, because they are adsorbed and nucleated on the surface of 4H-SiC without undergoing any chemical reaction with SiC substrates.