A method for determining the presence of defects in a covering layer overlying an underlying layer in accordance with an embodiment of the invention comprises providing a substrate comprising the covering layer, where the covering layer is at least partially exposed. The covering layer is subjected to a first substance, such as a solvent, and then subjected to a light beam. An optical property of the covering layer is determined and compared with a threshold value. The presence of defects in the covering layer is determined by the difference of the optical property from the threshold value, where the optical property indicates a level of penetration of the first substance through the covering layer.