A method for detecting the presence and location of defects over a substrate is disclosed. In an embodiment, the method may include: forming a semiconductor material in a plurality of openings in a reference wafer using an epitaxial growth process; performing one or more measurements on the reference wafer to obtain a baseline signal; forming a plurality of gate stacks and stressor regions in a plurality of substrates; after forming the plurality of gate stacks, forming the semiconductor material in a plurality of openings in a batch wafer; performing the one or more measurements on the batch wafer to obtain a batch signal; comparing the batch signal to the baseline signal; and determining whether a defect in present in the plurality of substrates based on the comparison.