An advanced method of photoreflectance spectroscopy (PRS) is studied to enable the microscale optical characterization of Si substrates, physically damaged by energetic ions from plasma during etching. The method examined in this study (mu-PRS) features a microscope module that focuses a probe beam into a 15-mu m-wide "microspot" on the wafer surface. Silicon wafers were exposed to argon plasma and then measured by mu-PRS. The obtained spectra were analyzed, and the damaged wafers were quantitatively characterized in terms of the change in their surface potential. In this study, we demonstrate the mu-PRS's capability for the microscopic characterization of plasma-damaged wafers. (C) 2014 The Japan Society of Applied Physics