The damage of a Si substrate processed in a 30 eV Ar magnetron discharge has been revealed, for the first time, from the non-destructive measurement of carrier bulk lifetime, carrier diffusion constant and surface recombination velocity by the photoinduced modulation absorption technique. It was found that slight damage occurring at substrate enhances the surface recombination velocity only little, while severe damage in the bulk much reduces the carrier diffusion. However, no significant change of the carrier bulk lifetime due to bulk damage was observed.