We have examined minority-carrier recombination lifetimes of a silicon wafer＇s backside after plasma processing. The decrease in lifetime reflects the degree of Si-SiO2 interface degradation caused by plasma-induced damage. We found that even if the silicon wafer＇s backside is fully covered by the stage during plasma processing, there was a further decrease in the lifetime in a region about 20 mm from the wafer＇s edge. We propose that when charges are ejected from the silicon wafer to the outside of the wafer, a portion of the charges flows via the interface between SiO2 and the stage. To fully understand plasma-induced damage, in addition to examining the nature of the decrease in the lifetime of the wafer＇s frontside, it is important to examine the nature of the decrease in the lifetime of the wafer＇s backside in detail.