There are provided a wafer processing method comprising the steps of grinding an underside (21) of a wafer which is provided, on its front surface (29), with a plurality of semiconductor devices (10); polishing a ground surface (22) formed by the grinding operation; and carrying out a plasma-processing for a polished surface (23) formed by the polishing operation under a predetermined gaseous atmosphere in a plasma chamber, to form an oxide layer on the polished surface, and a wafer processing method comprising the steps of carrying out a first plasma-processing for a polished surface formed by the polishing operation under a first gaseous atmosphere (CF 4 or SF 6 ) in a plasma chamber, to clean the polished surface; and carrying out a second plasma-processing for the polished surface after the cleaning operation under a second gaseous atmosphere (O 2 ) in the plasma chamber, to form an oxide layer on the polished surface, and a wafer processing apparatus for carrying out these methods. Thus, the wafer can be processed while the occurrence of an electrical failure in a thin wafer is restricted.