In a wafer processing method, the back side of a wafer having a plurality of devices on the front side thereof is ground, thereby reducing the thickness of the wafer to a predetermined thickness. The back side of the wafer is polished after performing the back grinding step, thereby removing a grinding strain, and a silicon nitride film is formed on the back side of the wafer. The thickness of the silicon nitride film to be formed in the silicon nitride film forming step is set to 6 to 100 nm. Thus, the silicon nitride film having a thickness of 6 to 100 nm is formed on the polished back side of the wafer from which a grinding strain has been removed. Accordingly, each device constituting the wafer can ensure a sufficient die strength and a sufficient gettering effect.