Wafer processing method

A wafer processing method for dividing a wafer into individual device chips along a plurality of crossing division lines, a front side of said wafer being partitioned by said division lines to define a plurality of separate regions where a plurality of devices corresponding to said device chips are formed, said wafer processing method comprising:

• a cover plate providing step of providing a cover plate on the front side of said wafer to thereby form a composite wafer;
• a welding step of applying a laser beam having a transmission wavelength to said wafer or said cover plate along each division line in the condition where the focal point of said laser beam is set at the interface between said wafer and said cover plate on opposite sides of the lateral center of each division line, after performing said cover plate providing step, thereby forming two parallel welded lines for joining said wafer and said cover plate along each division line;
• and
• a dividing step of forming a cut line between said two parallel welded lines formed along each division line after performing said welding step, thereby cutting said composite wafer along each division line to obtain said individual device chips each covered with said cover plate.