A method of processing a wafer includes applying a laser beam having a wavelength that is transmittable through a sapphire substrate to the wafer while positioning a focused spot of the beam within the wafer in regions corresponding to projected dicing lines through a reverse side of the wafer, thereby forming a plurality of shield tunnels made up of a plurality of pores and an amorphous body surrounding the pores, at predetermined spaced intervals in the wafer along the projected dicing lines. A laser beam having a wavelength that is transmittable through the sapphire substrate to the wafer is applied while positioning a focused spot of the laser beam within the wafer in the projected dicing lines through the reverse side of the wafer, thereby forming modified layers between adjacent shield tunnels. Exerting external forces to the wafer divides the wafer into a plurality of optical device chips.