Wafer processing method for dividing a wafer, including a shield tunnel forming step

A wafer processing method for dividing a wafer including a single-crystal silicon substrate having on a face side thereof a plurality of devices disposed in respective areas demarcated by a plurality of intersecting projected dicing lines, into individual device chips, wherein the single-crystal silicon substrate includes a metal film of a test element group deposited on the projected dicing lines, the method comprising:

• a protective member placing step of placing a protective member on the face side of the wafer;
• a shield tunnel forming step of, after performing the protective member placing step, applying a laser beam, which has a wavelength that is transmittable through single-crystal silicon, to areas of the wafer that correspond to the projected dicing lines from a reverse side of the wafer, thereby successively forming a plurality of shield tunnels in the wafer, each including a fine pore extending from the reverse side to the face side of the wafer and an amorphous region surrounding the fine pore;
• a dividing step of, after performing the shield tunnel forming step, dividing the wafer into individual device chips by etching the shield tunnels according to plasma etching;
• and
• an external force applying step of using a tape expanding device to apply an external force to the wafer to sever the metal film along perforations formed therein during the shield tunnel forming step,
• wherein the pulsed laser beam used in the shield tunnel forming step has a wavelength of 1950 nm or higher.

A wafer processing method for dividing a wafer including a single-crystal silicon substrate having on a face side thereof a plurality of devices disposed in respective areas demarcated by a plurality of intersecting projected dicing lines, into individual device chips, wherein the single-crystal silicon substrate includes a low-k film deposited on the projected dicing lines, the method comprising:

• a protective member placing step of placing a protective member on the face side of the wafer;
• a shield tunnel forming step of, after performing the protective member placing step, applying a laser beam, which has a wavelength that is transmittable through single-crystal silicon, to areas of the wafer that correspond to the projected dicing lines from a reverse side of the wafer, thereby successively forming a plurality of shield tunnels in the wafer, each including a fine pore extending from the reverse side to the face side of the wafer and an amorphous region surrounding the fine pore;
• a dividing step of, after performing the shield tunnel forming step, dividing the wafer into individual device chips by etching the shield tunnels according to plasma etching;
• and
• an external force applying step of using a tape expanding device to apply an external force to the wafer to sever the low-k film along perforations formed therein during the shield tunnel forming step,
• wherein the pulsed laser beam used in the shield tunnel forming step has a wavelength of 1950 nm or higher.