Workpiece cutting method

A method of cutting an object to be processed, the method of irradiating a sheet-like object to be processed equipped with a silicon substrate with a laser light so as to form a modified region in the silicon substrate along a line to cut the object and cutting the object along the line from the modified region acting as a cutting start point, the method comprising the steps of:

• forming a first modified region as the modified region so as to generate a first fracture from the first modified region to one main face of the object along the line, and a second modified region as the modified region on the other main face side of the first modified region such that an unmodified region is interposed between the first and second modified regions so as to generate a second fracture from the second modified region to the other main face along the line without connecting the second fracture to the first fracture in the unmodified region;
• and
• generating a stress in the object so as to connect the first and second fractures to each other and cut the object along the line.