To remove a deteriorated layer generated in forming a scribing trench by laser irradiation. A scribing trench is formed by irradiating a laser beam along a device dividing line on the rear surface of a substrate. At this time, a deteriorated layer is formed on the bottom surface or side surface of the scribing trench. Next, a protective film is formed so as to cover the entire top surface of the device structure, and the deteriorated layer is removed by wet etching. Wet etching is performed by alternately repeating BHF (buffered hydrofluoric acid) wet etching and MEA (monoethanolamine) wet etching several times.