Semiconductor device and semiconductor device manufacturing method

Proton irradiation is performed a plurality of times with different ranges from a substrate rear-surface side to form first to fourth n-type layers (10a) to (10d) with different depths, after which the protons are activated. The substrate rear surface is then irradiated with helium to a position deeper than the proton irradiation range in order to introduce lattice defects. During heat treatment for adjusting the amount of lattice defects, protons in the fourth n-type layer (10d) that have not been activated are diffused, thereby forming a fifth n-type layer (10e) on the anode side of the fourth n-type layer (10d), the fifth n-type layer (10e) being adjacent to the fourth n-type layer (10d) and having a carrier density distribution which decreases toward the anode side with a more gradual gradient than in the fourth n-type layer (10d). The fifth n-type layer (10e) including protons and helium and the first to fourth n-type layers (10a) to (10d) including protons constitute an n-type FS layer (10). In this way