Semiconductor device fabrication method and semiconductor device

A semiconductor device comprising:

• a substrate;
• a first semiconductor region formed at a front surface of the substrate, the first semiconductor region including an active element that regulates current flowing in a thickness direction of the substrate;
• an implantation region in which phosphorus is implanted such that a peak portion of density per unit volume is disposed at a predetermined distance from a rear surface of the substrate;
• and
• a second semiconductor region between the implantation region and the rear surface of the substrate, in which impurities of a predetermined conduction type are implanted, that is formed with a predetermined thickness, and through which the current flows,
• wherein a density per unit volume of phosphorus in the second semiconductor region is at most 1/10 of a density per unit volume of the impurities of the predetermined conduction type in the second semiconductor region.

A semiconductor device comprising:

• a substrate;
• a first semiconductor region formed at a front surface of the substrate, the first semiconductor region including an active element that regulates current flowing in a thickness direction of the substrate;
• an implantation region in which phosphorus is implanted such that a peak portion of density per unit volume is disposed at a predetermined distance from a rear surface of the substrate;
• and
• a second semiconductor region between the implantation region and the rear surface of the substrate, in which impurities of a predetermined conduction type are implanted and through which the current flows,
• wherein a density per unit volume of phosphorus in the second semiconductor region is at most 1/5 of a peak density per unit volume of phosphorus in the implantation region, and a density per unit volume of the impurities of the predetermined conduction type in the second semiconductor region is at most 5×1017 atoms/cm3.