Manufacturing method of semiconductor device and semiconductor device

A semiconductor device comprising:

• a semiconductor substrate having an upper surface and a lower surface;
• a drift region of a first conductivity type provided in the semiconductor substrate;
• and
• a buffer region of the first conductivity type provided between the drift region and the lower surface, wherein
• the buffer region includes, in an adjacent region in contact with the drift region, a plurality of hydrogen chemical concentration peaks in which a hydrogen chemical concentration decreases as a distance from the lower surface increases, and
• a slope α of a straight line approximating a doping concentration distribution in the adjacent region is 20 (/cm) or more and 200 (/cm) or less, wherein
• when a depth position of one end of the adjacent region is x1 [cm], a depth position of an other end is x2 [cm], a doping concentration at the depth position x1 is N1 [/cm3], and a doping concentration at the depth position x2 is N2 [/cm3], the slope α is given by a following equation
• α=(|log10(N2)−log10(N1)|)/(|x2−x1|).