Manufacturing method of forming a buffer region of semiconductor device and semiconductor device

A semiconductor device comprising:

• a drift region of a first conductivity type provided in a semiconductor substrate;
• and
• a buffer region of a first conductivity type provided below the drift region and having a plurality of peaks of a doping concentration,
• the buffer region having:
• a standard peak closest to a back surface among a peak group having peaks at depth positions that are more than or equal to 10 μm from the back surface of the semiconductor substrate;
• and
• a first deepest peak closest to a front surface of the semiconductor substrate among the peak group, wherein
• Xs is a depth position of an end portion on a side of a front surface of the standard peak,
• Xd1 is a depth position of an end portion on a side of a front surface of the first deepest peak,
• Xb is Xs+ (Xd1−Xs)×0.3,
• n1 is an integrated concentration of a doping concentration from a depth position Xs to Xb,
• n2 is an integrated concentration of a doping concentration from a depth position Xb to a Xd1,
• an oxygen chemical concentration of the semiconductor substrate is Co[cm−3],
• a carbon chemical concentration of the semiconductor substrate is Cc[cm−3], and
• in a semi-log graph whose vertical axis is an integrated concentration ratio (n2/(n1+n2)) and whose horizontal axis is a substrate concentration index (Co×[{Cc/(1E15)}×exp(Co/(1E17))]) [cm−3],
• the semiconductor substrate has an oxygen chemical concentration and a carbon chemical concentration such that the substrate concentration index is in a range of more than or equal to 1E15 [cm−3] and less than or equal to 1E22 [cm−3],
• the integrated concentration ratio is in a range between an upper limit line A1 and a lower limit line B1, wherein
• the upper limit line A1:
• y=2.259E−02×In(x)−4.900E−01 and
• the lower limit line B1:
• y=2.259E−02×In(x)−7.300E−01.

A semiconductor device comprising:

• a drift region of a first conductivity type provided in a semiconductor substrate including a front surface and a back surface, and
• a buffer region of a first conductivity type provided below the drift region and having a plurality of peaks of a doping concentration,
• the buffer region having:
• a shallowest peak closest to a side of the back surface in a depth direction of the semiconductor substrate;
• a standard peak closest to the back surface among a peak group provided closer to a side of the front surface than the shallowest peak and having three or more peaks at depth positions that are more than or equal to 10 μm from the back surface;
• a first deepest peak closest to the front surface among the peak group;
• and
• a second deepest peak second closest to the front surface of the semiconductor substrate after the first deepest peak among the peak group, wherein
• Xs is a depth position of an end portion on a side of a front surface of the standard peak,
• Xd1 is a depth position of an end portion on a side of a front surface of the first deepest peak,
• Xd2 is a depth position of an end portion on a side of a front surface of the second deepest peak,
• a value obtained by dividing the Xd1 by the Xd2 is more than 1 and less than or equal to 20, and
• a value obtained by dividing a peak concentration of the first deepest peak by a peak concentration of the second deepest peak is more than or equal to 0.2 and less than or equal to 3.