Method for manufacturing semiconductor device, and power conversion device

A method for manufacturing a semiconductor device, the semiconductor device including:

• a semiconductor substrate of a first conductivity type;
• an epitaxial layer of the first conductivity type, the epitaxial layer being formed on a first principal surface of the semiconductor substrate;
• a first semiconductor region of the first conductivity type, the first semiconductor region being formed from an outermost surface to an inner portion of the epitaxial layer;
• a second semiconductor region of a second conductivity type, the second semiconductor region being formed in contact with a side surface of the first semiconductor region;
• a source region and a drain region of the second conductivity type, the source region and the drain region being selectively formed in an upper layer portion of the first semiconductor region;
• a gate electrode formed on the first semiconductor region between the source region and the drain region through a gate insulating film;
• and
• a third semiconductor region of the second conductivity type, the third semiconductor region being formed from a bottom surface of the first semiconductor region to an inner portion of the semiconductor substrate, the method comprising the steps of:
• (a) polishing a second principal surface opposite to the first principal surface of the semiconductor substrate above which at least the source region, the drain region, and the gate electrode are formed to thin the semiconductor substrate;
• and
• (b) ion-implanting impurities of the second conductivity type from the second principal surface of the polished semiconductor substrate to form the third semiconductor region,
• wherein step (b) includes (b-1) ion-implanting the impurities of the second conductivity type so that the third semiconductor region is higher in impurity concentration than the second semiconductor region.