Patent ID: 7981747

Claim:
A method of manufacturing a semiconductor device including a trench gate type MISFET, the trench gate type MISFET comprising: a semiconductor substrate having a main surface and a bottom surface opposite to the main surface, the semiconductor substrate having a first conductivity type; a first semiconductor layer formed on the main surface of the semiconductor substrate, the first semiconductor layer having a top surface apart from the semiconductor substrate, the first semiconductor layer having the first conductivity type, and the first semiconductor layer acting as a drain region of the MISFET; a trench formed on the top surface of the first semiconductor layer, a distance between the top surface of the first semiconductor layer and a bottom of the trench being not more than 1 μm; a gate insulating film of the MISFET formed on an inner surface of the trench; a gate electrode of the MISFET formed on the gate insulating film in the trench; a channel forming region of the MISFET formed in the first semiconductor layer, the channel forming region being in contact with the trench, the bottom of the trench being positioned below a bottom of the channel forming region, and the channel forming region having a second conductivity type opposite to the first conductivity type; a source region of the MISFET formed over the channel forming region in the first semiconductor layer; the source region being in contact with the trench, and the source region having the first conductivity type; and a punch through stopper region formed between the source region and channel forming region in the first semiconductor layer, the punch through stopper region having the second conductivity type, and the punch through stopper region having a higher impurity concentration than the channel forming region, wherein the method comprising steps of: forming the trench formed in the first semiconductor layer; forming the gate insulating film on the trench; forming the gate electrode of the MISFET on the gate insulating; after the gate electrode forming step, introducing a first impurity to form the channel forming region by a first ion implantation; and after the gate electrode forming step, introducing a second impurity to form the punch through stopper region by a second ion implantation in the channel region different from the first ion implantation such that a concentration distribution of the punch through stopper region is decided by a concentration distribution of the second ion implantation and such that the punch through stopper region has an impurity concentration relatively flat, wherein the second impurity is diffused by heat treatment such that the channel forming region has an impurity concentration gradually decreased, in a depth direction along the trench, from an interface portion between the channel region and the punch through stopper region to an interface portion between the channel region and the semiconductor layer.