Manufacturing method for semiconductor device

A manufacturing method for a semiconductor device comprising a first conduction type MIS transistor provided in a first region and a second conduction type MIS transistor provided in a second region, the method comprising:

• forming a structure comprising a first gate insulating film provided in the first region, a first conducting portion provided on the first gate insulating film, a second gate insulating film provided in the second region, and a second conducting portion provided on the second gate insulating film, the first conducting portion and second conducting portion being formed of the same conducting film, a work function of a bottom of the first conducting portion being equal to a work function of a bottom of the second conducting portion;
• replacing an upper part of the second conducting portion with a third conducting portion by a plating method;
• and
• varying the work function of the bottom of the second conducting portion by diffusing a metal element contained in the third conducting portion to a lower part of the second conducting portion.