Semiconductor device and its manufacturing method

A semiconductor device, comprising:

• a gate insulating film and a gate electrode stacked in this order;
• wherein said gate insulating film and said gate electrode are in contact with each other;
• and
• wherein said gate insulating film comprises a silicon oxide film formed on a silicon substrate so as to be in contact therewith, and a nitrogen containing high-dielectric-constant insulating film formed on said silicon oxide film so as to be in contact therewith;
• and
• wherein said nitrogen containing high-dielectric-constant insulating film which has a structure in which nitrogen is introduced into metal oxide or metal silicate;
• and
• wherein a nitrogen concentration in said nitrogen containing high-dielectric-constant insulating film has a distribution in a direction of a film thickness;
• and
• a position at which the nitrogen concentration in said nitrogen containing high-dielectric-constant insulating film reaches a maximum in the direction of the film thickness is present in a region at a distance from the silicon substrate such that a maximum impurity concentration of the nitrogen concentration is greater than a nitrogen concentration at an interface between the silicon oxide film and the nitrogen containing high-dielectric-constant insulating film.