Patent ID: 7821060

Claim:
A semiconductor device comprising: an active region having a groove comprising an expanded portion having a width which is greater than a width of an opening of the groove; a gate insulating film extending along the inside wall of the groove; and a gate electrode in the groove, the gate electrode comprising: a first layer extending along the gate insulating film, the first layer being electrically conductive; and a second layer extending along the first layer, the second layer being separate from the gate insulating film by the first layer, the second layer being different in thermal property from the first layer, and the second layer comprising an innermost layer of the gate electrode in the expanded portion and including a material comprising one of glass, silicon nitride and refractory metal silicide, wherein the first layer comprises a first material, and the material of the second layer comprises one of a second material that is thermally more stable than the first material, and a third material that is thermoset at a lower temperature than a temperature at which migration or deformation of the first layer is caused, and wherein the first material is silicon and the second material is silicon nitride.