The semiconductor device fabrication method comprises the step of forming a first insulation film 48 on a semiconductor substrate 10 and a ferroelectric capacitor 42; the step of forming first interconnections 56a 56c; the step of forming a second insulation film 60; the step of planarizing the surface of the second insulation film 60; the step of making heat treatment with a heat treatment furnace to remove water from the second insulation film 60; the step of making heat treatment in a plasma atmosphere generated by using N.sub.2O gas or N.sub.2 gas; the step of removing water from the second insulation film 60 and nitriding the surface of the second insulation film 60; the step of forming a barrier film 62 on the second insulation film 60; the step of forming contact holes 68 in the barrier film 62 and the second insulation film 60; and the step of burying conductor plugs 70 in the contact holes 68.