A semiconductor memory device includes a semiconductor substrate, an
isolation insulation film filled in a plurality of trenches formed in the
semiconductor substrate to define a plurality of element formation
regions, a floating gate of polysilicon provided on each of the element
formation regions through a first insulation film, a second insulation
film, provided on the floating gate, containing a metal element, a
control gate of polysilicon, provided on the second insulation film, and
source/drain regions provided in the semiconductor substrate, both a
polysilicon conductive layer containing a metal element and a mutual
diffusion layer composed of a silicate layer of a mixed oxide material
composed of a silicon element contained in the floating gate and the
control gate and a metal element contained in the second insulation film
are provided on a surface of each of the floating gate and the control
gate, respectively.