There has been a problem in conventional Si-type floating-gate type nonvolatile
semiconductor memory devices that the
charge retention characteristic is low due to insufficiently large
electron affinity of Si, therefore improvement of the memory performances, such as scaling down of a
memory cell and increasing operation speed, have been difficult to be achieved due to the essential problem. In order to solve the above problem, in the nonvolatile
semiconductor memory device of the present invention, a material having large
work function or large
electron affinity or a material having a
work function close to that of
semiconductor substrate or of a control gate, is employed for a floating gate retaining charges. Further, an amorphous material having small
electron affinity for an insulating matrix is used. Further, at a time of deposition of
charge retention layer, the supply ratio of the nano-
particle material and the insulating matrix material, such as the mixture ratio of materials of both phases in a target in a
sputtering method, is adjusted. By these methods, the
charge retention characteristic of the floating-gate type nonvolatile
semiconductor memory device can be improved, and the above-mentioned problem of the nonvolatile
semiconductor memory device can be solved.