Gate stack structure for semiconductor flash memory device and preparation method thereof

The invention belongs to the technical field of manufacturing technology of semiconductor integrated circuits, and in particular relates to a gate stack structure for a flash memory device and a preparation method thereof. The gate stack structure comprises an Al2O3 thin film, ruthenium-based nanocrystals, a HfxAlyOz thin film, an Al2O3 thin film and a top electrode layer from bottom to top in turn by taking a silicon slice in P-type (100) crystal orientation as a substrate, wherein the Al2O3 thin film is used as a charge tunneling layer; the ruthenium-based nanocrystals are used as a first charge trapping layer; the HfxAlyOz thin film is used as a second charge trapping layer; and the Al2O3 thin film is used as a charge barrier layer. In the invention, the ruthenium-based nanocrystals have high thermal stability and are difficult to diffuse at a high temperature; the HfxAlyOz thin film has high charge trapping density; and the top electrode is made of metal palladium and has large work function. Thus the gate stack structure has broad application prospect in nanocrystalline memory capacitors.