Abstract: A method of manufacturing the semiconductor memory comprises element described below; (a) forming a first oxide film on a semiconductor substrate; (b) forming a polysilicon electrode on the first oxide film by sub-steps of forming a low impurity density polysilicon layer, forming a high impurity density polysilicon layer, and forming a low impurity density polysilicon layer in this order; (c) forming a second oxide film on the polysilicon electrode.

Abstract: The present invention aims to prevent the thickness of the element separation insulating film of the high voltage withstanding area from being thinned and reliability of the memory cell from being reduced. Element separation insulating films are formed on a surface of a silicon substrate. A silicon oxide film, serving as a gate insulating film of a high voltage withstanding area, is formed on the surface of the silicon substrate. A first polycrystalline silicon film is deposited on the oxide film and the element separation insulating films, and a first resist pattern is formed on the polycrystalline silicon film of the high voltage withstanding area and the low voltage withstanding area. The resist pattern is used as a mask to etch the polycrystalline silicon film. After separating the resist pattern, the silicon oxide film of the cell area is removed, and an oxide-nitride film, serving as a gate insulating film of the cell area is formed on the surface of the silicon substrate of the cell area.

Abstract: A silicon nitride film and a silicon oxide film are deposited in that order on a WSi film. In a single session of lithography, the gate electrode of a memory cell and the gate electrode of a transistor constituting a peripheral circuit are formed. The silicon oxide film makes a mask used to form a floating gate of the memory cell. The silicon nitride film makes a mask used to form a common source region by etching a gate oxide film and a field oxide film. The silicon nitride film covers the WSi film to prevent impurities from entering the WSi film when impurities are introduced into the common source region. This prevents abnormal oxidation in a subsequent process.

Abstract: A method of manufacturing the semiconductor memory comprises a plurality of steps. The steps include forming a first oxide film on a semiconductor substrate, forming a polysilicon electrode on the first oxide film by the sub-steps of forming a low impurity density polysilicon layer, forming a high impurity density polysilicon layer, and forming a low impurity density polysilicon layer in this order, and forming a second oxide film on the polysilicon electrode.

Abstract: The present invention aims to prevent the thickness of the element separation insulating film of the high voltage withstanding area from being thinned and reliability of the memory cell from being reduced. Element separation insulating films are formed on a surface of a silicon substrate. A silicon oxide film, serving as a gate insulating film of a high voltage withstanding area, is formed on the surface of the silicon substrate. A first polycrystalline silicon film is deposited on the oxide film and the element separation insulating films, and a first resist pattern is formed on the polycrystalline silicon film of the high voltage withstanding area and the low voltage withstanding area. The resist pattern is used as a mask to etch the polycrystalline silicon film. After separating the resist pattern, the silicon oxide film of the cell area is removed, and an oxide-nitride film, serving as a gate insulating film of the cell area is formed on the surface of the silicon substrate of the cell area.