Patent ID: 7205197

Claim:
A method of fabricating a nonvolatile semiconductor memory having a silicon substrate, a gate oxide film formed on the silicon substrate, a floating gate electrode separated from the silicon substrate by the gate oxide film, and a tunnel oxide film formed within the gate oxide film, the tunnel oxide film permitting electrons to tunnel into and out of the floating gate electrode to write and erase data, the method comprising: obtaining a silicon substrate having a tunnel oxide film formation area on one surface; forming an oxide film having a predetermined thickness on said surface of the silicon substrate; forming a resist mask having an opening within the tunnel oxide film fabricating area on the oxide film; etching the oxide film through the opening by an anisotropic dry etching process employing a mixture of argon, carbon tetrafluoride, and trifluoromethane etching gases, using the resist mask as an etching mask, the anisotropic dry etching process proceeding to a certain depth but stopping short of the surface of the silicon substrate and not exposing the surface of the silicon substrate; etching the remaining oxide film exposed in the opening by a wet etching process that proceeds down to the surface of the silicon substrate, again using the resist mask as an etching mask, thereby forming a tunnel window; and forming the tunnel oxide film in the tunnel window.