Manufacturing method of semiconductor nonvolatile memory device

Claim 1

A manufacturing method of semiconductor nonvolatile memory device comprising: a step of forming a mask on the surface of a silicon substrate, and patterning said mask, a step of injecting nitrogen ions into the surface of said silicon substrate from above said mask, a step of removing said mask, `a step of forming oxide films on the surface of said silicon substrate by simultaneously oxidizing the nitrogen ion injection region and the injection-free region of said silicon substrate surface, thereby forming an ultrathin tunnel oxide film on said nitrogen ion injection region and a thick first gate oxide film on said injection-free region of said silicon substrate surface respectively, a step of depositing a first semiconductor thin film on the surface of said tunnel oxide film and said first gate oxide film, a step of forming a first gate in a shape of covering at least said nitrogen ion injection region by patterning said first semiconductor thin film, a step of forming an insulating film on the surface of said first gate, a step of depositing a second semiconductor thin film on the surface of said insulating film, and a step of forming a second gate overlapping with said first gate and said insulating film, by patterning said second semiconductor thin film.