Method of manufacturing semiconductor device

A method of manufacturing a semiconductor device, comprising:

• (a) preparing a semiconductor substrate having a main surface;
• (b) forming a floating gate electrode of a first transistor for storage on the main surface of the semiconductor substrate via a first gate insulating film, and forming a gate electrode of a second transistor on the main surface of the semiconductor substrate via a second gate insulating film;
• (c) forming a first sidewall spacer on a side surface of the floating gate electrode, and forming a second sidewall spacer on a side surface of the gate electrode;
• (d) forming a first semiconductor region of the first transistor and a second semiconductor region of the second transistor in the semiconductor substrate, the first semiconductor region of the first transistor being for source or drain, and the second semiconductor region of the second transistor being for source or drain;
• (e) after the (c) and the (d), forming a silicon oxide film on the main surface of the semiconductor substrate so as to cover the floating gate electrode, the gate electrode, the first sidewall spacer, and the second sidewall spacer;
• (f) forming a mask layer on the silicon oxide film;
• (g) performing an isotropic etching on the silicon oxide film with the mask layer used as an etching mask;
• (h) after the (g), performing an anisotropic etching on the silicon oxide film with the mask layer used as the etching mask;
• (i) after the (h), removing the mask layer;
• (j) after the (i), forming a metal silicide layer on each of the second semiconductor region and the gate electrode;
• and
• (k) after the (j), forming a silicon nitride film on the main surface of the semiconductor substrate so as to cover the floating gate electrode, the gate electrode, the first sidewall spacer, and the second sidewall spacer,
• wherein, in the (h), the silicon oxide film exposed from the mask layer is removed by the anisotropic etching, and a first insulating film made of the silicon oxide film which remains below the mask layer is formed,
• wherein the first insulating film covers the floating gate electrode, and
• wherein, in the (k), the first insulating film is interposed between the floating gate electrode and the silicon nitride film.