Manufacture method of a split gate nonvolatile memory cell

1. A manufacture method of a semiconductor device, said manufacture method comprising steps of:

(a) forming a first insulating film on a semiconductor substrate;

(b) forming a polysilicon film on said first insulating film;

(c) implanting first dopants into said semiconductor substrate to form a first channel region after said (b) step;

(d) etching said polysilicon film after said (c) step;

(e) forming a first diffusion region adjacent to said first channel region after said (d) step, said first diffusion region being used as a source or a drain;

(f) implanting second dopants of the same conductive type as said first dopants into a portion of said semiconductor substrate after said (e) step to form a second channel region including said second dopants and a third channel region positioned between said first and second channel regions and including said first and second dopants, said portion of semiconductor substrate partially overlapping said first channel region, and said third channel region having a higher impurity concentration than those of said first and second channel regions;

(g) etching said polysilicon film after said (f) step to form a floating gate which is formed as a portion of said polysilicon film;

(h) forming a control gate positioned adjacent to said floating gate across a second insulating film after said (g) step; and

(i) after said (h) step, forming a second diffusion region which is used as a drain or a source in a region adjacent to said second channel region, so that said second channel region is positioned between said third channel region and said second diffusion region.

2. The manufacture method according to claim 1 , wherein said (d) step includes forming an opening by etching a portion of said polysilicon film overlapping said first channel region, and

wherein said (e) step includes implanting third dopants having a conductivity type different from that of said first dopants.

3. A manufacture method of a nonvolatile memory cell including a control gate and a floating gate, said manufacture method comprising steps of:

forming a first mask having an opening exposing a region in which said floating gate is to be formed;

diffusing first dopants into a semiconductor substrate through said opening;

forming a second mask in said opening;

diffusing second dopants into a portion of said semiconductor substrate to be positioned under said control gate, said portion being uncovered with said second mask; and

forming said floating gate and said control gate through etching polysilicon films formed over said semiconductor substrate,

wherein said first dopants are implanted with such a dopant concentration that a hot electron effect is suppressed under said floating gate, and

wherein said second dopants are implanted with such a dopant concentration that a hot electron effect is suppressed under said control gate, and

wherein said first dopants are diffused into a portion of said semiconductor substrate under said first mask, and

wherein said second dopants are diffused into a portion of said semiconductor substrate under said second mask to thereby form a channel region including said first and said second dopants.

4. The manufacture method according to claim 3 , further comprising:

implementing an annealing after said first and second dopants are diffused.

5. A manufacture method of a split gate nonvolatile memory cell including a floating gate and a control gate, said method comprising:

forming a polysilicon film to cover a semiconductor substrate across a first insulating film;

forming a second insulating film on said polysilicon film;

etching said second insulating film to form a first opening exposing a portion of said polysilicon film to be processed into said floating gate;

etching said polysilicon film to form a slope adjacent to a side of said first opening;

diffusing first dopants into said semiconductor substrate through said first opening;

forming a third insulating film to cover said second insulating film and said first opening;

etching back said third insulating film to form a spacer on a side of said first opening;

removing said second insulating film to form a second opening;

diffusing second dopants into a portion of said semiconductor film through said second opening;

etching a portion of said polysilicon film exposed by said second opening to form said floating gate; and

forming said control gate so that said control gate is opposed to said floating gate and said semiconductor substrate,

wherein first dopants are diffused with such a dopant concentration that a hot electron effect is suppressed under said floating gate, wherein second dopants are diffused with such a dopant concentration that a hot electron effect is suppressed under said control gate,

wherein said first dopants are diffused under said second insulating film, and

wherein said second dopants are diffused under said spacer to automatically form a channel region including first and second dopants.

6. The manufacture method according to claim 5 , further comprising:

implementing an annealing after said diffusing said first and second dopants.