Method of making a semiconductor device having floating source and drain regions

Claim 1

A method of making a semiconductor device, comprising the steps of: forming field oxide films on a semiconductor substrate; forming an oxide film on said semiconductor substrate; forming a nitride film on said oxide film; coating a photoresist film on said nitride film; patterning said photoresist film to define channel regions; etching said nitride film and said oxide film on said channel regions using said photoresist film as an etch mask; forming epitaxial layers on said channel regions; implanting impurity ions of a first type for controlling a threshold voltage into said semiconductor substrate; removing said nitride film and said oxide film to provide recess regions on said semiconductor substrate; forming spacers at sidewalls of said epitaxial layers; forming buried oxide films on said semiconductor substrate and said epitaxial layers; removing said spacers; depositing a polysilicon film on said buried oxide films that are formed on said semiconductor substrate; etching back said polysilicon film to fill said recess regions with said polysilicon film; forming a gate oxide film on said polysilicon film and said epitaxial layers; forming gates on said gate oxide film corresponding to said epitaxial layers; and implanting impurity ions of a second type into said polysilicon film filled in said recess regions, to form source and drain regions.

Claim 2

A method of making a semiconductor device, comprising the steps of: forming field oxide films on a semiconductor substrate; forming an oxide film on said semiconductor substrate; forming a nitride film on said oxide film; coating a photoresist film on said nitride film; patterning said photoresist film to define channel regions; etching said nitride film and said oxide film on said channel regions using said photoresist film as an etch mask; forming epitaxial layers on said channel regions; implanting impurity ions of a first type for controlling a threshold voltage into said semiconductor substrate; removing said nitride film and said oxide film to provide recess regions on said semiconductor substrate; forming spacers at sidewalls of said epitaxial layers; forming buried oxide films on said semiconductor substrate and said epitaxial layers; removing said spacers; depositing a polysilicon film on said buried oxide films that are formed on said semiconductor substrate; etching back said polysilicon film to fill said recess regions with said polysilicon film; forming a gate oxide film on said polysilicon film and said epitaxial layers; forming gates on said gate oxide film corresponding to said epitaxial layers; and implanting impurity ions of a second type into said polysilicon film filled in said recess regions, to form source and drain regions.

Claim 10

A method of making a semiconductor device, comprising the steps of: forming field oxide films on a semiconductor substrate; forming an oxide film on said semiconductor substrate; forming a nitride film on said oxide film; coating a photoresist film on said nitride film; patterning said photoresist film to define channel regions; etching said nitride film and said oxide film except for said channel regions using said photoresist film as an etch mask; etching said semiconductor substrate using said nitride film and said oxide film as etching mask to form trenches; removing said nitride film and said oxide film; implanting impurity ions of a first type for controlling a threshold voltage into said semiconductor substrate; forming spacers at sidewalls of said trenches; forming insulating films on said channel regions and a bottom of said trenches; removing said spacers; forming a polysilicon film on said insulating films that are formed on said semiconductor substrate; etching back said polysilicon film to fill said trenches with said polysilicon film; forming a gate oxide film on said channel regions said polysilicon film and said field oxide films; forming gates on said gate oxide film corresponding to said channel regions; and implanting impurity ions of a second type into said polysilicon film filled in said trenches using said gates as an ion implantation mask to form source and drain regions.

Claim 11

A method of making a semiconductor device, comprising the steps of: forming field oxide films on a semiconductor substrate; forming an oxide film on said semiconductor substrate; forming a nitride film on said oxide film; coating a photoresist film on said nitride film; patterning said photoresist film to define channel regions; etching said nitride film and said oxide film except for said channel regions using said photoresist film as an etch mask; etching said semiconductor substrate using said nitride film and said oxide film as etching mask to form trenches; removing said nitride film and said oxide film; implanting impurity ions of a first type for controlling a threshold voltage into said semiconductor substrate; forming spacers at sidewalls of said trenches; forming insulating films on said channel regions and a bottom of said trenches; removing said spacers; forming a polysilicon film on said insulating films that are formed on said semiconductor substrate; etching back said polysilicon film to fill said trenches with said polysilicon film; forming a gate oxide film on said channel regions said polysilicon film and said field oxide films; forming gates on said gate oxide film corresponding to said channel regions; and implanting impurity ions of a second type into said polysilicon film filled in said trenches using said gates as an ion implantation mask to form source and drain regions.