Field effect transistor with recessed buried source and drain regions

Claim 1

A method of forming improved spaced buried conductive regions in a semiconductor substrate of a background impurity with a first conductivity type, comprising the steps of: forming a first gate oxide on the substrate surface; forming a first lightly doped layer of a first conductivity type in the substrate near the surface; forming a second lightly doped layer of a first conductivity type at a greater depth than said first lightly doped layer in the substrate; forming a resist layer over the first gate oxide having a pattern of elongated spaced parallel first openings; removing the first gate oxide in the first openings; forming shallow trenches in said substrate through the first openings; obliquely ion injecting impurity ions of a second conductivity type through the first openings forming buried implanted regions in the trench sidewalls and bottoms; vertically ion injecting impurity ions of a second conductivity type through the first openings implanting additional impurity ions into the buried implanted regions on the trench bottoms; removing the thin oxide layer; annealing the implanted regions in the trench sidewalls and trench bottoms to electrically activate the impurity atoms to form buried conductive lines; oxidizing the trench surfaces forming a second gate oxide layer so that the surface of the second gate oxide layer is approximately the same height of the oxide on the adjacent substrate surface; and using conventional semiconductor fabrication techniques forming and completing a semiconductor device.

Claim 2

A method of forming improved spaced buried conductive regions in a semiconductor substrate of a background impurity with a first conductivity type, comprising the steps of: forming a first gate oxide on the substrate surface; forming a first lightly doped layer of a first conductivity type in the substrate near the surface; forming a second lightly doped layer of a first conductivity type at a greater depth than said first lightly doped layer in the substrate; forming a resist layer over the first gate oxide having a pattern of elongated spaced parallel first openings; removing the first gate oxide in the first openings; forming shallow trenches in said substrate through the first openings; obliquely ion injecting impurity ions of a second conductivity type through the first openings forming buried implanted regions in the trench sidewalls and bottoms; vertically ion injecting impurity ions of a second conductivity type through the first openings implanting additional impurity ions into the buried implanted regions on the trench bottoms; removing the thin oxide layer; annealing the implanted regions in the trench sidewalls and trench bottoms to electrically activate the impurity atoms to form buried conductive lines; oxidizing the trench surfaces forming a second gate oxide layer so that the surface of the second gate oxide layer is approximately the same height of the oxide on the adjacent substrate surface; and using conventional semiconductor fabrication techniques forming and completing a semiconductor device.

Claim 8

The method of claim I wherein the masking layer is composed of silicon nitride with a thickness in the range of 1000 to 2000 angstroms.

Claim 13

The method of claim I wherein the ion injection forming the second lightly doped layer uses boron with a dosage in the range of 1E11 to 1E13 atoms/cm 2 and an implant energy in the range of 60 to 120 Kev.

Claim 22

A method of forming improved spaced buried conductive lines in a semiconductor substrate with a background impurity of a first conductivity type, comprising the steps of: forming a plurality of field oxide regions on the substrate surface; forming a first gate oxide on the substrate surface; forming a pattern of elongated spaced parallel trenches in the substrate which defined buried conductive lines; obliquely ion injecting impurity ions of a second conductivity type into the trenches forming buried implanted regions at the trench sidewalls and bottom; vertically ion injecting impurity ions of a second conductivity type into the trenches bottoms implanting additional impurity ions into the buried implanted regions in the trench bottoms; annealing the implanted regions to electrically activate the impurity atoms forming buried conductive lines; oxidizing the trench surfaces forming a second gate oxide layer so that the surface of the second gate oxide layer is approximately the same height as the adjacent oxide layer on the substrate surface; and using conventional semiconductor fabrication techniques forming and completing a semiconductor device.

Claim 23

A method of forming improved spaced buried conductive lines in a semiconductor substrate with a background impurity of a first conductivity type, comprising the steps of: forming a plurality of field oxide regions on the substrate surface; forming a first gate oxide on the substrate surface; forming a pattern of elongated spaced parallel trenches in the substrate which defined buried conductive lines; obliquely ion injecting impurity ions of a second conductivity type into the trenches forming buried implanted regions at the trench sidewalls and bottom; vertically ion injecting impurity ions of a second conductivity type into the trenches bottoms implanting additional impurity ions into the buried implanted regions in the trench bottoms; annealing the implanted regions to electrically activate the impurity atoms forming buried conductive lines; oxidizing the trench surfaces forming a second gate oxide layer so that the surface of the second gate oxide layer is approximately the same height as the adjacent oxide layer on the substrate surface; and using conventional semiconductor fabrication techniques forming and completing a semiconductor device.