Graded extended drain concept for reduced hot electron effect

Claim 1

A method for the production of graded buried channels in MOSFET devices, said method comprising the steps of: implanting a first light concentration of a first dopant, of a selected polarity, a fixed distance beneath the surface of a semiconductor body so that said first dopant is concentrated in a single buried region spaced apart from the surface of said semiconductor body to create an intermediate area between the buried region and the semiconductor body surface that is relatively devoid of the first dopant with respect to the buried region; implanting a second light concentration of a second dopant of the same polarity as the first dopant in substantially the same single buried region as said first dopant, said intermediate area also being relatively devoid of the second dopant with respect to the buried region; and selecting one of the dopants to have a higher diffusivity than the other dopant, to cause a completely buried protrusion of the higher diffusivity dopant, defining a diffused grading structure, to be formed within the semiconductor body and spaced below the semiconductor body surface to move high density current away from a silicon/silicon-oxide interface boundary of the MOSFET device to reduce hot electron effect.

Claim 2

A method for the production of graded buried channels in MOSFET devices, said method comprising the steps of: implanting a first light concentration of a first dopant, of a selected polarity, a fixed distance beneath the surface of a semiconductor body so that said first dopant is concentrated in a single buried region spaced apart from the surface of said semiconductor body to create an intermediate area between the buried region and the semiconductor body surface that is relatively devoid of the first dopant with respect to the buried region; implanting a second light concentration of a second dopant of the same polarity as the first dopant in substantially the same single buried region as said first dopant, said intermediate area also being relatively devoid of the second dopant with respect to the buried region; and selecting one of the dopants to have a higher diffusivity than the other dopant, to cause a completely buried protrusion of the higher diffusivity dopant, defining a diffused grading structure, to be formed within the semiconductor body and spaced below the semiconductor body surface to move high density current away from a silicon/silicon-oxide interface boundary of the MOSFET device to reduce hot electron effect.