Method for fabricating MOS transistor

Claim 1

A method for fabricating a MOS transistor, comprising the steps of: subjecting a silicon substrate of a first conductivity type to a field oxidation, thereby forming a field oxide film for an active region isolation; thickly depositing an oxide film over the entire exposed surface of the resulting structure after the formation of said field oxide film and etching said thick oxide film, thereby forming a first opening over an active region; growing a thin oxide film over the entire exposed surface of the resulting structure after the formation of said first opening; forming spacers at respective side walls of said thin oxide film disposed in said first opening; implanting impurity ions of the first conductivity type in said silicon substrate through the first opening under a condition that said spacers are used as a mask, thereby forming a channel region; partially removing the thin oxide film at its portion disposed over said channel region, thereby partially exposing the silicon substrate through the first opening; depositing a first polysilicon film, thereby filling the first opening with said first polysilicon film; removing the spacers, thereby forming a pair of second openings respectively in both sides of the first polysilicon film; implanting impurity ions of a second conductivity type in a low concentration in the silicon substrate through said second openings, thereby forming low concentration source and drain regions respectively disposed adjacent to both lateral ends of the channel region; removing the first polysilicon film, thereby forming a third opening for exposing the channel region and said low concentration source and drain regions; growing an oxide film over the entire exposed surface of the resulting structure after the formation of said third opening, thereby forming a gate oxide film; depositing a second polysilicon film, thereby filling the third opening with said second polysilicon film; patterning the gate oxide film under a condition that the second polysilicon film is used as a mask; removing the remaining thick oxide film; and implanting impurity ions of the second conductivity type in a high concentration in the silicon substrate under a condition that the second polysilicon film is used as a mask, thereby forming high concentration source and drain regions respectively disposed adjacent to the low concentration source and drain regions.

Claim 2

A method for fabricating a MOS transistor, comprising the steps of: subjecting a silicon substrate of a first conductivity type to a field oxidation, thereby forming a field oxide film for an active region isolation; thickly depositing an oxide film over the entire exposed surface of the resulting structure after the formation of said field oxide film and etching said thick oxide film, thereby forming a first opening over an active region; growing a thin oxide film over the entire exposed surface of the resulting structure after the formation of said first opening; forming spacers at respective side walls of said thin oxide film disposed in said first opening; implanting impurity ions of the first conductivity type in said silicon substrate through the first opening under a condition that said spacers are used as a mask, thereby forming a channel region; partially removing the thin oxide film at its portion disposed over said channel region, thereby partially exposing the silicon substrate through the first opening; depositing a first polysilicon film, thereby filling the first opening with said first polysilicon film; removing the spacers, thereby forming a pair of second openings respectively in both sides of the first polysilicon film; implanting impurity ions of a second conductivity type in a low concentration in the silicon substrate through said second openings, thereby forming low concentration source and drain regions respectively disposed adjacent to both lateral ends of the channel region; removing the first polysilicon film, thereby forming a third opening for exposing the channel region and said low concentration source and drain regions; growing an oxide film over the entire exposed surface of the resulting structure after the formation of said third opening, thereby forming a gate oxide film; depositing a second polysilicon film, thereby filling the third opening with said second polysilicon film; patterning the gate oxide film under a condition that the second polysilicon film is used as a mask; removing the remaining thick oxide film; and implanting impurity ions of the second conductivity type in a high concentration in the silicon substrate under a condition that the second polysilicon film is used as a mask, thereby forming high concentration source and drain regions respectively disposed adjacent to the low concentration source and drain regions.

Claim 10

A method for fabricating a MOS transistor, comprising the steps of: subjecting a silicon substrate of a first conductivity type to a field oxidation, thereby forming a field oxide film for an active region isolation; thickly depositing an oxide film over the entire exposed surface of the resulting structure after the formation of said field oxide film and etching said thick oxide film, thereby forming a first opening over an active region; depositing an insulating film over the entire exposed surface of the resulting structure after the formation of said first opening and anisotropically etching said insulating film, thereby forming spacers at respective side walls of said thick oxide film disposed in said first opening such that said silicon substrate is partially exposed through the first opening; implanting impurity ions of the first conductivity type in said silicon substrate under a condition that said spacers are used as a mask, thereby forming a channel region; depositing a first polysilicon film over said channel region under a condition that the spacers are used as a mask, thereby filling the first opening with said first polysilicon film; removing the spacers, thereby forming a pair of second openings respectively in both sides of the first polysilicon film; implanting impurity ions of a second conductivity type in a low concentration in the silicon substrate through said second openings, thereby forming low concentration source and drain regions respectively disposed adjacent to both lateral ends of the channel region; removing the first polysilicon film, thereby forming a third opening; forming a gate oxide film over a portion of the silicon substrate disposed in said third opening; depositing a second polysilicon film over said gate oxide film under a condition that the thick oxide film is used as a mask, thereby filling the third opening with said second polysilicon film; removing the remaining thick oxide film; and implanting impurity ions of the second conductivity type in a high concentration in the silicon substrate under a condition that the second polysilicon film is used as a mask, thereby forming high concentration source and drain regions respectively disposed adjacent to the low concentration source and drain regions.

Claim 11

A method for fabricating a MOS transistor, comprising the steps of: subjecting a silicon substrate of a first conductivity type to a field oxidation, thereby forming a field oxide film for an active region isolation; thickly depositing an oxide film over the entire exposed surface of the resulting structure after the formation of said field oxide film and etching said thick oxide film, thereby forming a first opening over an active region; depositing an insulating film over the entire exposed surface of the resulting structure after the formation of said first opening and anisotropically etching said insulating film, thereby forming spacers at respective side walls of said thick oxide film disposed in said first opening such that said silicon substrate is partially exposed through the first opening; implanting impurity ions of the first conductivity type in said silicon substrate under a condition that said spacers are used as a mask, thereby forming a channel region; depositing a first polysilicon film over said channel region under a condition that the spacers are used as a mask, thereby filling the first opening with said first polysilicon film; removing the spacers, thereby forming a pair of second openings respectively in both sides of the first polysilicon film; implanting impurity ions of a second conductivity type in a low concentration in the silicon substrate through said second openings, thereby forming low concentration source and drain regions respectively disposed adjacent to both lateral ends of the channel region; removing the first polysilicon film, thereby forming a third opening; forming a gate oxide film over a portion of the silicon substrate disposed in said third opening; depositing a second polysilicon film over said gate oxide film under a condition that the thick oxide film is used as a mask, thereby filling the third opening with said second polysilicon film; removing the remaining thick oxide film; and implanting impurity ions of the second conductivity type in a high concentration in the silicon substrate under a condition that the second polysilicon film is used as a mask, thereby forming high concentration source and drain regions respectively disposed adjacent to the low concentration source and drain regions.

Claim 12

A method for fabricating a MOS transistor, comprising the steps of: subjecting a silicon substrate of a first conductivity type to a field oxidation, thereby forming a field oxide film for an active region isolation; thickly depositing a first oxide film over the entire exposed surface of the resulting structure after the formation of said field oxide film and etching said thick oxide film, thereby forming a first opening over an active region; growing a second oxide film over the entire exposed surface of the resulting structure after the formation of said first opening to a thickness larger than a thickness of a gate oxide film to be formed; forming spacers at respective side walls of said second oxide film disposed in said first opening; implanting impurity ions of the first conductivity type in said silicon substrate under a condition that said spacers are used as a mask, thereby forming a channel region; etching a portion of the second oxide film disposed over said channel region to a depth such that it has a thickness smaller than those of other portions of the second oxide film; depositing a first polysilicon film over said thinner portion of the second oxide film under a condition that the spacers are used as a mask, thereby filling the first opening with said first polysilicon film; removing the spacers, thereby forming a pair of second openings respectively in both sides of the first polysilicon film; implanting impurity ions of a second conductivity type in a low concentration in the silicon substrate through said second openings, thereby forming low concentration source and drain regions respectively disposed adjacent to both lateral ends of the channel region; removing the first polysilicon film, thereby forming a third opening for exposing the channel region and the low concentration source and drain regions; depositing a second polysilicon film over said exposed channel region and low concentration source and drain regions, thereby filling said third opening with said second polysilicon film; patterning the second polysilicon film under a condition that the second polysilicon film is used as a mask, thereby forming a gate oxide film; removing the remaining first oxide film; and implanting impurity ions of the second conductivity type in a high concentration in the silicon substrate under a condition that the second polysilicon film is used as a mask, thereby forming high concentration source and drain regions respectively disposed adjacent to the low concentration source and drain regions.

Claim 13

A method for fabricating a MOS transistor, comprising the steps of: subjecting a silicon substrate of a first conductivity type to a field oxidation, thereby forming a field oxide film for an active region isolation; thickly depositing a first oxide film over the entire exposed surface of the resulting structure after the formation of said field oxide film and etching said thick oxide film, thereby forming a first opening over an active region; growing a second oxide film over the entire exposed surface of the resulting structure after the formation of said first opening to a thickness larger than a thickness of a gate oxide film to be formed; forming spacers at respective side walls of said second oxide film disposed in said first opening; implanting impurity ions of the first conductivity type in said silicon substrate under a condition that said spacers are used as a mask, thereby forming a channel region; etching a portion of the second oxide film disposed over said channel region to a depth such that it has a thickness smaller than those of other portions of the second oxide film; depositing a first polysilicon film over said thinner portion of the second oxide film under a condition that the spacers are used as a mask, thereby filling the first opening with said first polysilicon film; removing the spacers, thereby forming a pair of second openings respectively in both sides of the first polysilicon film; implanting impurity ions of a second conductivity type in a low concentration in the silicon substrate through said second openings, thereby forming low concentration source and drain regions respectively disposed adjacent to both lateral ends of the channel region; removing the first polysilicon film, thereby forming a third opening for exposing the channel region and the low concentration source and drain regions; depositing a second polysilicon film over said exposed channel region and low concentration source and drain regions, thereby filling said third opening with said second polysilicon film; patterning the second polysilicon film under a condition that the second polysilicon film is used as a mask, thereby forming a gate oxide film; removing the remaining first oxide film; and implanting impurity ions of the second conductivity type in a high concentration in the silicon substrate under a condition that the second polysilicon film is used as a mask, thereby forming high concentration source and drain regions respectively disposed adjacent to the low concentration source and drain regions.