Method for fabricating lightly doped drain metal oxide semiconductor field effect transistor

Claim 1

A method for making an LDD MOSFET structure at a major surface of a semiconductor substrate having a first conductivity type, comprising: forming a silicon nitride shield on a portion of the major surface; forming field oxide on the substrate, adjacent to the shield; coating a photoresist onto the shield and the field oxide, and defining a window in the photoresist on the shield; implanting first impurities, of the first conductivity type, into the substrate using the photoresist as a mask to form a surface counter dope; anisotropically etching the shield using the photoresist as a mask to form an opening in the shield over the surface counter dope; removing the photoresist; implanting second impurities, of the second conductivity type, into the substrate using the shield and the field oxide as a mask to form a lightly doped source-and-drain region under the surface counter dope; depositing an oxide layer on the field oxide and the shield and in the opening in the shield; anisotropically etching the oxide layer to form spacers on the sidewalls of the opening in the shield; implanting third impurities, of the first conductivity type, into the substrate using the spacers, the shield and the field oxide as a mask to a form a punch-through stop and to separate the source-and-drain region into a source region and a drain region; removing the spacers; forming a gate oxide layer on the surface counter dope and the punch-through stop, thereby further forming a silicon nitride oxide layer on the shield; forming a total-overlap gate on the gate oxide layer; removing the silicon nitride oxide layer and the shield; and implanting fourth impurities, of the second conductivity type, into the substrate using the total-overlap gate and the field oxide as a mask to form heavily doped source and drain regions adjacent to the lightly doped source and drain regions.

Claim 2

A method for making an LDD MOSFET structure at a major surface of a semiconductor substrate having a first conductivity type, comprising: forming a silicon nitride shield on a portion of the major surface; forming field oxide on the substrate, adjacent to the shield; coating a photoresist onto the shield and the field oxide, and defining a window in the photoresist on the shield; implanting first impurities, of the first conductivity type, into the substrate using the photoresist as a mask to form a surface counter dope; anisotropically etching the shield using the photoresist as a mask to form an opening in the shield over the surface counter dope; removing the photoresist; implanting second impurities, of the second conductivity type, into the substrate using the shield and the field oxide as a mask to form a lightly doped source-and-drain region under the surface counter dope; depositing an oxide layer on the field oxide and the shield and in the opening in the shield; anisotropically etching the oxide layer to form spacers on the sidewalls of the opening in the shield; implanting third impurities, of the first conductivity type, into the substrate using the spacers, the shield and the field oxide as a mask to a form a punch-through stop and to separate the source-and-drain region into a source region and a drain region; removing the spacers; forming a gate oxide layer on the surface counter dope and the punch-through stop, thereby further forming a silicon nitride oxide layer on the shield; forming a total-overlap gate on the gate oxide layer; removing the silicon nitride oxide layer and the shield; and implanting fourth impurities, of the second conductivity type, into the substrate using the total-overlap gate and the field oxide as a mask to form heavily doped source and drain regions adjacent to the lightly doped source and drain regions.