Method of forming asymmetric extension mosfet using a drain side spacer

Abstract

A method of forming an asymmetric extension MOSFET using a drain side spacer which allows a choice of source and drain sides for each individual MOSFET device and also allows an independent design or tuning of the source and drain extension implant dose as well as its spacing from the gate. A photoresist mask is formed over at least a portion of each drain region, followed by an angled ion implant during which the photoresist mask and the gate conductor shield the nitride layer over at least a portion of the drain region and at least one sidewall of the gate conductor from damage by the angled ion implant which selectively damages portions of the nitride layer unprotected by the photoresist mask and the gate conductor. Then damaged portions of the nitride layer are removed while leaving undamaged portions of the nitride layer as a nitride mask to protect at least a portion of each drain region and at least one gate sidewall from a subsequent dopant implant, which is performed into the source regions and the drain regions while using the undamaged portions of the nitride layer as a mask to form the asymmetric extension MOSFET device. In some embodiments the nitride mask can be etched to form drain side spacers to provide different spacings for the source and drain extension ion implants.