Field effect transistors with improved implants and method for making

Abstract

Metal oxide semiconductor field effect transistor (MOSFET) including a drain region and a source region adjacent to a channel region. A gate oxide is situated on the channel region and a gate conductor with vertical side walls is placed on the gate oxide. The MOSFET further includes a threshold adjust implant region and/or punch through implant region being aligned with respect to the gate conductor and limited to an area underneath the gate conductor. Such a MOSFET can be made using the following method: forming a dielectric stack on a semiconductor structure; defining an etch window on the dielectric stack having the lateral size and shape of a gate hole to be formed; defining the gate hole in the dielectric stack by transferring the etch window into the dielectric stack using a reactive ion etching (RIE) process; implanting threshold adjust dopants and/or punch through dopants through the gate hole; depositing a gate conductor such that it fills the gate hole; removing the gate conductor covering portions of the semiconductor structure surrounding the gate hole; and removing at least part of the dielectric stack.