Fabrication of a gate structures having a longer length toward the top for formation of a rectangular shaped spacer

Abstract

The gate structure of the MOSFET of the present invention is formed to have a longer length toward the top of the gate structure such that a spacer having a substantially rectangular shaped is formed at the sidewalls of the gate structure. For fabricating a gate structure of a field effect transistor on a semiconductor substrate, a layer of gate structure material is deposited on the semiconductor substrate. The composition of the layer of gate structure material is adjusted along a depth of the layer of gate structure material for a slower etch rate toward a top of the layer of gate structure material that is further from the semiconductor substrate. The gate structure is then formed by patterning and etching the layer of gate structure material. The slower etch rate toward the top of the layer of gate structure material results in a longer length toward a top of the gate structure that is further from the semiconductor substrate. Spacer dielectric is deposited conformally on exposed surfaces of the gate structure. The spacer dielectric is anisotropically etched such that the spacer dielectric remains on sidewalls of the gate structure. The longer length toward the top of the gate structure results in a substantially rectangular shaped spacer dielectric remaining on the sidewalls of the gate structure. The present invention may be used to particular advantage when the gate structure and the spacer having the rectangular shape are formed as part of a field effect transistor such as a MOSFET.