Methods of forming field effect transistors (fets) with gate cut isolation regions between replacement metal gates

Abstract

The method includes steps for improving gate cut isolation region critical dimension (CD) control. Prior to replacement metal gate (RMG) formation, a first sacrificial gate adjacent to first and second channel regions and made of a first sacrificial material (e.g., polysilicon or amorphous silicon) is replaced with a second sacrificial gate made of a second sacrificial material (e.g., amorphous carbon) that is more selectively and anisotropically etchable. A cut is made, dividing the second sacrificial gate into first and second sections, and the cut is then filled with a dielectric to form the gate cut isolation region. The second sacrificial material ensures that, when an opening in a mask pattern used to form the cut extends over a gate sidewall spacer and interlayer dielectric (ILD) material, recesses are not form within the spacer or ILD. Thus, the CD of the isolation region can be controlled.