The present invention relates to a method of selectively fabricating metal
gate electrodes in one or more device regions by fully siliciding (FUSI)
the gate electrode. The selective formation of FUSI enables metal gate
electrodes to be fabricated on devices that are compatible with
workfunctions that are different from conventional n+ and p+ doped poly
silicon electrodes. Each device region consists of at least one Field
Effect Transistor (FET) device which consists of either a polysilicon
gate electrode or a fully silicided (FUSI) gate electrode. A gate
electrode comprised of silicon and a Ge containing layer is used in
combination with a selective removal process of the Ge containing layer.
The Ge containing layer is not removed on devices with threshold voltages
that are not compatible with the FUSI workfunction. Devices that are
compatible with the FUSI workfunction have the Ge containing layer
removed prior to the junction silicidation step. The remaining thin
silicon layer of the gate electrode becomes fully silicided during the
same step as the junction silicidation step.