A first set of semiconductor devices is formed on a first semiconductor
substrate comprising a first semiconductor material having a first
melting point. A first via-level dielectric layer containing first
contact vias is formed on the first semiconductor substrate. A second
semiconductor substrate comprising a second semiconductor material having
a second melting point lower than the first melting point is formed
either by bonding or deposition. A second set of semiconductor devices is
formed on the second semiconductor substrate. A second via-level
dielectric layer, second contact vias contacting the second set of
semiconductor devices, and inter-substrate vias electrically connecting
the first contact vias are thereafter formed. A metal interconnect layer
containing a metal interconnect structure is formed over the second
via-level dielectric layer to electrically connect the first and second
set of semiconductor devices through the second contact vias and the
inter-substrate vias.