forming a second interconnect structure having {HEAD ~ a second interfacial structure} different from {TAIL ~ the first interfacial structure}, 
forming a second interconnect structure having { HEAD ~ a second interfacial structure } different from { TAIL ~ the first interfacial structure } ,
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH