For this purpose, {HEAD ~ step S1} may represent a degassing step, as discussed above, while steps S2 and S3 may represent the deposition of {TAIL ~ a tantalum based material} and a copper based material, respectively 
For this purpose , { HEAD ~ step S1 } may represent a degassing step , as discussed above , while steps S2 and S3 may represent the deposition of { TAIL ~ a tantalum based material } and a copper based material , respectively
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH