A TSV-Last Approach for 3D-IC Integration and Packaging using WNi Platable Barrier Layer

A physical vapor deposition (PVD) formed WNi thinfilm over M1 (metal level 1) after its revealing in the via-last through-Si-via (TSV) process has been investigated for its ability in protecting the M1 metal during electroless (EL) plating of barrier/seed layers or Cu electroplating (EP). The WNi protection layer was also checked for (i) its platability of Cu by both EL and EP methods (the void-free formation of Cu-TSVs by direct Cu-EPing over WNi layer), (ii) its barrier performance against Cu diffusion (from the absence of Cu singal in both WNi and Si region of Auger electron depth profile), (iii) its adhession nature (intactness of film after the tape-peel test), and (iv) its endurance during Cu-CMP (chemical mechanical polishing). All the results confimed that PVD formed WNi not only protects the M1 metal layer from the EL or EP bath, but also forms a very good barrier-cum-seed layer in the Cu-TSVs.