The stand-by current performance improvement by reducing post-etch Cu-F residue to prevent Cu extrusion for 28nm-node Cu interconnect and beyond

Copper (Cu) interconnect at back-end of the line is one of key factors to impact the stand-by current (Isb) performance. However, issue of Cu-loss deteriorates Cu interconnect integration. The formation of Cu-loss is attributed to that fluorine produced by via etching process catalyzes Cu oxidation reaction to form Cu-F. Following up, Cu extrusion of metal lines through by contact vias is carried out. This paper provides the solution to overcome the formation of Cu-loss. The post-etch Cu-F residue plays a key role in forming Cu-loss. By analysis of Cu2p3 X-ray photoelectron spectroscopy, using the N2 plasma treatment after via etching reduces 48% of Cu-F. Following up, the additional NH3 flush step successfully removes the remaining Cu-F. With the above two steps, Cu extrusion free on the top of contact vias is found. Moreover, 5 times the queue time extension between via etching to tungsten barrier deposition is achieved. Finally, the Isb yield impact by Cu-loss is successfully eliminated, and EM is improved.