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 N-2 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.