Paper PS+TF-ThM10
Improving the Quality of PVD Cu Seed Layer for Interconnect Metallization

Thursday, October 21, 2010, 11:00 am, Room Galisteo

Physical Vapor Deposition (PVD) of Ta(N) barrier and Cu seed layers has been traditionally used in interconnect metallization process flow in VLSI manufacturing. Reliability of the manufactured devices greatly depends on the quality of different interfaces, particularly the barrier/seed one. Failure to ensure continuous seed coverage with good adhesion to the barrier may result in voided electrofill, post-CMP defects, and stress/electro-migration failures. Quality of the barrier/seed interface was greatly improved by enhancing Cu nucleation on the Ta surface through filtering of non-energetic species from the deposition flux, increasing the fraction of Cu ions, improving flux uniformity, and minimizing gas ion bombardment. The self-sputtering ability of Cu was combined with magnetically confined high density plasma in the Novellus HCM^TM PVD source. Spatial profiles of plasma density and temperature, as well as ion flux, ion metal fraction, and ion energy, were measured by planar Langmuir probes, quartz crystal microbalance, and gridded energy analyzer, all located at the wafer level. Multiple criteria, such as seed step coverage and roughness, its resistance to agglomeration, and its stability in the plating bath, have been used to evaluate interface quality. As a result new and improved Cu PVD process which demonstrated superior stability during subsequent process steps and ensured successful electrofill performance with more than 50% reduction in minimal sidewall thickness requirement has been developed.