A Novel Bottom up Fill Mechanism for the Metallization of Advanced Node Copper Interconnects
Authors: Mevellec Vincent , Thiam Mikailou , Suhr Dominique , Religieux Laurianne , Blondeau Paul , Chaumont Jean-Baptiste , Raynal Frederic 
Published: February 2020

Copper electrodeposition for on-chip interconnection has been widely described in the semiconductor industry. Most copper plating chemistries currently used for copper interconnects are acidic, involving special additives that provide bottom up fill of the narrow structures[1]. However, as copper interconnects continue to be scaled down in order to improve device performance within a minimum area, conventional acidic bath chemistries have shown limitations, due to the non-uniform coverage of the copper seed layer obtained with physical vapor deposition (PVD). In fact, acidic copper plating baths require a perfectly continuous copper seed layer in order to achieve void-free filling, which is mainly due to poor nucleation density of the acidic bath on resistive under layers (e.g., the barrier layer). Several years ago, a cobalt liner was widely studied as an additional layer to promote copper seed layer coverage on the barrier layer by improving copper wetting[2,3]. It resulted in a thin, continuous and conformal copper layer that facilitates the repair of discontinuities and the formation of a robust seed layer favorable to void-free copper filling. Also, geometry shrinking created high line resistance and the trend toward copper line failure. Interface quality between the copper and dielectric barrier then appeared to be vital, justifying again the introduction of a cobalt layer to ensure chip reliability, especially electromigration. Nevertheless, next generation interconnects will tend to adopt new integration schemes with increased copper volume inside the features in order to decrease RC delay. Additionally, aggressive critical dimensions (CD) will require a greater suppressing effect of the copper plating chemistries to avoid premature closure of the trenches / vias. In order to achieve void-free filling of advanced node copper interconnects, novel and innovative plating chemistries have to be developed. The conventional acidic three-component bath (accelerator, suppressor, and leveler) used for decades must be reinvented in order to improve the suppressing effect and bottom up efficiency, and to prevent any pinch-off during the gap fill of very aggressive and narrow trenches (<20 nm CD). Those new plating chemistries should be efficient enough to allow void-free gap fill, perfect nucleation, and ideally, to enable the removal of the cobalt liner in order to improve line resistance and reduce cost. In this paper, we present a novel alkaline copper plating chemistry that addresses all of the above requirements for advanced node metallization (N10,N7 and N5)), thanks to a new and innovative bottom-up mechanism based on the in-situ formation of an ultra-supressing layer made of polynuclear Copper (I) complex. Mechanism explanation, electrochemical caracterization and void free filling results obtained with this innovative bottom-up mechanism will be detailled during the presentation.
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[2] T. Nogami, et al., ‘CVD Co and its application to Cu damascene interconnections’, Interconnect Technology Conference (IITC), 2010, 1.
[3] T. Nogami et al., ‘CVD-Co/Cu(Mn) integration and reliability for 10 nm node’, Interconnect Technology Conference (IITC), 2013,1