Cleaning Solutions for Ultrathin Co Barriers for Advanced Technology Nodes

Abstract

Co, a candidate material for barrier and capping layers in 10 nm and smaller Cu interconnects, is prone to corrosion and galvanic corrosion during chemical mechanical planarization (CMP) and wet cleaning in aqueous environments posing a serious challenge to its use since the Co liner in the advanced nodes is desired to be only ∼2 to 3 nm thick. We show that E corr between Cu and Co (2 nm) films can be reduced to <10 mV, with Cu being more noble, in an aqueous solution of 6.6 mM (0.05 wt%) Glycine + 15 mM 1,2,4 Triazole, while maintaining an excellent surface finish making it an excellent cleaning solution for Cu/Co (2 nm) structures. We also show that such thin Co films behave electrochemically very differently from thicker (physical vapor deposited 200 nm and even 20 nm) films, perhaps due to differences in deposition methods, differences in surface interactions as determined by XPS and in grain sizes as revealed by SEM imaging, and that (post-CMP) cleaning solutions available for the thicker films do not work for them.

A review on chemical and mechanical phenomena at the wafer interface during chemical mechanical planarization

“…should be avoided during polishing. Since this is not always possible, post-CMP cleaning has become a crucial step to eliminate many of these defects [141,142,143,144]. Recently, the author not only showed that the rupture of a strong chemical bonding between abrasive particles and the SiO 2 films via a nucleophilic attack could help remove the particles from the surface [141] but also reported a stability constant-based strategy to study reagents that can remove Cu-BTA and Co-BTA complexes from various surfaces (Cu, Co, TaN, and SiO 2 films) [109,110].…”

Chemical Mechanical Planarization-Related to Contaminants: Their Sources and Characteristics

“…In some cases, the alumina particles (pH IEP ~ 7) are used as the abrasive for W CMP, and they are observed on the W films after polishing due to its positive charge in the acidic medium [13,24]. Co films and other metal films can also be contaminated with the silica abrasive during polishing [14,15]. These particle contaminants can be controlled by the chemical reactions between slurry components and films being polished.…”

“…are presented on the polished wafer surfaces. The removable defects, also known as CMP-related to contaminants, should be completely removed in the subsequent cleaning process while minimizing the further formation of non-removable defects [14,15]. CMP consumables themselves can be the source of the contaminants during polishing and cleaning [13].…”

Abrasive for Chemical Mechanical Polishing

“…Therefore Ru CMP has a lot of limitation to achieve enough removal rate by CMP. Cobalt (Co) is the most potential candidate metal for replacing tungsten as contact metal (or replacing Ta/TaN as barrier metal) and its CMP slurry abrasive development is upmost challenge for device fabrication [52][53][54]. Known issues by Co CMP are residual abrasive particle defects and Co corrosion.…”