The Development of Cu Filling and Reliability Performance with Ru-Ta Alloy Barrier for Cu Interconnects

Abstract

Ru-Ta alloy was investigated as the diffusion barrier layer in Cu dual damascene interconnects, and Cu filling property and reliability performances with RuTa/RuTa(N) stacked barrier structure were mainly evaluated. RuTa strongly orientated to Ru(002) and the lattice misfit between Ru(002) and Cu(111) was lower than that between Ta(110) and Cu(111). The wettability of Cu seed on RuTa was much better than that on Ta. The barrier property against Cu diffusion of RuTa/RuTa(N) stacked barrier structure kept the equivalent barrier property of conventional Ta/TaN one. Filling property of Cu electroplating was improved by using Ru-Ta alloy barrier, and trenches of 45 nm in width could be filled successfully due to the suppression of the agglomeration of Cu seed on the sidewall of trench. Via resistance with RuTa/RuTa(N) barrier was much lower than that with Ta/TaN one due to its low resistivity. The estimated life time of via electromigration with RuTa/RuTa(N) barrier was longer than that with Ta/TaN one because of the good wettability and filling property inside via. Consequently, Cu filling property and reliability performance can be improved with RuTa/RuTa(N) stacked barrier structure in Cu interconnects. Copper (Cu) interconnects have been applied to ultra large scale integrated circuits (ULSIs) to reduce the resistance of wiring and resistive-capacitive (RC) delay since the introduction of 130 nm complementary metal oxide semiconductors (CMOSs). As the feature size of trench and via continues to shrink, filling the gaps with Cu electroplating becomes more difficult. For perfectly gap filling, the opening of trench and via after the deposition of barrier and Cu seed have to be kept enough by thinning barrier and/or Cu seed. However, thinning Cu seed leads to Cu being agglomerated on the sidewall of both trench and via where Cu seed is too thin due to its poor coverage, resulting in the formation of voids inside trench and via. Therefore, one challenging issue for Cu interconnects is to fill trench and via completely without the agglomeration of Cu seed on the diffusion barrier layer.New barrier metals that have better wettability with Cu than conventional Tantalum (Ta) have been studied to achieve continuous and smooth Cu film on them.1-26 Among them, Cobalt (Co) and Ruthenium (Ru) have been most frequently suggested for suppressing the agglomeration of Cu seed. Co is known to have the good film properties such as the low resistivity, the high melting point and the good adhesion with Cu. However, Co has the serious problems with chemical mechanical polishing (CMP) process and wet etching process. Co is corroded readily during CMP process and wet etching process, and the slits are occurred between Cu wiring and the interlayer dielectric. It results in the degradation of the device yield and reliability performance. As for Ru, the barrier property against Cu diffusion is not enough, and CMP process for Ru is a difficult technology and the scratch occurred during CMP process leads to the degradation of the device yie...

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