Effects of N Doping in Ru-Ta on Barrier Property and Reliability Performance for Cu Interconnects

Abstract

The effects of N doping in Ru-Ta alloy on film property, barrier property against Cu diffusion and reliability performance in Cu interconnects were investigated. RuTa(N) film which was doped with N in Ru-Ta alloy was applied as a diffusion barrier layer in Cu interconnects, and barrier property and reliability performance with RuTa(N) barrier were mainly evaluated. As RuTa(N) film was annealed, N desorbed easily from RuTa(N) film due to its low thermal stability and the crystal size became larger because of the recrystallization. RuTa(N) film had the poor barrier property against Cu diffusion due to the structure of high-angle grain boundaries despite the crystal size of RuTa(N) increases and the density of grain boundaries decreases after annealing. Reliability performance of via electromigration could be improved by using Ru-Ta based alloy barrier. However, there was remarkable difference of reliability performance between RuTa and RuTa(N) barrier, and RuTa(N) had inferior reliability performance of via electromigration. On the other hand, RuTa had both good barrier property and superior reliability performance. It was found that doping N in Ru-Ta alloy degraded barrier property and reliability performance. Consequently, it is appropriate to apply RuTa single film as the diffusion barrier layer for 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 gapped filling, the opening of trench and via after the deposition of barrier and Cu seed have to be kept far 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 the 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.1-23 Among them, Ruthenium (Ru) has been most frequently suggested as a layer for suppressing the agglomeration of Cu seed. The barrier property against Cu diffusion of pure Ru and Ru-N is not enough. [22][23][24] In addition, chemical mechanical polishing (CMP) process for Ru is a difficult technology and the scratch occurred during CMP process leads to the degradation of the device yield and time dependent dielectric breakdown (TDDB) reliability performance. However, Ru has the good wettability with Cu and can improve the filling property of Cu electroplating, and has another possibility in Cu interconnects such as the seed layer for direct plating onto R...

Seedless Cu Electroplating on Ru-W Thin Films for Metallisation of Advanced Interconnects

“…Ru is chemically inert and stable, contrasting with its counterparts, such as Co, which is prone to dissolution during conventional acidic electroplating, requiring electrolyte modification to be used in seedless diffusion barrier systems [11,12]. However, similar to other candidates, Ru alone is not effective as a diffusion barrier [13], thus, driving the research on coupling Ru with other species to improve the barrier properties against Cu diffusion, including Ru-Co [14], Ru-Cr [15], Ru-Mn [16][17][18], Ru-N [19], Ru-P [20,21], Ru-Ta(-N) [16,22,23], and Ru-W(-N) [16,24,25] compositions.…”