Effects of Ti insertion between Cu and TiN layers on reliability in Cu/Ti/TiN/Ti layered damascene interconnects

Abstract

Experimental characterization and modeling of the reliability of three-terminal dual-damascene Cu interconnect treesIn situ electron microscopy studies of electromigration in stacked Al(Cu)/TiN interconnects Appl.We investigated the effects of Ti insertion between Cu and TiN layers on electromigration ͑EM͒ in Cu/Ti/TiN/Ti layered damascene interconnects. The Cu damascene interconnects with Ti insertion show an EM lifetime of up to 100 times longer than those without Ti insertion, depending on the inserted Ti thickness. The lifetime improves as Ti thickness increases from 10 to 20 nm. Ti insertion increased the sheet resistance of the layered film after annealing and enhanced the adhesion of Cu to underlayer TiN. The resistance change was mainly caused by formation of Cu-Ti reaction products resulting in reduced cross-sectional area in the Cu film, and was also caused by Ti incorporation into the Cu film. Ti insertion, however, does not have any effect on Cu film microstructure such as median grain size, standard deviation of grain size distribution, and texture. During EM testing, the resistance in Cu interconnects with Ti insertion initially decreases, then rises gradually, and finally increases rapidly until failure occurs. This behavior is probably caused by Ti redistribution in Cu during the EM testing. EM lifetime consists mainly of the time when the interconnect resistance is lower than the initial resistance, that is, the time before void growth occurs ͑incubation time͒. Improved Cu adhesion to underlayer TiN is an important factor because the void growth rate of Cu interconnects during EM testing is considerably decreased by Ti insertion. The void growth rate, however, does not depend on Ti thickness and Ti surface treatment before Cu deposition. As a result, EM lifetime is mainly governed by the incubation time, and the void growth rate is determined by Cu EM through the Cu/barrier interface path.

Material Consideration on Ta, Mo, Ru, and Os as Glue Layer for Ultra Large Scale Integration Cu Interconnects

“…In a recent study, the strength of Cu adhesion to surrounding materials shows a linear relationship with lifetime for electromigration. 5,[8][9][10][11]13) Thus, the evaluation of the strenght of Cu adhesion to glue layers can be an important factor for estimating electromigration resistance. One of the simple methods to measure the strength of Cu adhesion to glue layers is the evaluation of wetting angle of Cu on glue layers.…”

“…1,2,8,11,12) Therefore, an adhesion promoter (glue layer), such as Ta, Ti, or Ru, is inserted to improve of electromigration resistance. [12][13][14][15] However, there has been no investigation about glue layer materials, and there are few reports of a systematic explanation of the Cu adhesion property on glue layer materials.…”

Adhesion of Copper With Diffusion Barrier Layer for Copper Interconnection

“…The wettability of Cu on the glue layer (adhesion promoter) is an important factor for electromigration resistance, because a good Cu wettability on the glue layer means high strength of Cu adhesion to glue layers. In a recent study, the strength of Cu adhesion to surrounding materials shows a linear relationship with lifetime for electromigration (Hu et al, 2002(Hu et al, , 2003a(Hu et al, , 2003bAbe and Onoda, 2003;Lane et al, 2003). Thus, the evaluation of the strength of Cu adhesion to glue layers can be an important factor for estimating electromigration resistance.…”

“…If a metallic capping layer were adopted in Cu interconnects, the interface between Cu and the diffusion barrier can become a new main path of electromigration (Lloyd et al, 1999;Hayashi et al, 2003;Hu et al, 2003a;Tu, 2003). Therefore, an adhesion promoter (glue layer), such as Ti, Ta or Nb, is inserted to improve the electromigration resistance (Abe and Onoda, 2003;Hayashi et al, 2003;Maniruzzaman et al, 2006).…”

Highly Reliable and Low Resistive Cu/Low-k Dual Damascene Interconnects by Using TaTi Barrier Metal

“…Then, modulation of barrier metal instead of conventional Ta and/or TaN is also a candidate to obtain highly reliable interconnect performance. For example, Titanium-based barrier metals (Ti, TiN) are proposed, [38][39][40] where the Ti-based barrier metal has better wettability to Cu than that of Ta-based barrier metal. Thus, it basically shows longer EM lifetime than Ta-based barrier metal.…”