Investigation On CoMo Based Alloy As Novel Copper Interconnection Diffusion Barrier

As the feature sizes of VLSI devices continue to shrink to14nm and beyond, the RC delay and the reliability issues of the interconnect have become major factors of restricting the chip performance. Novel ultra-thin barrier layer/adhesive layer are needed to meet the requirements of the interconnect. This dissertation gives a comprehensive study of novel CoMo alloy film as barrier/adhesion layer for Cu interconnect.First the thermal stability of Cu/CoMo system is studied on different substrates. It is found that the ultrathin5nm CoMo barrier layer is able to maintain its copper diffusion barrier properties after being annealed at500℃for30minutes, without obvious interdiffusion and misciblity with Cu and the Si substrate. The transmission electron microscopy (TEM) and the energy dispersive X-ray spectroscopy (EDX) results show that, the Cu/CoMo(-6nm)/Low K(k=2.25) system has good thermal stability after being annealed at500C/30min, while the Cu/Ta(5nm)/low k already failed. The surface SEM profiles show that for the sample with CoMo (1:3) barrier layer annealed at600℃/30min, the Cu surface remains smooth and continuous without agglomeration, which indicates that CoMo and Cu has good adhesion, and is suitable for using as copper adhesive layer in the interconnect.The IMEC p-cap testing structure is used to study the electrical properties of CoMo barriers. It is found that the CoMo (1:3) samples have a breakdown electrical field of6.25-7.5MV/cm, which is higher than that (5.9-7.1MV/cm) of Ta(3nm)/TaN(2nm) samples. The BTS method is used to characterize the movable charge density and flat band shift in the oxide layer of the CoMo barrier samples. The flat band shift of CoMo(1:3) barrier is2.1V biasing at±MV/cm electrical field150℃for600s, which is smaller than2.24V for Ta/TaN barrier. Triangle voltage sweeping (TVS) measurement results show that there is no movable charge for the CoMo(1:3) samples biased at1MV/cm at150℃for300s, while there are high amount of Cu ions in the Ta samples. This result shows better diffusion barrier properties of CoMo than that of Ta.The preliminary etching and polishing performance of CoMo barrier are studied. It is found that hydrogen peroxide can accelerate the corrosion of CoMo alloy, while ethylenediamine can suppress static corrosion of CoMo alloy. At pH=3,1mL/L ethylenediamine can suppress static etch rate of CoMo from66.6nm/min to 12.5nm/min. It is also found that glycine can reduce the galvanic corrosion between Cu and CoMo(1:3). After adding100M glycine, the Ecorr(Cu)-Ecorr(CoMo) can decrease from0.228V to0.067V.Our results show that single layer CoMo is a very good diffusion barrier and has good potential to be used in the next generation Cu interconnect.