Investigation On Molybdenum Based Film As Copper Diffusion Barrier And Its Chemical Mechanical Polishing

With further downscaling of the critical dimension in ULSI back-end technology, conventional PVD deposited Ta/TaN barrier has faced challenge with poor conformality. It is proposed that direct electroplating of Cu onto a seed layer can mitigate this problem. Mo and its nitride have already been widely investigated as copper barrier. Is also reported that the thermal stability of both of them were not desirable. In this paper, novel barrier MoTa and Mo Ta/TaN was investigated as copper diffusion barrier and basic research on the chemical mechanical polishing CMP of Mo was carried out.We compare the thermal stability of CoMo, RuMo and MoTa in the Cu/barrier/Si structure and the5nmMoTa alloy exhibits good thermal stability. After optimization, the Cu/5nm MoTa/Si can prevent Cu diffusion up to500℃for30min. We succeed in electroplating Cu in300nm thick on the single30nm MoTa alloy surface. Then the thickness of barrier is kept at5nm and we add a thin2nm TaN into the barrier structure. The structure of Cu/Mo(3nm)/TaN(2nm)/Si and Cu/MoTa(3nm)/TaN(2nm)/Si is thermal stable after annealing up to550℃and600℃, respectively. The MoTa(3nm)/TaN(2nm) structure has be is the best thermal stability among all the investigated. The electrical measurements were conducted on Cu-gated MIS structure with Mo, MoTa, Mo/TaN and MoTa/TaN barrier on the low k (k=2.5) substrates. The sample with5nm MoTa barrier shows the lowest leakage current around9E-9A/cm2at the stressing electrical field of1MV/cm. The breakdown field of Cu/MoTa(3nm)/TaN(2nm)/Si is the highest with field around3.7MV/cm. After analyzing the data, we consider the Mo/TaN, MoTa and MoTa/TaN are good at preventing Cu diffusion and Mo is promising material for next generation Cu diffusion barrier.There is no report on CMP of Mo until now. We investigate the effect of H2O2, pH value, and additives on the CMP properties of Mo. In the solution containing peroxide, we find insoluble MO2O5at pH=3and soluble MoO42-at pH=10from the XPS data. We find the peroxide can enhance the etch rate of Mo. The SER of Mo in the solution with5wt%peroxide is around33nm/min. In the solution containing glycine, glycine can suppress the SER and PR of Mo and that means the glycine is one of the inhibitor of Mo. By changing the concentration of glycine and peroxide, we adjust the PR of Cu and Mo to13nm/min. At that time, the galvanic voltage difference is0.23V. We try different additive into solution to enhance the SER of Mo and ammonia sulfate is effective in improving the SER and PR of Mo. In the solution containing5wt%colloidal silica5wt%peroxide and0.05M ammonia sulfate, the PR of Mo at pH=10is around37.8nm/min. We explain the surface reaction of Mo in the solution containing peroxide and ammonia sulfate and consider the enhanced dissolution of MoO42-help increasing the PR of Mo.