Barrierless Cu-Ni-M Ternary Alloy Films Based On The Stable Solid Solution Cluster Model

In the Ultra Large Scale Integration (ULSI) Cu-low k interconnects, barrierless Cu seed layer doped with insoluble elements or their nitrides has received wide attention because of its low resistivity, high thermal stability and easy preparation. In the prior researches, the Cu-Ni-M stable solute cluster-plus-glue-atom model has successfully modified the stability of the Cu-Ni-M alloy films. According to the model, the third element M exhibited a positive enthalpy of mixing with Cu, and negative enthalpy of mixing with Ni at the same time, therefore, M tended to be surrounedd completely by 12 Ni to form an octahedral (M1N12) cluster structure and separated from Cu. These octahedral clusters were uniformly dispersed in the Cu lattice to enhance the thermal stability of Cu films.In order to explore the effects of Cu-Ni-M model in the suitable barrier copper seed layer, this thesis selected Fe、Cr、V、Mo、Ti、Nb、Ta、Sn and Zr elements as the third element M based on this model. Cu-Ni-M (M=Fe、Cr、V and Zr) thin films and Cu-Ni sample films were deposited on Si substrates by RF magnetron sputtering. The microstructure. stability and resisitivity of these films were analyzed. It also summarized the prior results of Cu-Ni-M (M=Mo、Nb、Sn、Ti and Ta) films and finished Cu-Ni-M (M=Nb and Sn) additional TEM experiment to analyze the Cu-Ni-M films systematically.The results showed that the solid solution cluster model is suitable in the barrierless Cu-Ni-M seed layers. The XRD and TEM measurements showed that the stability of the Cu-Ni-M films (except Cu-Ni-Fe films) was improved in varying degrees. Moreover, the thermal stability of the Cu-Ni-M films enhances with the increase of the atomic radius of the third element.The unstability of Cu-Ni-M films was achieved when ΔR<0, (ΔR=(RCu-RM)/RCu). The Cu-Ni-M (M=Cr and V) such as (Cr1.4/13.4Ni12/13.4)0.4Cu99.6and (V0.8/12.8Ni12/12.8)0.5Cu99.5 films begin to achieve good stability (0%<ΔR<9%). The stability of the Cu-Ni-M (M=Mo、Nb、Ta、Ti、Sn and Zr) films can be kept near the ideal cluster (M1N12) ratio and enhanced with the ratio (ΔR>9%). Noteworthy, the stability of Cu-Ni-Sn and Cu-Ni-Zr films with the larger radius M is well with all ratios (15%<ΔR<25%). It also can be confirmed that the third element M (M=Ti and Zr) with negative mixing enthalpy with both Cu and Ni can also be applied in the cluster-plus-glue-atom model, however, it is requested that the mixing enthalpy between M and Ni is more negative.The post-annealed Cu-Ni-M films can achieve the low resistivity directly affected by the cluster ratio (M/Ni=1/12). The Cu-Ni-M films (M/Ni∈[0.6/12,1.6/12], Cu at.%∈[99.5, 99.7], especially close to the Cu at.%=99.7%, M/Ni=1/12) after 1h and 40h annealing can achieve the low resistivity below 3 μΩ·cm. The Cu-Ni-Zr films with the largest radius have highest stability and lowest resistivity.