Abstract
The major goal of this study is to combine the techniques of using plasma immersion ion implantation (PIII) and electroless plating to implant seeds (Pd or Cu) onto the diffusion barrier layer ( β-Ta or a-TaN) as catalyst for the electroless Cu plating to accomplish the ULSI interconnection metallization. Electroless Cu plating in the deep 180 nm line-width ULSI interconnect metallization has been successfully achieved by the PIII Pd catalytic treatment. Under the circumstances of higher substrate bias voltage and plasma ionization in the PIII process, the electroless copper grows upward from the bottom of the vias (bottom width: 0.25 μm; aspect ratio: 7) and trenches (bottom width: 0.18μm; aspect ratio: 7), with an excellent gap filling ability. The result of this process, by employing the mechanical pull-up tests, showed that higher substrate bias and higher plasma ionization can effectively enhance the adhesion strength between the copper film and the a-TaN layer. The phase transformation from a-TaN into crystallized Ta2N phase was observed after annealing treatment. Furthermore, the Cu(111) texture was strengthened at 300 ℃ annealing for 1 h because of the relaxation of the residual stress and recovery of the copper film. The texture was reduced at the 500 ℃ annealing for 1 h because of the copper grain growth. The adhesion strength of copper films on a-TaN barrier layer was enhanced by the annealing because of the interdiffusion of copper layer, Pd clusters and a-TaN barrier layer. The annealing temperatures lower than 300 ℃ help to reduce the electric resistivity of copper film, to strengthen the Cu(111) preferred orientation, and to enhance the adhesion strength of copper films on a-TaN layer. However, the specimen annealed at 500 ℃ manifested the diffusion of Pd atoms into the copper film and resulted in a significant increase of the electric resistivity of copper film if PIII Pd as seeds. In the comparison of catalytic effects of PIII Pd and PIII Cu as seeds for electroless Cu plating, the growth rate of electroless plated copper films was found to be different at the initial stage; faster copper films’ growth rate was observed on the PIII Pd seeds compared to the PIII Cu seeds. The average grain size of the as-deposited copper films was found to be different, too; larger copper grain (~292.4 nm) was formed on the PIII Cu seeds compared to those formed on the PIII Pd seeds (~86.2 nm). After 700 ℃ annealing, the similar copper grain size was formed similarly on both seed; the average copper grain sizes became ~1112.4 for Pd seeds and ~1176.5 nm for Cu seeds, respectively. Under the higher biased voltage (-4000 V), either PIII Cu or PIII Pd as catalysts can get the bottom-up copper grain growth mechanism in the electrolesss copper metallization process in trenches/vias. Under the lower biased voltage (-500 V), larger electroless plated copper grain was observed in the PIII Cu self-catalytic specimen, resulting in the formation of voids inside the interconnects. On the other hand, the excellent electrolesss copper step coverage was clearly observed in the case of PIII Pd as seeds.