Barrierless Cu-Ni-Nb thin films on silicon with high thermal stability and low electrical resistivity
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i School of Mechanical Engineering, Dalian University of Technology, Dalian 116024, China
Li Jun Liu Key Laboratory of Materials Modification by Laser, School of Mechanical Engineering, Dalian University of Technology, Ministry of Education, Dalian 116024, China
Cui Min Bao Shenyang Blower Works Group, Ltd., Shenyang 110142, China
Jinn P. Chu Department of Materials Science and Engineering, National Taiwan University of Science and Technology, Taipei 10607, Taiwan
Chuang Dong Key Laboratory of Materials Modification by Laser, School of Mechanical Engineering, Dalian University of Technology, Ministry of Education, Dalian 116024, China (Received 16 April 2013; accepted 18 November 2013)
In this paper, we demonstrate a thin film Cu–Ni–Nb alloy deposited directly on silicon, without a designated barrier, showing very high thermal stability at a temperature up to 700 °C for 1 h. Thin [Nb–Ni12]Cux films were sputter deposited and annealed, and their material and electrical properties were studied. The results can be explained by the “cluster-plus-glue atom” model for stable solid solutions, where [Nb–Ni12] cuboctahedral clusters are embedded in a Cu matrix. In this model, the clusters are congruent with the Cu minimizing atomic interactions allowing a good stability. The properties of the films were found to be affected by the Ni/Nb ratios. Especially, the (Nb1.2/13.2Ni12/13.2)0.3Cu99.7 film annealed at 500 °C for 1 h had the lowest electrical resistivity of about 2.7 lX cm. And even after 40 h annealing at 500 °C, it maintained a low resistivity of about 2.8 lX cm, demonstrating extremely high stabilities against silicide formation.
I. INTRODUCTION
Cu metallization in Si devices has been widely used for its high electrical conductivity and large resistance to electromigration. However, Cu readily reacts with Si at low temperatures even below 200 °C, which results in device failures.1–3 The presence of a thin native SiO2 on the surface of Si cannot inhibit Cu diffusion, and silicide is formed above 625 K.4 Diffusion barrier layers such as Ta, Ta/TaN, (TiVCr)N, AlCrRuTaTiZr, and Co(W,P) have to be used to prevent Cu from diffusing into the transistor region and from forming Cu3Si.5 9 With the feature size of interconnect shrinking, the fabrication of a barrier structure with good thermal stability and small dimension is becoming more and more challenging.5,10–12 Alternatively, there is also a barrierless scheme where the Cu seed layer is alloyed with Ru, W, Nb, and Mo to enhance the diffusion a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2013.355 J. Mater. Res., Vol. 28, No. 24, Dec 28, 2013
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barrier property.2,3 These elements all have large positive enthalpies of mixing with Cu so that they have very limited solid solubilities in Cu. The solute segregation and precipitation retard recrystallization and grain growth.3 Consequently, the enhanced chemical stability is often accompanied by a poor electrical conductivity. T
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