Evolution and Stability of a Nanocrystalline Cu 3 Ge Intermetallic Compound Fabricated by Means of High Energy Ball Mill
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I.
INTRODUCTION
THE Cu3Ge intermetallic compound has attracted a lot of attention in large-scale integrated circuit technology over the past 2 decades principally on account of its low metallic resistivity at ambient temperature[1–5] and shape memory effects[6] as well as its excellent mechanical,[7] electrochemical,[8–11] and optical properties.[12] The e1-Cu3Ge ordered intermetallic phase suppresses the diffusional transport of Cu into Si, making it an attractive material for applications as contacts and interconnects in Si devices.[13–17] Moreover, it does not have the serious problems commonly associated with Cu used as interconnects in microelectronic devices, and is also reported to have outstanding oxidation resistance at temperatures up to 723 K (450 C).[7,13,18,19] According to the mechanism proposed by Aboelfotoh et al. for the formation of ordered e1 in Cu-Ge thin films, this phase originates from an hcp f-Cu5Ge phase and is
MAHBOOBEH NAZARIAN-SAMANI, formerly Graduate Student with the Department of Materials Science and Engineering, University of Semnan, Semnan, Iran, is now Researcher with the School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran, Tehran, Iran. ALI REZA KAMALI, Senior Research Fellow, is with the Department of Materials Science and Metallurgy, University of Cambridge, Cambridge, U.K. MASOUD NAZARIAN-SAMANI, Senior Researcher, and SEYED FARSHID KASHANI-BOZORG, Associate Professor, are with the School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran, Tehran, Iran. Contact e-mail: [email protected], [email protected]. Manuscript submitted July 1, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS A
formed through an entirely coherent interface.[20,21] In addition, the f phase has a crystallographic relation with the a-Cu(Ge) solid solution, and the a fi f transition coherently occurs throughout the close-packed planes and directions of two phases as follows:[21]
ð111Þa ð0001Þf
: ½1 ½110 1120 a
f
Therefore, the a fi f fi e1 sequence could be considered for the binary Cu-Ge alloys located in the e1-phase formation range. To the best of the authors’ knowledge, no exhaustive account has been yet offered of the various phase transitions leading to the formation of the Cu3Ge intermetallic compound upon non-equilibrium MA processing. Therefore, it is the objective of this study to shed light on the underlying mechanism of e1-Cu3Ge intermetallic formation. To this end, two Cu-22 wt pct Ge and Cu-26 wt pct Ge alloys were MA-ed at room temperature, and simultaneously, the evolution of Cu3Ge and its ordering/disordering characteristics upon MA and annealing processes was evaluated. These two alloys were selected for the present study mainly due to their positions in the binary Cu-Ge phase diagram.[22] The former alloy falls in the e1 + f two-phase region, but the latter one falls in the e1 single phase, which is very close to the stoichiometric composition of the e1Cu3Ge intermetallic compound at ambient te
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