A novel technique for making self-encapsulated and self-aligned copper films Amit Chugh, Ashutosh Tiwari, A. Kvit, J. Narayan * Department of Materials Science and Engineering, NSF Center for Advanced Materials and Smart Structures, North Carolina State University, Raleigh, NC 27695-7916, USA Received 4 September 2002; received in revised form 17 March 2003; accepted 21 April 2003 Abstract We provide a method to grow self-aligned epitaxial MgO/Cu/MgO films on silicon substrates by pulsed laser deposition (PLD) technique. Here, a thin layer of Cu/Mg (Mg 5%) is deposited using a PLD over Si (100) specimens, followed by annealing at 500 8C in a controlled oxygen environment resulting in the segregation of Mg on either side of the copper film. Mg on the upper side of copper reacts with ambient oxygen and on the lower side with the adsorbed oxygen in the substrate to form layers of MgO. High- resolution transmission electron microscopy (HRTEM) measurements showed thin layers of MgO formed on either side of the copper films. The lower MgO layer acts as a diffusion barrier and inhibits the diffusion of Cu into the system while the upper MgO layer acts as a passivating layer and protects copper against oxidation. This approach can also be used to grow high quality epitaxial YBa 2 Cu 3 O 7d films with MgO acting as a buffer for the superconducting device applications. # 2003 Elsevier B.V. All rights reserved. Keywords: Pulsed laser ablation; Self-aligned passivated contacts; Domain matching epitaxy; Transmission electron microscopy; Annealing Demand for improved performance in integrated circuits has lead to the integration of an increasing number of semiconductor devices on chips of decreasing size. This has been achieved largely by scaling down the device feature size, while increasing the number of interconnect layers. As a result, the topography has become more complicated with each successive device generation. In addition, as metal line widths enter into the sub-half-micron regime, device speed is expected to be limited by the interconnect performance [1  /3]. The current metallization material Al suffers from poor step coverage, poor electromigration resistance, stress migra- tion and stress resistance. As a result current intercon- nect schemes, which are based on Al alloy metallization, have become performance limiting. The continuing drive for achieving higher perfor- mance of integrated circuit devices necessitates newer and improved interconnecting materials. Copper has received considerable attention [4  /6] as a potential interconnection material in advanced metallization technology due to its outstanding electromigration resistance (exhibited resistance to electromigration above current densities of 10 6 A cm 2 ) and lower bulk resistivity (1.6 mV cm) [4,7] as compared with aluminum. As a result, copper based interconnects possess the ability to operate at higher frequencies and are not limited by current densities. However, the use of copper as an interconnect also has certain limitations. Copper has not been considered for application in silicon- integrated circuits because of its ability to rapidly diffuse into silicon and degrade the semiconductor devices. This degradation is caused by acceptor levels in the middle of the Si bandgap with respect to valence edge, which provide traps and recombination centers for charge carriers [8]. To overcome these undesirable effects of copper, development of advanced diffusion barriers is required. Another problem that needs to be addressed includes the oxidation of the exposed Cu surface at high temperatures. Thus it requires the growth of a passivat- ing layer to protect it from an oxidizing ambient. Due to recent developments of copper passivation methods and * Corresponding author. Tel.:  /1-919-515-7148; fax:  /1-919-513- 1699. E-mail addresses: achugh@unity.ncsu.edu (A. Chugh), j_narayan@ncsu.edu (J. Narayan). Materials Science and Engineering B103 (2003) 45  /48 www.elsevier.com/locate/mseb 0921-5107/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0921-5107(03)00148-X