Copper thin films for metallization have attracted much attention during the last decades, particularly in the field of microelectronics. Copper deposition by electroplating requires a thin conducting seed layer. The sputtering technique has the disadvantage of poor step coverage, yielding difficulties for deposition into structures with high aspect ratios. Atomic Layer Deposition (ALD) and chemical vapour deposition (CVD) are well-known techniques for producing films with excellent step coverage. However, growth of copper usually exhibits nucleation problems especially on oxide surfaces (1). To overcome this problem an intermediate layer of Cu3N can be deposited on an oxide surface. When the metastable Cu3N is heated, it decomposes into metallic copper and nitrogen gas.
In this study, both CVD and ALD techniques have been used to deposit Cu3N on SiO2 using copper(II) hexafluoroacetylacetonate, water and ammonia as precursors. Introduction of water was found to be crucial for initiating film growth as well as for improvement of film morphology.
The aim of this work was to investigate the annealing procedure in order to obtain low resistivity copper films. Prior to and subsequent to the annealing the deposited films were analyzed by XRD, SEM and ESCA to detect differences in phase, morphology and composition. For ALD films (15 nm) the lowest resistivity, 7-8 µΩcm, was obtained after vacuum annealing for 15 minutes at 450 °C (2). Li and Gordon deposited Cu3N films on Ru/Ta/SiO2/Si substrates and reached resistivity values around 10 µΩcm (3). For the CVD films the kinetics of the phase transformation was also studied in-situ, using the four point probe method, as a function of annealing temperature, annealing time and film thickness both in vacuum and hydrogen.
1. P. Mårtenson, J.-O. Carlsson, Chem. Vapor. Dep. 3 (1997) 45.
2. T. Törndahl, Thesis, Faculty of Sci. and Tech. ISBN 91-554-6081-X, Uppsala University (2004).
3. Z. Li and R. Gordon, Chem. Vapor. Dep. 12 (2006) 435.
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