Increasing the mean grain size in copper films and features
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S.H. Brongersma Stichting Interuniversity Microelectronics Centre (IMEC) Nederland, High Tech Campus 48, 5605 KN Eindhoven, The Netherlands
Zs. Tokei and L. Carbonell Interuniversity Microelectronics Centre (IMEC) vzw, 3001 Leuven, Belgium
W. De Ceuninck, J. D’Haen, and M. D’Olieslaeger Hasselt University, Institute for Materials Research, 3590 Diepenbeek, Belgium; and Interuniversity Microelectronics Centre (IMEC) vzw, Division Imomec, 3590 Diepenbeek, Belgium (Received 19 April 2007; accepted 27 August 2007)
A new grain-growth mode is observed in thick sputtered copper films. This new grain-growth mode, also referred to in this work as super secondary grain growth (SSGG) leads to highly concentric grain growth with grain diameters of many tens of micrometers, and drives the system toward a {100} texture. The appearance, growth dynamics, final grain size, and self-annealing time of this new grain-growth mode strongly depends on the applied bias voltage during deposition of these sputtered films, the film thickness, the post-deposition annealing temperature, and the properties of the copper diffusion barrier layers used in this work. Moreover, a clear rivalry between this new growth mode and the regularly observed secondary grain-growth mode in sputtered copper films was found. The microstructure and texture evolution in these films is explained in terms of surface/interface energy and strain-energy density minimizing driving forces, where the latter seems to be an important driving force for the observed new growth mode. By combining these sputtered copper films with electrochemically deposited (ECD) copper films of different thickness, the SSGG growth mode could also be introduced in ECD copper, but this led to a reduced final SSGG grain size for thicker ECD films. The knowledge about the thin-film level is used to also implement this new growth mode in small copper features by slightly modifying the standard deposition process. It is shown that the SSGG growth mode can be introduced in narrow structures, but optimizations are still necessary to further increase the mean grain size in features.
I. INTRODUCTION
The transition from aluminum to copper as the metal used in interconnect lines was one of the most important changes in materials that the semiconductor industry has experienced since its creation. This has necessitated a firm understanding of the physical properties of this material in both thin films and narrow structures. At the same time, a regime had been entered into where the metal linewidth is smaller than its depth. This implies that the conformal deposition of copper would result in the formation of seams and voids. It quickly became a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2008.0080 642 J. Mater. Res., Vol. 23, No. 3, Mar 2008 http://journals.cambridge.org Downloaded: 16 Mar 2015
clear that patterning trenches into a dielectric layer using optical lithography, combined with filling these features electrochemically with copper provid
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