Texture in Ti/Al and Nb/Al multilayer thin films: Role of Cu
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K. Barmakb) Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213
K.P. Rodbell T.J. Watson Research Center, IBM, P.O. Box 218, Yorktown Heights, New York 10598 (Received 5 December 2000; accepted 27 February 2001)
Fiber texture in Ti/Al and Nb/Al polycrystalline multilayer thin films, with bilayer thicknesses (⌳) ranging from 20–333 nm and having a fixed stoichiometry of 1/3, has been investigated by using x-ray pole figures and transmission electron microscopy. Two sets of films were deposited; one set contained pure Al and the other Al–1.0 wt% Cu. The results indicated that texture was strengthened by the formation of a coherent superlattice for the Nb/pure-Al film with the smallest bilayer thickness. By contrast, the texture in Ti/pure-Al films with a similar period was not as strong. The texture also decreased with increasing ⌳ for both the Ti/pure-Al and Nb/pure-Al films. An increase in the width of the Al (111) peak and an offset of the fiber axis from the substrate normal of 5–8° was observed in the ⌳ ⳱ 333 nm films prepared by using Al–1.0 wt% Cu. The decrease in texture on addition of Cu to Al was attributed primarily to an increase in interlayer roughness as a consequence of reduction in the Al(Cu) grain size. These observations were interpreted in the context of structure zone and dynamic roughness models of film growth.
I. INTRODUCTION
The texture of thin, polycrystalline metal films continues to be a topic of significant technological and scientific interest. For example, experiments have sought to quantify and understand texture formation in polycrystalline Al and Al(Cu) thin films, because of the widespread use of the latter as an interconnect material in integrated circuits. One of the first means of quantifying film texture used comparisons of the relative heights of diffraction peaks obtained from conventional Bragg– Brentano x-ray diffraction (XRD) scans.1 These comparisons indicated that physical vapor-deposited Al formed a polycrystalline film composed of grains that had their (111) planes aligned parallel to the substrate surface.1 The corresponding electromigration studies revealed that films with stronger 〈111〉 fiber texture had the largest resistance to electromigration failures.
a)
Present address: Sandia National Laboratories, Department of Thin Film and Interface Science, MS 9161, P.O. Box 969, Livermore, CA 94551. b) Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 16, No. 5, May 2001
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Later studies, based on pole figures and pole plots of Al and Al(Cu) films, provided a more quantitative approach to evaluation of thin-film texture that included a measurement of the volume fraction of random and textured grains, the peak half-width of the fiber component, and the orientation of the fiber pole with respect to the substrate normal.2– 6 A low random fraction of grains and small peak half-width values were found to correlate with i
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