J. Phys. IV France
Volume 112, October 2003
Page(s) 853 - 856

J. Phys. IV France
112 (2003) 853
DOI: 10.1051/jp4:20031015

Composition of sputtered NiTiX shape-memory and superelastic thin films

D.S. Grummon1 and T. LaGrange2

1  Department of Chemical Engineering and Materials Science, 3525 Engineering Building, Michigan State University, East Lansing, MI 48824, U.S.A
2  Swiss Federal lnstitute of Technology Lausanne (EPFL), Dépannent of Physics, Institute of Atomic Engineering, 1015 Lausanne, Switzerland

Obtaining desired mechanical and transformational properties in shape-memory and superelastic alloys in the NiTiX system (X=Cu, Hf, Pd, Pt, etc.) requires very tight control of alloy composition. While this is not difficult to achieve in melt-solidification, the sputtering process involves a number of mechanisms, such as preferential resputtering, or species-dependent divergence of the sputter flux, which may cause film composition to deviate from that of the sputter cathode. Of particular concern is the tendency for composition to vary with position on the substrate, and to drift over time as the sputter cathode erodes. Neither problem can be addressed by simple adjustment of the cathode composition. In this paper we consider the often-observed tendency for sputtered TiNi films to be deficient in Ti relative to the cathode composition. A preliminary model is presented which simulates the effect of differential angular distribution of the sputter flux between Ti and Ni by adopting a modified cosine law [1] in which the elemental flux is proportional to $\cos\theta/(\rho_{\rm i} \sin^2\theta+\cos^2\theta)$. It is found that different species-dependent values of $\rho_{\rm i}$, for Ni and Ti respectively, have only modest effect on in-plane composition gradients and time-evolution of composition, but that a systematic Ti deficiency is readily produced by setting $\rho_{\rm Ti}<\rho_{\rm Ni}$.

© EDP Sciences 2003