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R.A. Bernstein Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139

C.V. Thompson Singapore-MIT Alliance, 4 Engineering Drive 3, Singapore 117576; and Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (Received 14 July 2003; accepted 25 November 2003)

Using continuous wafer-curvature measurements, stress generation was monitored as nickel thin films reacted with silicon substrates to form Ni2Si during isothermal anneals. A large compressive force developed during the reaction, but gradually relaxed after the reaction was complete. From a model for reactive film formation, a lower limit for the instantaneous stress associated with compound formation was found to be −2.00 ± 0.75 GPa. This instantaneous stress can be explained by a volumetric strain of 1.65 ± 0.62%, which is much smaller than the theoretical volume expansion of 62% in this system. These results suggest that significant inelastic deformation occurs during silicide formation. It was also found that diffusive creep relaxes the growth stress after the reaction. The observed instantaneous stress indicates that the energy of deformation associated with the reaction is of the same order as the energy that drives it, suggesting that stress generation and stress relaxation can play a significant role in the kinetics of reactive film formation.

I. INTRODUCTION

Films formed through thin film reactions, such as metal silicides, play critical roles in a wide range of applications in microelectronics and other microsystems. In many cases, the phase formation sequence and the kinetics of film formation are not well understood. While the effects of temperature have been explored in detail,1 and stress evolution during silicide formation has also been recently studied in some detail,2,3 the effects of volume changes and associated strain and deformation on the energetics and kinetics of reactive film formation are not well understood, despite experimental and theoretical evidence that stress and stress evolution are important.4–10 Earlier discussions suggest that the stress that develops during the thin film reactions can be explained by the volumetric strain at the reaction interface.11 However, because the instantaneous stress that develops upon compound formation would necessarily exceed any possible adhesion forces, d’Heurle and Thomas11 argued that

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Present address: Institute of Materials Research & Engineering 3, Research Link, Singapore 117602.

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J. Mater. Res., Vol. 19, No. 2, Feb 2004 Downloaded: 17 Mar 2015

some relaxation mechanism must be active during the reaction. Zhang and d’Heurle12 proposed a model that takes into account the simultaneous stress development due to the reaction, assumed to follow a parabolic growth law, and the relaxation of these stresses by diffusive creep. The force generated by the growth and relaxation is

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