• PDF / 1,821,882 Bytes
• 10 Pages / 612 x 828 pts Page_size
• 31 Downloads / 171 Views

DOWNLOAD

REPORT

---

P. A. Flinn Intel Corporation, SC9-45, 2250 Mission College Boulevard, Santa Clara, California 95124, and Department of Materials Science and Engineering, Stanford University, Stanford, California 94305

E. Arzt Max-Planck-Institut fur Metallforschung, Institut fur Werkstoffwissenschaft, Stuttgart, Germany

W. D. Nix Department of Materials Science and Engineering, Stanford University, Stanford, California 94305 (Received 1 March 1993; accepted 6 October 1993)

The influence of finely dispersed, stable particles on the mechanical strength and microstructure of Al films on Si substrates has been studied. Aluminum oxide particles were produced in Al films by oxygen ion implantation, and the grain size was increased by a laser reflow treatment. Transmission electron microscopy (TEM) was employed to observe the oxide particles and the grain structure in the films after subsequent annealing, and the wafer curvature technique was used to study the deformation properties of the films as a function of temperature. Significant particle strengthening was obtained in the coarse-grained films in tension as well as in compression. In the as-deposited and ion-implanted films a very fine grain size of only 0.35 /xm is stabilized after annealing which causes considerable softening of the film in compression at higher temperature because of the enhancement of grain boundary and volume diffusion controlled relaxation mechanisms. However, in tension at low temperature these films show high stresses comparable to those of the laser reflowed and ion-implanted films. The results are discussed in the light of TEM observations.

I. INTRODUCTION Aluminum is widely used as an interconnect material in microelectronic devices. Failure of the interconnect lines in these devices can severely limit reliability. In some cases these failures can be caused by insufficient mechanical strength of the materials involved. Thermal stresses arise in interconnect lines during device fabrication and in service at elevated temperatures because of large differences in thermal expansion between aluminum and the silicon substrate. These stresses can relax by dislocation glide and diffusional deformation processes,1 which, in turn, can cause hillock or void formation to occur and may result in short or open circuits. Electromigration is another important failure mechanism for conductor lines. The discovery that electromigration causes stresses to develop in conductor lines has led to the suggestion that mechanical strength may be an important factor in determining electromigration failure resistance.2'3 Recent theories suggest that materials which can sustain higher hydrostatic stresses will show better resistance to electromigration failure. Thus, the development of interconnect materials (especially 318

http://journals.cambridge.org

J. Mater. Res., Vol. 9, No. 2, Feb 1994

Downloaded: 21 Mar 2015

aluminum alloys) with higher mechanical strength may be a promising way to improve reliability. A well-established method for strengthening bulk materials involve