Molecular dynamics study of adhesion strength and diffusion at interfaces between interconnect materials and underlay materials |
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Authors: | T Iwasaki |
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Affiliation: | (1) Mechanical Engineering Research Laboratory, Hitachi, Ltd., 502 Kandatsu, Tsuchiura, Ibaraki 300-0013, Japan, JP |
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Abstract: | A molecular-dynamics technique for determining the adhesion strength and analyzing diffusion at interfaces between different
materials has been developed. The adhesion strength is determined by calculating the adhesive fracture energy defined as the
difference between the total potential energy of the material-connected state and that of the material-separated state. This
technique is used to determine the adhesion strength and analyze diffusion at the interfaces between Cu films and high-melting-point
materials that are used as underlay materials for Cu interconnects in ULSIs. The adhesive fracture energy shows that the adhesion
strength of the Cu/Ru and Cu/Ir interfaces is much higher than that of the Cu/W, Cu/TiN, and Cu/Ta interfaces. Because the
diffusion of Cu atoms at the Cu/Ru and Cu/Ir interfaces is suppressed, the surface smoothness of Cu films on Ru and Ir is
much better than that on W, TiN, and Ta. It is also found that adhesion strength and smoothness increase with decreasing lattice
mismatch between Cu and the underlay material. These results are confirmed by SEM (scanning electron microscope) and scratch
testing.
Received 27 October 1999 |
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