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Initial hillock formation and changes in overall stress in Al–Cu films and pure Al films during heating

Published online by Cambridge University Press:  31 January 2011

C. Kylner  and
L. Mattsson
C. Kylner
Affiliation:
Department of Physics II (Optics), Royal Institute of Technology, SE-100 44 Stockholm, Sweden, and Surface Evaluation Laboratory, Institute of Optical Research, Electrum 236, SE-164 40 Kista, Sweden
L. Mattsson
Affiliation:
Surface Evaluation Laboratory, Institute of Optical Research, Electrum 236, SE-164 40 Kista, Sweden and Department of Materials Processing Technology (Industrial Metrology and Optics), Royal Institute of Technology, SE-100 44 Stockholm, Sweden
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Abstract

The effect of adding a few percent (3 at.%) Cu to Al films on the initial hillock formation and the changes in overall film stress were studied. Al films were evaporated by an electron-beam gun onto Si wafers in an ultrahigh vacuum deposition system and Al–Cu films were coevaporated with a thermally heated source used for the Cu. The as-deposited samples were radiatively heated at 3 °C/s in an air environment. During heating, the initial hillocking and the changes in overall stress were measured simultaneously and in real time with a specially designed optical instrument. The measurement principle of this instrument is based on laser beam deflection, caused by wafer bending due to film stress, and collection of the laser light scattered off from the hillocks appearing on the film surface. The experimental results show that Cu alloying has a strengthening effect on Al films, resulting in delayed and considerably reduced hillock formation. Before heating, the as-deposited Al–Cu samples were investigated by total integrated scattering and atomic force microscopy. These investigations showed that Al–Cu films are considerably smoother and have smaller grains than Al films of similar thickness (340 nm). It was found that the small grains of Al–Cu films contribute to increasing the tensile stress–temperature slope. In addition, Al–Cu films can withstand higher compressive stresses than Al films.

Type
Articles
Information
Journal of Materials Research , Volume 14 , Issue 10 , October 1999 , pp. 4087 - 4092
Copyright
Copyright © Materials Research Society 1999

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