Continuous microscratch measurements of the practical and true works of adhesion for metal/ceramic systems
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Continuous microscratch measurements of the practical and true works of adhesion for metal/ceramic systems S. Venkataraman Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455
D. L. Kohlstedt Department of Geology and Geophysics, University of Minnesota, Minneapolis, Minnesota 55455
W. W. Gerberich Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455 (Received 22 May 1995; accepted 24 June 1996)
Using a continuous microscratch technique, the adhesion strengths of Pt, Cr, Ti, and Ta2 N metallizations to NiO and Al2 O3 substrates have been characterized. The practical work of adhesion was determined as a function of both thickness and annealing conditions. For all except the Ta2 N films, the practical work of adhesion increases nonlinearly from a few tenths of a Jym2 to several Jym2 as the thickness of the thin film is increased, indicating that a greater amount of plastic work is expended in delaminating thicker films. Further, the practical work of adhesion also increases with increasing annealing temperature, indicating stronger bonding at the interface. In the limit that the film thickness tends to zero, the plastic energy dissipation in the film tends to zero. As a result, the extrapolation to zero thickness yields the true work of adhesion for that system.
I. INTRODUCTION
The adhesion strengths of Pt, Cr, and Ta2 N metallizations are of interest to the microelectronics industry. Pt has a low resistivity and hence is used as electrical interconnects, as ohmic contacts, and in conductivity experiments. Moreover, Pt is extremely useful in applications involving metal/ceramic systems, as it is very stable at high temperatures. Further, Pt has a coefficient of thermal expansion close to many ceramics. Cr metallization is typically used on printed circuit boards and ceramic chip carriers, while Ta2 N is used in resistors and as protective and wear-resistant coatings in hightemperature and corrosive environments. In this paper the adhesion strengths of PtyNiO, PtyAl2O3 , CryAl2 O3 , TiyAl2 O3 , and Ta2 NyAl2O3 interfaces are characterized using the continuous microscratch technique. The aim of the study is threefold. First, can the practical work of adhesion be determined accurately and reproducibly using the continuous microscratch technique for a variety of film thicknesses? Second, can the practical work of adhesion be determined if the metal/ceramic system is annealed to produce interfacial reaction products that changed the adhesion strength? For example, for the PtyNiO system, heat treatments at reduced oxygen partial pressures result in diffusion of Ni into the Pt, which produces either an intermetallic, NiPt, at the interface or a solid solution of Ni in Pt.1–3 Finally, can the true work of adhesion J. Mater. Res., Vol. 11, No. 12, Dec 1996
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be determined for unreacted and reacted metal/cer
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