ADHESION OF THIN-FILMS OF EVAPORATED TITANIUM-COPPER AFTER ELECTROPLATING

Titanium-palladium-gold is a highly reliable multilayer metallization for thin-film integrated circuits. Efforts to reduce the amount of Au and hence the cost of the circuits have led to development of a Ti-Cu-Ni-Au metallization. This system is fabricated by selectively electroplating Cu-Ni-Au onto evaporated Ti-Cu. During the introduction of the new metallization into manufacture, it was observed that evaporated Cu frequently delaminated from evaporated Ti after Cu-Ni-Au plating. The factors investigated were the nature of the substrate surface, residual gas pressure during evaporation of the Ti and/or Cu, thickness of the evaporated Cu, various combinations of plated films and postplating heat treatment. Adherence was evaluated by a tape test, thermocompression bonding and pull testing of leads, and by a simple substrate break-and-peel test. In-depth profiles of the evaporated TiCu interface were obtained by sputter removal and Auger electron spectroscopy techniques. Oxidation of the evaporated Ti layer at pressures greater than 2. 7 multiplied by 10** minus **4 Pa prior to evaporation of the Cu layer was found to be a significant factor leading to subsequent delamination after electroplating. Solutions to the delamination problem include optimization of the evaporation equipment, use of a thin layer ( similar 150 A) of Pd between the Ti and Cu, elimination of a distinct interface between the Ti and Cu by coevaporation techniques to produce a graded film, or sputtering of the films rather than evaporation.