Abstract
Integrated circuits with aluminum metallization for products with high current densities need a metal stack with liner and antireflective coating (ARC) which can fulfill several requirements (e.g. low sheet resistance, high reliability, smooth surface, good adhesion, thermal stability, etc.). In this work different multilayer metal stacks are investigated and several phenomena which can be observed after thermal annealing of Ti/TiN/AlCu/TiN stacks are described and discussed. Metallurgical, electrical and mechanical properties of different layer combinations are investigated after thermal annealing and stress tests are done to compare the electromigration and life time behavior of each metal stack. For all investigated metal stacks it is shown that an interface reaction between Ti and aluminum will form TiAl3 phase. Even with very thick TiN layers on top of titanium or with only TiN liner the phase formation occurred. Explanations and models for the formation of different phenomena (hillocks, depressions and elevations), are discussed. The origin of each phenomena is stress related and assisted either by the liner material and/or the ARC layer. A qualitative model which explains the different observed layer reactions is discussed.
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