COPPER METALLIZATION FOR ULSI AND BEYOND

The investigation of copper for use as an interconnection metal in the ultra large-scale integration (ULSI) era of silicon integrated circui ts has accelerated in the past several years. The obvious advantages f or using copper to replace currently used Al are related to its lower resistivity (1.7 mu Omega-cm vs. 2.7 mu Omega-cm for Al) and its highe r electromigration resistance (several orders of magnitude higher comp ared with Al). The goal of this review is to examine the properties of copper and its applicability as the interconnection metal. A comparis on of electromigration behavior of various possible interconnection me tal in standard ''bulk'' state is made. This is followed by a review o f the calculations made comparing (a) the RC (resistance x capacitance ) time constants of various material systems and (b) the joule heating of the interconnection materials. A comparative study of various meta l systems for the application as the interconnect metal is then made. These discussions will clearly establish the superiority of copper ove r other metals despite certain limitations of copper. We then review t he properties, both physical and chemical, and materials science of co pper. The concept of using alloys of copper with a minimal sacrifice o n resistivity to gain reliability is also discussed. This is followed by the review of the deposition, pattern definition and etching, passi vation, need of the diffusion barrier (DB) and adhesion promoter (AP), planarization and dual damascene process using chemical mechanical pl anarization, and reliability. This review shows that copper will satis fy the needs of the future integrated circuits and provide high perfor mance and reliability as long as we provide an appropriate barrier to diffusion in the underlying devices and the dielectric.