Study on Ultra High Speed Integrated Circuit Employing Metals in the Heart of the Device Structure

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Realization of ultra high speed integrated circuits using ultimate-small dimension devices requires the abundant use of low-resistance metals in the heart of device structures. For this purpose, the development of technologies for high quality metal thin film formation, ideal metal/silicon contact formation and low temperature processing is most essential. We have attained great achievements in these technologies by employing ultra clean technologies.High quality metal films have been successfully grown using low kinetic-energy particle bombardment process. Excellent surface smoothness of Ta and Ti thin films have been obtained by the optimization of ion energy and flux conditions as well as by the employment of low-energy H_2 plasma cleaning techniques. Almost single crystal Cu thin films have been also grown on SiO_2 by the combination of low-energy ion bombardment and following thermal anneal. The Cu interconnects thus formed exhibit very large resistance against electromigration failure, ensuring 3 to 4 orders of magnitude larger lifetime as compared to conventional AI interconnects. By combining these film formation processes with clean nitrogen seal processing, ideal metal/silicon interfaces can be successfully formed. Use of metals in the heart of device structures very much depends on the temperature of pn junction formation. We have developed ultraclean ion implantation technology that enables us to anneal As implanted silicon at temperatures as low as 450ﾟC. We fabricated metal-gate self-aligned MOSFET's using this low temperature annealing process. It has been experimentally shown that the metal gate MOS transistor operates much faster than silicon gate MOSFET's when the gate-capacitance-load is sufficiently large for driving large current. Thus the basic technologies necessary for ultra high speed device fabrication as well as the actual device structures employing these advanced processes have been successfully developed in this research project.