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

利用极小尺寸器件实现超高速集成电路，需要在器件结构的核心大量使用低阻金属。为此，开发高质量的金属薄膜形成技术、理想的金属/硅接触形成技术和低温加工技术至关重要。通过采用超清洁技术，我们在这些技术上取得了巨大的成就。利用低动能粒子轰击法制备了高质量的金属薄膜。通过优化离子能量和通量条件以及采用低能H_2等离子体清洗技术，获得了良好的表面光洁度。采用低能离子轰击和后续热退火相结合的方法，在SiO_2上生长出了几乎单晶的Cu薄膜。由此形成的铜互连具有非常大的抗电迁移故障的能力，与传统的人工智能互连相比，确保了3到4个数量级的寿命。通过将这些成膜工艺与干净的氮密封工艺相结合，可以成功形成理想的金属/硅界面。金属在器件结构中心的使用很大程度上取决于pn结形成的温度。我们已经开发了超净离子注入技术，使我们能够在低至450℃的温度下退火As注入硅。我们利用这种低温退火工艺制备了金属栅自对准MOSFET。实验表明，当栅极电容负载大到足以驱动大电流时，金属栅极MOSFET的工作速度比硅栅极MOSFET快得多。因此，超高速器件制造所需的基本技术以及采用这些先进工艺的实际器件结构已在本研究项目中成功开发。

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.