Ultra-clean processing for ULSI

Abstract

The simultaneous fulfilment of three principles, viz. ultra-clean water surface, ultra-clean processing environment, and perfect process-parameter control, is the key to high-performance fabrication of advanced subhalf-micron and subquarter-micron ULSI devices. The importance of this ultra-clean processing concept is demonstrated by the experimental results of low-temperature silicon epitaxy by low-kinetic-energy Ar ion bombardment. By optimizing process parameters under ultra-clean conditions, high-crystallinity silicon epitaxial layers are successfully grown at temperatures as low as 250°C, with accompanying simultaneous doping. Advanced copper metallization for large-current driving interconnect is also achieved. Giant-grain copper thin films, also formed by low-kinetic-energy Ar ion bombardment, exhibit very low resistivity and excellent reliability against electromigration and stress migration. Native and chemical-oxide-free processing produces ideal metal-to-silicon contacts with very low resistance, i.e. 10 −9 Ω·cm 2. Ultra-clean—hydrogen-radical-balanced and surface-microroughness-free—oxidation is confirmed to form high quality, very thin oxide films of 5 to 10 nm, with complete uniformity and very strong resistance to hot electron injection. Low-temperature annealing ion implantation makes practical a metal gate self-aligned MOS LSI, which is crucial for high current driving capability in high-speed CMOS. All of these advanced fabrication technologies, realized for the first time by ultra-clean techniques, allow total low-temperature processing, such as gate oxidation at 450°C, implanted region annealling at 450°C and single-crystal silicon epitaxy at 300°C, which is essential for high-performance subhalf-micron and subquarter-micron ULSI. Oxide layer-free metal-to-silicon and metal-to-metal film deposition is freely available in ultra-clean processes, so that field-programmable anti-fuse technology is achievable by current drive silicidation as well as by very low resistance metal/silicon and metal/metal contact.