Strategy of future ULSI metallization

Contact and interconnect are two major issues in ULSI metallization. TiSi₂ is currently the most commonly used silicide in IC industry. CoSi₂ has been introduced to replace TiSi₂ in sub-quarter micron technology. However, its use in sub-0.1 micron devices is in doubt unless raised source/drain scheme becomes feasible. NiSi is the only silicide left with comparable resistivity with TiSi₂ and CoSi₂. On the other hand, ingenious scheme may be found to utilize metal layer as contacts as illustrated for several refractory metal/Si systems. For interconnects, technology for Cu interconnect is being heavily invested and Cu chips are implemented. Au and Ag interconnects are being explored. In this paper, recent progresses in developing UHV-CVD selective epitaxial Si as raised source/drain, NiSi and refractory metals as contact, Au and Ag as interconnects will be reviewed. Their viability for device applications will be discussed.