On the optimization of VLSI contacts

The contact-resistance characteristic of silicon devices has been a subject of research and development since the early days of silicon integrated-circuit technology. The contact-chain losses suffered by very large scale integration (VLSI), however, have made the minimization of contact resistance a critical parameter due to the large number of contacts per circuit and due to the increase of contact resistance with decreasing contact size. This paper will present a brief review of the theory of contact resistance, the literature, measurement techniques, and of the transmission-line model (TLM) for analyzing contact-resistance data. Contact-resistance data pertaining to shallow high-conductivity contacts for VLSI will be presented as a function of the junction parameters (implant dose, etc.) and of the contact area for BF2and arsenic implants with aluminum-silicon metallization. Contact-resistance data for a sputtered molybdenum silicide contact barrier for boron and arsenic implants versus contact area will also be presented and compared to the aluminum-silicon control samples with a discussion regarding the uniformity of contacts to silicon.