Effective schottky barrier lowering for contact resistivity reduction using silicides as diffusion sources

Abstract

In this work we present a potential solution for forming ultra-shallow junctions with extremely low contact resistivities in which dopants are implanted into silicides and diffused to the semiconductor interface using low temperature anneals. Conventional silicide process requires a fine tuning of silicide thickness and deep source/drain doping profile to achieve low contact resistance and low source/drain diffusion sheet resistance. With the silicide implantation approach, we show that they can be engineered independently, providing a larger design space for the reduction of total external resistance. We demonstrate that contact resistance for NiPt silicide can be significantly reduced down to 7×10-9-cm2 for p+ Si and 6×10-9-cm2 for n+ Si by using Schottky Barrier Height (SBH) tuning through the implantation of B/As into pre-formed NiPtSi followed by low-temperature drive-in annealing (see Fig. 1 for the process flow). Moreover, we find that the same low contact resistance can be achieved for both heavily and moderately doped junctions, which grants an additional degree of freedom in junction design to reduce series resistance. With this technology, the ultra-shallow junction process can be simplified to the formation of ultra-thin silicide followed by shallow implantation and low temperature RTA (<600C) without any demand of ultra-high thermal budget for the S/D doping. Implantation into silicides, as an alternative to surface implantation prior to silicidation, prevents silicide morphology degradation (encroachment, roughness, or inverted pyramids) induced by extra defects from the surface implantation. © 2010 IEEE.