Applications of Ni-based silicides to 45 nm CMOS and Beyond

Abstract

This paper presents an overview of Ni-alloy (Ni, Ni-Pt and Ni-Ta) silicide development for the 45 nm node and beyond, including applications to self-aligned silicide (SALICIDE) processes, reaction with SiGe and strained Si on SiGe, and applications to fully silicided (FUSI) gates. Key SALICIDE issues addressed include the use of spike or low temperature rapid thermal processes (RTP) to control silicidation and junction leakage on small features, factors affecting the formation of epitaxial pyramidal NiSi₂ grains, and NiSi thermal stability and agglomeration kinetics. Alloying with Pt or Ta is shown to improve thermal stability of NiSi films, although with quite different behaviors. While Pt is incorporated predominantly in solution in NiSi, Ta segregates to the surface of the films. Ni-Pt alloy silicides were also found to achieve low sheet resistance on narrow gates, low contact resistivity and low junction leakage, making them attractive for CMOS applications. For the Ni/SiGe reaction, a narrower RTP process window for low sheet resistance and a lower activation energy for agglomeration were observed when compared to the Ni/Si reaction. The lower thermal stability was correlated to Ge segregation from the Ni(SiGe) films. The Ni/doped poly-Si reaction was studied for FUSI gate applications, showing a retardation of the silicidation kinetics for high B doses and a large pile- up of dopants (for As, B or P) at the NiSi/SiO₂ interface due to dopant snowplow during silicidation. The work function (WF) of NiSi was observed to shift with the addition of dopants, effect attributed to modifications of the interface dipole by the pile-up of dopants. No significant degradation was observed when comparing gate oxide breakdown statistics for Ni FUSI to conventional poly-Si gates. The process window for a FUSI gate-last process (performed after S/D Ni silicidation) was evaluated showing a potential integration problem due to possible degradation of the S/D silicide during the FUSI gate reaction.