On the Manifestation of Ge Pre-Amorphization Implantation (PAI) in Forming Ultrathin TiSix for Ti Direct Contact on Si in Sub-16/14 nm Complementary Metal-Oxide-Semiconductor (CMOS) Technology Nodes

Abstract

From the 22 nm 3D FinFET technology node, the Ti silicide-last contact scheme based on ultrathin TiSix (0 < x< 2) has replaced the Ni(Pt)Si employed widely in previous planar CMOS nodes, due to its inherent advantages. Most work on Ti direct contacting with Si focuses on improving the specific contact resistivity (ρc) by all means. The detailed investigation on the formation of ultrathin TiSix at relatively low temperature (≤600°C), is, however, rarely reported. In this work, a fundamental material’ study of the formation of ultrathin TiSix on highly P-doped Si substrates with different Ge pre-amorphization implantation (PAI) conditions is described, for the future application in Ti direct contact scheme on n-Si. The sheet resistance (Rsh), phase identity, morphology, as well as the elemental distribution for the resulting TiN/Ti/TiSix stacking films were characterized using four-point probe measurements, X-ray diffraction (XRD), Secondary Ion Mass Spectrometry (SIMS), cross-sectional transmission electron microscopy (XTEM) in conjunction with energy-dispersive X-ray spectroscopy (EDX), and Nano-Beam-Diffraction (NBD). It is found that Ge PAI can significantly promote the Ti silicidation at relatively low temperature, which is also consistent with previous publications. The optimal temperature for Ti silicidation is ∼550°C, at which amorphous Si (α-Si) caused by Ge PAI is crystallized by Solid Phase Epitaxial Regrowth (SPER), while the silicidation process is also adequate. Across as-formed TiSix films, the composition is not constant and altered from Ti-rich at the metal side to Si-rich at the Si substrate side. Furthermore, the as-formed ultrathin TiSix film is proposed to be not completely amorphous, instead it is a mixture of amorphous TiSix embedded with numerous fine grains at the early growth stage.