Person:

Yang, Jing

The formation of smooth, conformal cobalt disilicide (CoSi2) without facets or voids is critical for microelectronic device reliability owing to the ultra-shallow contact areas. Here we demonstrate the formation of smooth and conformal CoSi2 films by chemical vapor deposition (CVD) of cobalt nitride (CoxN) films on silicon (Si) or on silicon on insulator (SOI) substrates, followed by in-situ rapid thermal annealing (RTA) at 700°C. To reveal the CoSi2/Si interfacial morphology, we report a back-to-front sample preparation method, in which mechanical polishing, anisotropic tetramethylammonium hydroxide (TMAH) wet etching, hydrofluoric acid (HF) wet etching, and isotropic xenon difluoride (XeF2) dry etching are employed to remove the SOI substrate from the back side to expose the CoSi2/Si interface. This method offers a robust and reliable procedure for quantitative assessment of the CoSi2/Si interfacial roughness, as well as analytical support for advanced fabrication process development.

Low-resistance and uniform contacts are needed for modern 3-D silicon transistors. The formation of high-quality and conformal nickel silicide at the interface between silicon and metal contacts is a possible solution. Direct-liquid-evaporation chemical vapor deposition is used to deposit nickel films conformally inside narrow silicon trenches. The deposited Ni is then reacted with a silicon substrate to form nickel monosilicide. Atom probe tomography (APT) is used to find and count the atoms in nanoscale regions inside these 3-D structures. APT shows that these NiSi films are stoichiometrically pure, single-phase, and conformal even inside trenches with high aspect ratios. The APT technique measures all impurities, including carbon, nitrogen, and oxygen, to have concentrations less than 0.1 at. %.