Person:

Yang, Jing

An interlayer of face centered cubic (fcc) Co4N has demonstrated significant improvements in adhesion between copper and diffusion barrier layers. This fcc phase of Co4N was prepared by chemical vapor deposition (CVD) using bis(N-tert-butyl-N′-ethyl-propionamidinato)cobalt(II) and a reactant mixture of NH3 and H2 at substrate temperatures from 100 to 180°C. The Co/N atomic ratio and the phase of cobalt nitride film can be modified by adjusting the ratio of NH3 and H2 in the gas feedstock. The cobalt nitride films prepared by CVD are smooth, highly conformal, and stable against intermixing with copper up to at least 400°C. This fcc cobalt nitride material has very strong adhesion to copper due to the small lattice mismatch (−1 to 2%) between (fcc-Co_4N) and fcc Cu. Copper wires should be stabilized against failure by electromigration when fcc cobalt nitride interlayers are placed between the copper and surrounding diffusion barriers.

In microelectronics, the device size continues to shrink to improve the performance and functionality, which sets technical challenges for the integrated circuit (IC) fabrication. Novel materials and processing techniques are developed to maintain excellent device performances and structural reliability. Cobalt-based thin films possess numerous applications in microelectronics with the potential to enhance the device performance and reliability. This thesis explores the fabrication, characterization and application of cobalt-based thin films for microelectronics. Chemical vapor deposition (CVD) technique has been applied for depositing cobalt-based thin films, because CVD can produce high quality thin films with excellent conformality in complex 3D architectures required for future microelectronics.

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. %.