XRR metrology for advanced interconnect material process characterization

Ta-based films were deposited with various nitrogen flows during processing to produce films with different nitrogen contents. Rutherford Back-Scattering Spectroscopy (RBS), Transmission Electron Microscopy (TEM), Four-Point Probe, photo-acoustic metrology, and a newly introduced, Rapid X-ray Reflectometry (RXRR) technique were utilized to make thickness, sheet resistance, stoichiometry, and density measurements. Thickness results obtained by the RXRR technique are shown to be comparable with data from RBS, TEM and photo-acoustic techniques. However, thickness differences, alone, are not sufficient to determine microstructural variations due to changes in TaN stoichiometry. The RXRR technique provides additional material independent data, such as density and reveals significant clues about stoichiometry differences caused by modifications to process conditions. The ability for this tool to non-destructively measure wafers at a rapid speed and determine necessary process control parameters, while providing material independent film characterization, sets this method apart from many others. RXRR measurements from hybrid PVD/MOCVD Ti/TiN liner/barrier stacks for W-plugs are presented as a function of subtle changes in process conditions. It is shown that minor alterations in liner/barrier stack process conditions can have a major effect on barrier characteristics, since stack substructure depends on both thickness and density differences, which are highly dependent on process subtleties, unlike conventional PVD Ti/TiN films. The independent thickness and density measurements made with this tool, are shown to be valuable to understand process behavior and identify yield-impacting process excursions for advanced interconnect processes.