High-quality Co films with low resistivity ͑10 ⍀ cm͒ were deposited by plasma-enhanced atomic layer deposition ͑PE-ALD͒ from metallorganic precursors and NH 3 plasma. The deposition characteristics and film properties were investigated. Especially, we compared the results using two cyclopentadienyl Co precursors, CoCp͑CO͒ 2 and CoCp 2 . While low resistivity Co films were deposited by both precursors, much better self-limiting behavior was observed for CoCp 2 . Rutherford backscattering and X-ray photoelectron spectroscopy analysis have shown that the impurity contents in PE-ALD Co film were very low. CoSi 2 formation by post deposition annealing with Ti capping layer was studied by synchrotron X-ray diffraction.The contact resistance increase with decreasing line width for the source/drain contact using TiSi 2 as a contact material poses a serious problem with device scaling. 1 CoSi 2 has been studied as an alternative due to its immunity to the shrinkage of line width, low resistivity, and thermal stability. 2,3 In other words, the sheet resistance of CoSi 2 remains almost constant with scaling down while that of TiSi 2 steeply increases. The effect is routinely mentioned as a fine line effect. 4 Sputtering has been a standard deposition technique for Co, which is annealed to form CoSi 2 contact through self-aligned silicide process. In current dynamic random access memory ͑DRAM͒ technology, stacked capacitor structure has benefits over trench capacitor for abiding by the scaling down of the memory devices. 5 For stacked capacitor structure, however, the capacitor-over-bitline ͑COB͒ requires that the contact material should be formed in deep contact holes with high aspect ratio. Thus, inherent poor step coverage of sputtering is becoming more problematic for sub-50 nm technology node high density DRAM fabricaiton. 6,7 Atomic layer deposition ͑ALD͒ is a promising deposition technique in the nanoscale regime due to its excellent conformality and thickness controllability at atomic scale. However, ALD of Co has rarely been reported except for recent reports using laboratorysynthesized acetamidinate precursor, without detailed film properties. 8,9 The ALD of high-quality Co using commercially available Co precursors is important for the implementation of Co ALD for nanoscale device contact fabrication. In this study, we developed a plasma-enhanced ALD ͑PE-ALD͒ process using metallorganic ͑MO͒ precursors and NH 3 plasma. High purity Co thin films with low resistivity, close to the bulk value, were successfully deposited using various metallorganic Co precursors, including biscyclopentadienyl Co ͑CoCp 2 ͒ and cyclopentadienyl dicarbonyl Co ͑CoCp͑CO͒ 2 ͒. We compared the growth characteristics and film properties of PE-ALD from these two cyclopentadienyl Co precursors.A remote plasma-enhanced ALD system was built and used in this study. A detailed configuration of the chamber can be found in our previous report. 10 To produce adequate vapor pressure, the temperature of the bubbler containing CoCp 2 ͑solid͒ was maintai...

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The influence of radiation-induced (1 MeV energy H+ to ∼0.1 displacements per atom (dpa) at 450 °C), nonequilibrium point defect populations on mass transport is studied with an integrated campaign of experimental and theoretical methods. Using epitaxial thin films of hematite (α-Fe2O3) with embedded 18O tracer layers and nanoscale atom probe tomography measurements, it is shown that anion self-diffusion is enhanced by at least 2 orders of magnitude under irradiation compared to thermal diffusion alone. Complementary scanning transmission electron microscopy of vacuum-annealed and irradiated specimens reveals associated microstructural changes near the surface of the oxide films, including local phase transformation to Fe3O4 and the development of nanoscale voids from vacancy coalescence. Point defect formation and migration energies were computed from density functional theory and applied within the context of the chemical rate theory to analyze contributions from both interstitial and vacancy mechanisms to self-diffusion in thermal and irradiation conditions. Comparisons are made between calculated, literature, and newly measured self-diffusion values, revealing good agreement on the magnitude of radiation-enhanced anion diffusion. Further, the model suggests a transition from vacancy to interstitialcy mechanisms at low temperatures and high oxygen activity, providing an explanation for the varied activation energies reported from prior studies.

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