Cheng-Yu Wu

Effects of a new combination of additives in electroplating solution on the properties of Cu films in ULSI applications

Effects of a new combination of additives in acid electroplating solution on the properties of Cu thin films have been investigated. The electroplated Cu films exhibit an excellent superfilling behavior. 0.18 μm vias with an aspect ratio exceeding 5 were filled completely without any void or seam. Strong (111) texture was found for the electroplated Cu films. The resistivity of a 450-nm-thick Cu film was measured to be 1.84 μΩ cm.Effects of a new combination of additives in acid electroplating solution on the properties of Cu thin films have been investigated. The electroplated Cu films exhibit an excellent superfilling behavior. 0.18 μm vias with an aspect ratio exceeding 5 were filled completely without any void or seam. Strong (111) texture was found for the electroplated Cu films. The resistivity of a 450-nm-thick Cu film was measured to be 1.84 μΩ cm.

Diffusion barrier properties of metallorganic chemical vapor deposited NbNxOyCz films for Cu metallization

Abstract Amorphous NbN x O y C z films were deposited on SiO 2 by metallorganic chemical vapor deposition using ethylimidotris(diethylamido)niobium(V) [NEt=Nb(NEt 2 ) 3 ] source with and without ammonia (NH 3 ) at various temperatures. The diffusion barrier properties of NbN x O y C z films for Cu metallization were investigated. Both deposition temperature and resistivity of the film was found to decrease drastically upon the addition of NH 3 . The activation energy for the surface reaction was measured to be 0.71±0.05 eV in the temperature range of 500–600 °C and decreased to 0.23±0.04 eV by adding 20 sccm NH 3 in the temperature range of 300–425 °C. The NbN x O y C z films were found to be nearly amorphous. The concentration of C in films was reduced significantly and the concentration ratio of N to Nb was varied from 1.67 to 1.1 by using NH 3 as a reactant gas. Fifty-nanometer-thick NbN x O y C z film was found to effectively prevent the penetration of Cu into the substrate in samples annealed at 600 °C for 1 h. The barrier failure mechanism in NbN x O y C z is the diffusion of Cu through the barrier layer with the formation of niobium silicide.

Facile and controllable one-pot synthesis of nickel-doped LiMn0.8Fe0.2PO4 nanosheets as high performance cathode materials for lithium-ion batteries

To improve the kinetic performance of LiMn0.8Fe0.2PO4, a facile and controllable non-stoichiometric one-pot stepwise feeding solvothermal approach is successfully developed for preparing nickel-doped LiMn0.8Fe0.2PO4 nanosheets. LiMn0.8Fe0.19Ni0.01PO4 nanosheets, with an appropriate particle size, ideal lattice volume, smooth surface morphology and high phase purity, could be fabricated through trace amount of nickel doping, modest lithium hydroxide deficiency and stepwise feeding mode, and exhibit the optimal cycling performance and rate capability after carbon coating. After 200 charge/discharge cycles at 0.5C, the LiMn0.8Fe0.19Ni0.01PO4 cathode only slightly decreases to 148 mA h g−1, corresponding to the capacity retention of 94.1%. Even if increased to 10C and 20C, 75.7% and 65.2%, respectively, initial capacities at 0.1C can still be maintained. These results demonstrate that a suitable Ni2+ content and a rational synthesized route are helpful to improve electronic conductivity and Li-ion mobility.

Improvement of the Ar/N2 binary plasma-treated carbon passivation layer deposited on Li4Ti5O12 electrodes for stable high-rate lithium ion batteries

In this study, nanoscale carbon overlayers, with and without nitrogen doping, have been investigated as surface passivation layers to enhance the rate capability and cycling stability of Li4Ti5O12 (LTO). As indicated by optical emission spectroscopy, Raman spectra and high resolution X-ray photoelectron spectroscopy analysis, nitrogen successfully dopes into the carbon overlayer by Ar/N2 binary plasma irradiation, owing to the interaction between the carbon overlayer and chemically reactive plasma species such as N2+ and N. In addition, the results of SEM and XPS depth profiles also prove that the N-doped carbon overlayer can effectively suppress the formation of a resistive solid–electrolyte-interface (SEI) film. The electrochemical test results demonstrate that the LTO coated with N-doped carbon overlayer (NC-overlayer/LTO) exhibits superior capacity (133 mA h g−1) and excellent stability with 91% capacity retention over 300 cycles at a high C rate (10C). The excellent electrochemical performance of NC-overlayer/LTO can be attributed to the N-doped carbon passivation layer that effectively facilitates Li+ ion diffusion and reduces internal resistance.

Metal-organic chemical vapor deposition of NbxTa(1-x)NyOmCn films as diffusion barriers for Cu metallization

NbxTa(1−x)NyOmCn diffusion barriers deposited by chemical vapor deposition (CVD) for copper metallization have been investigated. The barriers were deposited at 375 °C with tetrakis-diethylamido-niobium and pentakis-diethylamido-tantalum as precursors. Amorphous thin films can be obtained by thermal deposition at temperatures from 500 to 600 °C. The activation energy of the metal-organic CVD (MOCVD) process was determined to be 79.1±4.8 kJ/mol. By the incorporation of NH3 gas into reactants, both MOCVD deposition temperature and carbon concentration in the NbxTa(1−x)NyOmCn films were reduced. In addition, NH3-plasma post-treatment was implemented to prevent oxygen from being introduced into the barrier films.

Rational design of a synthetic strategy, carburizing approach and pore-forming pattern to unlock the cycle reversibility and rate capability of micro-agglomerated LiMn0.8Fe0.2PO4 cathode materials

Nanometer-sized LiMn0.8Fe0.2PO4 (nano-LMFP) is one of the most suitable LiMnPO4 derived cathode materials to maximize gravimetric capacity and rate capability. However, the poor cycling performance, low volumetric energy density and safety hazards of nano-LMFP limit its large-scale commercialization. To overcome these development bottlenecks, a uniform three-dimensional interconnected conductive carbon network modified LiMn0.8Fe0.2PO4 nanoporous micro-agglomerated (micro-LMFP/C) composite was synthesized via a three-step solid-state reaction (3S) combined with three-step carburizing (3C) and two-step pore-forming (2P). The novel micro-LMFP/C composite exhibits excellent gravimetric/volumetric reversible capacities, weak electrochemical polarization and high rate capability. Even if increased to 20C, a satisfactory discharge capacity of 92.5 mA h g−1 (70.2% of the initial value at 0.1C) and an outstanding discharge plateau of 3.76 V can be observed. More importantly, for the 3S synthetic strategies, the novel 3C2P-assisted synthesis of micro-LMFP/C composites can simultaneously deliver 2.6 and 1.5 times higher volumetric capacity than that of synchronous and stepwise carburizing assisted synthesis of samples, respectively.