Previous studies of the size dependent properties of LiFePO4 have focused on the diffusion rate or phase transformation pathways by bulk analysis techniques such as x-ray diffraction (XRD), neutron diffraction and electrochemistry. In this work, in situ Raman spectroscopy was used to study the surface phase change during charge and self-discharge on a more localized scale for three morphologies of LiFePO4: (1) 25 ± 6 nm width nanorods, (2) 225 ± 6 nm width nanorods and (3) ∼2 μm porous microspheres. Both the large nanorod and microsphere geometries showed incomplete delithiation at the end of charge, which was most likely caused by anti-site defects along the 1D diffusion channels in the bulk of the larger particles. Based on the in situ Raman measurements, all of the morphologies studied exhibited self-discharge with time. Among them, the smallest FePO4 particles self-discharged (lithiated) the fastest. While nanostructuring LiFePO4 can offer advantages in terms of lowering anti-site defects within particles, it also creates new problems due to high surface energies that allow self-discharge. The in situ Raman spectroscopy also showed that carbon coating did not provide significant improvement to the stability of the lithiated particles.

We examined a new Li-ion battery system based on the combination of a high voltage LiMn0.8Fe0.2PO4 (LMFP) cathode with a Li4Ti5O12 (LTO) anode. Due to the relatively high red-ox voltage of LTO (1.5 V vs. Li) and the excellent stability of its spinel structure, as well as the fact that the red-ox potential of a Li[MnFe]PO4 cathode, up to 4.1 V, does not endanger the anodic stability of a standard electrolyte solutions, it is assumed that such cells can be safe, stable, highly reversible, and suitable for load-leveling applications. The LMFP/LTO cells exhibited excellent rate capability and cycle life at 30°C, delivering discharge capacity of 153, 152, 146, and 118 mAhg−1 (cathode) at 0.1 C, C, 2 C, and 5 C rates. These cells demonstrated excellent high temperature performance when the LTO anodes were pre-passivated before cell operation. By XRD and ICP analyzes of C-LiMn0.8Fe0.2PO4 electrodes before and after charge/discharge cycles, the capacity fading of these systems at high temperatures was attributed to depletion of active Li from the electrodes, due to side reactions on the anode side. These were avoided by pre-passivation of the LTO electrodes. The surface chemistry of Li4Ti5O12 anodes was investigated with the anodic surface reactions arising mainly from the salt (LiPF6).

As the technology nodes in integrated circuit (IC) fabrication continue to approach molecular dimensions, the defectivity and planarization provided by conventional chemical mechanical planarization (CMP) processes are no longer sufficient. Therefore, it is necessary to develop new chemistries and innovative screening techniques to solve difficult CMP challenges, including the use of new materials such as cobalt in advanced IC fabrication. For advanced nodes at 14 nm and below, cobalt is currently being implemented on top of Ta/TaN barrier layers and below the copper seeds for the first few metal lines, due to its better conformational coverage within high aspect ratio features and good adhesion to copper. In addition, replacing copper with cobalt in the trenches of interconnect lines for the first few metal layers in the BEOL has demonstrated lower resistivity at smaller dimensions, therefore cobalt interconnects are being considered for < 10 nm nodes for M1 and M2. All these new integration schemes require CMP to achieve planarity with requirements such as low dishing, defectivity, roughness, and tunable selectivity depending on the stack. Under CMP conditions, however, cobalt can suffer from corrosion and static-etch issues, especially when in contact with copper (galvanic corrosion), due to the lower standard reduction potential of cobalt in aqueous solutions across a broad pH range. The corrosion issues must be solved in CMP slurries that deal with cobalt processes (both liner and bulk/plug) to successfully commercialize cobalt-based IC design for next generation semiconductor manufacturing. In this poster, we will discuss the results and learnings from corrosion inhibitor screening techniques such as electrochemical, static-etch, and quartz crystal microbalance (QCM) studies and their correlation with polishing results for developing cobalt slurry formulation platforms. Furthermore, fundamental understanding on the effects of pH and slurry components such as complexors/oxidizers/corrosion inhibitors on the corrosion and removal rate behavior of cobalt films will be discussed.

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In advanced nodes at 10 nm and below, cobalt (Co) metal is under investigation to replace copper (Cu) in metal lines and vias in back end of line (BEOL) for the first few metal layers due to its better electromigration performance, lower resistivity, conformal coverage in high aspect ratio features, and overall improved device performance. These new integration schemes require Co chemical mechanical planarization (CMP) steps to achieve planarity and desired target thickness. However, Co metal is prone to corrosion in aqueous solutions and its lower redox potential makes it an easy galvanic corrosion target under CMP conditions. Commercial Cu bulk slurries are not compatible for Co polishing as they show significant corrosion defects such as pitting, rough surface, and missing lines after CMP. Advanced Co bulk CMP slurries, therefore, need to contain effective chelator, corrosion inhibitor, and additives at suitable slurry pH to eliminate corrosion defects, while still delivering high Co removal rates (2000 to 5000 Å/min). In this presentation, we will discuss the systematic approach taken to develop a Co bulk CMP slurry formulation platform that can provide high removal rates and low/no corrosion, through development of fundamental understanding of Co surface chemistry, chelation, and corrosion properties. Results and key learnings from the extensive screening techniques such as Tafel polarization, galvanic corrosion, static-etch corrosion, quartz crystal microbalance, and X-ray photo electron spectroscopy analyses used to identify the ideal slurry pH, effective chelators, and corrosion inhibitors will be shared. In addition, Co blanket and pattern wafer polishing performances will be presented for the leading slurry formulations.