Material Characterization in the Electro-Analytic Approach for Applications in Chemical Mechanical Planarization and Electrochemical Energy Systems

The work presented in this thesis covers electro-analytical characterization for multiple applications in material science. Electrochemical techniques were used to investigate soluble film formation on metals used in chemical mechanical planarization in order to better understand the removal rate process by studying new chemicals proposed by groups in industry. Second, an ionic liquid was used as an electrolyte in a lithium ion cathode half cell to show the essential functionality of the IL and the temperature advantage over traditional electrolytes. Lastly, a comprehensive measurement for charge recombination in dye-sensitized solar cells was performed using both open-circuit voltage decay and impedance spectroscopy, which may be used to better understand the limiting factors that affect the cell's efficiently. Electrochemical techniques were applied to new methods and materials to extend the development of material manufacturing and advance the measurement process.;The fabrication of interconnect structures for semiconductor devices requires low down-pressure chemical mechanical planarization (CMP) of Ta barrier layers. Guanidine carbonate (GC) serves as an effective surface-complexing agent for such CMP applications, where the rate of Ta removal can be chemically controlled through pH-tuned selectivity with respect to the removal of Cu lines. Electrochemical techniques are employed in this work to study the surface-modifying roles of GC that make this chemical an attractive complexing agent for Ta CMP. In addition, the effects of including H2O2 (an oxidizer) and dodecyl benzene sulfonic acid (DBSA, a dissolution inhibitor for Cu) in GC-based CMP solutions are investigated to examine the selective CMP mechanisms of Ta and Cu in these solutions. The results suggest that the removal of Ta is supported in part by structurally weak guanidinium-tantalic-acid surface complexes formed on Ta/Ta2O5. The bicarbonate/carbonate anions of GC also facilitate Ta removal through the generation of ion-incorporated tantalum pentoxide. DBSA strongly affects the CMP chemistry of Cu, but exhibits relatively weaker effects on the surface activity of Ta, and thus plays a vital role in dictating the selectivity of Ta:Cu polish rates.;CMP of tantalum nitride is also an essential step of material processing in the fabrication of integrated circuits, which is looked separately in this thesis. The present work investigates certain chemical aspects of this strategy of TaN-CMP by also using guanidine carbonate (GC) as a surface complexing agent, and employing electrochemical experiments. The experiments are designed to study the chemical and electrochemical origins of the CMP-specific surface complex films formed on a TaN wafer in acidic solutions of GC and hydrogen peroxide. Open circuit potential, polarization resistance, and electrochemical impedance measurements are employed to probe the surface effects that facilitate material removal in chemically prevailing CMP of TaN. The results are discussed in view of designing slurry variables to support barrier layer planarization with reduced roles of mechanical abrasion.;Nonvolatile and nonflammable ionic liquids (ILs) have distinct thermal advantages over the traditional organic solvent electrolytes of lithium ion batteries. However, this beneficial feature of ILs is often counterbalanced by their high viscosity (a limiting factor for ionic conductivity) and, sometimes, by their unsuitable electrochemistry for generating protective layers on electrode surfaces. In an effort to alleviate these limiting Aspects of ILs, we have synthesized a PEGylated imidazolium bis(triflouromethylsulfonyl)amide (bistriflamide) IL that exhibited better thermal and electrochemical stability than a conventional electrolyte based on a blend of ethylene carbonate and diethyl carbonate. The electrochemical performance of this IL has been demonstrated using a cathode consisting of ball-milled LiMn2O4 particles. A direct comparison of the ionic liquid electrolyte with the nonionic low-viscosity conventional solvent blend is presented.;Charge recombination at the electrolyte-photoanode interface of a dye sensitized solar cell (DSSC) is a major efficiency-limiting factor of the cell. To mitigate this recombination effect it is necessary to ensure that the effective electron lifetime in the DSSC is longer than the electron's transit time across the photoanode of mesoporous TiO2. While the efforts aimed at accomplishing this goal are often based on new materials/designs of photoanodes, a quantitative evaluation of these designs relies on the precision of the benchmarking measurements of electron lifetimes. The open circuit voltage decay (OCVD) technique offers an effective yet straightforward method for such measurements. The present work focuses on certain experimental criteria for ensuring the accuracy of these experiments, and probes the associated effects of temperature variations in the solar cell. The results demonstrate that, a high rate of data sampling is essential for adequately resolving the fast initial stages of charge recombination. The results also show the effects of nonlinear recombination where second order OCV variations are operative. The findings of the OCVD experiments are compared with a parallel set of tests carried out using impedance spectroscopy. The relative roles of the two sets of analytical measurements are examined.