| Summary: | 博士 === 國立清華大學 === 化學工程學系 === 91 === Void-free electroplating for IC copper interconnects was examined theoretically and experimentally. In Chapter 2, a theoretical model based on electrochemistry and thermodynamic calculation for species’ microscopic concentrations was developed to discuss the effect of base electrolyte concentration on the wafer-scale deposition uniformity and the feature-scale filling ability. The results show that the competitive effects of kinetic resistance to ohmic resistance and the reaction flux to the diffusion flux govern the deposition uniformity and the filling ability, respectively. Inverse contribution of CuSO4 and H2SO4 for deposition uniformity or filling ability was found. Process operation could be divided into two regions, concentration-preferred and kinetic-preferred. The model was also extended to simulate a 12-inch wafer to show the uniformity of the filling ability. Simulation results were compared to experiments and good agreement was found.
According to the adsorption study of PEG on copper electrode at 1ASD (1 A dm-2), a void-free deposition by single additive is achievable. The idea of developing a single additive system was raised from the characteristics of current-potential response of acid copper sulfate bath with PEG, Cl- and their combination. Surface coverage of adsorbent could be obtained by either chronopotentiometry (calculated by the equation derived in this study) or EIS (calculated by Frumkin’s parallel plate model). Adsorption isotherm was fitted to Toth isotherm and good agreement was found. Large negative value of the standard free energy for PEG adsorption implies the strong adsorption of PEG on copper surface. Results derived by CV and adsorption study suggested a new filling mechanism called “uneven adsorption mechanism” induces the super-filling. The shortcomings of the previous two filling mechanisms were also discussed in Chapter 3.
In Chapter 4, a theoretical model was proposed to involve the effect of hydrodynamics on the adsorption kinetics of PEG. Some assumptions were applied to estimate the fluid flow condition inside the submicron trench. In combination with adsorption kinetic parameters experimentally determined, the model provides a theoretical support for the occurrence of uneven adsorption in moderate PEG concentration.
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