| Summary: | Non-uniformity in chemical-mechanical planarization (CMP) due to diverse pattern geometry in copper damascene structures has been a critical limit to process yield. Fundamental understanding in tribology and electrochemistry is crucial to solve this problem. This research develops novel triboelectrochemical techniques to characterize the polished wafer surface and to understand mechanisms of materials removal. There are two approaches in this research. Experimentally, a setup containing a tribometer and a potentiostat was built. It enabled simultaneous measurement in friction coefficient and electrochemical response of wafer materials. Theoretically, electrochemical reactions and Hertzian contact were analyzed on ECMPed wafers in terms of mechanisms of step height reduction in anodic and cathodic ECMP in corresponds to surface chemistry. Results revealed the nature of limitation of ECMP for global planarization.
In order to further the fundamental investigation of ECMP, the potentiostatic electrochemical impedance spectroscopy (EIS) was utilized to study the interface kinetics. It was revealed that the formation of Cu oxide films was affected by the electrical potentials. Through in situ measurement, it was found that the tribological behavior depend on the surface chemistry and surface morphology under the influence of anodic potentials. The potentiodynamic polarization results explained the removal and formation mechanisms of interface. The results showed that the cycle of passivation/removal was a function of mechanical factor such as the load and speed.
The new model was developed via material removal rate (MRR) in both electrochemical and mechanical aspects. The quantitative contribution of electrochemical potential to overall removal was established for the first time. It was further confirmed by Ru and the electrochemical constant j was developed for metal ECMP.
This dissertation includes seven chapters. Chapter I Introduction and II Motivation and Objectives are followed by the materials setup and testing conditions discussed in Chapter III. The tribological and electrochemical characterization of the Cu patterned geometry is discussed in Chapter IV. Chapter V discusses the kinetics of the interface during polishing and its removal mechanisms. Chapter VI discusses the synergism of ECMP, followed by Conclusions and Future work.
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