Chemical mechanical polishing (CMP) of metals has emerged as a critical process step for the fabrication of advanced integrated circuit devices in the semiconductor industry. In a typical metal CMP process, the metal film is blanket deposited to fill recessed features on a patterned dielectric on silicon. Following metal deposition and gap fill, the metal overabundance is polished away by CMP, leaving an inlayed metal pattern or damascene structure on the substrate. Removal of the metal overabundance also planarizes the wafer surface for subsequent processing steps. The material removal process occurring during CMP is thought to involve the combined action of chemical oxidation and dissolution, and mechanical removal of material by abrasives. However, the relative contribution of mechanical and chemical effects during metal CMP is not well understood. The objective of this research was to characterize the fundamental electrochemical behavior of tungsten and aluminum thin films in polishing chemistries of interest to CMP. It was also of interest to determine the extent to which electrochemical oxidation and dissolution, or mechanical removal by abrasive action assists in material removal during CMP. A simultaneous electrochemical tester and polishing tool was developed to characterize the electrochemical behavior of tungsten and aluminum during and after abrasion. Small-scale polishing experiments were also carried out to measure polishing (removal) rates of the metals during CMP. Electrochemical dissolution rates and polishing rates were compared. It was found that the electrochemical dissolution rate of tungsten or aluminum during or after abrasion was very small compared to actual polishing rates. However, the presence of an oxidant enhanced polishing rates dramatically. The findings indicate that the mechanism for removal during CMP is primarily corrosion assisted metal removal, and not electrochemical dissolution and/or removal of the oxidation product of the metal.
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