Electrochemical investigation of the surface-modifying roles of guanidine carbonate in chemical mechanical planarization of tantalum

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.

► This work contributes to the development of CMP slurries for Ta and Cu at low pressure.
► We present here a model of the chemical mechanism of the CMP of Ta and Cu using guanidine slurries.
► Removal of Ta occurs as structurally weak guanidinium–tantalic-acid surface complexes.
► The results will be useful for the CMP processing of interconnects with low-k dielectrics.
► We demonstrate the utility of electro-analytical techniques in the development of CMP slurries.