Effects of ceric ammonium nitrate (CAN) additive in HNO3 solution on the electrochemical behaviour of ruthenium for CMP processes

In order to develop a new chemical mechanical polishing process for ruthenium (Ru), the present work deals with the effect of a ceric ammonium nitrate (CAN) additive on the electrochemical behaviour of physical vapour deposited Ru films in a 1 M HNO₃ solution employing electrochemical methods and surface analytical techniques. By adding CAN to HNO₃ solution, the polarisation curves showed an increase in the corrosion potential and current, suggesting that Ru is anodically polarised by CAN as an oxidising additive. To characterise the influence of CAN, open-circuit potential (OCP) and potentiostatic anodic current transient curves were examined in CAN-containing HNO₃ solution and the resulting surfaces were then characterised by scanning electron microscopy and X-ray photoelectron spectroscopy. It is proposed that Ru is oxidised to heterogeneous Ru₂O₃ and RuO₂ films on the Ru surface in CAN-containing HNO₃ solution and galvanic corrosion occurs at grain boundaries, caused by the difference in OCP between the grain interiors and boundaries. The grain boundaries are oxidised to RuO₄, a volatile species, resulting in a roughened and porous structure.