Synergy of Ammonium Oxalate and Hydrogen Peroxide on the Dissolution of Copper at Neutral pH

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Abstract
Complexing agents in Cu chemical mechanical planarization slurries promote dissolution of the copper surface. We explored the effect of two chelating compounds, ammonium oxalate and oxalic acid, with and without hydrogen peroxide, on the dissolution and surface morphology of a Cu(111) surface at neutral pH. Without hydrogen peroxide, static etch rate (SER) measurements were highest for oxalic-acid-containing solutions, but with peroxide, ammonium-oxalate-containing solutions demonstrated the highest rates. The largest anodic and cathodic currents were seen in solutions containing ammonium oxalate and peroxide using cyclic voltammetry. In the presence of oxalic acid, atomic force microscopy revealed a thick layer on the surface, identified as Cu2OCu2O on the basis of X-ray photoelectron spectroscopy measurements, that changed little over time. In the presence of ammonium oxalate, the film was thinner and showed accelerated dissolution. It is proposed that the dissolution processes of oxalate and ammonium operate independently at the same time. In the presence of peroxide, more Cu2+Cu2+ is created which allows for the formation of more copper oxalate, and H2O2H2O2 also increases the concentration of copper oxide species at the surface, which drives the ammonia complexation reaction. These two events give rise to a large increase in SER.

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