Organic additives based alkaline alumina slurry for selective removal of barrier layer metals

Abstract

In the present work, tantalum (Ta) and copper (Cu) chemical mechanical polishing (CMP) has been carried out using a polishing slurry containing 2 wt% alumina (abrasive), 1 wt% potassium carbonate (oxidizer), and 0.25 wt% each urea and citric acid (additives). The Cu removal rate (RR) decreases with an increase in pH and is found to be minimum at pH 11 while Ta RR increases till neutral pH and then decreases till pH 11 having maximum RR at pH 7. Ta to Cu removal rate selectivity of 1:1.02 is attained at pH 11. Other parameters such as the effect of additives concentration, applied pressure, and platen rotational speed are also studied and results are reported to get a clear scenario. Surface charge analysis reveals that with change in pH, zeta potential alters and 30mV zeta potential is found at pH 11 which confirms the stability of the formulated slurry. To comprehend the removal mechanism of the metals, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) are employed. The same trend is encountered for both corrosion current density (I_corr) and film resistance (R_film)values resulting from Tafel and EIS. Based on the research conducted a plausible material removal mechanism is suggested.