Analysis of copper dissolution in glutamic acid and hydrogen peroxide using EIS

Copper chemical mechanical polishing (CMP) is a key step in microelectronic interconnect fabrication [1]. Slurries containing glycine and hydrogen peroxide have been widely studied as suitable candidates for Cu CMP[2,3]. Glycine based slurries show drastic changes in removal rate with changes in hydrogen peroxide concentration. Slurries based on glutamic acid (Glu) as complexing agent present a more robust removal rate trend. The dissolution of copper in solutions containing Glu and hydrogen peroxide is analyzed using EIS. Potentiodynamic polarization studies show that there is no strong passivating layer formed on the copper surface in solutions containing 0.5 wt % Glu and 0.1 vol% hydrogen peroxide. EIS studies were conducted from a frequency of 0.1 Hz to 10 kHz, at 6 anodic dc potentials. Kramers Kronig Transform was employed to validate the data [4]. The data shows that at lower dc potentials, inductive loops appear at intermediate frequencies and at higher dc potentials, they appear at the low frequencies. At higher potentials, an additional capacitive loop appears in the intermediate frequencies. The EIS data were modeled using electrical equivalent circuits and reaction mechanism analysis [5]. An electrical circuit with a solution resistance, a constant phase element to represent the double layer and a set of resistances and capacitances was used to model the data. A reaction mechanism with two adsorbed intermediates is proposed to explain the kinetics