Copper CMP Modeling: Millisecond Scale Adsorption Kinetics of BTA in Glycine-Containing Solutions at pH 4

Abstract

Millisecond scale benzotriazole (BTA) adsorption kinetics in acidic aqueous solution containing 0.01M glycine and 0.01M BTA have been investigated. Chronoamperometry was used to measure current densities on the surface of a micro-copper electrode in pH 4 aqueous solutions containing 0.01M glycine with or without 0.01M BTA. In the presence of BTA the current density decreased as the inverse of the square root of time for a few seconds due to adsorption of BTA. At potentials above 0.4V saturated calomel electrode the current leveled off after a second or so due to the formation of a Cu(I)BTA monolayer on the copper surface. Based on these data a governing equation was constructed and solved to determine the initial kinetics of BTA adsorption. Analysis shows that material removal during copper chemical mechanical planarization (CMP) in this slurry chemistry occurs mostly by direct dissolution of copper species into the aqueous solution rather than mechanical removal of oxidized or pure copper species and that each interaction between a pad asperity and a given site on the copper removes only a small fraction of the Cu(I)BTA species present at that site.

Editors' Choice—Efficiency of a CMP Pad at Removing Protective Material from Copper during CMP

“…Despite the difference in the magnitude of the oxidation rates for the two types of electrode, the intrinsic mechanism for passivation would be unchanged. Therefore, the approach used by Choi et al 3 of considering the fractional coverage of the copper by Cu(I)BTA complexes as a function of time was adopted to examine the material removal efficiencies from the measured current densities. Figure 6 shows the average steady-state current densities of copper during polishing with different down pressures or sliding velocities.…”

“…Throughout the following analysis, a fraction of a monolayer of the protective material is assumed to be formed on the surface of copper during CMP, on the basis of the findings of Choi et al 3 A complete monolayer of protective material is taken as a coverage ratio of unity.…”

“…t 0 was evaluated for different experimental conditions using the measured average current densities and the kinetics of adsorption of BTA onto the surface of copper (coverage ratio by Cu(I)BTA with time) reported by Choi et al 3 for a micro-electrode, scaled down by a…”

“…It is notable that the evaluated removal efficiencies were insensitive to the down pressure and the sliding velocity, regardless of the choice of the pad surface topography parameters, supporting our adoption of these parameters from the literature. In contrast, the removal efficiency was very sensitive to the scatter of the measured current density, especially when t as-as was large, due to the very rapid adsorption of BTA onto copper in a very short time after the copper was anodically polarized (the curve for the coverage ratio by Cu(I)BTA with time appears to be almost a step function; 3 this curve is schematically shown as a blue line in Figure 9). When t as-as is large, the positions of t 0 and t 0 + t as-as are distant, leading to a large difference in the coverage ratios at Error bars correspond to one standard deviation of the experimental data in Figure 6.…”

Material Removal Mechanism during Copper Chemical Mechanical Planarization Based on Nano-Scale Material Behavior

“…Choi et al subsequently suggested that at steady state during CMP using an acidic slurry containing benzotriazole (BTA) and glycine, (Cu(I)BTA and Cu(II)BTA 2 ) form only a fraction of a monolayer on average, partly protecting the surface of a wafer from dissolution. 11 In this model, removal of the passive layer contributed only a small portion of the electrochemically measured MRR; most of the electro- † Deceased.…”