Fundamental Mechanisms of Copper CMP – Passivation Kinetics of Copper in CMP Slurry Constituents

Abstract

During copper CMP, abrasives and asperities interact with the copper at the nano-scale, partially removing protective films. The local Cu oxidation rate increases, then decays with time as the protective film reforms. In order to estimate the copper removal rate and other Cu-CMP output parameters with a mechanistic model, the passivation kinetics of Cu, i.e. the decay of the oxidation current with time after an abrasive/copper interaction, are needed. For the first time in studying Cu-CMP, microelectrodes were used to reduce interference from capacitive charging, IR drops and low diffusion limited currents, problems typical with traditional macroelectrodes. Electrochemical impedance spectroscopy (EIS) was used to obtain the equivalent circuit elements associated with different electrochemical phenomena (capacitive, kinetics, diffusion etc.) at different polarization potentials. These circuit elements were used to interpret potentialstep chronoamperometry results in inhibiting and passivating solutions, notably to distinguish between capacitive charging and Faradaic currents.Chronoamperometry of Cu in acidic aqueous glycine solution containing the corrosion inhibitor benzotriazole (BTA) displayed a very consistent current decay behavior at all potentials, indicating that the rate of current decay was controlled by diffusion of BTA to the surface. In basic aqueous glycine solution, Cu (which undergoes passivation by a mechanism similar to that operating in weakly acidic hydrogen peroxide slurries) displayed similar chronoamperometric behavior for the first second or so at all anodic potentials. Thereafter, the current densities at active potentials settled to values around those expected from polarization curves, whereas the current densities at passive potentials continued to decline. Oxidized Cu species typically formed at 'active' potentials were found to cause significant current decay at active potentials and at passive potentials before more protective passive films form. This was established from galvanostatic experiments.

Effects of H2O2 and pH on the Chemical Mechanical Planarization of Molybdenum

“…The similar Mo SERs and the different Mo RRs at pH 2-8 suggest that the amount of Mo oxides formed during the interval (τ) between sequential mechanical abrasions may be different. This time interval (τ) has been calculated in several studies, [30][31][32] which reported τ to be on the order of milliseconds. To characterize the formation of Mo oxides by H 2 O 2 in milliseconds, chronoamperometry was used.…”

Passivation Kinetics of 1,2,4-Triazole in Copper Chemical Mechanical Polishing

“…It was reported that the current density transients I t measured in the similar solutions, containing both the complexing agent such as glycine and the inhibitor such as BTA, should include the non-faradaic double layer charging in addition to the faradaic current. 24,31,32 As a result, I t can be fitted with a double-exponential decay law as follows: 31,32 I t = I f e −t/τ f + I c e −t/τc + I 0 [9] Where I f and I c are the peak responses of the current density from the faradaic reactions and the double-layer charging, respectively. τ f and τ c are the corresponding time constants, separately.…”

“…In order to remove the native copper oxides and to prepare a fresh copper surface, the electrode was held at −1.2 V (vs. E Ag/AgCl ) for 60 s as a standard pretreatment procedure for all the electrochemical experiments. 23,24 The OCP experiments were first conducted, and then were followed by the linear sweep experiments, including the potentiodynamic polarization experiments and the cyclic polarization experiments, and the chronoamperometry experiments. Specifically, for the linear sweep experiments, the step height was set to 2 mV and the scan rate was set to 5 mV/s; 25 for the chronoamperometry experiments, the externally applied electrical potential provided a thermodynamic driving force for the oxidation reaction of the fresh copper surface, by which the reaction product could further react with the complexing agent such as glycine and the inhibitor such as 1,2,4-triazole in the solution.…”

A Comparison of Active Particle Models for Chemical Mechanical Polishing

“…24 Complicating the material removal prediction further is the effect of the chemicallyactive slurry and complex particle-surface interactions which dictate the wear process. [25][26][27][28] Early CMP models began as mostly-empirical, wafer-scale correlations for the global MRR based upon the Preston's equation 29 (Eq. 2) where K p is the empirical Preston's coefficient, P is the applied pressure, and V is the relative velocity between the wafer and the pad.…”