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

Published online by Cambridge University Press:  31 January 2011

Shantanu Tripathi ,
Fiona M. Doyle  and
David A. Dornfeld
Shantanu Tripathi
Affiliation:
[email protected], University of California, Mechanical Engineering, Berkeley, California, United States
Fiona M. Doyle
Affiliation:
[email protected], University of California, Materials Science and Engineering, 210 Hearst Mining Bldg, Berkeley, California, 94720-1760, United States, 510-643-1666, 510-643-8653
David A. Dornfeld
Affiliation:
[email protected], University of California, Mechanical Engineering, Berkeley, California, United States
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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 potential-step 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.

Keywords

Cuoxidationpassivation
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1157: Symposium E – Science and Technology of Chemical Mechanical Planarization (CMP) , 2009 , 1157-E06-02
Copyright
Copyright © Materials Research Society 2009

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References

1 Elmufdi, C.L., Muldowney, G.P., “A Novel Optical Technique to Measure Pad-Wafer Contact Area in Chemical Mechanical Planarization” Mater. Res. Soc. Symp. Proc. V91, 2006 SpringGoogle Scholar
2 Tripathi, S., “Tribochemical Mechanisms of Copper Chemical Mechanical Planarization (CMP) – Fundamental Investigations and Integrated Modeling”, Ph.D. Dissertation, University of California, Berkeley, December 2008.Google Scholar