Effect of Tool Kinematics, Brush Pressure and Cleaning Fluid pH on Coefficient of Friction and Tribology of post-CMP PVA Brush Scrubbing Processes

Ara Philipossian, Lateef Mustapha

Research output: Contribution to journalConference article


Real-time coefficient of friction (COF) analysis is used to determine the extent of normal and shear forces during post-CMP PVA brush scrubbing and identify the tribology of the process. Fluid pH and applied pressure have pronounced effects on process tribology and the magnitude of COF. In cases where brush rotation is the only kinematic attribute of the system, low pH results in 'mixed lubrication' where increasing brush velocity causes a dramatic reduction in COF in accordance with classical tribological arguments. At lower pressures the tribological mechanism shifts to 'hydrodynamic lubrication' with significantly lower values of COF. Regardless of pressure, increasing the pH to 7 and 10.7 causes the tribology to remain in 'hydrodynamic lubrication' and results in even lower values of COF. Trends are explained qualitatively by considering the effect of pH on the solubility and gellation characteristics of silica in the silica-water system. Stribeck curves fail to shed light on the tribology of the system when complex ranges of tool kinematics (i.e. wafer rotation and brush oscillation superimposed on brush rotation) are employed. The results are counter-intuitive since they indicate nearly an order of magnitude increase in COF with increasing brush velocity. Nevertheless, results demonstrate the utility of having complex ranges of motion in PVA brush scrubbing such that very low or very high values of COF can be realized by simply increasing the rotational velocity of the brush while maintaining a constant wafer rotation and brush oscillation.

Original languageEnglish (US)
Pages (from-to)209-215
Number of pages7
JournalMaterials Research Society Symposium - Proceedings
StatePublished - Nov 10 2003
EventChemical-Mechanical Planarization - San Francisco, CA, United States
Duration: Apr 22 2003Apr 24 2003


ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering

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