Improving Selectivity on Germanium CMP Applications

In this study, slurry formulations are evaluated to enhance selectivity for germanium silica planarization systems.  Initial selectivity analyses were studied by material removal rate responses measured at a single particle-surface level through atomic force microscopy (AFM) wear tests using both anionic (sodium dodecyl sulfate-SDS) and cationic (cetyl trimethyl ammonium bromide-CTAB) surfactants at their sub-micelle and above critical micelle concentrations (CMC) as a function of pH and oxidizer concentration [1].  CMP performances of Ge and SiO₂ wafers were evaluated in terms of material removal rates, selectivity and surface quality [2]. The surfactant adsorption characteristics were studied through surface wettability (measured by contact angle technique) and FTIR analyses.  It was determined that the very strong or loose self-assembled surfactant structures can help obtain selectivity on the silica/germanium systems and good defectivity control with a sufficient material removal rate values yet the surface charge of the wafer and the hydrophobic nature of the germanium surface add to the complex surface assembly of the surfactant systems. In addition, since the slurry stability is necessary to prevent unacceptable levels of surface roughness and defects, the impact of adding surfactants on particle-particle interactions is investigated in the paper.

References:

1. Vakarelski I. U., Brown, S.C, Basim G.B, Rabinovich, Y. I., and Moudgil B.M., "Tailoring Silica Nanotribology for CMP Slurry Optimization: Ca²⁺ Cation Competition in C₁₂TAB Mediated Lubrication", ACS Applied Materials & Interfaces, Vol. 2, No 4, pp. 1228-1235, 2010.
2. Basim, G.B., Vakarelski, I.U. Karagoz, A. Chen, L., “Surfactant Mediated Slurry Formulations for Ge CMP Applications” MRS Proceedings, MRS Spring Meeting, San Francisco, CA, April 2013, V. 1560, DOI http://dx.doi.org/10.1557/opl.2013.971.