Daniel Cole

Development of a Classical Force Field for the Oxidised Si Surface: Application to Hydrophilic Wafer Bonding

Daniel J. Cole,1 Gabor Csányi,2 Mike C. Payne,1 S. Mark Spearing,3 Lucio Colombi Ciacchi4,5

1Theory of Condensed Matter Group, Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, UK
2Centre for Micromechanics, Department of Engineering, University of Cambridge, Cambridge CB2 1PZ, UK
3Engineering Materials Group, School of Engineering Sciences, University of Southampton, Southampton SO17 1BJ, UK
4Fraunhofer Institut für Werkstoffmechanik, 79108 Freiburg, Germany
5Institut für Zuverlässigkeit von Bauteilen und Systemen, University of Karlsruhe, 76131 Karlsruhe, Germany

We have developed a classical two- and three-body interaction potential to simulate the hydroxylated, natively oxidised Si surface in contact with water solutions, based on the combination and extension of the Stillinger-Weber potential and of a potential originally developed to simulate SiO2 polymorphs. The potential parameters are chosen to reproduce the structure, charge distribution, tensile surface stress and interactions with single water molecules of a natively oxidised Si surface model previously obtained by means of accurate density functional theory simulations. We have applied the potential to the case of hydrophilic silicon wafer bonding at room temperature, revealing maximum room temperature work of adhesion values for natively oxidised and amorphous silica surfaces of 97 mJ/m2 and 90 mJ/m2, respectively, at a water adsorption coverage of approximately 1 monolayer. The difference arises from the stronger interaction of the natively oxidised surface with liquid water, resulting in a higher heat of immersion (203mJ/m2 vs. 166 mJ/m2), and may be explained in terms of the more pronounced water structuring close to the surface in alternating layers of larger and smaller density with respect to the liquid bulk. The computed force-displacement bonding curves may be a useful input for cohesive zone models where both the topographic details of the surfaces and the dependence of the attractive force on the initial surface separation and wetting can be taken into account.

Journal of Chemical Physics 127, 204704 (2007)