Van der Waals and electrostatic forces in adhesion between irregular particles and surfaces

This work extended the current fundamental particle adhesion models to better understand and quantify the adhesion of particles to thin films. Adhesion between particles and surfaces is important in many processes including chemical mechanical planarization (CMP) in the semiconductor industry. A fundamental understanding of particle adhesion is required to develop a more complete understanding of the processes used to clean particles from the surface. The ability to quantitatively predict and simulate the adhesion of particles to surfaces will lead to a better optimization of these processes. This work combines fundamental adhesion equations with computer simulations to model van der Waals (vdW) and electrostatic double layer interactions for real particles in contact with a surface. A previously developed vdW adhesion model was used to determine Hamaker constants for materials of interest in the semiconductor industry. Comparison of these Hamaker constants with theoretical values allowed some limitations of the vdW adhesion model to be realized. Specifically, the previous model assumed surface roughness could be approximated with a combination of ideal hemispheres, however this assumption overestimated the force in systems that had asperities larger than 10 or 15 nm. A method using the Fourier transform to generate more accurate surface roughness models was developed. It was found that the Fourier transform gave accurate predictions in all cases. The vdW adhesion model with an accurate description of surface roughness was also used to examine electrostatic double layer interactions. A boundary element technique was used to solve the Poisson-Boltzmann equations and account for the roughness of the surfaces and the geometry of the particle. The combined vdW electrostatic model accounts for the effects of surface roughness, particle geometry, and deformation on the adhesion force. The parameters required to describe these effects were characterized experimentally and used in the model simulations. The model was validated through comparison with experimental measurements made with an atomic force microscope (AFM) using materials of interest in post-CMP cleaning.