The interactions between nanoparticles and rough surfaces are of great scientific and engineering importance and have numerous applications in surface science and biotechnology. Surface geometry and roughness play crucial roles in observed particle adhesion forces. We previously developed a model and simulation approach to describe adhesion between microscale bodies. This work provides detailed descriptions of the modeling framework, with associated experimental validation, applied to nanoscale systems. The physical systems of interest include nanoscale silicon nitride adhering to different surfaces in both dry and aqueous environments. To perform the modeling work, precise descriptions of the geometry of the particle and the roughness of the particle and substrate were generated. By superimposing the roughness and geometry models for the particle and the substrate, it was possible to precisely describe the spatial configurations of the adhering surfaces. The interacting surfaces were then discretized, and the adhesion force between the two surfaces was calculated by using Hamaker's additive approach, based on van der Waals interactions. In the experimental work, an atomic force microscope (AFM) was used to measure the adhesion force (pull-off force) between nanoscale silicon nitride cantilever tips and a range of substrates in different environments. The measured and predicted force distributions were compared, and good agreement was observed between theory and experiment.

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Work performed to study the scalability of continuum force models to describe particle adhesion from the micro-to the nano-scale is described. This work employed silicon nitride particles with nominal diameters on the micrometer scale and silicon nitride atomic force microscope cantilevers with nanometer-scale radii of curvature to determine adhesion interaction forces to substrates relevant to advanced lithography applications in the semiconductor industry. The force required to dislodge the particles or cantilevers from the substrates was taken to be the adhesion force. For all systems studied, a distribution of adhesion forces was observed resulting from roughness on the particles and/or substrates and geometry variations on the particles. Previously developed adhesion models that included van der Waals (vdW) and electrostatic (ES) interactions, and that also included the geometry and morphology of the interacting surfaces, were used to describe the force distributions. In air, the ES forces were found to be insignificant compared to the vdW forces. In aqueous electrolytes, the ES forces may play an important role, even at the point of particlesubstrate contact, due to the formation of electrical double layers under certain conditions. The predicted force distributions showed good agreement with the experimental data.  Koninklijke Brill NV, Leiden, 2008

Effective removal of particulate contaminants from wafer surfaces during semiconductor manufacturing is essential for high-yield processing. To improve cleaning effectiveness, experimental and theoretical evaluations of undercut cleaning were conducted. A model system of polystyrene latex ͑PSL͒ spheres being removed from a tetraethyl ortho-silicate ͑TEOS͒-sourced silicon dioxide surface was examined. 7 and 15 m PSL particles were spray deposited on wafer surfaces and allowed to settle for 24 h. Undercutting was then carried out using 20:1 buffered hydrofluoric acid to etch the silicon dioxide under nonflow conditions. Preand postetch scans of the wafer surface were obtained using a Tencor SP1 Surfscan in the laboratories of SEZ America in Phoenix, AZ. The percentage of particles that remained adhered to the surface after etching for varying lengths of time was monitored. A model for undercut removal of particles from surfaces was proposed. Chemical etching of the silicon dioxide surface was assumed to cause a reduction in the particle-wafer contact area. Undercut removal was hypothesized to occur due to a subsequent reduction in the van der Waals force of adhesion and an increase in the area over which repulsive electrostatic forces were dominant. Interactions between the PSL and the silicon dioxide were calculated based on computer simulation of a van der Waals adhesion model and an electrostatic force model. Particle and surface morphology, mechanical properties, and geometry were included in the van der Waals calculation, and the electrostatic force calculation considered the particle and silicon dioxide zeta potentials and local separation distance. The model and experiments agreed to within 10%.

To meet increasingly demanding performance requirements, the microelectronics industry is required to deliver new technology solutions that will include new device architectures, ever-smaller feature dimensions, new high-performance materials, and novel processing schemes.