Nanoparticle Adhesion Models: Applications in Particulate Contaminant Removal from Extreme Ultraviolet Lithography Photomasks

Photomask contamination is a critical issue in the microelectronics manufacturing industry, and this problem has grown more challenging with the advent of extreme ultraviolet lithography (EUVL). Experimental studies of nanoscale contaminant particle adhesion and removal have limitations associated with metrology to accurately detect and quantify the nanoscale contaminants themselves. In this work, we have utilized our experimentally-validated simulation scheme as a tool to estimate the adhesion forces between hypothetical nanosized silicon nitride particles and EUVL mask materials. Specifically, this study focuses on the importance of different physical parameters such as the shape, size and surface roughness of the interacting bodies on the force of adhesion between them, with particular attention to particle size as the size is varied from the micro- to the nanoscale. The effective Hamaker constant (a force constant for the van der Waals force) for nanoscale particle-substrate systems was derived from the force measurements between a nanoscale silicon nitride AFM probe and the substrates of interest. By using hypothetical surface descriptions (geometry and roughness) of the nanoparticles, it was determined that surface roughness generally reduces adhesion of both micro- and nanoscale particulates. However, the effect of roughness on the adhesion force is greatly reduced for particles with diameters below 50 nm. The particle geometry can directly influence the adhesion force by altering the area of interaction between the particle and substrate. As a result, it remains important for systems of all particle sizes. Finally, an adhesion force map (a 'force-band diagram') was developed to bound the adhesion forces for any given particle-substrate system irrespective of the particle geometry and surface morphology. (C) Koninklijke Brill NV, Leiden, 2011