Nanoparticle removal using laser induced plasma (LIP) technique and study of detachment modes based on molecular dynamics simulations

Nanoparticle contamination is a major problem in many industries. In the semiconductor industry, as the device (integrated circuit) size shrinks with each technological node (DRAM half-pitch), the feature size that has to be fabricated shrinks. Consequently, the minimum tolerable particle defect size also reduces to sub-100 nm level. In order to attain the stringent small size features, Extreme Ultraviolet Lithography (EUVL) technique is being explored in the semiconductor industry. As the EUVL masks are reflective and pellicle free, the cleaning techniques employed to remove the native particle defects must be more effective for the removal of the sub-100 nm particles without any substrate damage. The effectiveness of Laser Induced Plasma (LIP) technique, considered as a next generation cleaning method, for removal of 30 nm PSL particles from silicon substrate was previously demonstrated by our group. In the current study, the removal of 100 nm PSL particles from photomask and 300 nm PSL particles from 500 nm patterns was investigated. It was observed that the patterns were damaged which could be attributed to the radiation heating of the plasma, and this necessitated pressure amplification techniques to amplify the transient pressure and minimize the risk of damage. As a potential solution, shocktubes were designed and transient pressure measurements were carried out in air medium. Also, plasma was generated in water, in order to take advantage of the density of the medium, to generate stronger shocks and consequently higher pressure. The performance of the shocktubes was characterized based on their pressure amplification factor. The shocktubes resulted in a pressure amplification factor of 11 in air. The particle removal experiments with shocktubes on 150 nm patterns were performed and no damage to the patterns was observed. However, there were particle adders due to the ablation of the shocktube material.;Molecular Dynamics (MD) simulations were initiated and the objective was two fold, to understand (i) nanoparticle-shockwave and (ii) nanoparticle-substrate, interactions. To study the effect of nano-scale particle size on and their interaction with the LIP shockwaves, Direct Simulation Monte Carlo (DSMC) simulations were performed. Two potential nanoparticle removal mechanisms, namely rolling resistance moment and the rocking frequency criterion were identified. Large scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) simulations were initiated to understand the nanoparticle-substrate adhesion at atomic levels. The rolling resistance moment calculated from the slope of force-displacement curves obtained when the particle was pushed in the lateral direction was in good agreement with the rolling resistance moment calculated using the two-dimensional adhesion theory. In the case of an irregular particle, rolling is initiated and this resulted in the liftoff of the particle from the substrate, as most of the particle lost contact with the substrate during rolling. The experimental results demonstrating successful local area (spot) cleaning of the native particles from the EUVL mask, using the Laser Shock Cleaning tool were presented.