Particle adhesion and removal on EUV mask layers during wet cleaning

Extreme ultraviolet (EUV) masks have a very stringent cleanliness requirement that present new challenges to nanolithography industry. The cleaning of EUV mask surface is required at every exposure level due to the absence of a pellicle layer. In this study, the adhesion and removal of particles on EUV masks is investigated by calculating the interaction force and measuring the adhesion force using atomic force microscopy (AFM). Zeta potential measurements showed that the calculated interaction force was attractive on Si capping layer and Cr absorbed layer for both silica and alumina particle at all pH ranges investigated. However, the measured adhesion force of Si capping layer was similar to that of bare Si at neutral and alkaline pHs. The calculated interaction force Of SiO(2) buffer layer was most repulsive and the lowest adhesion force was measured. This indicates that the SiO(2) buffer layer has a better cleaning efficiency at neutral and alkaline pH. The calculation of interaction force between particle and surface and measurement of adhesion force shows that a lower particle removal efficiency was expected on Cr absorber layer surface.