Modeling, detection and protection schemes for extreme ultraviolet lithography (EUVL) mask carrier systems

Extreme Ultraviolet Lithography (EUVL) is considered as a prominent candidate for the next generation lithography to achieve 32 nm feature-size or smaller by utilizing a light of 13.4 nm wavelength. Pellicles, which are polymer films or thin modified fused silica plates used in conventional optical lithography, are unavailable for protecting the EUVL masks against contaminant particles, because the EUV beam is easily absorbed by most solid materials. Particles can be generated at any stages of mask handling, shipping and storage, and may deposit on the critical surfaces of EUVL masks without the pellicles. Particle contamination of masks is therefore a serious challenge in the EUVL technology and is the motivation of this study. In order to reduce particle generation, it is important to understand particle generation mechanisms in the mask carriers. Particle contamination of masks without the pellicles was experimentally investigated during vibration or shipment of the mask carriers. In order to avoid particle contamination, it is needed to develop schemes to protect the EUVL masks against particles. The protection schemes include mounting the critical surface facing-down, using a cover plate with particle trap and applying electrophoresis or thermophoresis. These schemes were experimentally and numerically evaluated with the critical surfaces exposed to vertical and horizontal aerosol flows at atmospheric pressure. Another crucial aspect of particle contamination control is the calibration of mask surface inspection tools, since they are very useful for mask contamination monitoring and mask surface cleaning studies. Nanoparticle metrology to characterize the mask surface inspection tools was developed.