Technical Note: Concepts for protection of EUVL masks from particle contamination

Extreme ultraviolet lithography (EUVL) is a leading lithography technology for the next generation of semiconductor chips. Due to the lack of any useable common membrane pellicles, different approaches have to be considered in order to protect the EUV photomasks from particle contamination during all handling steps, i.e. during shipping and storage at atmospheric pressure as well as during exposure in dedicated lithography tools at low pressure (e.g. 50 mTorr). In this manuscript we present the evolution of schemes for protecting the very valuable EUVL masks from nanoparticle contamination. The proposed protection schemes are (1) maintaining the critical mask surface upside down to avoid gravitational settling of particles onto the mask; (2) use of a cover plate to reduce the volume from where particles might reach the surface; (3) apply thermal and/or electrical gradient to expose particles to a repelling thermophoretic and/or electrophoretic force and (4) use of a particle trap, surrounding the mask.