Recent advance in protection technology for extreme ultraviolet lithography masks under low-pressure condition

Extreme ultraviolet lithography (EUVL) is considered a leading lithography technology for the next generation of semiconductor devices. Various noncontact approaches for protection of the EUVL masks from particle contamination have to be used due to the lack of any usable common membrane pellicles during all handling steps. In this article, protection schemes for EUVL masks from nanoparticle contamination are given and proper experimental verifications are followed. The experimental investigations for the proposed protection schemes are examined with (i) maintaining the critical surfaces upside down to avoid gravitational settling of particles onto the mask; (ii) use of a cover plate to reduce the volume from where particles might reach the surface; (iii) application of a thermal and/or electrical gradient to expose particles to a repelling thermophoretic and/or electrophoretic force. The proposed schemes showed excellent effects on protection of critical surfaces under low-pressure condition.