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Extreme ultraviolet lithography (EUVL) is considered the next generation lithography to produce 32-nm feature-size or smaller. The challenge is that conventional pellicles are unavailable for protecting the EUVL masks against contaminant particles, because the EUV beam is easily absorbed by most solid materials. The masks are usually transported or stored in mask carriers. Without the protective pellicles, particles generated inside the mask carrier may deposit on the critical surface of the mask. It is therefore important to identify where the particles are generated inside the mask carrier during shipping. In this paper, two shipping carrier models of different mask holder designs were used. The mask carriers with quartz mask blanks inside were shaken manually, vibrated with a computer-controlled vibration table, or shipped via air freight. In order to simulate the EUVL mask shipping, no pellicles were used. Several online and offline particle detection techniques were employed to investigate particle generation inside the mask carrier during vibration or shipping. It was shown that particles were mostly generated at the contact points between the mask surface and the carrier element. The design of the mask-holding element in the mask carrier played an important role in reducing particle generation. [ABSTRACT FROM AUTHOR]

In extreme ultraviolet lithography (EUVL), conventional pellicles are unavailable for protecting the EUVL masks, since they highly absorb the EUV radiation. One of the serious challenges is therefore to prevent particulate contamination of the EUVL masks. In this paper, EUVL mask protection schemes proposed by Asbach et al. were experimentally challenged against horizontal aerosol flow simulating particle transport from the side during mask handling, shipping, and storage at atmospheric pressure. The protection schemes include mounting the critical surface facing down, using a cover plate with particle trap, and applying electrophoresis or thermophoresis. Both electrophoresis and thermophoresis showed very good protection capabilities. Electrophoresis, however, might be counterproductive due to the unknown particle charge polarity in real situations. A particle trap, on which contaminant particles can deposit before they reach the critical surface, could then be used to collect all particles irrespective of their polarity with a sufficiently high electric field but might not work against zero-charged particles. On the other hand, thermophoresis acts on all particles and transports them in the same direction. Therefore, the upside-down mounting and thermophoresis with the cover plate and particle trap are considered the promising protection schemes for the EUVL mask carrier systems. [ABSTRACT FROM AUTHOR]