EUVL masks: requirements and potential solutions

Abstract

Extreme ultraviolet lithography (EUVL) is a leading next generation lithography technology. Significant progress has been made in developing mask fabrication processes for EUVL. The mask blank for EUVL consists of a low thermal expansion material substrate having a square photomask form factor that is coated with Mo/Si multilayers. A SEMI standard is now available for mask substrates. SEMI standards are also being developed for mask mounting, for mask blank multilayers and absorbers and for mask handling and storage. Several commercial suppliers are developing polishing processes for LTEM substrates, and they are progressing toward meeting the requirements for flatness, surface roughness, and defects defined in the SEMI standard.One of the challenges in implementing EUVL is to economically fabricate multilayer-coated mask blanks with no printable defects. Significant progress has been made in developing mask blank multilayer coating processes with low added defect density. Besides lowering added defect density, methods to reduce defect printability are being developed to effectively enable repair of many defect types. These repair processes might significantly increase yield of EUV mask blanks before defect density is lowered to production targets. Calculations of EUVL mask cost indicate that defect repair processes could allow the initial defect density targets for mask blanks to be relaxed.The mask patterning process for EUVL is nearly the same as that for conventional binary optical lithography masks. EUVL mask patterning efforts are focused on developing the EUV-specific aspects of the patterning process. Eight absorbers have been evaluated against the requirements for EUVL masks, and two absorbers-TaN and Cr--will probably meet the requirements after some further development.

Lattice instability and elastic response of metastable Mo1−xSixthin films

“…Due to their high contrast in electron density, Mo-Si multilayer structures are widely used as high-reflectance optical elements for the development of extreme ultraviolet lithography tools. 9,10 Additionally the large acoustic impedance mismatch between Mo and Si gives rise to large stop bands in the phonon dispersion curves, which are of potential interest for phonon filtering, generation, or detection in the high-frequency range. 11 The objective of the present study is to provide a comprehensive picture of the correlation between structure and elastic properties of metastable disordered Mo 1−x Si x films in the whole composition range (0 < x < 1).…”

Amplitude versus phase effects in extreme ultraviolet lithography mask scattering and imaging

“…EUV lithography masks [7] are comprised of multilayer [8] coated plates with a capping layer and a patterned absorber on top (Fig. 1).…”

High-throughput EUV reflectometer for EUV mask blanks

“…The whole chain of developing EUVL and especially the development of EUV masks and mask blanks require tools to check the specifications implied on 2,3 . AIXUV collaborates with JENOPTIK Mikrotechnik for developing source metrology, with the Fraunhofer Institute for Laser Technology (ILT) for basic research in metrology (e.g.…”