EUV Interference Lithography

Progress in nanotechnology is essential for producing faster computers and high-density data storage. This progress is fueled by the downscaling of integrated circuit (IC) technology, which was predicted decades ago by Gordon Moore. Currently high-volume semiconductor manufacturing uses the optical double patterning methods and immersion lithography at the wavelength of 193 nm to reach the 22 nm node but these techniques may reach their limits because of fundamental limitations. Therefore, particular interest is channeled towards extreme ultraviolet (EUV) lithography at the wavelength of 13.5 nm, whereas its cost-effective introduction requires further development of resists capable of printing dense patterns down to this resolution in addition to other challenges such as development of powerful light sources.

In parallel with the projection optical systems developed for industrial applications, EUV interference lithography (EUV-IL) using synchrotron, laser, and plasma sources have emerged as powerful tools for both scientific and industrial research. Whereas the latter focuses mainly of developing novel high-resolution resists, the advantage of being a parallel fabrication process with both high resolution and throughput makes EUV-IL attractive also for academic research. For image forming EUV-IL requires spatially coherent illumination and transmission diffraction gratings. EUV-IL tool at PSI is the world-leading tool reaching a resolution down to 8 nm half-pitch.

Advantages of EUV-IL

    • No proximity effect (e-- mean-free-path < 1-3 nm)
    • No depth of focus: Mask-to-wafer = 0.1-10 mm
    • Pitch independent aerial image.
    • High resolution:
    • Theoretical limit= 3.5 nm
    • Current limit < 8 nm (world record in photon based lithography)
    • Large area: up to 5x5 mm2
    • Step and repeat: up to 80x80 mm2 with stitching
    • High throughput: typically 10 s: 10’000x e-beam
    • Quality, reproducibility: enabling industrial operation
    • Versatile structures


L. Wang, B. Terhalle, V. A. Guzenko, A. Farhan, M. Hojeij, and Y. Ekinci
“Generation of high-resolution kagome lattice structures using extreme ultraviolet interference lithography,”
Appl. Phys. Lett. 101, 093104 (2012).

L. Wang, B. Terhalle, M. Hojeij, V. A. Guzenko, and Y. Ekinci
“High-resolution nanopatterning by achromatic spatial frequency multiplication with electroplated grating structures,”
J. Vac. Sci. Technol. B 30, 031603 (2012).

L. Wang, H. H. Solak, and Y. Ekinci,
“Fabrication of high-resolution large-area patterns using EUV interference lithography in a scan-exposure mode,”
Nanotechnology 23, 305303 (2012).

Y. Ekinci, M. Vockenhuber, B. Terhalle, M. Hojeij, L. Wang, and T. R. Younkin,
“Evaluation of resist performance with EUV interference lithography for sub-22 nm patterning,”
Proc. SPIE 8322, 83220W (2012).

A. Langner, B. Päivänranta, B. Terhalle, and Y. Ekinci,
“Fabrication of quasiperiodic nanostructures with EUV interference lithography,”
Nanotechnology 23, 105303 (2012).

B. Terhalle, A. Langner, B. Päivänranta, C. David, and Y. Ekinci,
“Generation of EUV vortex beams using computer generated holograms,”
Optics Lett. 36, 4143 (2011).

B. Terhalle, A. Langner, B. Päivänranta, and Y. Ekinci,
“Advanced holographic methods in extreme ultraviolet interference lithography,”
Proc. SPIE 8192, 81020V (2011).

B. Päivänranta, A. Langner, E. Kirk, C. David, and Y. Ekinci,
“Sub-10 nm patterning using EUV interference lithography,”
Nanotechnology 22, 375302 (2011).

D. Bleiner, F. Staub, V. Guzenko, Y. Ekinci, and J. Balmer, 
“Evaluation of lab-scale EUV microscopy using a table-top laser source,”
Opt. Commun. 284, 4577 (2011). 

A. Langner, H. H. Solak, R. Gronheid, E. van Settend, V. Auzelyte, Y. Ekinci, K. van Ingen Schenaud, K. Feenstrad,
“Measuring resist-induced contrast loss using EUV interference lithography,”
Proc. SPIE 7636, 1117 (2010).