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Interference lithography

January 01, 1970

Interference lithography (or holographic lithography) is a technique for patterning regular arrays of fine features, without the use of complex optical systems or photomasks.

Basic principle edit

The basic principle is the same as in interferometry or holography. An interference pattern between two or more coherent light waves is set up and recorded in a recording layer (photoresist). This interference pattern consists of a periodic series of fringes representing intensity minima and maxima. Upon post-exposure photolithographic processing, a photoresist pattern corresponding to the periodic intensity pattern emerges.

For 2-beam interference, the fringe-to-fringe spacing or period is given by  , where λ is the wavelength and θ is the angle between the two interfering waves. The minimum period achievable is then half the wavelength.

By using 3-beam interference, arrays with hexagonal symmetry can be generated, while with 4 beams, arrays with rectangular symmetry or 3D photonic crystals are generated. With multi wave interference (by inserting a diffuser into the optical path) aperiodic patterns with defined spatial frequency spectrum can be originated. Hence, by superimposing different beam combinations, different patterns are made possible.

Coherence requirements edit

For interference lithography to be successful, coherence requirements must be met. First, a spatially coherent light source must be used. This is effectively a point light source in combination with a collimating lens. A laser or synchrotron beam are also often used directly without additional collimation. The spatial coherence guarantees a uniform wavefront prior to beam splitting. Second, it is preferred to use a monochromatic or temporally coherent light source. This is readily achieved with a laser but broadband sources would require a filter. The monochromatic requirement can be lifted if a diffraction grating is used as a beam splitter, since different wavelengths would diffract into different angles but eventually recombine anyway. Even in this case, spatial coherence and normal incidence would still be required.

Beam splitter edit

Coherent light must be split into two or more beams prior to being recombined in order to achieve interference. Typical methods for beam splitting are Lloyd´s mirrors, prisms and diffraction gratings.

Electron holographic lithography edit

The technique is readily extendible to electron waves as well, as demonstrated by the practice of electron holography.[1][2] Spacings of a few nanometers[1] or even less than a nanometer[2] have been reported using electron holograms. This is because the wavelength of an electron is always shorter than for a photon of the same energy. The wavelength of an electron is given by the de Broglie relation  , where   is the Planck constant and   is the electron momentum. For example, a 1 keV electron has a wavelength of slightly less than 0.04 nm. A 5 eV electron has a wavelength of 0.55 nm. This yields X-ray-like resolution without depositing significant energy. In order to ensure against charging, it must be ensured that electrons can penetrate sufficiently to reach the conducting substrate.

A fundamental concern for using low-energy electrons (≪100 eV) with this technique is their natural tendency to repel one another due to Coulomb forces as well as Fermi–Dirac statistics, though electron anti-bunching has been verified only in a single case.

Atom holographic lithography edit

The interference of atomic de Broglie waves is also possible provided one can obtain coherent beams of cooled atoms. The momentum of an atom is even larger than for electrons or photons, allowing even smaller wavelengths, per the de Broglie relation. Generally the wavelength will be smaller than the diameter of the atom itself.

Uses edit

The benefit of using interference lithography is the quick generation of dense features over a wide area without loss of focus. Seamless diffraction gratings on areas of more than one square meter have been originated by interference lithography.[3] Hence, it is commonly used for the origination of master structures for subsequent micro or nano replication processes[4] (e.g. nanoimprint lithography) or for testing photoresist processes for lithography techniques based on new wavelengths (e.g., EUV or 193 nm immersion). In addition, interfering laser beams of high-power pulsed lasers provides the opportunity of applying a direct treatment of the material's surface (including metals, ceramics and polymers) based on photothermal and/or photochemical mechanisms. Due to the above-mentioned characteristics, this method has been called in this case "Direct Laser Interference Patterning" (DLIP).[5][6][7] Using DLIP, the substrates can be structured directly in one-step obtaining a periodic array on large areas in a few seconds. Such patterned surfaces can be used for different applications including tribology (wear and friction reduction), photovoltaics (increased photocurrent),[8] or biotechnology. Electron interference lithography[9][10] may be used for patterns which normally take too long for conventional electron beam lithography to generate.

The drawback of interference lithography is that it is limited to patterning arrayed features or uniformly distributed aperiodic patterns only. Hence, for drawing arbitrarily shaped patterns, other photolithography techniques are required. In addition, for electron interference lithography non-optical effects, such as secondary electrons from ionizing radiation or photoacid generation and diffusion, cannot be avoided with interference lithography. For instance, the secondary electron range is roughly indicated by the width of carbon contamination (~20 nm) at the surface induced by a focused (2 nm) electron beam.[10] This indicates that the lithographic patterning of 20 nm half-pitch features or smaller will be significantly affected by factors other than the interference pattern, such as the cleanliness of the vacuum.

References edit

  1. ^ a b Dunin-Borkowski, RE; Kasama, T; Wei, A; Tripp, SL; Hÿtch, MJ; Snoeck, E; Harrison, RJ; Putnis, A (2004). "Off-axis electron holography of magnetic nanowires and chains, rings, and planar arrays of magnetic nanoparticles". Microsc. Res. Tech. 64 (5–6): 390–402. CiteSeerX 10.1.1.506.6251. doi:10.1002/jemt.20098. PMID 15549694. S2CID 432466.
  2. ^ a b Hasselbach, F. (1997). "Selected topics in charged particle interferometry". Scanning Microscopy. 11: 345–366.
  3. ^ Wolf, Andreas J.; Hauser, Hubert; Kübler, Volker; Walk, Christian; Höhn, Oliver; Bläsi, Benedikt (2012-10-01). "Origination of nano- and microstructures on large areas by interference lithography". Microelectronic Engineering. Special issue MNE 2011 – Part II. 98: 293–296. doi:10.1016/j.mee.2012.05.018.
  4. ^ Bläsi, B.; Tucher, N.; Höhn, O.; Kübler, V.; Kroyer, T.; Wellens, Ch.; Hauser, H. (2016-01-01). "Large area patterning using interference and nanoimprint lithography". In Thienpont, Hugo; Mohr, Jürgen; Zappe, Hans; Nakajima, Hirochika (eds.). Micro-Optics 2016. Vol. 9888. pp. 98880H–98880H–9. doi:10.1117/12.2228458. S2CID 32333348.
  5. ^ Lasagni, A.; Holzapfel, C.; Mücklich, F. (2005). "Periodic Pattern Formation of Intermetallic Phases with Long Range Order by Laser Interference Metallurgy". Adv. Eng. Mater. 7 (6): 487–492. doi:10.1002/adem.200400206. S2CID 137980942.
  6. ^ Lasagni, A.; Mücklich, F.; Nejati, M. R.; Clasen, R. (2006). "Periodical Surface Structuring of Metals by Laser Interference Metallurgy as a New Fabrication Method of Textured Solar Selective Absorbers". Adv. Eng. Mater. 8 (6): 580–584. doi:10.1002/adem.200500261. S2CID 135516098.
  7. ^ Lasagni, A.; Holzapfel, C.; Weirich, T.; Mücklich, F. (2007). "Laser interference metallurgy: A new method for periodic surface microstructure design on multilayered metallic thin films". Appl. Surf. Sci. 253 (19): 8070–8074. Bibcode:2007ApSS..253.8070L. doi:10.1016/j.apsusc.2007.02.092.
  8. ^ Ring, Sven; Neubert, Sebastian; Schultz, Christof; Schmidt, Sebastian S.; Ruske, Florian; Stannowski, Bernd; Fink, Frank; Schlatmann, Rutger (2015-01-01). "Light trapping for a-Si:H/µc-Si:H tandem solar cells using direct pulsed laser interference texturing". Physica Status Solidi RRL. 9 (1): 36–40. Bibcode:2015PSSRR...9...36R. doi:10.1002/pssr.201409404. ISSN 1862-6270. S2CID 93490614.
  9. ^ Ogai, Keiko; Kimura, Yoshihide; Shimizu, Ryuichi; Fujita, Junichi; Matsui, Shinji (1995). "Nanofabrication of grating and dot patterns by electron holographic lithography". Appl. Phys. Lett. 66 (12): 1560–1562. Bibcode:1995ApPhL..66.1560O. doi:10.1063/1.113646.
  10. ^ a b Fujita, S.; Maruno, S.; Watanabe, H.; Kusumi, Y.; Ichikawa, M. (1995). "Periodical nanostructure fabrication using electron interference fringes produced by scanning interference electron microscope". Appl. Phys. Lett. 66 (20): 2754–2756. Bibcode:1995ApPhL..66.2754F. doi:10.1063/1.113698.

External links edit

  • Large-area patterning using interference and nanoimprint lithography
  • Interference lithography at Fraunhofer ISE

January 01, 1970
interference, lithography, holographic, lithography, technique, patterning, regular, arrays, fine, features, without, complex, optical, systems, photomasks, contents, basic, principle, coherence, requirements, beam, splitter, electron, holographic, lithography. Interference lithography or holographic lithography is a technique for patterning regular arrays of fine features without the use of complex optical systems or photomasks Contents 1 Basic principle 2 Coherence requirements 3 Beam splitter 4 Electron holographic lithography 5 Atom holographic lithography 6 Uses 7 References 8 External linksBasic principle editThe basic principle is the same as in interferometry or holography An interference pattern between two or more coherent light waves is set up and recorded in a recording layer photoresist This interference pattern consists of a periodic series of fringes representing intensity minima and maxima Upon post exposure photolithographic processing a photoresist pattern corresponding to the periodic intensity pattern emerges For 2 beam interference the fringe to fringe spacing or period is given by l 2 sin 8 2 textstyle frac lambda 2 sin bigl tfrac theta 2 bigr nbsp where l is the wavelength and 8 is the angle between the two interfering waves The minimum period achievable is then half the wavelength By using 3 beam interference arrays with hexagonal symmetry can be generated while with 4 beams arrays with rectangular symmetry or 3D photonic crystals are generated With multi wave interference by inserting a diffuser into the optical path aperiodic patterns with defined spatial frequency spectrum can be originated Hence by superimposing different beam combinations different patterns are made possible Coherence requirements editFor interference lithography to be successful coherence requirements must be met First a spatially coherent light source must be used This is effectively a point light source in combination with a collimating lens A laser or synchrotron beam are also often used directly without additional collimation The spatial coherence guarantees a uniform wavefront prior to beam splitting Second it is preferred to use a monochromatic or temporally coherent light source This is readily achieved with a laser but broadband sources would require a filter The monochromatic requirement can be lifted if a diffraction grating is used as a beam splitter since different wavelengths would diffract into different angles but eventually recombine anyway Even in this case spatial coherence and normal incidence would still be required Beam splitter editCoherent light must be split into two or more beams prior to being recombined in order to achieve interference Typical methods for beam splitting are Lloyd s mirrors prisms and diffraction gratings Electron holographic lithography editThe technique is readily extendible to electron waves as well as demonstrated by the practice of electron holography 1 2 Spacings of a few nanometers 1 or even less than a nanometer 2 have been reported using electron holograms This is because the wavelength of an electron is always shorter than for a photon of the same energy The wavelength of an electron is given by the de Broglie relation l h p displaystyle lambda frac h p nbsp where h displaystyle h nbsp is the Planck constant and p displaystyle p nbsp is the electron momentum For example a 1 keV electron has a wavelength of slightly less than 0 04 nm A 5 eV electron has a wavelength of 0 55 nm This yields X ray like resolution without depositing significant energy In order to ensure against charging it must be ensured that electrons can penetrate sufficiently to reach the conducting substrate A fundamental concern for using low energy electrons 100 eV with this technique is their natural tendency to repel one another due to Coulomb forces as well as Fermi Dirac statistics though electron anti bunching has been verified only in a single case Atom holographic lithography editThe interference of atomic de Broglie waves is also possible provided one can obtain coherent beams of cooled atoms The momentum of an atom is even larger than for electrons or photons allowing even smaller wavelengths per the de Broglie relation Generally the wavelength will be smaller than the diameter of the atom itself Uses editThe benefit of using interference lithography is the quick generation of dense features over a wide area without loss of focus Seamless diffraction gratings on areas of more than one square meter have been originated by interference lithography 3 Hence it is commonly used for the origination of master structures for subsequent micro or nano replication processes 4 e g nanoimprint lithography or for testing photoresist processes for lithography techniques based on new wavelengths e g EUV or 193 nm immersion In addition interfering laser beams of high power pulsed lasers provides the opportunity of applying a direct treatment of the material s surface including metals ceramics and polymers based on photothermal and or photochemical mechanisms Due to the above mentioned characteristics this method has been called in this case Direct Laser Interference Patterning DLIP 5 6 7 Using DLIP the substrates can be structured directly in one step obtaining a periodic array on large areas in a few seconds Such patterned surfaces can be used for different applications including tribology wear and friction reduction photovoltaics increased photocurrent 8 or biotechnology Electron interference lithography 9 10 may be used for patterns which normally take too long for conventional electron beam lithography to generate The drawback of interference lithography is that it is limited to patterning arrayed features or uniformly distributed aperiodic patterns only Hence for drawing arbitrarily shaped patterns other photolithography techniques are required In addition for electron interference lithography non optical effects such as secondary electrons from ionizing radiation or photoacid generation and diffusion cannot be avoided with interference lithography For instance the secondary electron range is roughly indicated by the width of carbon contamination 20 nm at the surface induced by a focused 2 nm electron beam 10 This indicates that the lithographic patterning of 20 nm half pitch features or smaller will be significantly affected by factors other than the interference pattern such as the cleanliness of the vacuum References edit a b Dunin Borkowski RE Kasama T Wei A Tripp SL Hytch MJ Snoeck E Harrison RJ Putnis A 2004 Off axis electron holography of magnetic nanowires and chains rings and planar arrays of magnetic nanoparticles Microsc Res Tech 64 5 6 390 402 CiteSeerX 10 1 1 506 6251 doi 10 1002 jemt 20098 PMID 15549694 S2CID 432466 a b Hasselbach F 1997 Selected topics in charged particle interferometry Scanning Microscopy 11 345 366 Wolf Andreas J Hauser Hubert Kubler Volker Walk Christian Hohn Oliver Blasi Benedikt 2012 10 01 Origination of nano and microstructures on large areas by interference lithography Microelectronic Engineering Special issue MNE 2011 Part II 98 293 296 doi 10 1016 j mee 2012 05 018 Blasi B Tucher N Hohn O Kubler V Kroyer T Wellens Ch Hauser H 2016 01 01 Large area patterning using interference and nanoimprint lithography In Thienpont Hugo Mohr Jurgen Zappe Hans Nakajima Hirochika eds Micro Optics 2016 Vol 9888 pp 98880H 98880H 9 doi 10 1117 12 2228458 S2CID 32333348 Lasagni A Holzapfel C Mucklich F 2005 Periodic Pattern Formation of Intermetallic Phases with Long Range Order by Laser Interference Metallurgy Adv Eng Mater 7 6 487 492 doi 10 1002 adem 200400206 S2CID 137980942 Lasagni A Mucklich F Nejati M R Clasen R 2006 Periodical Surface Structuring of Metals by Laser Interference Metallurgy as a New Fabrication Method of Textured Solar Selective Absorbers Adv Eng Mater 8 6 580 584 doi 10 1002 adem 200500261 S2CID 135516098 Lasagni A Holzapfel C Weirich T Mucklich F 2007 Laser interference metallurgy A new method for periodic surface microstructure design on multilayered metallic thin films Appl Surf Sci 253 19 8070 8074 Bibcode 2007ApSS 253 8070L doi 10 1016 j apsusc 2007 02 092 Ring Sven Neubert Sebastian Schultz Christof Schmidt Sebastian S Ruske Florian Stannowski Bernd Fink Frank Schlatmann Rutger 2015 01 01 Light trapping for a Si H µc Si H tandem solar cells using direct pulsed laser interference texturing Physica Status Solidi RRL 9 1 36 40 Bibcode 2015PSSRR 9 36R doi 10 1002 pssr 201409404 ISSN 1862 6270 S2CID 93490614 Ogai Keiko Kimura Yoshihide Shimizu Ryuichi Fujita Junichi Matsui Shinji 1995 Nanofabrication of grating and dot patterns by electron holographic lithography Appl Phys Lett 66 12 1560 1562 Bibcode 1995ApPhL 66 1560O doi 10 1063 1 113646 a b Fujita S Maruno S Watanabe H Kusumi Y Ichikawa M 1995 Periodical nanostructure fabrication using electron interference fringes produced by scanning interference electron microscope Appl Phys Lett 66 20 2754 2756 Bibcode 1995ApPhL 66 2754F doi 10 1063 1 113698 External links editLarge area patterning using interference and nanoimprint lithography Interference lithography at Fraunhofer ISE Retrieved from https en wikipedia org w index php title Interference lithography amp oldid 1188207188, wikipedia, wiki, book, books, library,

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