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Hamid Nejati ELEC 527 Professor Tour, Professor Zhong 03/29/2007

Nano-Photolithography and an Introduction to Fabrication and Characterization of Plasmonic Waveguides. Hamid Nejati ELEC 527 Professor Tour, Professor Zhong 03/29/2007. Outline. Motivation and Introduction Nano-photolithography Excitation Fabrication Characterization Conclusion.

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Hamid Nejati ELEC 527 Professor Tour, Professor Zhong 03/29/2007

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  1. Nano-Photolithography and an Introduction to Fabrication and Characterization of Plasmonic Waveguides Hamid Nejati ELEC 527 Professor Tour, Professor Zhong 03/29/2007

  2. Outline • Motivation and Introduction • Nano-photolithography • Excitation • Fabrication • Characterization • Conclusion

  3. Photomask substrate Laser light Light Aqueous development Chromium etch Photoresist strip Motivation • Photolithography: • Diffraction limit of light: resolution >100nm • Higher speed and repeatable • Lift off process • E-beam lithography: • Higher resolution: around 20nm • Lower speed and non repeatable • Nano-imprint • Industrial

  4. ~50 nm Motivation • Photolithography (Mercury lamp) • Diffraction limit of light • Plasmonics • Sub wavelength operation Idea: Use near-field coupling between closely spaced metal nanoparticles or planar plasmonic waveguides for information propagation below the diffraction limit of light Y. Xia et al., “Soft lithography”, Angewandte Chemie International Edition, Vol. 37, pp. 550–575, 1998

  5. Plasmonic Review • Plasmonics • Surface plasmon polaritons (SPPs) • Plasmonic waveguides J. Dionne et al., Nanoletters, Vol. 6, Issue 9, pp. 1928-1932, 2006. Maier et al., Physical review B, Vol. 67, p. 205402, 2003.

  6. EXPOSE DEVELOP Comparing the plasmon printing to photolithography Projection lithography smallest feature size ~ P. Kik et al., Mat. Res. Soc. Symp. Proc. Vol. 705, 2002 Plasmon printing smallest feature size ~0.1 

  7. Field enhancement • Plasmon nano-sphere field profile

  8. Plasmon Printing P. Kik et al., Mat. Res. Soc. Symp. Proc. Vol. 705, 2002

  9. Final resolution P. Kik et al., Mat. Res. Soc. Symp. Proc. Vol. 705, 2002

  10. Plasmon Excitation • Plasmonic waves have bigger K vector in comparison to the light waves • Sources: • He-Ne Laser (632.8 nm) • Excimer laser 248nm • Laser diode 1550nm

  11. Excitation ideas • Trick1: excitation from a high index medium for surface plasmon at air/metal interface (prism) • Trick2: K vector in periodic structures due to Bloch theorem is not single (periodic with reciprocal lattice vector) (grating)

  12. Excitation ideas • Trick3: excitation with dots • Trick4: array of dots

  13. Incident light dp Otto method Evanescent wave Grating coupling End fire coupling Prism coupling Methods of excitation • Methods: • Prism coupling (Kretschmann technique) => MI,IMI • Grating or roughness coupling => MI,IMI, MIM • End-fire excitation technique => MIM, IMI

  14. Prism coupling • Excitation of MI, IMI setups, and Asymmetric mode • Excitation angle is dependent on the thickness of the film • Cons: • Adjustment of gap separation & beam position, poor stability • Expensive high-index prism and adjustment system • Pros: • High efficiency and Selecting any guide mode (K-matching) • Adjusting in experiment (detachable prism)

  15. Inherent Roughness of the Metal Film • Inherent roughness of the metal film acts as a statistically determined distribution of inelastic scatter centers for an SPP => scattered light method • Cons: • Low intensity • Inhomogeneous distribution • Sharp tip of microscope: tip scatters part of the local optical near field into the fiber and then to the photo detector.

  16. End-Fire Coupling • Coupling with the direct excitation from the end of waveguide • Butt coupling of Polarization maintained fiber to the input and a single mode fiber at output • Optical index matched gel (OCF446 Nye optical) • Lens system and IR camera • Thermoelectric cooler • Tunable laser or EE-LED diode (1.55μm)+ polarization controller • Optical spectrum analyzer

  17. photodetector Source Waveguide grating grating Grating Coupling • Pros: • High efficiency with optimum design • Any guided mode can be excited • Compact, stable, and inexpensive for Integration in waveguides • Cons: • Complex theoretical calculation and advanced fabrication technique • Device parameters can’t be adjusted after fabrication • Other Coupling methods • Tapered coupling • Prism-grating coupling • Holographic coupling • Inherent roughness of film

  18. Grating coupling • Grating structure: coupling and shape

  19. Corrugated surface • Perforated or imperforated surfaces can invert plasmon to light and light to plasmon (even the incident light from mercury lamp in photolithography) • Periodic structures like gratings have different values of K vector (As Bloch waves), which helps the coupling of light to plasmon. • Surface plasmon wavelength is proportional to the periodicity of the lattice

  20. Interference pattern Luo et al., Appl. Phys. Let., Vol. 84, No. 23, 2004. Luo et al., Optics Express, Vol. 12, No. 14, 3055, 2004. Resolution: 50nm

  21. RH LH RH Superlens Image Source n=1 n=-1 n=1 Superlens • Snell’s law • Negative refractive index (left handed material LH) • Subwavelength resolution

  22. 0.08 μm thickness Transmission • Un/Perforated surface Bonod et al., Optics Express, Vol. 11, No. 5, 482, 2003. Jiao et al., Progress In Electromagnetics Research Symp. 2005.

  23. Interference patterns Luo et al., Optics Express, Vol. 12, No. 14, 2004. Incident light: λ=436nm; E=2843mev

  24. Periodic Corrugated Setup Resolution: 25nm G-line 436nm Luo et al., Appl. Phys. Let., Vol. 84, No. 23, 2004.

  25. Bragg grating M I M Bragg grating I M I M I M I I I I I I M IM IMI MIM Nano-shell Nano-sphere Plasmonic structures • Planar structures • Simple MI waveguide • IMI waveguide • MIM waveguide • Bragg grating • Non-planar structures • Nano-particle • Nano-shell L. Hirish et al, PNAS, Vol. 100, No. 23, p. 13549, 2003.

  26. Material choice • Metal: • Negative permittivity • Low loss in desired frequency • Gold: low loss in 1.55μm, Negative permittivity • Silver: low loss in He-Ne laser range, Negative permittivity • Insulator: • Positive permittivity • Compatibility to substrate, or function as photoresist • Sio2 (PECVD) • BCB (photo resist for photolithography) • PMMA (photo resist for e-beam lithography)

  27. Silicon substrate ITO coated glass Quartz substrate Fused silica glass Substrate choice • Silicon substrate • SOI substrate • Oxidation • Photoresist • Silica substrate • Quartz • Fused silica glass • ITO: special usage for e-beam lithography, need low conductance (Indium tin oxide coating)

  28. E-beam PMMA Sub PMMA Sub PMMA Sub Sub Fabrication • Photoresist spinning • (PMMA) for E-beam lithography • BCB, … for photolithography • Exposure • an incident beam • Beam • Electron with microscope (SEM) • X-ray • Light • UV • Visible • Development • Aqueous developer • Metal deposition • E- beam evaporation • Lift off

  29. Au Sio2 Mo/Ti Si IMI fabrication • Sputtering 20μm Sio2 on Si Wafer. • Molybdenum or Ti adhesive layer (e-beam evaporated, vacuum < Micro Torr) • Gold e-beam evaporation under vacuum (24.4nm). • Lift off (still & ultrasonic bath) • Sputtering 20μm Sio2 on Au. • Replacing Sio2 with 15μm BCB. • Can be done on Sio2 substrate. Charbonneau et al., J. of lightwave Tech., Vol.24, No.1, 2006. Nikolajsen et al., Appl. Phys. Let., Vol. 82, No. 5, 2003.

  30. Cyclotene (20μm) Adhesion promoter Si wafer UV light Mask + photo resist (S1813) Cyclotene (20μm) Si wafer undercut + photo resist (S1813) Cyclotene (20μm) Si wafer Gold + photo resist (S1813) Cyclotene (20μm) Si wafer Gold Cyclotene (20μm) Si wafer Cyclotene Gold Cyclotene Si wafer 10-20nm IMI Fabrication • Spin coat adhesion promoter (AP3000) and cyclotene @ 1000rpm(10s) and 2000rpm(30s) • Soft bake @ 210 (10min) + hard bake @ 250 (10min) • Spin coat shipley1813 photoresist @ 4000rpm(30s) • Pre bake @ 115 (10min) expose (karl-suss MJB3 mask aligner) soak sample in chlorobenzene (10min) • Develop microposit MF-319 (2min) => undercut => prevent the metal to be coated on side walls=> increase the lift off quality • Deposit 20nm gold with e-beam evaporation • Acetone rinsing+ lift off+ isopropanol rinsing • Spin coat cyclotene + pre and post bake

  31. MIM Fabrication Gold Insulator Substrate Insulator: cyclotene or SiO2 Insulator Adhesion promoter if needed Gold Substrate: oxidized Si or SiO2 Insulator Substrate UV light Undercut Mask + photo resist + photo resist Gold Insulator + adhesion metal if needed Insulator Substrate Substrate Undercut Gold + photo resist + photo resist Gold Insulator Insulator Substrate Substrate Gold Insulator + photo resist Insulator Insulator Gold Substrate Insulator Substrate

  32. ITO PMMA Spin coating E-beam exposure Glass developer development Metal evaporation acetone Lift off Nano-particle chain fabrication

  33. MIM fabrication • Au deposition on fused silica substrate by magnetron sputtering (150nm) • Sio2 PECVD (3.3nm, 56nm, 14nm) • No annealing + cleaving • Au deposition on fused silica substrate by magnetron sputtering (150nm) • Covered by Sio2 or air Miyazaki et al., Phys. Rev. Let., PRL 96, 097401, 2006

  34. Bragg grating • Photoresist spin coating • Pre baka • Post bake • Patterning • lithography • Etching • KOH • Enchants • Au deposition • E-beam evaporation

  35. Fabrication of Plasmon Waveguides Use e-beam lithography with liftoff to fabricate 50 nm Au nanoparticles on ITO coated glass • Particles are almost spherical in shape • Good control over size and inter-particle spacing

  36. NSOM excitation NSOM characterization Characterization of Metallic Nanoparticle Waveguide and Fabrication of Nanoshell • NSOM excitation • Far field detection • Fabrication methods: • Silica sphere: stober method, std < 5% • Surface modification: APTMS • Attachment of gold nanoparticle (1-2nm) • Reductive growth of thin gold shell

  37. Experimental Setup HP81680A Tunable laser HP81610A interface HP8164A lightwave Measurement mainframe Thorlabs MDT693 Piezo stage controller Hamatasu infrared Camera controller Hamatasu C5332 IR camera Filter Objective lens Optical fiber Plasmo1n waveguide HP 81624A Detector Fiber stage Device stage Obj. stage Mirror Polarizer Microscope field of view Characterization • Optical table • Butt coupling • NSOM, Photon-STM

  38. Methods of characterization • Near field probing • Fluorescence imaging • Light scattering from surface roughness • Fourier domain observation of scattering in a grating array • Optical spectroscopy • NSOM • PSTM • Leakage radiation microscopy

  39. Photodetector Lock-in amplifier Fiber probe Prism recorder Scanning waveguide Photodetector Sliding <------ Prism Prism Lens Lens Waveguide Waveguide Matching liquid Photodetector cutting Transmission loss • Cut-back method • Prism sliding method • Scattering detection method

  40. NSOM • Aperture near field scanning optical microscopy • Aperture less NSOM

  41. Multi-application 4 probe NSOM, AFM,SPM,… NSOM

  42. NSOM

  43. Conclusion • Plasmon assisted Nanophotolithography was reviewed • Fabrication, Excitation, and characterization of a plasmonic waveguide is reviewed • Special methods for characterization of MI, MIM, IMI, and Grating setups understood

  44. Thank you

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