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Characterization and Fabrication of plasmonic waveguides

VIEWS: 16 PAGES: 44

									Nano-Photolithography and an Introduction to
Fabrication and Characterization of Plasmonic
                Waveguides

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




                                            1
                    Outline


Motivation and Introduction
Nano-photolithography
Excitation
Fabrication
Characterization
Conclusion




                              2/44
                        Motivation

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

                                                            3/44
                                               Motivation


           Photolithography (Mercury lamp)
                Diffraction limit of light
           Plasmonics
                Sub wavelength operation



             ~50 nm

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   4/44
                           Plasmonic Review

Plasmonics
Surface plasmon polaritons (SPPs)
Plasmonic waveguides




J. Dionne et al., Nanoletters, Vol. 6, Issue 9, pp. 1928-1932, 2006.   5/44
Maier et al., Physical review B, Vol. 67, p. 205402, 2003.
                    Comparing the plasmon printing to
                           photolithography


                                                                 MASK



                                                           PHOTORESIST

                                                            SUBSTRATE




                                                             410 nm




                                                                         EXPOSE
        Projection lithography
        smallest feature size ~

P. Kik et al., Mat. Res. Soc. Symp. Proc. Vol. 705, 2002
                                                                         DEVELOP

                                                                  Plasmon printing
                                                                                                 6/44
                                                                  smallest feature size ~0.1 
           Field enhancement


Plasmon nano-sphere field profile




                                    7/44
         Plasmon Printing




P. Kik et al., Mat. Res. Soc. Symp. Proc. Vol. 705, 2002   8/44
                 Final resolution




P. Kik et al., Mat. Res. Soc. Symp. Proc. Vol. 705, 2002   9/44
               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




               Metal Dielectric
K SP  K 0
              Metal   Dielectric

                                              10/44
              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)




                                                    11/44
              Excitation ideas


Trick3: excitation with dots



Trick4: array of dots




                                 12/44
                               Methods of excitation


                Methods:
                     Prism coupling (Kretschmann technique) => MI,IMI
                     Grating or roughness coupling => MI,IMI, MIM
                     End-fire excitation technique => MIM, IMI

     Incident
       light




                                      Grating coupling
dp

                        Evanescent

     Prism coupling        wave
                                                              Otto method
                                      End fire coupling


                                                                            13/44
                           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                        Metal Dielectric 
                                                    K 0 nSin   K 0 Re                        
Pros:                                                                      Metal   Dielectric 
  High efficiency and Selecting any guide mode (K-matching)
  Adjusting in experiment (detachable prism)




                                                                                      14/44
    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.




                                                      15/44
                 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




                                                                    16/44
                 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
                                                                     photodetector
   Tapered coupling
   Prism-grating coupling       Source
   Holographic coupling
Inherent roughness of film
                                            Waveguide
                                 grating                         grating




                                                                      17/44
             Grating coupling


Grating structure: coupling and shape




                                        18/44
            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




                                                   19/44
Interference pattern




          Resolution: 50nm

              Luo et al., Appl. Phys. Let., Vol. 84, No. 23, 2004.
              Luo et al., Optics Express, Vol. 12, No. 14, 3055, 2004.


                                                      20/44
                   Superlens


  Snell’s law
  Negative refractive index (left handed material LH)
  Subwavelength resolution
RH    LH RH                       Superlens




                        Source                 Image




n=1   n=-1 n=1


                                                       21/44
                           Transmission


 Un/Perforated surface




                                                           0.08 μm thickness




Bonod et al., Optics Express, Vol. 11, No. 5, 482, 2003.                  22/44
Jiao et al., Progress In Electromagnetics Research Symp. 2005.
             Interference patterns




Incident light: λ=436nm; E=2843mev




     Luo et al., Optics Express, Vol. 12, No. 14, 2004.   23/44
                       Periodic Corrugated Setup




        Resolution: 25nm
        G-line 436nm

Luo et al., Appl. Phys. Let., Vol. 84, No. 23, 2004.




                                                       24/44
                     Plasmonic structures
                                           M I M I M I M                                    I M
     Planar structures                                       Bragg grating
        Simple MI waveguide
        IMI waveguide                  IM
        MIM waveguide
        Bragg grating
     Non-planar structures
        Nano-particle
        Nano-shell                   IMI


MI   I     I     I    I     I

         Bragg grating
                                       MIM
               Nano-shell       Nano-sphere
                                                                                           25/44
                                L. Hirish et al, PNAS, Vol. 100, No. 23, p. 13549, 2003.
                 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)



                                                               26/44
               Substrate choice
                                                          Silicon substrate

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


                                              Fused silica glass




                                                                        27/44
                          Fabrication

                                                      E-beam
Photoresist spinning
                                                      PMMA
    (PMMA) for E-beam lithography
    BCB, … for photolithography
Exposure
                                                Sub
    an incident beam
                                                               PMMA
        Beam
              Electron with microscope (SEM)

              X-ray

        Light                                  Sub
              UV                                              PMMA
              Visible

Development
    Aqueous developer                          Sub

Metal deposition
       E- beam evaporation
Lift off                                        Sub



                                                               28/44
                                            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.                   Au
              Can be done on Sio2 substrate.       Sio2       Mo/Ti




                                                                 Si
Charbonneau et al., J. of lightwave Tech., Vol.24, No.1, 2006.
Nikolajsen et al., Appl. Phys. Let., Vol. 82, No. 5, 2003.



                                                                      29/44
                      IMI Fabrication
                                                              Cyclotene (20μm)
                                                              Adhesion promoter
                                                              Si wafer

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

•Deposit 20nm gold with e-beam evaporation                    Cyclotene (20μm)
                                                              Si wafer
•Acetone rinsing+ lift off+ isopropanol rinsing
                                                              Cyclotene
•Spin coat cyclotene + pre and post bake                      Gold
                                                              Cyclotene
                                                              Si wafer

                                                    10-20nm




                                                                             30/44
MIM Fabrication


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

 Substrate                              Gold
                                        + photo resist
                                        Gold
 Gold                                   Insulator
 + photo resist                         Substrate
 Insulator
 Substrate
                                        Insulator
                                        Insulator
                                        Gold
                                        Insulator
                                        Substrate




                                                         31/44
 Nano-particle chain fabrication

              ITO             PMMA
     Spin coating


                             E-beam

       exposure      Glass


                             developer
    development




Metal evaporation



          Lift off             acetone



                                         32/44
                                     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


                                                           33/44
                     Bragg grating


Photoresist spin coating
   Pre baka
   Post bake
Patterning
      lithography
Etching
      KOH
      Enchants
Au deposition
   E-beam evaporation



                                     34/44
           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




                                                   35/44
    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




     NSOM excitation




              NSOM characterization
                                          36/44
                 Characterization

                                                                                             HP81680A        HP81610A
                    Experimental Setup                                                       Tunable laser   interface


•Optical table       Thorlabs MDT693
                     Piezo stage controller
                                                Hamatasu infrared
                                                Camera controller
                                                                       HP8164A lightwave
                                                                       Measurement
                                                                       mainframe

•Butt coupling
•NSOM, Photon-STM
                                                                                  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




                                                                                                               37/44
      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


                                                  38/44
                   Transmission loss


   Cut-back method
   Prism sliding method                               Photodetector
                                                              Lock-in amplifier
   Scattering detection method                 Fiber probe

                                            Prism                       recorder
                                                        Scanning
                                             waveguide


Lens                Lens                                    Photodetector
       Waveguide

                                                Sliding <------
                                           Prism          Prism

                           Photodetector      Waveguide           Matching liquid

       cutting



                                                                         39/44
                   NSOM


Aperture near field scanning optical microscopy
Aperture less NSOM




                                                  40/44
                      NSOM




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




                             41/44
NSOM




       42/44
                 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




                                                 43/44
Thank you




            44/44

								
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