E-Beam and Conventional Lithography E-Beam and Conventional

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					E-Beam and Conventional Lithography
E-Beam

 DSSC Head and Medium Research Seminar



                          Yi Jiang
                   Outline

Introduction
Optical lithography
  Contact printing
  Proximity printing
  Projection printing
E-Beam Lithography
  E-Beam System
  PMMA Photo-resist
  Electron Scattering
Examples
Lithography Process

      1. Wafer Cleaning
      2. Dehydration Baking
      3. Wafer Priming
      4. Photo-resist Coating
      5. Soft-Baking
      6. Exposure
      7. Development
      8. Lift-off or etching

      9. After-Development
                                Lithography Technologies
                                        Parallel
                                          Optical
                                          X-ray
                                          Ion Beam
                                          Extreme Ultraviolet (EUV)
                                          Direct Transfer
                     Photolithography
                                              Imprint
                                              Step&Flash

                                        Serial
                                          Electron Beam
                                          Laser writers
                                              Laser printers
                                              Digital micromirror arrays
                                          Focused Ion Beam (FIB)
E-Beam Lithography
                            Optical Lithography
       Contact             Proximity           Projection
                 Source




                                                       Objective Lens
Mask                        Gap (z)


              Substrate


       Resolution controlled by λ and z   Resolution affected by λ, NA
       Mask issues: 1x, damage            Mask 4x, protected
                               Diffraction in Optical Lithography

Near Field (Fresnel) Diffraction            Far Field (Fraunhofer) Diffraction




        W
                                                                                 z




                      W2/ λz < 1                             W2/ λz > 1

     Ideally, Light that pass mask is square, eg. Contact Printing
     In near field, Lights have Frensel Diffraction, eg. Proximity Printing
     In far field, lights have Fraunhofer diffraction, eg. Projection printing
                        Contact/Proximity Lithography

                                 Light pass the mast should be
                               square wave.
                                 It is never a square wave
2bmin = 3(λS / 2)1/ 2          because diffraction.
                                  Photo-resist help to compensate
                               for diffraction and give us a uniform
                               pattern

                                 the Resolution limits
                                   2bmin = 3(λS )1/ 2

                                            λ = 405nm    λ = 220nm
                                 s = 1µm     0.68µm      0.50µm

                                s = 0.5µm    0.48µm      0.25µm
                 Stepper in Optical Lithography

Stepper Optics

                     Stepper used in projection printing.
                      The wafer steps and repeat lithography.
                      Resolution
                                   λ    NA = n sin θ max
                         R = k1
                                   NA
                      Depth of Focus
                                           λ
                             DOF = k 2
                                          NA2
                       E-Beam Lithography

Why E-Beam
 Photo-lithography              E-Beam


 High speed for large shapes    High speed for complex
                                patterns


 High Speed, Parallel Exposure Point by Point Exposure,
                               limits speed


 Light Diffraction Limits       Not Diffraction-limited,
 Minimum feature size 50nm at   Resolution 20nm
 best
Schematic of E-Beam Lithography




   Source Type     Brightness    Source   Energy   Vacuum
                 [amp/cm2/str]   Size     Spread   Required
                                                   (Torr)

 Tungeston       105             25um     2-3eV    10-6

  LaB6           106             10um     2-3eV    10-8


 TFE             108             25nm     0.9eV    10-9

 Cold FE         109             5nm      0.22eV   10-10
Schematic of E-Beam Lithography



     Magnetic Lens: focus beam
     Blanker: blank or pass beam
     Beam Deflector: Deflect beam
                             E-Beam Scan
Writing Method




                               Shaped Beam Rastor Scan             Vector Scan


  direct write systems use a electron beam spot that is moved with respect to the
wafer to expose the wafer one pixel at a time.
                             Photo-resist for E-Beam
PMMA (poly methyl methacrylate)

   PMMA is the most commonly
 used photo-resist for E-Beam
   PMMA is a clear plastic




 PMMA thickness vs. Spin Speed
                                Scattering in E-Beam
                                            Monte-carlo simulation for scattering
  Scattering

                                                                             10kv




                                                                             20kv


Forward
Scattering

                                                                             50kv

Backward
Scattering

       Resolution depends less on spot size, and more on scattering.
                                Examples
Magnetic Rings fabricated by E-Beam Lithography




         L. Heyderman, “Nano-scale magnetic rings”, JAP, Vol. 93, Nov 12, 2003
                             Examples
Small Gap




     Two Au electrods exposed in two separate steps
     By changing offset between the electrodes, can obtain sub-10nm gap
     Investigate electron transport in atomic-scale diameter contacts
                            Examples

Nano-Scale Fabrication




    50 nm string on “nano-guitar”
    Harold. G. Craighead, Dustin Carr (Cornell Univeristy)
                           Summary

  E-Beam Lithography is a modified SEM system
   E-Beam lithography is suitable for complex patterns like circles,
rings, and for small structures.
   A serial process, expose a single pixel at a time and move to next
pixel
   Resolution is not limited by diffraction limits, but by scattering of
electron, the resolution is around 10nm-20nm
E-Beam Lithography
E-Beam Lithography

				
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posted:7/26/2011
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