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Characterization of DiamondLike Carbon Thin Films and Their Application for Diffractive Optical Elem

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Characterization of Diamond-Like Carbon Thin Films and Their Application for ... of a Fresnel CGH. Full Complex. Modulation. Phase-only. Modulation ... – PowerPoint PPT presentation

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Title: Characterization of DiamondLike Carbon Thin Films and Their Application for Diffractive Optical Elem


1
Characterization of Diamond-Like Carbon Thin
Films and Their Application for Diffractive
Optical Elements
Luiz G. Neto EESC University of São Paulo São
Carlos - SP, Brazil G.A. Cirino R.D.
Mansano P. Verdonck LSI - EPUSP -
University of São Paulo São Paulo - SP,
Brazil
2
Outline
1. Introduction Goals 2. Results 4.
Conclusions 5. Acknowledgments
3
Introduction
  • Diffractive Optical Elements (DOE) have a wide
    range of applications
  • Amorphous hydrogenated carbon thin films (aC-H),
    also called Diamond-Like Carbon (DLC), can be
    employed as a thin film in several optical
    applications

4
Main Goals
  • Show the applicability of amorphous hydrogenated
    carbon films (aC-H) in the micro-optics field,
    for the fabrication of gt Diffractive
    devices - Phase-only CGH
    active - Full complex DOEs
    material gt Refractive Devices - Thin
    films protective

  • material

(
)
(
)
5
Deposition of carbon thin films
  • Our Diamond-Like Carbon (DLC) thin film is
    deposited by reactive magnetron sputtering

gt 3-inch diameter substrate gt transparent
substrate (mechanical support) gt process
conditions ? Temp. lt 100oC (!!!!) ? CH4
plasma ? Deposit. rate 16 nm/min ? Rrms 2.5
nm
6
Techniques to Characterize DLC Thin Film
  • gt Ellipsometry
  • ? a priori knowledge of the film
    thickness is necessary
  • ? very good results if silicon substrate
    is used gt UV / Vis / NIR spectrometry
    ? wavelengths at which film absorption is
    negligible / nearly complete

7
Mechanical Property of DLC Thin Film
  • Lexan samples with and without DLC
    thin film were submmited to
    scratch test

8
Phase-only CGH employing DLC
  • Design in the scalar domain
  • Fabrication using the following process
    steps gt Sputter deposition of DLC gt
    lithography plasma etching of the
    (?/2) phase delay 1 micron feature size
    gt lithography plasma etching of the (?) phase
    delay

9
Fabrication of the DLC-based Phase-only DOE
  • Sequence for the entire manufacturing process

10
Fabrication results
gt very low induced roughness level, after
plasma etchinggt nearly vertical side walls,
after the (anisotropic) plasma etching.
S.E.M. characterization
A.F.M. characterization
11
Full complex DLC-based DOE
  • Design through direct and inverse light
    propagation gt 4 phase 9
    amplitude levels
  • Fabrication process steps gt same as
    phase-only DOE

gt 3 lithographic masks
12
Fabrication of the Full Complex DLC-based DOE
  • Sequence for the entire manufacturing process

13
Optical characterizationof a Fresnel CGH
Full Complex Modulation
Phase-only Modulation
14
Diffractive Phase Shift Mask for Micro-Electronic
Fabrication
  • Phase shift photo masks dramatically improve the
    resolution of exposure systems
  • A full-complexDOE can act as anear-fieldpatter
    ngenerator(50 mm gap)

15
Fabrication of the proximity mask
  • Introducing DLC thin layer to implement the
    amplitude modulation at l 364 nm
  • Almost transparent in the visible region
  • Very easy alignment procedure !!

16
Optical Results
  • Some test structures were generated in order to
    observe differences between contact and proximity
    exposure schemes

17
DLC Thin Films as a Protective Coating for
Polymeric Microlens Arrays
3-D panoramic view
Cross sectional view
18
Conclusions
  • DLC thin films are suited to be used as active
    parts (and protective coating) of micro-optical
    devices gt phase-only modulation CGH, gt full
    complex modulation CGH gt full complex
    modulation phase shift masks gt protection layer
    of polymeric micro-lenses array
  • Optical characterization of the fabricated
    devices showed a high quality image with very low
    speckle noise level

19
Conclusions (cont)
  • A full complex-amplitude modulation phase-shift
    proximity photo mask was designed and fabricated
    improvement of the exposure system resolution
  • A DLC thin layer was introduced to implement the
    amplitude modulation and a four-phase
    micro-relief on a fused silica substrate to
    implement the phase modulation
  • Optical results showed that diffraction effects
    are minimized at the mask pattern edges

20
Acknowledgments
  • The authors would like to thank the financial
    support of

gt FAPESP,gt CenPRAgt FINEP andgt CNPq.
and gt L. Cescato from UNICAMP, Brazil, for
yielding laboratory infra-structure
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