2002 OSA Annual Meeting - Orlando, Florida Technical Session WJJ5 - Thin Films II 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

2002 OSA Annual Meeting - Orlando, Florida Technical Session WJJ5 - Thin Films II Outline 1. Introduction & Goals 2. Results 4. Conclusions 5. Acknowledgments

2002 OSA Annual Meeting - Orlando, Florida Technical Session WJJ5 - Thin Films II Introduction àDiffractive Optical Elements (DOE) have a wide range of applications àAmorphous hydrogenated carbon thin films (a:C-H), also called Diamond-Like Carbon (DLC), can be employed as a thin film in several optical applications

2002 OSA Annual Meeting - Orlando, Florida Technical Session WJJ5 - Thin Films II Main Goals àShow the applicability of amorphous hydrogenated carbon films (a:C-H) in the micro-optics field, for the fabrication of: > Diffractive devices: - Phase-only CGH active - Full complex DOEs material > Refractive Devices: - Thin films protective material ( ( ) )

2002 OSA Annual Meeting - Orlando, Florida Technical Session WJJ5 - Thin Films II Deposition of carbon thin films àOur Diamond-Like Carbon (DLC) thin film is deposited by reactive magnetron sputtering > 3-inch diameter substrate > transparent substrate (mechanical support) > process conditions: Temp. < 100 o C (!!!!) CH 4 plasma Deposit. rate: 16 nm/min Rrms: 2.5 nm

2002 OSA Annual Meeting - Orlando, Florida Technical Session WJJ5 - Thin Films II > Ellipsometry  a priori knowledge of the film thickness is necessary  very good results if silicon substrate is used > UV / Vis / NIR spectrometry  wavelengths at which film absorption is negligible / nearly complete Techniques to Characterize DLC Thin Film

2002 OSA Annual Meeting - Orlando, Florida Technical Session WJJ5 - Thin Films II à Lexan samples with and without DLC thin film were submmited to scratch test Mechanical Property of DLC Thin Film

2002 OSA Annual Meeting - Orlando, Florida Technical Session WJJ5 - Thin Films II Phase-only CGH employing DLC à Design in the scalar domain à Fabrication using the following process steps: > Sputter deposition of DLC > lithography + plasma etching of the (  /2) phase delay: ~ 1 micron feature size > lithography + plasma etching of the (  ) phase delay

2002 OSA Annual Meeting - Orlando, Florida Technical Session WJJ5 - Thin Films II Fabrication of the DLC-based Phase-only DOE àSequence for the entire manufacturing process Glass Substrate 1.5  m thick DLC sputtering  / 2-phase dry etching 4 (n-1)  - phase mask lithography  - phase dry etching 2 (n-1)  / 2-phase mask Lithography over the DLC thin film

2002 OSA Annual Meeting - Orlando, Florida Technical Session WJJ5 - Thin Films II Fabrication results A.F.M. characterization S.E.M. characterization > very low induced roughness level, after plasma etching; > nearly vertical side walls, after the (anisotropic) plasma etching.

2002 OSA Annual Meeting - Orlando, Florida Technical Session WJJ5 - Thin Films II Full complex DLC-based DOE à Design through direct and inverse light propagation > 4 phase + 9 amplitude levels à Fabrication process steps > same as phase-only DOE => 3 lithographic masks

2002 OSA Annual Meeting - Orlando, Florida Technical Session WJJ5 - Thin Films II Fabrication of the Full Complex DLC-based DOE àSequence for the entire manufacturing process Glass Substrate Aluminum layer deposition 1.5  m thick DLC sputtering Amplitude mask lithography  / 2-phase dry etching 4 (n-1)  - phase mask lithography  - phase dry etching 2 (n-1)  / 2-phase mask Lithography over the DLC thin film Aluminum layer wet etching

2002 OSA Annual Meeting - Orlando, Florida Technical Session WJJ5 - Thin Films II Optical characterization of a Fresnel CGH Full Complex Modulation Phase-only Modulation

2002 OSA Annual Meeting - Orlando, Florida Technical Session WJJ5 - Thin Films II Diffractive Phase Shift Mask for Micro-Electronic Fabrication àPhase shift photo masks dramatically improve the resolution of exposure systems  A full-complex DOE can act as a near-field pattern generator (50  m gap)

2002 OSA Annual Meeting - Orlando, Florida Technical Session WJJ5 - Thin Films II Fabrication of the proximity mask  Introducing DLC thin layer to implement the amplitude modulation at  = 364 nm àAlmost transparent in the visible region àVery easy alignment procedure !!

2002 OSA Annual Meeting - Orlando, Florida Technical Session WJJ5 - Thin Films II Optical Results Contact ExposureProximity (50µm) Exposure àSome test structures were generated in order to observe differences between contact and proximity exposure schemes

2002 OSA Annual Meeting - Orlando, Florida Technical Session WJJ5 - Thin Films II DLC Thin Films as a Protective Coating for Polymeric Microlens Arrays Cross sectional view 3-D panoramic view

2002 OSA Annual Meeting - Orlando, Florida Technical Session WJJ5 - Thin Films II Conclusions àDLC thin films are suited to be used as active parts (and protective coating) of micro-optical devices: > phase-only modulation CGH, > full complex modulation CGH > full complex modulation phase shift masks > protection layer of polymeric micro-lenses array àOptical characterization of the fabricated devices showed a high quality image with very low speckle noise level

2002 OSA Annual Meeting - Orlando, Florida Technical Session WJJ5 - Thin Films II Conclusions (cont) àA full complex-amplitude modulation phase-shift proximity photo mask was designed and fabricated: improvement of the exposure system resolution àA 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 àOptical results showed that diffraction effects are minimized at the mask pattern edges

2002 OSA Annual Meeting - Orlando, Florida Technical Session WJJ5 - Thin Films II Acknowledgments àThe authors would like to thank the financial support of > FAPESP, > CenPRA > FINEP and > CNPq. and > L. Cescato from UNICAMP, Brazil, for yielding laboratory infra-structure