2002 OSA Annual Meeting - Orlando, Florida Technical Session WJJ5 - Thin Films II Characterization of Diamond- Like Carbon Thin Films and Their Application

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 PauloSão Carlos - SP, Brazil

G.A. Cirino ; R.D. Mansano ; P. Verdonck

LSI - EPUSP - University of São Paulo São Paulo - SP, Brazil



Outline

1. Introduction & Goals

2. Results

4. Conclusions

5. Acknowledgments



Introduction

Diffractive Optical Elements (DOE) have a wide range of applications

Amorphous hydrogenated carbon thin films (a:C-H), also called Diamond-Like Carbon (DLC), can be employed as a thin film in several optical applications



Main Goals

Show 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

(

(

)

)



Deposition of carbon thin films Our Diamond-Like Carbon (DLC) thin film is

deposited by reactive magnetron sputtering

> 3-inch diameter substrate

> transparent substrate (mechanical support)

> process conditions:

Temp. < 100oC (!!!!) CH4 plasma

Deposit. rate: 16 nm/min Rrms: 2.5 nm



> 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



0 1 2 3 4 5 6 7

10

15

20

25

30

35

40

45

Blank Lexan Lexan with Si

xN

yO

z

Lexan with DLC

Dep

th [m

]

Load [Newtons]

Lexan samples with and without DLC thin film were submmited to scratch test

Mechanical Property of DLC Thin Film



Phase-only CGH employing DLC

Design in the scalar domain

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



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

Glass Substrate

1.5 m thick DLC

sputtering

/ 2-phasedry

etching

4 (n-1)

- phase mask

lithography - phase

dryetching

2 (n-1)

/ 2-phase maskLithography

over the DLC thin film



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.



Full complex DLC-based DOE

Design through direct and inverse light propagation > 4 phase + 9 amplitude levels

Fabrication process steps > same as phase-only DOE

=> 3 lithographic masks



Fabrication of the Full Complex DLC-based DOE Sequence for the entire manufacturing process

Glass Substrate

Aluminumlayer

deposition

1.5 m thick DLC

sputtering

Amplitudemask

lithography

/ 2-phasedry

etching

4 (n-1)

- phase mask

lithography - phase

dryetching

2 (n-1)

/ 2-phase maskLithography

over the DLC thin film

Aluminumlayer

wetetching



Optical characterizationof a Fresnel CGH Full Complex

Modulation

Phase-onlyModulation



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-fieldpatterngenerator

(50 m gap)



Fabrication of the proximity mask

Introducing DLC thin layer to implement the amplitude modulation at = 364 nm

Almost transparent in the visible region

Very easy alignment procedure !!



Optical Results

Contact Exposure Proximity (50µm) Exposure

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



DLC Thin Films as a Protective Coating for Polymeric Microlens Arrays

Cross sectional view

3-D panoramic view



Conclusions DLC 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

Optical characterization of the fabricated devices showed a high quality image with very low speckle noise level



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



Acknowledgments

The 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

Documents

2002 OSA Annual Meeting - Orlando, Florida Technical Session WJJ5 - Thin Films II Characterization of Diamond- Like Carbon Thin Films and Their Application