lithography c

8/2/2019 Lithography c

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3/13

Antireflex coatings

Antireflex coating ARC @ INESC: 150, 400 TiWN2

Resist was exposedboth to the light sourceand to reflected beamsfrom resist/sampleinterfaces

Impact of standing waves on the developed resist

Problem solved after coating the film with an

anti-reflex material (e.g. oxinitride) beforeexposure


4/13

Multilevel exposure


5/13

Wafer processing - Vetching / lift-off process

NEXT WEEK


6/13

Next generation lithography

- Air environment

- Complex mask fabrication ($4k-$12k)- Resists have low sensivity

- High cost X-ray sources

- vacuum environment

- direct write systems (software masks)

-slow writting over large areas- very high system cost


7/13

X-ray lithography

Advantages:No vacuum environment required (no charged particles involved)Very small wavelength (< 14) - can produce 0.15 m featuresHigh reproducibility (exposure independent of substrate type, surface reflections)

Disadvantages:No optics involved limited to 1:1 shadow printing (no image reduction is possible)Very expensive and complex mask fabrication (~10 days, cost is $4k-$12k)Low sensivity of the resistsHigh cost of sufficiently bright X-ray sources

(e.g. Synchrotron)


8/13

E-beam lithography

Leica EBL-100, shown here with a 100 kV LaB6 electron source and a

conventional SEM stage. The system is also available with a TFE sourceand laser-controlled stage. (Courtesy of Leica Lithography Systems Ltd.)COSTS ~$1M, for 2 inch areas maximum.

Advantages:

vacuum environment required (charged particlesinvolved) Direct write system (software mask) the smaller the beam sizes, the better the resolution can produce down to 0.01mm features low defect densities

At 30 keV, electrons travel >14 mm deep into a resist layer

Disadvantages: Very expensive system Slow writting

10-100 keV electron beam


9/13

E-beam lithography comercial systems


10/13

Ion Beam lithographyAdvantages:

Computer-controlled beamNo mask is neededCan produce sub-1 m featuresResists are more sensitive than electron beam resistsDiffraction effects are minimized

Less backscattering occursHigher resolutionIon beam can detect surface features for very accurate registration

Disadvantages:Reliable ion sources neededSwelling occurs when developing negative ion beam resists, limiting resolutionExpensive as compared to light lithography systemsSlower as compared to light lithography systemsTri-level processing required


11/13

Paul Scherrer Institute

Electrom Beam Lithography System

Co-axial Ion Source

Multi-Cusp Ion Source

http://lmn.web.psi.ch

Ion Beam Source

Ion Optics

VacuumChamber

Ion energies : 20 eV - 200 KeV

Beam Current : up to 500 A/cm2

Ion Specimens : H, He, Ar, Hf, Ga,Si, Au, Co, Pr, P+, BF2+, etc

E ~ 6 eV (75KeV)

E ~ 0.5 eV (75KeV)


12/13

Focused Ion Beam Lithography (FIBS)

IonBeamCannon

Scanning Beam Exposure System

Feature size is limited by spot size

Can take up to 6 orders of magnitude longer thanmask projection technology, depending on samplesize Not suitable for Industrial Purposes

Allows the exposure of very complex patterns inonly one lithography step


13/13

Bibliography

- VLSI Technology, S.M.Sze, McGraw-Hill International Editions

-Nanoelectronics and information technologyAdvanced Electronic Materials andNovel Devices, Rainer Waser (Ed.), Wiley-VCH (2003)

- Microsystems: mechanical, chemical, optical, S.D.Sentura, M.A.Schmidt and J.Harrison, MIT press

- Fundamentals of MicrofabricationThe science of miniaturization, Marc J.Madou, CRC press (2002)

- Spin Electronics - Chap.16, M.Ziese and M.J.Thornton (Ed.), Lecture Notes in Physics, Springer-Verlag

http://www.cnf.cornell.edu/spiebook/toc.htm

http://semiconductorglossary.com/default.asp?searchterm=lithography

lithography c

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