Download - Lithography c
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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
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Multilevel exposure
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Wafer processing - Vetching / lift-off process
NEXT WEEK
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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
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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)
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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
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E-beam lithography comercial systems
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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
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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)
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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
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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