lithography nano 101 introduction to nanotechnology 1

Lithography

NANO 101Introduction to Nanotechnology

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Lithography

• Photolithography• Electron beam lithography• X-ray lithography• Focused ion beam lithography

“Photoengraving”- Transfer pattern into reactive polymer film (“resist”)- Use resist to replicate pattern into thin film or substrate

3Photolithography

• “Printing”

• Transfer of the pattern using an optical technique

• Resist = photoresist; photoactive polymer, positive or negative

1. Coat substrate with resist

2. Mask; expose with light

3. Develop (dissolve exposed OR unexposed areas with chemicals)

4. Etch unprotected areas or deposit layer of metal

5. Strip resist

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Photolithography

• Maximum resolution (minimum size) of individual features limited by diffraction

Diffraction: • bending of light

• around an edge• through a slit• past an object (edges)

• direction changes• wavelength, frequency

stay the same

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Photolithography

232 min

dsb

Maximum resolution:

λ

b sd

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Three Modes of Photolithography

http://www.ece.gatech.edu/research/labs/vc/theory/photolith.html

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Photolithography: Shadow Printing

• Contact mode:• s = 0• Best resolution; near 100% accuracy

• Maximum resolution rarely achieved• Substrate and resist film rarely completely

uniform

• Proximity mode:• Small gap between mask and substrate• Need extremely flat substrates and resist

films

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Photolithography: Projection Printing

Resolution

• Worse resolution than shadow printing

• Lens imperfections

• Increased diffraction

• type of resist material

• optical system (apertures)

• exposure wavelength (λ)

• Best resolution ~ λ/2

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Radiation with smaller wavelengths

• Deep Ultra-Violet (DUV): λ < 300 nm • Need to use special lasers• Minimum pattern size ~ 100 nm

• Extreme UV (EUV): λ = 11-13 nm• Minimum pattern size ~ 60 nm• Strong absorption of light by lenses• Low reflectance of light by mirrors

http://www.lcse.umn.edu/specs/labs/images/spectrum.gif

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Current State of EUV

• Sustained 100W average source power• 1,000 wafers processed in 24 hrs

http://www.extremetech.com/computing/199782-tmsc-announces-lithography-milestone-as-euv-moves-closer-to-production

Other Options:• ArF laser (193

nm) is current state of art – Immersion

(change refractive index)

– Double Patterning

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http://www.extremetech.com/computing/190845-intel-forges-ahead-to-7nm-without-the-use-of-euv-lasers

Diffraction limitn = index of refractionn air : 1.0n water: 1.3

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Double Patterning

http://willson.cm.utexas.edu/Research/Sub_Files/DoubleExposure/index.php

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X-Ray Lithography• X-Rays

• 0.04 nm < λ < 0.4 nm

• System• Mask

• X-ray absorbing material pattern on a thin X-ray transparent material

• X-ray source• Bright enough in

necessary wavelength range

• Expensive

• X-ray sensitive materialhttp://www.camd.lsu.edu/microfabrication/latech.htm

LIGA• Lithography, Electroplating, Molding

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http://sylmand.info/features/x-ray-lithography/

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Electron Beam Lithography

E-beam:– Finely focused beam of electrons (few nm

dia.)– Electrons deflected accurately and precisely

to “write” pattern without maskResolution

– Diffraction not an issue• λ < 1 Å (0.1 nm)

– Scattering• Forward (in resist layer)• Backwards (substrate)

http://nanotechweb.org/cws/article/tech/18642

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Electron Beam Lithography

System• Electron source (gun)• Electron column (forms beam)• Mechanical stage• Control Computer

https://smif.lab.duke.edu/pict.htm

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Focused Ion Beam (FIB) Lithography

• Ions scatter much less than electrons• Sources:

– Liquid metal ions (Ga; Au-Si-Be alloys)– Long lifetime, high stability

• Resolution– sub-µm dimensions (~250 nm)– High resist exposure sensitivity– Negligible ion scattering in resist– Low back scattering from substrate

• Extensive substrate damage

• Also used for etching, deposition, and doping

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Focused Ion Beam (FIB) Applications

• Etching– Physical sputtering etching

• Bombard areas to be etched with energetic ion beams

• Simple, applicable to any sample material– Chemical etching

• Chemical reactions between substrate surface and gas molecules adsorbed onto surface

• Increased etching rate, little residual damage

• Deposition– Direction deposition (low energy ions)– Chemical-assisted deposition

FIB – etching/deposition

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Nano Factory Achieved by Focused Ion BeamToshiaki Fujii, and Takashi Kaito, Microsc Microanal 11(Suppl 2), 2005 - See more at: http://glia.ca/meanderings-wordpress/focus#sthash.06BIxsK8.dpuf

FIB - Deposition

• Deposition of Pt on Al substrate to form micro-grating for measuring material deformation 20

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Soft Lithography

Techniques:• Microcontact printing• Nanoimprint

• Alternative to photolithography• Cheaper / more flexible

• Printing of Self-Assembled Monolayers (SAMs)

• Molding of liquid precursors

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Microcontact Printing• “Stamp” made

– Pour liquid polymer into a mold to make a “stamp”

– Mold often made by photolithography

• “Ink” the stamp– Dip into solution so SAM formed on surface of

stamp

• Stamp the substrate– Place the inked stamp on a substrate– SAM transferred to substrate in specific

pattern

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Microcontact Printing

Voskuhl, J., Wendeln, C., Versluis, F., Fritz, E.-C., Roling, O., Zope, H., Schulz, C., Rinnen, S., Arlinghaus, H. F., Ravoo, B. J. and Kros, A. (2012), Immobilization of Liposomes and Vesicles on Patterned Surfaces by a Peptide Coiled-Coil Binding Motif . Angew. Chem. Int. Ed., 51: 12616–12620. doi: 10.1002/anie.201204836

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Nanoimprint

1. Make template

2. Coat substrate with polymer

3. Press stamp into polymer at high temperature; polymer deforms

4. Cool polymer and pull stamp away

5. Polymer can be then be etched or used as is

D.R. Hines et al., Appl. Phys. Lett. 86 (16), 163101 (2005).

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Nanomanipulation and Nanolithography

Based on Scanning Probe Microscopy (SPM) techniques- can be used for molecular manipulation

Types of Scanning Probe Microscopy (SPM)• Scanning Tunneling Microscopy (STM)

– Electrically conducting materials

• Atomic Force Microscopy (AFM)– Dielectric (insulating) materials

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Nanomanipulation

• STM with Tungsten tip• Placed Xenon atoms on surface• UHV and low temperature

– Clean environment and surface– Absence of thermal diffusion on surface

D.M. Eigler and E.K. Schweizer, Nature 344, 524 (1990).

The World’s Smallest Movie

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Nanomanipulation with AFM

• Perpendicular Processes: atoms lifted, then dropped

• Parallel Processes: atoms dragged along surface• Pushing• Pulling• Sliding

C. Baur, et al., Nanotechnology 9, 360 (1998).

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SPM Nanofabrication

Advantages• Nanoscale control in three dimensions, necessary

for atomic manipulation

• Manipulation and characterization

Disadvantages• Small scanning area

• Slow scanning

• Tips must be high quality and consistent

• Surface must be flat and smooth

• UHV and low temperatures

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Dip-Pen Nanolithography (DPN)

• Works under ambient conditions• Scan tip across substrate, atoms or molecules

move from AFM tip to substrate

C. Mirkin, Northwestern Univ.

Polymer Pen Lithography• DPN + µCP

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Science 19 September 2008:vol. 321 no. 5896 1658-1660

http://cen.acs.org/articles/87/i12/Boron-Dreams.html

11 million pen array

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Summary

• Photolithography– Reaching size limits (diffraction, etc.)

• Soft Lithography– Relatively new– Fabrication of nanostructrures and

nanodevices

• SPM-based techniques – Relatively new– Promise for using atoms and molecules as

building blocks