Lithography - UW-Madison Department of...

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Nanofabrication Lithography Directed Assembly Self-assembly

Transcript of Lithography - UW-Madison Department of...

Page 1: Lithography - UW-Madison Department of Physicsuw.physics.wisc.edu/~himpsel/Nano/Nanofabrication.pdfEUV Interference Lithography 500 nm Paul Nealey (Madison), ... Narrow the size distribution

Nanofabrication

Lithography

+ bio Directed Assembly

+ bio + info Self-assembly

Page 2: Lithography - UW-Madison Department of Physicsuw.physics.wisc.edu/~himpsel/Nano/Nanofabrication.pdfEUV Interference Lithography 500 nm Paul Nealey (Madison), ... Narrow the size distribution

Lithography

Precise, but expensive and difficult at small sizes (< 50 nm)

Photolithography: Widely used for microchip mass production

Electron-Beam Lithography: High resolution, individual research devices

Ion Beam Lithography: Special purpose (milling, direct deposition)

Page 3: Lithography - UW-Madison Department of Physicsuw.physics.wisc.edu/~himpsel/Nano/Nanofabrication.pdfEUV Interference Lithography 500 nm Paul Nealey (Madison), ... Narrow the size distribution

Resolution limit λ/2

Large object:Optical ruler counts λ/2 interference fringes

λ/2 limit

Smaller objectsneed shorter λ

Page 4: Lithography - UW-Madison Department of Physicsuw.physics.wisc.edu/~himpsel/Nano/Nanofabrication.pdfEUV Interference Lithography 500 nm Paul Nealey (Madison), ... Narrow the size distribution

Going to Shorter Wavelength (DUV)

Can’t go farther: There is one more excimer laser line at 157 nm (the F2 laser). However, one cannot produce good enough optics with CaF2 (or any other material that remains transparent at such a short wavelength).

Page 5: Lithography - UW-Madison Department of Physicsuw.physics.wisc.edu/~himpsel/Nano/Nanofabrication.pdfEUV Interference Lithography 500 nm Paul Nealey (Madison), ... Narrow the size distribution

Trick 1 to Push beyond λ/2 :

Immersion Lithography

The higher refractive index of water reduces the wavelength (n = 1.44 at 193 nm).

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Trick 2 to Push beyond λ/2 :

Phase Shift Mask + Enhanced Resist Contrast

Absorbing Mask Phase Mask Enhanced Contrast

In contrast to the traditional absorbing masks, a phase shift mass contains regions of transparent material with high refractive index for shifting the phase. Thereby the oscillations originating from diffraction are converted to a damped decay.

A photoresist with a high contrast narrows the decay width. This requires very good control of the exposure and the resist development.

Page 7: Lithography - UW-Madison Department of Physicsuw.physics.wisc.edu/~himpsel/Nano/Nanofabrication.pdfEUV Interference Lithography 500 nm Paul Nealey (Madison), ... Narrow the size distribution

Leapfrog to 13 nm (EUV)

Need to go to mirror optics, since all materials absorb. Regular mirrors only reflect at oblique incidence, leading to asymmetric optics that are difficult to control. Use multilayer mirrors, where interference of multiple layers enhances the reflectivity. 13 nm is preferred, because it allows the use of silicon-based multilayer mirrors. (Si begins to absorb below 13 nm due to the Si 2p core level at about 100 eV.)

Use synchrotron radiation for testing.

Need lab-based light source for mass production.

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-1 Diffraction +1 Diffraction

Sample

Transmission Grating Mask

EUV

By interference of the ±1st orders one can cut the mask period in half.

Two, three, or four diffracted beams interfere to yield dense lines and spaces,

or cubic or hexagonal arrays of dots

550 nm550 nm550 nm1:1 Lines, 55 nm Pitch

PMMA

Cubic Array of Holes, 57 nm pitch

EUV Interference Lithography

500 nm500 nm500 nm

Paul Nealey (Madison), Harun Solak (Switzerland)

Page 9: Lithography - UW-Madison Department of Physicsuw.physics.wisc.edu/~himpsel/Nano/Nanofabrication.pdfEUV Interference Lithography 500 nm Paul Nealey (Madison), ... Narrow the size distribution

Self-assembly

Cheap, atomically-precise at small sizes (< 5 nm), but poor positioning at large distances (> 50 nm)

Page 10: Lithography - UW-Madison Department of Physicsuw.physics.wisc.edu/~himpsel/Nano/Nanofabrication.pdfEUV Interference Lithography 500 nm Paul Nealey (Madison), ... Narrow the size distribution

Nanocrystals

These are surprisingly simple to make

Page 11: Lithography - UW-Madison Department of Physicsuw.physics.wisc.edu/~himpsel/Nano/Nanofabrication.pdfEUV Interference Lithography 500 nm Paul Nealey (Madison), ... Narrow the size distribution

Synthesis of Nanocrystals in Inverse Micelles I

Surfactant: Hydrophilic Head Example: Phospholipid

+ Hydrophobic Tail

Micelle: Inverse Micelle:Heads outside, Water outside Heads inside, Water inside

A nanoscale chemical beaker with aqueous solution inside

Page 12: Lithography - UW-Madison Department of Physicsuw.physics.wisc.edu/~himpsel/Nano/Nanofabrication.pdfEUV Interference Lithography 500 nm Paul Nealey (Madison), ... Narrow the size distribution

Synthesis of Nanocrystals in Inverse Micelles II

Recipe:

1) Fill inverse micelles with an ionic solution of the desired material.

2) Add a reducing agent to precipitate the neutral material.

3) Narrow the size distribution further by additional tricks.

Page 13: Lithography - UW-Madison Department of Physicsuw.physics.wisc.edu/~himpsel/Nano/Nanofabrication.pdfEUV Interference Lithography 500 nm Paul Nealey (Madison), ... Narrow the size distribution

Lin, Jaeger, Sorensen, Klabunde,J. Phys. ChemB105, 3353 (2001)

Nanocrystalswith equal size form perfect arrays

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"Perfect" Magnetic Particles: FePt (4nm)

Sun, Murray , Weller, Folks, Moser, Science 287, 1989 (2000)

Oleic acid spacer ad-justs the distance

3D array 2D array

Page 15: Lithography - UW-Madison Department of Physicsuw.physics.wisc.edu/~himpsel/Nano/Nanofabrication.pdfEUV Interference Lithography 500 nm Paul Nealey (Madison), ... Narrow the size distribution

Shape control of nanocrystals via selective surface passivationby adsorbed molecules. Only the clean surface facets will grow.

Manna, Scher, Alivisatos, JACS 122, 12700 (2000)

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Supported CatalystsRhodium nanoparticles on a TiO2 support

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Zeolites

Channels for incorporating catalysts or filtering ions

O

Si,Al

Tetrahedra

Page 18: Lithography - UW-Madison Department of Physicsuw.physics.wisc.edu/~himpsel/Nano/Nanofabrication.pdfEUV Interference Lithography 500 nm Paul Nealey (Madison), ... Narrow the size distribution

Self-assembled Nanostructures at SurfacesPush Nanostructures to the Atomic Limit

Reach Atomic Precision

Page 19: Lithography - UW-Madison Department of Physicsuw.physics.wisc.edu/~himpsel/Nano/Nanofabrication.pdfEUV Interference Lithography 500 nm Paul Nealey (Madison), ... Narrow the size distribution

> 100 atoms rearrange themselves to minimize broken bonds.

Hexagonal fcc (diamond)(eclipsed) (staggered)

Si(111)7x7

Most stable silicon surface

Page 20: Lithography - UW-Madison Department of Physicsuw.physics.wisc.edu/~himpsel/Nano/Nanofabrication.pdfEUV Interference Lithography 500 nm Paul Nealey (Madison), ... Narrow the size distribution

Si(111)7x7 as 2D Template

One of the two 7x7 triangles

is more reactive.

Aluminum sticks there.

Jia et al., APL 80, 3186 (2002)

Page 21: Lithography - UW-Madison Department of Physicsuw.physics.wisc.edu/~himpsel/Nano/Nanofabrication.pdfEUV Interference Lithography 500 nm Paul Nealey (Madison), ... Narrow the size distribution

1 kink in 20 000 atoms

Straight steps because of the large 7x7 cell.

Wide kinks cost energy.

15 nm

Stepped Si(111)7x7

Viernow et al., APL 72, 948 (1998)

Page 22: Lithography - UW-Madison Department of Physicsuw.physics.wisc.edu/~himpsel/Nano/Nanofabrication.pdfEUV Interference Lithography 500 nm Paul Nealey (Madison), ... Narrow the size distribution

The 7x7 unit cell provides a precise 2.3 nm building block

Step Step

x-derivative of the topography

“ illumination from the left ”

Stepped Si(111)7x7 as 1D Template

Page 23: Lithography - UW-Madison Department of Physicsuw.physics.wisc.edu/~himpsel/Nano/Nanofabrication.pdfEUV Interference Lithography 500 nm Paul Nealey (Madison), ... Narrow the size distribution

Atomic Perfection by Self-AssemblyWorks up to 10 nm

One 7x7 unit cell per terrace Kirakosian et al., APL 79, 1608 (2001)

5.731 592 8 nm

Page 24: Lithography - UW-Madison Department of Physicsuw.physics.wisc.edu/~himpsel/Nano/Nanofabrication.pdfEUV Interference Lithography 500 nm Paul Nealey (Madison), ... Narrow the size distribution

Sweep out Kinks into Bunches by Electromigration

Yoshida et al., APL 87, 032903 (2005)

Page 25: Lithography - UW-Madison Department of Physicsuw.physics.wisc.edu/~himpsel/Nano/Nanofabrication.pdfEUV Interference Lithography 500 nm Paul Nealey (Madison), ... Narrow the size distribution

Clean Triple step + 7x7 facet

"Decoration" of Steps ⇒ 1D Atomic Chains

With Gold1/5 monolayer

Si chain

Si dopant

Page 26: Lithography - UW-Madison Department of Physicsuw.physics.wisc.edu/~himpsel/Nano/Nanofabrication.pdfEUV Interference Lithography 500 nm Paul Nealey (Madison), ... Narrow the size distribution

Clean 7×7

0.02 monolayer below optimum Au coverageChains

One-Dimensional Growth of Atom Chains

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Gold chain

GraphiticSilicon

First Principles Calculations:

Sanchez-Portal et al.,PRB 65, 081401 (2002)Crain, Erwin, et al.,PRB 69, 125401 (2004)

X-Ray Diffraction:Robinson et al., PRL 88, 096104 (2002)

Unexpected Structures :

Gold at the center, not the edge !

Graphitic silicon ribbon !

Si(557) - Au

Page 28: Lithography - UW-Madison Department of Physicsuw.physics.wisc.edu/~himpsel/Nano/Nanofabrication.pdfEUV Interference Lithography 500 nm Paul Nealey (Madison), ... Narrow the size distribution

Free-standing Nanowires

Page 29: Lithography - UW-Madison Department of Physicsuw.physics.wisc.edu/~himpsel/Nano/Nanofabrication.pdfEUV Interference Lithography 500 nm Paul Nealey (Madison), ... Narrow the size distribution

Zhao et al., PRL 90, 187401 (2003)

Carbon Nanowire

inside a Nanotube

Page 30: Lithography - UW-Madison Department of Physicsuw.physics.wisc.edu/~himpsel/Nano/Nanofabrication.pdfEUV Interference Lithography 500 nm Paul Nealey (Madison), ... Narrow the size distribution

Wu et al., Chem. Eur. J. 8, 1261 (2002)

Silicon Nanowire Growth

Works also for carbon nanotubes with Co, Ni as catalytic metal clusters.

Page 31: Lithography - UW-Madison Department of Physicsuw.physics.wisc.edu/~himpsel/Nano/Nanofabrication.pdfEUV Interference Lithography 500 nm Paul Nealey (Madison), ... Narrow the size distribution

Wu and Yang, JACS 123, 3165 (2001)

Catalytic Nanowire Growth of Ge by Precipitation from Solution in Au

Phase diagram for immiscible solids : The melting temperature of a mixture is lower than for the pure elements.

(L = liquid region)

Page 32: Lithography - UW-Madison Department of Physicsuw.physics.wisc.edu/~himpsel/Nano/Nanofabrication.pdfEUV Interference Lithography 500 nm Paul Nealey (Madison), ... Narrow the size distribution

Peidong Yang et al., Science 292, 1897 (2001) and Int. J. of Nanoscience 1, 1 (2002)

ZnO Nanowires Grown by Precipitation from a Solution

SEM images of ZnO nanowire arrays grown on sapphire substrates. A top view of the well-faceted hexagonal nanowiretips is shown in (E). (F) High-resolution TEM image of an individual ZnO nanowire showing its <0001> growth direction. For the nanowire growth, clean (110) sapphire substrates were coated with a 10 to 35 Å thick layer of Au, with or without using TEM grids as shadow masks.

Page 33: Lithography - UW-Madison Department of Physicsuw.physics.wisc.edu/~himpsel/Nano/Nanofabrication.pdfEUV Interference Lithography 500 nm Paul Nealey (Madison), ... Narrow the size distribution

ZnO Nanowires for Solar Cells

Leschkies et al., Nano Letters 7, 1793 (2007)

Need to collect the electrons quickly in a solar cell to prevent losses. This can be achieved by running many nanowires to the places where electrons are created (here in CdSe dots which coat the ZnO wires).

Page 34: Lithography - UW-Madison Department of Physicsuw.physics.wisc.edu/~himpsel/Nano/Nanofabrication.pdfEUV Interference Lithography 500 nm Paul Nealey (Madison), ... Narrow the size distribution

Ohgai, … , Ansermet, Nanotechnology 14, 978 (2003)

Striped Cu/Co Nanowires Grown by Electroplating into Etched Pores

(Superlattices for efficient sensors)

Page 35: Lithography - UW-Madison Department of Physicsuw.physics.wisc.edu/~himpsel/Nano/Nanofabrication.pdfEUV Interference Lithography 500 nm Paul Nealey (Madison), ... Narrow the size distribution

Directed Assembly

The best of both worlds

Use lithography to define a grid. Then attach self-assembled nano-objects (dots, wires, diodes, … ).

Page 36: Lithography - UW-Madison Department of Physicsuw.physics.wisc.edu/~himpsel/Nano/Nanofabrication.pdfEUV Interference Lithography 500 nm Paul Nealey (Madison), ... Narrow the size distribution

Unpatterned Surface Patterned Surface (48 nm pitch)

Assembly of Block Copolymers on Lithographically-Defined Lines

S. O. Kim, H. H. Solak, M. P. Stoykovich, N. J. Ferrier, J. J. de Pablo, P. F. Nealey, Nature 411, 424 (2003).

• Perfect positioning over large distances• Perfect line width, defined by the size of a molecule

Page 37: Lithography - UW-Madison Department of Physicsuw.physics.wisc.edu/~himpsel/Nano/Nanofabrication.pdfEUV Interference Lithography 500 nm Paul Nealey (Madison), ... Narrow the size distribution

Park, Chaikin, Register, ...

Transfer dot patterns from a block copolymer into a metal

Page 38: Lithography - UW-Madison Department of Physicsuw.physics.wisc.edu/~himpsel/Nano/Nanofabrication.pdfEUV Interference Lithography 500 nm Paul Nealey (Madison), ... Narrow the size distribution
Page 39: Lithography - UW-Madison Department of Physicsuw.physics.wisc.edu/~himpsel/Nano/Nanofabrication.pdfEUV Interference Lithography 500 nm Paul Nealey (Madison), ... Narrow the size distribution

Guided Self-Assembly of Block-Copolymers:

From a random “fingerprint” patterns to an ordered lattice

Polymer in groove:

Thomas, Smith (MIT)

Naito et al. (Toshiba)

Shear via PDMS:

Chaikin (Princeton) On a chemical pattern:

Kim et al. (Madison)

shear

Page 40: Lithography - UW-Madison Department of Physicsuw.physics.wisc.edu/~himpsel/Nano/Nanofabrication.pdfEUV Interference Lithography 500 nm Paul Nealey (Madison), ... Narrow the size distribution

Patterned Magnetic Storage Media for Perfect Bits

Page 41: Lithography - UW-Madison Department of Physicsuw.physics.wisc.edu/~himpsel/Nano/Nanofabrication.pdfEUV Interference Lithography 500 nm Paul Nealey (Madison), ... Narrow the size distribution

Co-polymers as etch masks

Spiral grooves as guide for dots

Naito et al. (Toshiba)IEEE Trans. Magn. 38, 1949 (2002)

Page 42: Lithography - UW-Madison Department of Physicsuw.physics.wisc.edu/~himpsel/Nano/Nanofabrication.pdfEUV Interference Lithography 500 nm Paul Nealey (Madison), ... Narrow the size distribution

A single magnetic dot for storing one bit.

Side view

Page 43: Lithography - UW-Madison Department of Physicsuw.physics.wisc.edu/~himpsel/Nano/Nanofabrication.pdfEUV Interference Lithography 500 nm Paul Nealey (Madison), ... Narrow the size distribution

Magnetic force microscope dark: spin ↑ light: spin ↓

Normal microscope Dot pattern