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Overview of Nanofabrication. Material depostion methods Thin films of materials Thickness measurement Lithography Pattern transformation on to planar suface Direct write, or mask reproduction Imaging and Metrology methods Electron Microscopy Scanning probe microscopy.

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overview of nanofabrication
Overview of Nanofabrication
  • Material depostion methods
    • Thin films of materials
    • Thickness measurement
  • Lithography
    • Pattern transformation on to planar suface
    • Direct write, or mask reproduction
  • Imaging and Metrology methods
    • Electron Microscopy
    • Scanning probe microscopy
thin film deposition techniques
Thin film deposition techniques
  • Vacuum deposition Methods
    • UHV (<10-8), HV
    • Sputtering
    • CVD
    • Laser Oblation
    • Thermal deposition
      • Boat or crucible, E-gun
    • Epitaxy, growth models
sputtering
Sputtering

substrate

Target material

B

E

Ar

Vacuum + 10-3 Torr Ar

  • RF plasma rectifies RF power, gives DC acceleration voltage
  • Ions circle B field lines, increase colisson probability

Ar, N2

RF Power

e gun

B

Permanent

Magnet

HV

E-gun

Filament

thermal cvd system
Thermal CVD system

Precurser Gas

For growing

Carbon Nanotubes

http://www.iljinnanotech.co.kr/en/material/r-4-4.htm

carbon nanotubes
Carbon Nanotubes

http://www.iljinnanotech.co.kr/en/material/r-4-4.htm

slide8
MBE

http://www.wsi.tu-muenchen.de/E24/resources/facilities.htm

the knudsen cell effusion cell
The Knudsen Cell (effusion cell)

http://www.grc.nasa.gov/WWW/RT2002/5000/5160copland.html

lithography
Lithography
  • Spin coat radiation sensitive polymer - Resist
  • Expose layer (through mask or direct write)
  • Develop
  • Etch away or deposit material
resist contrast curve

100%

Film Retention

0%

D2

D1

Resist Contrast Curve

Logarithmic measure of slope of contrast curve

Negative Resist

Positive Resist

100%

Film Retention

0%

D2

D1

typical positive resist process
Typical Positive Resist process
  • EXAMPLE PROCESS: AZ5206 POSITIVE MASK PLATE
    • Soak mask plate in acetone > 10 min to remove the original photoresist.
        • Rinse in isopropanol, blow dry.
    • Clean the plate with RIE in oxygen. Do not use a barrel etcher.
    • RIE conditions: 30 sccm O2, 30 mTorr total pressure, 90 W (0.25 W/cm2), 5 min.
    • Immediately spin AZ5206, 3 krpm.
    • Bake at 80 C for 30 min.
    • Expose with e-beam, 10 kV, 6 C/cm2, Make sure the plate is well grounded.
    • (Other accelerating voltages may be used, but the dose will be different.)
    • Develop for 60 s in KLK PPD 401 developer. Rinse in water.
    • Descum - important Same as step 2 above, for only 5 seconds
    • Or use a barrel etcher, 0.6 Torr oxygen, 150W, 1 min.
    • If this is a Cr plate, etch with Transene Cr etchant, ~1.5 min.
    • If this is a MoSi plate, then RIE etch:
    • 0.05 Torr total pressure, 0.05 W/cm2, 16 sccm SF6, 4.2 sccm CF4,1 min.
    • Plasma clean to remove resist: same as step 2 above, for 3 min.
typical negative resist process
Typical Negative resist process
  • EXAMPLE PROCESS: SAL NEGATIVE MASK PLATE
    • Soak mask plate in acetone > 10 min to remove photoresist.
    • Clean the plate with RIE in oxygen. Do not use a barrel etcher.
    • RIE conditions: 30 sccm O2, 30 mTorr total pressure, 90 W (0.25 W/cm2), 5 min.
    • Immediately spin SAL-601, 4 krpm, 1 min.
    • Bake in 90 C oven for 10 min. This resist is not sensitive to room light.
    • Expose at 50 kV, 11 C/cm2. Be sure the plate is grounded.
    • Post-bake for 1 min on a large hotplate, 115 C.
    • Cool for > 6 min.
    • Develop for 6 min in Shipley MF312:water (1:1) Be sure to check for underdevelopment.
    • Descum 30 s with oxygen RIE: same as step 2, 10 s.
    • Etch with Transene or Cyantek Cr etchant, ~1.5 min.
    • Plasma clean to remove resist: Same as step 2, 5 min.
photo lithography
Photo Lithography
  • Project UV light through Mask
    • Non contact with optical reduction (typical 4X)
    • Contact with one-to-one pattern transfer
    • Mask – very flat SiO2 plate with Cr thin film
    • Resolution limited by wave length (phase shift)
    • Optics hard for short wave lengths
electron beam lithograpy
Electron Beam Lithograpy
  • Literature, Resources
    • Handbook of Microlithography Micromachining and Microfabrication, ed. P. Rai-Choudhury, SPEI press (chapter two is on the web, linked from home page
    • J C Nabity web site: http://www.jcnabity.com
  • Course material is posted on web site in restricted area:
  • http://www.nanophys.kth.se education  Intro. to e-beam Lithography
  • Link to restricted area (password protected)

Username: ebeamlecture

Password: lithogr

some things you can do with ebl
Some things you can do with EBL

Circuit of SQUIDs and Josephson Tunnel Junctions

slide23

1.5 mm

Bonding Pads

Contact “cage” to nano-circuit -- for rapid testing

slide25

Ferromagnetic - Normal metal tunnel junctions

Co

100 nm

Al

Circuit to measure spin injection from ferromagnet (Co) to normal metal (Al)

slide26

Innerdigitated Capacitor in

coplanar waveguide

Cooper Pair Transistor

slide27
All these structure were made with

one layer of e-beam lithography and one vacuum deposition cycle!

electron optics

Aperture

Lens

a – convergence angle

Electron Optics

detector

sample

Scanning the electron beam

electron scattering limits resolution
Electron scattering limits resolution

Higher energy electrons have larger back-scattering range

overview of systems
Overview of systems
  • SEM conversion (NPGS)
  • SEM modification (Raith)
  • High end system
    • SEM conversion limited in speed by slow beam deflection system (induction in magnet coils).
    • Laser stage is big step in price, but necessary for accurate pattern writing and stitching.
    • The more complex the system, the more service and higher user costs
    • Industry Fab. machines not always well suited to research needs.
slide34
NPGS
  • Joe Nabity, one man company, good reputation, very helpful, good support
  • Works with many SEMS
  • Can do stage control, many SEMs come with micrometer, motor control (accuracy)
  • Can do precision alignment in single field by scanning in reduced area to find mark. Manual mark detection.

Good Web site: http://www.jcnabity.com list of references, pictures, ideas

fabricated with npgs
Fabricated with NPGS

This image shows a pattern of radially placed dots in PMMA after development. The white bar at the bottom of the image is 1 micron long. The pattern was designed as radial lines, but the spacing of the exposure points was set 0.3 microns to produce discrete dots. Notice how the dot size and spacing is very consistent in all directions. The exposure was done with an SEM with no beam blanker and the image was taken with the NPGS digital imaging feature. The pattern was written by Dr. ChiiDong Chen at the Institute of Physics, Academia Sinica, Taiwan.

This picture shows part of a circular grating with a period of 0.15 microns. The lines appear almost straight, because they are near the outer edge of the grating where the radius is ~100 microns. The pattern was written in PMMA and has been coated with gold for viewing. The lithography was done at the Optical Sciences Center at the University of Arizona.

proven resolution with our raith 150 courtesy of anders holmberg

L= 80 nm

50 nm

30 nm

25 nm

18 nm

16 nm

20 nm

15 nm

Proven resolution with our Raith 150 courtesy of Anders Holmberg

L=Line width (pitch = 2L)

nanophys positive process for one cycle tunnel junction fabrication
Nanophys positive process for one-cycle tunnel junction fabrication
  • Two layer resist, selective developers
  • Very large undercut – suspended bridge
  • Tunnel junction (top and base layer) in one layer

Top view of pattern

Exposed areas

Undercut region

Supporting resist

Next slides:

Cut on this axis

lithography and shadow evaporation42

Lithography and shadow evaporation

Evaporate Al at an angle

lithography and shadow evaporation43

Lithography and shadow evaporation

Oxidize the first layer

lithography and shadow evaporation44

Lithography and shadow evaporation

Evaporate Al at opposite angle

lithography and shadow evaporation45

Lithography and shadow evaporation

Lift off the resist and excess metal

Tunnel junctions

slide46
Voilà

Circuit of SQUIDs and Josephson Tunnel Junctions

3d structuring using contrast curve
3D structuring using contrast curve
  • Accurately measure thickness of film
  • Do test pattern with dose profile to accurately measure contrast curve
patterning in third dimension
Patterning in third dimension

Desired structure:

thickness

Dose

holography
Holography

Positive electron resist SAL 110 Developer SAL 101

(Shipley)

Chalmers Group, S. Hård et al.

Applied Optics vol. 33 p 1176, 1994

optical kinoforms
Optical Kinoforms

Chalmers Group, S. Hård et al.

Applied Optics vol. 33 p 1176, 1994

Optical Comm. Vol. 88, p 37, 1992

two basic types of pattern methods
Two basic types of pattern methods
  • Direct Writing
    • Change pattern with each run
    • Slow, serial method of fabrication
    • Good for research and development
    • Low through-put, too costly for large scale production
  • Lithography
    • pattern copying one process step
    • Fast, parallel method
    • High through-put makes low cost in large scale prod.
    • Not flexible enough for research and development.
comparison of lithographic methods
Comparison of Lithographic methods
  • Photo Lithography
    • UV, deep UV
    • Projection or contact
  • Micro contact printing
    • Stamp formed from Soft material
    • Molecules (ink) is wet on to stamp, transferred to surface
  • Printing Press
micro contact printing
Micro Contact printing

http://www.research.philips.com/technologies/light_dev_microsys/softlitho/

stamp fabrication
Stamp fabrication
  • Master made by direct writing methods (EBL on Si + etch)
  • Stamp gets dirty, wears out
  • Essentially old-style printing methods scaled to nm dimensions
optical stepper
Optical Stepper

http://www.sematech.org

http://www.nanonet.go.jp/

high through put direct writing tool
High through-put direct writing tool

Sigma 700 series from Micronic Laser systems, Täby Sweden

http://www.micronic.se

Spatial Light Modulator

(SLM) chip

10 6 electronically addressable mirrors

alignment and overlay
Alignment and overlay
  • Alignment and overlay are more serious problems than actually making the small structure!
  • Large area with fine detail requires “stitching” write fields together – laser interferometer stage, nm position and metrological accuracy!
  • Overlay requires accurate alignment marks, mark detection, registration and extremely accurate pattern placement over large area (scaling accuracy 1 part 106).
3 layer process done in albanova
3-layer process done in Albanova

Industry has MUCH more sophisticated circuits with 15-20 layers, 108 components, with very accurate overlay

metrology and imaging
Metrology and Imaging
  • Laser interferometers on Stage
    • 5nm “resolution”
    • Reproducibility
  • Thickness measurement
    • Profilometer, demonstration
  • Scanning Probe microscipe
    • Vertrical resolution 1 Å level
    • Latteral resolution depends on tip sharpness
scanning tunneling microscopy stm binnig and rohrer 1981 nobel prize in physics 1986

E(z)

E0

U

z

d

Scanning Tunneling Microscopy (STM)Binnig and Rohrer 1981 (Nobel Prize in Physics 1986)

Electric current proportional to quantum

mechanical probablility amplitude of ”tunneling”

through the energy barrier

Wave´function decays eponentially in barrier region

single atom imaging possible
Single Atom imaging possible
  • Sharp tip
  • Pristine surface
  • Ultra High Vacuum

The making of a Quanum Corral

Fe atoms on a Cu (111) surface

Check out this web page

http://www.almaden.ibm.com/vis/stm/gallery.html

atomic force microscopy afm
Atomic Force Microscopy (AFM)

Two Basic AFM Modes:

Contact mode (no vibrating tip)

Tapping mode (vibrating tip)

Many variations on Scanning Force Microscopy :

Liquid AFM

Magnetic Force Microscopy (MFM)

Latteral Force Microscopy (LFM)

Intermitant and non-contact AFM

Force Modulation Microscopy (FMM)

Electrostatic Force Microscopy (EFM)

atomic forces
Atomic Forces

Hard core repulsion

Contact region

Force

z

Seperation between tip and surface

Attractive force: van der Walls

Non-contact retion

image molecular monolayers in liquid
Image molecular monolayers in liquid
  • Molecules must be immobilized on surface
  • Local force measurements possible

S-layer protein monolayer on Si surface

in liquid environment, 500 nm x 500 nm

Zentrum für Ultrastrukturforschung - Universität für Bodenkultur. Austria

two basic scanning modes
Two basic scanning modes
  • Feedback off: Scan over surface with constant z0 (piezo voltage), control signal changes with tip-surface separation.
  • Feedback on: circuit regulates z piezo voltage to constant value of control signal (constantly changes tip-surface separation).
afm tapping mode
AFM tapping mode

Free space oscillation of cantilever

resonance 10-100 kHz

Cantilever hits surface

smaller amplitude of oscillation

feedback loop tapping mode
Feedback loop tapping mode

Free oscillation

Large amplitude

Hitting surface

lower amplitude

digital insturments multi mode head scanner and base
Digital Insturments Multi-Mode head, scanner and base
  • Turn on the controller (the computer should be left on)
  • Remove the scanner from under the microscope.