Transcript Argonne PowerPoint Presentation

Atomic Layer Deposition for SCRF
J. Norem
ANL/HEP
RF in the MTA 11/15/10
Atomic Layer Deposition
 Atomic Layer by Layer Synthesis Method similar to MOCVD
 Used Industrially
– Semiconductor Manufacture for “high K” gate dielectrics
• “Abrupt” oxide layer interfaces
• Pinhole free at 1 nm film thicknesses
• Conformal, flat films with precise thickness control
– Electroluminescent displays
• No line of sight requirement
• Large area parallel deposition
 Parallel film growth technique; Inside of large tubes can be
done at once.
2
ALD Reaction Scheme
4000
Ellipsometry
•ALD involves
the useForce
of a pairMicroscopy
of reagents.
Atomic
• each reacts with the surface completely
• eachof
will
not react
with itself
No uniform line
sight
requirement!
3000 •
•This setup eliminates line of site requirments
2500 •
Errors do•Application
not accumulate
of this AB Scheme with film
2000
thickness. •Reforms the surface
1500
•Adds precisely 1 monolayer
•
Fast!
(
mm’s
in
1-3 hrs ) and parallel
1000
•Pulsed Valves allow atomic layer precision in
Pinholes seem
growthto be removed.
500 •
•Viscous flow (~1 torr) allows rapid growth
Seagate, Stephen Ferro
0
• Bulk
0
500 1000 1500 2000 2500 •~1
3000 mm / 1-4 hours
AB Cycles
• RMS Roughness = 4 Å (3000 Cycles)
Flat,
Pinhole-Free Film
• Film growth is linear with
AB Cycles • ALD Films Flat, Pinhole free
Thickness (Å)
3500
3
Apparatus
 Hot wall reactor (RT-400 C)
 Always coat the wall – now it will be useful
4
Demonstrated ALD A/B Reactions
Oxide
Nitride
Element
S/Se/Te
Ph/As
C
F
5
Aerogels coated with W
 Conformal Coating and “sharp” points
 Aerogels are low density nanoporous materials consisting of bundles of
nm scale filaments
 ALD can be used to deposit W metal atomic layer by layer on this
filaments
Overall Reaction:
WF6 + Si2H6 → W + products
10 nm filaments
150 nm
6
Microscopy of W-Coated Carbon Aerogels
3cW
7cW
SEM
80 nm
80 nm
TEM
• Aerogel filament diameter increases with ALD W Cycles
7
Goal of ALD SCRF
Higher-TcSC: NbN,
Nb3Sn, etc
 Build “nanolaminates” of
superconducting materials
 ~ 10- 30 nm layer
thicknesses
Nb, Pb
Insulating
layers
8
Conclusions
 ALD is an intriguing synthesis technique with many useful properties
 Conformal coating means increased radius of curvature
 Parallel (non-line of sight) method
– Flat samples directly map to complex shape samples even with high
aspect ratios
– Layer by layer growth on complex shapes
 Useful for higher field gradients in SRF and NCRF
9