Atomic Layer Deposition for SCRF

RF in the MTA 11/15/10

J. NoremANL/HEP

2

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.

3

ALD Reaction Scheme

•ALD involves the use of a pair of reagents.• each reacts with the surface completely• each will not react with itself

•This setup eliminates line of site requirments•Application of this AB Scheme

•Reforms the surface•Adds precisely 1 monolayer

•Pulsed Valves allow atomic layer precision in growth•Viscous flow (~1 torr) allows rapid growth

•~1 m / 1-4 hours0

500

1000

1500

2000

2500

3000

3500

4000

0 500 1000 1500 2000 2500 3000AB Cycles

Th

ick

nes

s (Å

)

Ellipsometry Atomic Force Microscopy

• Film growth is linear with AB Cycles• RMS Roughness = 4 Å (3000 Cycles)• ALD Films Flat, Pinhole freeFlat, Pinhole-Free Film

Seagate, Stephen Ferro

• No uniform line of sight requirement!• Errors do not accumulate with film

thickness.• Fast! ( m’s in 1-3 hrs ) and parallel• Pinholes seem to be removed.• Bulk

4

Apparatus

Hot wall reactor (RT-400 C) Always coat the wall – now it will be useful

5

Demonstrated ALD A/B Reactions

Oxide Nitride S/Se/Te Ph/As C FElement

6

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

10 nm filaments

150 nm

Overall Reaction: WF6 + Si2H6 → W + products

7

• Aerogel filament diameter increases with ALD W Cycles

SEM

TEM

80 nm

3 c W 7 c W

80 nm

Microscopy of W-Coated Carbon Aerogels

8

Goal of ALD SCRF

Build “nanolaminates” of superconducting materials

~ 10- 30 nm layer thicknesses

Nb, Pb

Insulating layers

Higher-TcSC: NbN, Nb3Sn, etc

9

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