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Atomic Layer Deposition of High-K Dielectric Films

• David Brown

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Outline

• Overview
• Applications
• Precursors
• Reactor Design
• Future Work

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Atomic Layer Deposition

• Self-limiting growth of mono-layers by switching
  precursor flow

(Source Infineon)

• Atomic-Level Thickness Control
• Conformal Growth
• Low Growth Temperature
• Wide range of materials

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High-K Dielectrics
(Source Cambridge Nanotech)
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Applications DRAM Capacitors

• ALD can be used to deposit TiN/Al2O3/TiN stacks.
• Highly conformal coating on high aspect ratio
  (45-60) holes.
• Scalable to 45nm.

(Source Infineon)
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Applications CMOS Gate Oxide

• Lg? Vg? gm? Cox ?
• Cox e / tox ? tox?

• As feature sizes shrink, higher Cox is needed.
• SiO2 oxides are approaching 1nm in thickness!
• Carrier tunneling leads to leakage current and
  power loss.

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Applications CMOS Gate Oxide
Solution Increase e instead of decreasing tox

• By replacing SiO2 (er4) with HfO2 (er25), tox
  can be increased gt 5X with no loss of Cox!
• Low Gate Leakage
• Faster Switching
• Low Power
• Good Reliability
• Intel and IBM have announced adoption of a
  High-K / Metal process!

Low Resistance Layer
Metal
Hf-based Dielectric
Silicon
(Source Intel)
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Applications MEMS Coating

• Protective coating deposited by ALD greatly
  increases the reliability and lifetime of MEMS
  devices

Uncoated 1 million stress cycles
Coated 1 billion stress cycles
Mani S S et al, Mater. Res. Soc. Proc. 605 (2000)
Y.C. Lee et. al., Sensors and Actuators A
Physical, 103 (2003)
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Applications Nanostructures
ZnO Nanorods
Carbon Nanotube Transistors
High K
Chen et al, Appl. Phys. Lett. 90, (2007)
Nanotube
H Dai et al, Nature Materials, 1, (2002)
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Applications Thin Metal Layers
Cu

• Highly conformal metal layers
• Electroplating seed layers
• Capacitor Electrodes

(Source Cambridge Nanotech)
B Pathangey et al, Electrochemical and Solid
State Letters, 3 (2000)
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Other Applications

• Anti-reflective coating
• Optical Filters
• Ferroelectric RAM (FRAM)
• OLED Passivation
• Cu interconnect barriers
• Porous Structures
• Molecular Electronics
• Gas Sensors
• Piezoelectric Thin Films
• Transparent Conductors

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High-K Dielectric Precursors
R represents Alkyl groups (such as CH3 or C2H5)

• Precursor Requirements
• Thermally Stable
• Vaporize readily at a reproducible rate
• High volatility

• High reactivity with the other precursor
• Highly volatile and non-corrosive by-products

• H2O and O3 are typically used as O precursors.
• SiH4 and Si2H6 are good Si precursors.

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ALD Industry

• ALD processing equipment market is projected to
  exceed 600 Million in 2010

(Source BCC Research)
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ALD Surface Reactions

• Al2O3 with TMA and H2O
• Al-OH Al(CH3)3 ? Al-O-Al(CH3)2 CH4
• Al-O-Al(CH3)2 H2O ? Al-O-Al-OH CH4

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ALD Reactor Design for Al2O3

• T 400C
• P 1 torr
• Precursors TMA and H2O
• N2 Carrier/Purge gas
• Horizontal Reactor

(Source Bright et al)
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ALD Reactor Design

• Height 1.75cm
• Width 30.5cm
• Total Flow 100sccm
• Vo 1.9 cm/s

• Re 47
• ac 14.3
• Ra 172
• Len 5.44 cm

• Pr 0.712
• Gr 241
• Sc 1.8e-4

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Growth Rate

• Po for TMA and H2O is 0.005 torr
• Use 300ms pulse times for TMA and H2O
• 1s N2 flush
• Cycle time 2.6s
• Monolayer thickness is 3.6Å
• Growth rate is 1.4 Å/s

? 1-exp(-(kads-kdes)t)
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Future Work

• ALD of single-crystalline ZnO
• All ALD of ZnO has been polycrystalline
• III-V MOSFETs
• GaAs, InP, GaN
• BioMEMS Coating
• With bio-compatible films like TiO2

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Conclusion

• ALD is awesome
• Self-limiting growth
• Conformal growth
• Wide range of materials

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Questions?