Atomic Layer Deposition of Tantalum Nitride Liners for HighAspect Ratio 3D Integration Technologies

1
Atomic Layer Deposition of Tantalum Nitride
Liners for High-Aspect Ratio 3-D Integration
Technologies

• Oscar van der Straten, Yu Zhu, Guillermo Nuesca,
  Kathleen Dunn, Katharine Dovidenko, Eric
  Eisenbraun, Alain Kaloyeros

2
Motivation for ALD Approach to Copper Liner
Processing

• Allowable liner thicknesses are decreasing to
  below 10 nm
• Dual damascene processing is driving a
  requirement for exceptional liner conformality
  and continuity
• Any processing technique employed for copper
  liner deposition should enable the growth of
  uniform ultra-thin films with submonolayer
  thickness precision over large surface areas
• The liner should be robust, as well as highly
  integrable with the interconnect stack

3
ALD TaNx Processing Approach

• ASM F-120 ALCVD Reactor for RD Applications
• Hot-wall, flow type reactor

? Reactor chamber borosilicate glass ?
Substrate size 5 cm by 5 cm ? Substrates
vertically mounted ? No load-lock
heater elements
valve collar with pulsing valves
thermocouples
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Atomic Layer Deposition Sequence
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Atomic Layer Deposition Sequence
Precursor pulse
Post-precursor inert gas purge
Reactant pulse
Post-reactant inert gas purge
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ALD TaNx Precursor

• Tertbutylimido-tris(diethylamido)tantalum
  (TBTDET)
• (Et2N)3TaNBut
• orange/yellow liquid at room temperature
• moisture sensitive
• previously employed in MOCVD of TaN
  (stoichiometric TaN, C 10 at., O 5 at., r
  2000 µ?cm at 600 C)

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ALD TaNx Precursor Considerations

• Potential advantages
• Liquid source
• Enhanced precursor delivery control
• Non-halide chemistry
• No corrosive halides in resulting films

• Potential issues
• Influence of C, H contamination on thermal
  stability, resistivity, and barrier performance
  of ALD TaNx
• Steric hindrance effects may limit ALD growth rate

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ALD TaNx Proof of ConceptGrowth Rate Saturation
Growth rate saturates with increasing TBTDET
pulse time
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ALD TaNx Proof of ConceptGrowth Rate Saturation
Growth rate saturates with increasing NH3 pulse
time
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ALD TaNx Proof of ConceptFilm Thickness vs.
Number of Cycles

• Linearity of film thickness as a function of
  number of cycles
• consistent with ALD processing regime

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Surface RoughnessAtomic Force Microscopy
Analysis
15 nm
60 nm ALD TaNx on Si RMS surface roughness
0.5 nm (lt 1 of film thickness)
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ALD TaNx ConformalityScanning Electron
Microscopy Analysis
62 nm
62 nm
ALD TaNx coverage on AR 5 trench (230 nm feature
size)
ALD TaNx coverage on AR 4.5 via (230 nm feature
size)
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ALD TaNx Conformality Transmission Electron
Microscopy Analysis
20 nm
100 nm

• TEM images of ALD TaNx coverage on AR 4 trenches
  (360 nm feature size)
• Step coverage 100
• Selected area diffraction pattern shows amorphous
  TaNx texture

SADP
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ALD TaNx Film CompositionAuger Electron
Spectroscopy Analysis

• Tantalum to nitrogen ratio 11
• Consistent stoichiometry
• Carbon and oxygen contamination lt 10 at.

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Overview of ALD TaNx Film Properties
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Ongoing Research

• Complete proof of ALD concept study for TaNx
  using TBTDET and NH3
• Growth rate saturation curves
• Growth rate as a function of substrate
  temperature
• Investigations toward reduction of resistivity
• Integration with low-? dielectric materials
• Copper barrier performance tests

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Acknowledgements

• This work was funded in part by the Semiconductor
  Research Corporation (SRC) under its CAIST
  Program