Advanced Gate Stacks and Substrate Engineering

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• Advanced Gate Stacks and Substrate Engineering
• Eric Garfunkel and Evgeni Gusev
• Rutgers University
• Departments of Chemistry and Physics
• Institute for Advanced Materials and Devices
• Piscataway, NJ 08854

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Advanced Gate Stack Materials

• Motivation Severe power dissipation in
  aggressively scaled conventional SiO2 gate oxides

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• Goal develop understanding of
• interaction of radiation with CMOS materials

C ? Ae/d EOT - effective oxide thickness

• New materials metal electrodes, high-K
  dielectrics, substrates
• Electronic structure, defects, band alignment

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Advanced Gate Stack Materials Challenges

• Enormous materials/interface
• challenge
• rad. response not fully understood

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Selected material requirements for high-K
dielectric metal electrode CMOS gate stack

• High-K dielectric
• high thermal stability no reaction with
  substrate or metal
• high uniformity minimal roughness, single
  amorphous phase preferred
• low electrical defect concentration
• high permittivity

• Metal gate electrode
• Appropriate band alignment wrt substrate
  semiconductor and dielectric
• high thermal stability no reaction with
  dielectric
• high conductivity

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Rutgers CMOS Materials Analysis Capabilities

• Ion scattering RBS, MEIS, NRA, ERD
  composition, crystallinity, depth profiles, H/D
• Direct, inverse and internal photoemission
  electronic structure, band alignment, defects
• Scanning probe microscopy topography, surface
  damage, electrical defects, capacitance
• FTIR, XRD, TEM, STEM
• Electrical IV, CV
• Growth ALD, MOCVD, PVD

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Atomic Layer Deposition (ALD)
Why Atomic Layer Deposition?

• monolayer control of dielectric and metal film
  growth
• mixed oxides and nanolaminates - allows tailored
  films
• conformality advantage for novel structures
• low temperature deposition 300ºC

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MEIS depth profiling
depth profile

• Sensitivity
• ? 1012 atoms/cm2 (Hf, Zr)
• ? 1014 atoms/cm2 (C, N)
• Accuracy for determining total amounts
• ? 5 absolute (Hf, Zr, O), ? 2 relative
• ? 10 absolute (C, N)
• Depth resolution (need density)
• ? 3 Å near surface
• ? 8 Å at depth of 40 Å

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Isotope studies of diffusion and growth in
metal/high-K gate stacks
Isotope tracer studies
30Å Al2O3 annealed in 3 Torr 18O2
ZrO2 film re-oxidized in 18O2
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Nuclear resonance methods for light element
profiling
Differential cross section
Energy (keV)
Schematic of ion beam-film reactions for (p,g),
(p,a) and (p,ga) resonance reactions. Control
incident energy to get depth information
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Some low energy nuclear resonances
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Deuterium distribution in SiO2 films
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Determine electronic structure and band alignment
for metal/high-k/Si gate stack

• Use high resolution spectroscopic tools to
• Determine band alignment and defects
• Observe changes induced by radiation

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Experimental tools to examine electronic structure
Photoemission (Occupied States)
Inverse Photoemission (Unoccupied States)
EF
EVBM
CB
ECBM
EF
EF
VB
CL
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Additional experimental tools
XAS, EELS (Core? CB)
Optical methods
I-V
STM/C-AFM
probe
e-

Eg
hw
hw
V
V
CB
EF
EF
EF
EF
Eg
Eg
Eg
VB
Met
Si
Met
Si
Met
Si
CL
High-k
High-k
High-k
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Photoemission and Inverse Photoemission of ZrO2/Si
Theory Ä resolution
First Principles Theory
First Principles Theory

• VBM, CBM Determination
• Comparison with Theory (where possible)
• Extrapolation
• Establish band offsets

CBM EF 1.4 eV
VBM EF - 4.2 eV
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Internal Photoemission (IntPES)
?Si/Ox
Ec
EF
EF
EV
metal
semiconductor
high-k
(a) Ec(Hik)-EF(met.) e-IntPES (b)
photo-excitation optical band gap (c)
Ec(sc)-Ev (Hik) h-IntPES
Chopper
Probe station
Arc lamp
Monochromator
I-V Source Measure Unit
Lock-in amplifier
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IntPES W / SiO2 / n-Si Negative Bias on Si,
?Si/ SiO2 4.4 eV
Combine positive and negative bias data to
determine W and Si barriers with SiO2
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Conductive Tip AFM Image and I-V Behavior of a
Ru/HfO2/Si Stack
Image physical and spectroscopic behavior of
radiation induced defects
For simple F-N tunneling with an electron
effective mass of 0.18, the HfO2/Si conduction
band barrier height is 1.4eV
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I. High-mobility Channels Germanium

• Carrier mobility enhancement
• Interface-free high-K

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II. High-mobility Channels HfO2 on strained Si
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High-mobility Channels HfO2 on strained Si

• Significant mobility enhancement for HfO2 on
  strained Si

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III. High-mobility Channels Si orientations
PFET
NFET

• Hybrid (Si) Orientation Technology
• combines best NFET performance for Si(100)
  and PFET for Si(110)

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Logistics MURI Collaborations
Samples, Processes, Devices Rutgers,
NCSU, IBM
Materials Interface Analysis Rutgers
NCSU
Theory Vanderbilt
Radiation Exposure Vanderbilt
Sandia
Post-radiation Characterization
Vanderbilt Rutgers
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Plans
General goal to examine new materials for
radiation induced effects and compare with
Si/SiO2/poly-Si stacks

• Generation of films and devices with high-K
  dielectrics (HfO2) and/or metal gate electrodes
  (Al, Ru, Pt) with 1-50nm thickness
• Interface engineering SiOxNy (vary thickness and
  composition)
• Physical measurements of defects STM, AFM, TEM
  vs particle, fluence, energy
• H/D concentration and profiles, and effects on
  defect generation and passivation
• Correlate UHV-based studies with electrical and
  internal photoemission measurements.
• Explore different processing and growth methods.
• Correlate with first principles theory.
• Develop predictive understanding of radiation
  induced effects

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Industrial contacts

• Gusev, Guha - IBM
• Liang, Tracy - Freescale
• Tsai - Intel
• Chambers, Columbo - TI
• Vogel, Green - NIST
• Gardner, Lysaght, Bersuker, Lee Sematech
• Edwards, Devine AFOSR