Radiation Effects on Emerging Electronic Materials and Devices

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Radiation Effects on Emerging Electronic
Materials and Devices
June 14/15, 2007
Radiation Effects in Emerging Materials Overview

• Leonard C. Feldman
• Vanderbilt University
• Department of Physics and Astronomy
• Vanderbilt Institute on Nanoscale Science and
  Engineering

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Topics of Interest Basic radiation interaction
with electronic materials-review, educational,
modifications at the nanoscale Alternate
Dielectrics and Gate Stacks-in all
aspects-growth, spectroscopy, radiation
effects SiGe devices and other alternate
substrates (Ge, InGaAs, SiC) Strained silicon
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Basic radiation interaction with electronic
materials- review, educational, modifications at
the nanoscale Tutorials and review Interaction
of x-rays with MOS devices occurs primarily via
the generation of (photo) electrons in the metal
and the underlying silicon. The energetic
electrons (lt 10 KeV) create electron hole pairs
in the dielectric which may be trapped by
processing defects. The dielectric is too thin
to incur any substantial direct defect production
by the primary radiation. The outgoing electrons
are too low in energy for direct displacements,
but create further secondarys, and possibly
defects, through bond breaking leading
eventually to e-h pair production.
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MAJOR POINT FROM THE PREVIOUIS CONSIDERATIONS
Processing defects, defects from the
imperfection of the grown dielectric, are the
primary trapping centers even for the higher
atomic number, physically thicker HfO2
Processing defects, defects from the
imperfection of the grown dielectric, are the
primary trapping centers -nanocrystalline HfO2
-HfO2/SiO2 interface -classic defects such as
oxygen vacancies, etc -Hf penetration into the
SiO2 layer and its interaction with H
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Number of Hf atoms versus distance from interface
Single Hf atoms inside SiO2 interlayer
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Basic radiation interaction with electronic
materials- modifications at the
nanoscale Nanoscale Basic theory of e-h pair
production, particularly e, the average energy
required for e-h pair creation, is based on bulk
concepts, including bulk density of states. The
nanoscale thicknesses, and the new understanding
of nanoscale effects calls for re-examination of
these concepts.
?VQ/CNe (dE/dx) tox/e /C e
average energy/e-h pair
Ne number of electrons penetrating the
dielectric
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e vs. Eg
e 2.6Eg K Shockley-Klein
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Rutgers CMOS Materials Analysis

• Use high resolution characterization methods to
• Determine composition, structure and electronic
  properties gate stacks that use new (post-Si)
  materials
• Help determine physical and chemical nature of
  radiation induced defects

• Surface/interface analysis
• 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

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Materials stability, band alignment and defects
in CMOS nanoelectronics
L. Goncharova, S. Rangan, O. Celik, C.L. Hsueh,
R.A. Bartynski, T. Gustafsson and E.
Garfunkel Departments of Chemistry and Physics,
and Institute for Advanced Materials, Devices
and Nanoelectronics Rutgers University,
Piscataway, NJ
Collaboration Vanderbilt, Sematech, NIST, IMEC,
IBM, Intel, Bell Labs, NCSU, Penn State,
Stanford, UT-Dallas, UT-Austin, Albany.
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Defects in the post-Si eraAl/HfO2/InxGa1-xAs

• Surface passivation and composition of
  interfacial layer
• High-K deposition
• Post-deposition annealing
• Metal gate effects
• Normal and radiation induced defects nature
  and evolution

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length scales of order and defects in
nano-crystalline and non-crystalline Hf-based
gate dielectrics Gerry Lucovsky students and post
doc S. Lee, JP Long, H Seo and LB
Fleming collaborators J Whitten, D Aspnes, Jan
Luning (SSRL), G. Bersuker
and P Lysaght (Sematech) objective determine the
effect of different length scales of order for
nano- and non-crystalline Hf based dielectrics on
pre-existing intrinsic defects, and then on
radiation (X-ray) induced defects approach i)
prepare NCSU samples by plasma-CVD ii) determine
electronic structure, Hf d-state relative
energies, by near edge X-ray absorption, soft
X-ray photoelectron spectroscopy, and vis-VUV
spectroscopic ellipsometry using symmetry adopted
linear combinations (SALC-FA Cotton) of atomic
states as a guideline iii) study electrical
properties in MOSCAPs and compare electrical and
X-ray stress
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HfO2 sample details
HfO2 based nMOSFET
Samples
Experimental

• State-of-the-art samples, SEMATECH, Inc.
• 65 nm technology node
• nMOSFETs with W/L 10?m/0.2?m
• tphys 7.5 nm and 3.0 nm
• (EOT 1.2 nm and 0.5 nm)
• SiO2 interlayer ( 8Å)

• 10 keV X-rays, RT irradiation
• Function of dose
• Function of bias
• Characterization done using
• I-V measurements

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HfO2 total dose results

• nMOSFETs with W/L 10?m/0.2?m

tphys 7.5 nm
tphys 3.0 nm

• Thinner dielectric traps significantly less
  charge

S. K. Dixit et al., Radiation induced charge
trapping in ultra-thin HfO2 based MOSFETs,
accepted for NSREC 2007
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HfO2 results
?HfO2/TiN
SiO2
p-Si
HfO2
TiN
EC
Ei
n-MOSFET cross-section
Ef

• Carrier injection from tunneling
• Si- surface condition dependent
• Both electron and hole trapping observed
• Predominant bulk hole trapping (radiation)
• Zero bias - radiation induced trapping

EV
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Hafnium silicates
Limitations of HfO2 HfO2 - low thermal budget
500C Nanocrystalline HfO2 formed during
PMA Dopant penetration is an issue

• Need for HfSiO
• Increased thermal budget to 1000C

• Reduction in dielectric constant

Crystallization introduces defects and shallow
traps at the grain boundaries Radiation response
expected to be better for silicates
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RBS CV of HfSiO/SiO2/p-Si films
Electrical characterization
Physical characterization
Total dielectric thickness from RBS 10 to 11nm
Total dielectric thickness from CV 12nm
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Results
C-V results
RBS results

• Initial results confirm the trend ( Hf
  ?r)

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TID Response of Hf0.6 and Hf0.3 Films

• Devices prepared by RPECVD EOT 4 nm
• Two dielectric films
• Hf0.6 (containing crystalline HfO2)
• Hf0.3 (amorphous)
• Electron trapping observed in the Hf0.6 film
  under large positive bias

Probable explanation e-trapping at
nanocrystalline grain boundaries
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TID Response Comparison to Previous Hf Silicate
Films

• TID-induced charge trapping improved compared to
  previous Hf silicate devices J. A. Felix et al.,
  IEEE Trans. Nucl. Sci., vol. 49, pp. 3191-3196,
  2002
• ?Not factor of 17 smaller at 1 Mrad
• Reduced charge trapping indicates superior
  HfSiON film qualities and improvements in
  processing techniques

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Facilities at Vanderbilt
Radiation sources

• 10 keV X-ray source (in-situ bias and
  irradiations)
• 2 kV Van de Graaff electrostatic accelerator
• Low dose rate Ce source

Physical and Electrical characterization

• Ion beam characterization using RBS, PIXE,
  channeling studies
• C-V measurements
• I-V measurements

Future upgrades

• In-situ biased ion irradiations using H, He and
  Ne beams
• Low-temp (up to 7K) ion irradiations using a
  cryostat

Other facilities

• Thermal oxidation and gate metal deposition
  facilities
• Delta Oven furnace for high temp biased anneals
• Wire bonder for packaging wafer level devices

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Biased irradiations and anneals
Irradiation (-2V)
RT Annealing (0V)

• Partial recovery observed with a 0V annealing
  gate bias
• No additional voltage shifts observed for time
  scales of up to 13 hours indicating the existence
  of residual positive charge in the oxide

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Radiation Effects in SiGe Devices John D.
Cressler and Team

• Investigation of the Best Path to RHBD in Bulk
  SiGe HBT Technologies
• First Cryogenic Temperature (77K) Proton
  Experiment of SEU in Bulk SiGe HBTs
• Investigation of Radiation Effects in both Bulk
  C-SiGe HBTs and SiGe HBTs on SOI
• Investigation of Radiation Effects in both SiGe
  nMODFETs and SiGe pMODFETs

Bulk SiGe HBTs
C-SiGe HBTs (npn pnp) SiGe
p/n-MODFETs
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Voltage Stress and Biased Irradiation
S. K. Dixit et al., Radiation induced charge
trapping in ultra-thin HfO2 based MOSFETs,
accepted for NSREC 2007
MURI meeting June07
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CVS and biased irradiation
Hole injection - 2V bias stress
?HfO2/TiN
Hole injection saturates after an hour
SiO2
HfO2
TiN
EC
Ei
p-Si
Ef
EV
Accumulation
S. K. Dixit et al., Radiation induced charge
trapping in ultra-thin HfO2 based MOSFETs,
accepted for NSREC 2007
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CVS and biased irradiation
Electron injection 2V bias stress
EC
Electron injection saturates
Ei
SiO2
Ef
p-Si
?HfO2/TiN
HfO2
EV
TiN
Inversion
S. K. Dixit et al., Radiation induced charge
trapping in ultra-thin HfO2 based MOSFETs,
accepted for NSREC 2007