NBTI and Spin Dependent Charge
Pumping in 4H-SiC MOSFETs
Mark A. Anders, Patrick M. Lenahan,
Pennsylvania State University
Aivars Lelis, US Army Research Laboratory
Deviations from the resonance
condition provide useful information
about the nature of specific defects
Energy
Spin-Orbit Coupling: due to
electron’s orbital angular
momentum about the nucleus
E  h  g
g eHH+ mIA
Electron-Nuclear Hyperfine
Interaction: due to nearby
nucleus with magnetic moment
Magnetic Field
At resonance, spin flips
In the data shown, the factor most responsible for deviations from
hv=geβH
Bohr model: electron orbits nucleus;
angular momentum n h (units of h).
To an observer on the electron, it looks
like the nucleus is orbiting the electron.
The greater the nuclear charge and
orbital angular momentum quantum
number, the greater the spin orbit
coupling. The orbiting nucleus looks like
a current loop generating a magnetic
field. This contribution is expressed in
the g tensor.
Problem
Conventional EPR has a sensitivity of about 1010 total paramagnetic defects
It is also sensitive to ALL paramagnetic defects in a sample
1. We want to identify defects in transistors
2. We want to know what different defects do to device performance
A main problem for electronic materials science is performing resonance inside
fully processed transistors in integrated circuits
EDMR provides sensitivity about 7 orders of magnitude higher than
conventional EPR
Solution: EDMR, spin dependent recombination (SDR),
and spin dependent trap-assisted tunneling (SDT)
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What Are These Defects?
Anticipated spectrum of
the negatively charged
silicon vacancy with the
field parallel to the c-axis
utilizing the hyperfine
parameters of Isoya et al.
J. Isoya, T. Umeda, N. Mizuochi, N. T. Son,
E. Janzen, and T. Ohshima, Phys. Status
Solidi B 245(7), 1298 (2008).
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Silicon Vacancy Model
Experimental Results
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x5
Pre-stress
x5
190oC
x5
Post-stress
• Hydrogen or Nitrogen related defect
• At interface, bulk, or possibly oxide
• Possible nitrogen related defect
• At interface or bulk
• Utilizing VDMOSFET
geometry, we probe bulk
defects
• Biasing scheme:
Source
i
– Strongly accumulate channel
– Forward bias drain/body
diode
– “Bulk” recombination
dominant current
N+
P+
Gate
-Vg
N+
P
N SiC Epi
Source
P+
Gate
N+
N+ SiC substrate
+++++
P
accumulated
channel
Vd
Drain
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• 150, or 250, or 360 MHz (low field) vs. ~9.5 GHz (X-band)
• Broadening due to g is field/frequency dependent
• Broadening due to hyperfine interactions is field/frequency
independent (to first order)
Simulated using easyspin
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X-band
Low field
• Previously, X-band measurements suggests broadening due to g or
hyperfine
• EDMR measurements at low field reveal that broadening is at least
partially due to hyperfine interactions
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• This technique is appropriate
for levels around mid-gap.
• It does not, however, address
traps near the band edges.
• We are interested in what’s
happening near the conduction
band and valence band.
• Spin dependent charge
pumping: a solution.
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By utilizing a pulse wave at the gate
voltage, we can explore more of the band
gap with larger amplitude.
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G
oxide
S
D
n+
n+
p
Gate Voltage
Waveform
Generator
…
time
(Vary b Voltage)
(b)
(c)
EF
EF
Fill
Traps
c
c
𝑖
EF
a
b
b
semiconductor
(a)
a
a
Allow time
for traps
above EF
to empty
Flood interface
with holes to
recombine with
interface trap
electrons
Enhanced sensitivity (2000x greater)
NO-annealed pMOSFET
• Probing states throughout most of the bandgap shows a different line shape and
broader center line compared to only mid-gap states
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BAE
SDCP
• The “full bandgap” spectra have g-values much lower than the “mid-gap” spectra in
this sample
• Mid gap (BAE) spectra are mostly due to silicon vacancy
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350 MHz
c-axis
parallel to
magnetic
field
~9.5 GHz
c-axis
parallel to
magnetic
field
• C-axis is parallel to magnetic field
• NO annealed nMOSFET has broader shoulders than an nMOSFET which did not
receive an NO anneal
• Many abundant magnetic nuclei, likely nitrogen, would cause broadening
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350 MHz
~9.5 GHz
• NO annealed nMOSFET has a broader center line at both high and low fields
• Many abundant magnetic nuclei, likely nitrogen, would cause broadening
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~9.5 GHz
• The NO annealed device spectra is much broader than the non-NO device spectra
• More evidence for Nitrogen hyperfine interactions
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C dangling bond:
g //c = 2.0023
g⊥c = 2.0032
J. L. Cantin et al.
If carbon dangling bonds largely
contributed to the interface state
density, we would observe a line at
g //c = 2.0023 and g⊥c = 2.0032. We
do not. There are no carbon
dangling bonds at the interface.
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Non-NO nMOSFET
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Non-NO nMOSFET
• Side peak amplitudes
are reduced
• Defect responsible for
side peaks are not near
the conduction band
edge
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w/out NO nMOSFET
NO nMOSFET
• Lower charge pumping frequencies probe further into the oxide
• Could provide a way to look a little into the gate oxide
• More work needs to be done to fully understand multi-frequency SDCP results
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Low -field EDMR: GaN p-n diode
The complex spectra is clearly due to hyperfine interactions
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EDMR Amplitude vs Gate Bias
EDMR amplitude of
several different
spectrum peaks
Calculated
recombination
current
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