aset and tpa update - nasa · aset and tpa update dale mcmorrow and joseph s. melinger naval...
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ASET and TPA Update
Dale McMorrow and Joseph S. MelingerNaval Research Laboratory, Code 6812, Washington, DC 20375
William T. LotshawConsultant, Bethesda, MD 20817
Stephen BuchnerQSS Group., Inc., Seabrook, MD 20706
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Outline
• Two-Photon Absorption (TPA) Technique• Backside “through-wafer” carrier injection and
imaging• Determination of non-linear coefficients• ASETs in LMH6624
• Conclusions
Two-Photon Absorption Technique
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Two-Photon Absorption SEE Experiment
• Because the laser pulse wavelength is sub-bandgap the material is transparent to the optical pulse
• Carriers are generated by nonlinear absorption at high pulse irradiances by the simultaneous absorption of two photons
• Carriers are highly concentrated in the high irradiance region near the focus of the beam
• Because of the lack of exponential attenuation, carriers can be injected at any depth in the semiconductor material
• This permits 3-D mapping and backside illumination
400 600 800 1000 1200 140010-1
100
101
102
103
104
105
1.06 µm
1.26 µm
800 nm
600 nm
Abs
orpt
ion
Coe
ffici
ent,
cm-1
Wavelength, nm
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Two-Photon Absorption SEE Experiment
• Because the laser pulse wavelength is sub-bandgap the material is transparent to the optical pulse
• Carriers are generated by nonlinear absorption at high pulse irradiances by the simultaneous absorption of two photons
• Carriers are highly concentrated in the high irradiance region near the focus of the beam
• Because of the lack of exponential attenuation, carriers can be injected at any depth in the semiconductor material
• This permit 3-D mapping and backside illumination
ωβ
ωα
2),(),(
),( 2
2 zrIzrIdt
zrdN +=
Carrier generation equation:
1-photon absorption
2-photon absorption
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Two-Photon Absorption SEE Experiment
• Because the laser pulse wavelength is sub-bandgap the material is transparent to the optical pulse
• Carriers are generated by nonlinear absorption at high pulse irradiances by the simultaneous absorption of two photons
• Carriers are highly concentrated in the high irradiance region near the focus of the beam
• Because of the lack of exponential attenuation, carriers can be injected at any depth in the semiconductor material
• This permits 3-D mapping and backside illumination
-4 -2 0 2 4
030
1020
N α I2
w(z)
1/e Contour
Position, µm
Dep
th in
Mat
eria
l, µm
Defense Threat Reduction Agency
Two-Photon Absorption SEE Experiment
• Because the laser pulse wavelength is sub-bandgap the material is transparent to the optical pulse
• Carriers are generated by nonlinear absorption at high pulse irradiances by the simultaneous absorption of two photons
• Carriers are highly concentrated in the high irradiance region near the focus of the beam
• Because of the lack of exponential attenuation, carriers can be injected at any depth in the semiconductor material
• This permits 3-D mapping and backside illumination
-4 -2 0 2 4
030
1020
N α I2
w(z)
1/e Contour
Position, µm
Dep
th in
Mat
eria
l, µm
Defense Threat Reduction Agency
Two-Photon Absorption SEE Experiment
• Because the laser pulse wavelength is sub-bandgap the material is transparent to the optical pulse
• Carriers are generated by nonlinear absorption at high pulse irradiances by the simultaneous absorption of two photons
• Carriers are highly concentrated in the high irradiance region near the focus of the beam
• Because of the lack of exponential attenuation, carriers can be injected at any depth in the semiconductor material
• This permits 3-D mapping and backside illumination
Overlayers
P (C1)
P+ (iso)P+ (iso)
N (base)
P (substrate)
12 µm
P (C2)
N+ (buried layer)
P
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-4 -2 0 2 410
8
6
4
2
0
w(z)
1/e Contour
Position, µm
Dep
th in
Mat
eria
l, µm
Two-Photon Absorption SEE Experiment
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-4 -2 0 2 410
8
6
4
2
0
w(z)
1/e Contour
Distance, µm
Dep
th in
Mat
eria
l, µm
Two-Photon Absorption SEE Experiment
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-4 -2 0 2 410
8
6
4
2
0
w(z)
1/e Contour
Distance, µm
Dep
th in
Mat
eria
l, µm
-4 -2 0 2 4
030
1020
N α I2
w(z)
1/e Contour
Position, µm
Dep
th in
Mat
eria
l, µm
Two-Photon Absorption SEE Experiment
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Two-Photon Absorption SEE Experiment
COMPLEMENTARY TECHINQUE
• Not intended to replace “conventional” (above band gap) pulsed laser
• Not intended to replace heavy-ion irradiation
• WILL NOT replace these tools
• Is another “Tool” in our “SEE Toolbox”
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Two-Photon Absorption SEE Experiment
Ti:Al2O3 OPA
Polarizer
λ/2
DUT
xyz
120 fs1.26 µm
CCDPD2
PD1
Back Side Illumination
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Schematic Flip-Chip Cross Section
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Backside “Through-Wafer” TPA Illumination
Surface elements opaque to optical excitation
Tightly focused two-photon excitation
source
Substrate transparent to single photon
sub-bandgap excitationCircuit Layer(s)
Region of 2 PhotonCarrier Generation
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Backside “Through-Wafer” TPA IlluminationLM124 Operational Amplifier
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Photomicrograph of Q20 in LM124 Captured with IR Camera
Front Side Back Side
Evaluating two IR cameras – IR Sensors and Indigo
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Backside “Through-Wafer” TPA IlluminationLM124 Operational Amplifier
0 5 10 15 20
0.0
1.0
2.0Q18
Out
put S
igna
l, V
Time, µs
0.0
0.5
1.0
1.5 Q18
Front Side Back Side
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BAE SRAM “Through Wafer” Image
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Backside “Through-Wafer” TPA IlluminationSEU in Flip Chip SRAM Test Structure
2D SEU Map
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Backside “Through-Wafer” TPA IlluminationSEU in Flip Chip SRAM
• Issues• through-wafer imaging
• InGaAs FPA • highly-doped substrate
• linear loss from free-carrier absorption• attenuates IR beam • attenuates illumination light• wafer thinned to minimize absorption
• Results: SEUs successfully injected in SRAM by TPA at well characterized locations
Determination of TPA Parameters
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Two-Photon Carrier Injection for SEE Testing
The values for linear absorption (αααα), two-photon absorption (TPA) coefficient (ββββ), and Re n2 qualitatively affect optical propagation– Rigorous functional mapping, generic test &
measurement applications to diverse semiconductor devices requires quantified nonlinear optical parameters
• for understanding of axial and transverse injected carrier distribution
– esp. effects due to free (doped) and photo-generated carriers
• evaluation of energy transfer (LET)
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Nonlinear Optical Property Measurement: Z-scans
Laser Spectroscopy Facility
Nonlinear Property Measurement Requires– measured pulse duration– measured spot size– knowledge of laser mode quality– pulse-to-pulse stability
fs Ti:Soscillator
fs Ti:Samplifier fs OPA
Z-scan measurement
Pulse Diagnostics
VariableAttenuator
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Nonlinear Optical Property Measurement: Z-scans
lensf.l.= zo sample beam splitter
aperture
detector 2
detector 1
sample translationwrt lens focal plane, zo
fs laser pulse@ 1/2 Eg
pulse energymonitor
Ultrashort laser pulse induces1. nonlinear lensing in sample:
2. nonlinear absorption in sample:
( ) ),(2 , zrIntrn •=∆
( ) ),( , zrItr •=∆ βα
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Nonlinear Optical Property Measurement: Z-scans on Material with Positive n2
dete
ctor
2 s
igna
l
dete
ctor
1 s
igna
l
z = zo z = zo
lensbeam splitter
aperture
detector 2
detector 1
sample @ z < zo
For sample immediately in front of beamwaist (@ zo), focal power of sample adds to that of lens, the beam at detector 2 is more divergent and signal decreases
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Nonlinear Optical Property Measurement: Z-scans on Material with Positive n2
detector 2
dete
ctor
2 s
igna
l
dete
ctor
1 s
igna
l
z = zo z = zo
lensbeam splitter
aperture
detector 1
sample @ z = zo
At beamwaist, focal power of sample goes to zero so signal at detector 2 is due to lens only. Signal at detector 1 is a minimum because of TPA.
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Nonlinear Optical Property Measurement: Z-scans on Material with Positive n2
dete
ctor
2 s
igna
l
dete
ctor
1 s
igna
l
z = zo z = zo
lensbeam splitter
aperture
detector 2
detector 1
sample @ z > zo
For sample immediately behind beamwaist, focal power of sample decreases beam divergence, signal at detector 2 increases
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Materials for Z-Scan Measurements
Si:– P-type (B) <0.02 ΩΩΩΩ-cm– P-type (B) >10-20 Ω-cm– P-type (B) >30-40 ΩΩΩΩ-cm– N-type (Sb) <0.02 Ω-cm– N-type (P) 10 ΩΩΩΩ-cm
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Two-Photon Absorption Coefficient Measurement
0 5 10 15 20 25 30 35
0.4
0.6
0.8
1.0
Si(B), 30-40 Ohm-cm Z-scans @ 1250 nmN
orm
aliz
ed T
rans
mis
sion
(a.u
.)
Z (mm)
Io = 393 GW/cm2, ∆T = 0.593
I = 166 GW/cm2, ∆T = 0.391 I = 72.7 GW/cm2, ∆T = 0.206 I = 42.1 GW/cm2, ∆T = 0.113 I = 20 GW/cm2, ∆T = 0.03
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Two Photon Absorption Coefficient
( )
( ) ( )( )
( )eff
Z
L
effeff
LIz
eLZZ
LIz
z
L
o
0At
2o
2o
0T22
10%)(~ valueseapproximatFor
1 ,1
122
T
fit to bemust data T theanalysis, rigorousFor
:
. thicknesssample theis
t,coefficien absorptionlinear theis
t,coefficien absorptionphoton - two theis
=∆×≅
±
−=
+=∆
∆
=
−
β
αβ
α
β
α
When Z-scan ∆∆∆∆T (at detector 1) scales ∝∝∝∝ I 2:
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0 5 10 15 20 25 30 350.00
0.05
0.10
0.15
0.20
0.25
N
onlin
ear T
rans
mis
sion
Pulse Energy, nJ
Z-Scan Data Linear Fit
Open Aperture Z-Scan Measurement of TPAAntimony-Doped Silicon (0.02 Ω-cm)
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Two Photon Absorption Coefficient
For I ≤≤≤≤ 166 GW/cm2, the ∆∆∆∆T for all Si z-scans are ∝∝∝∝ I 2, and
for 30 Ω-cm Si(B): ββββ ≅≅≅≅ 0.195 cm/GW; αααα ≅≅≅≅ 0
for 0.02 Ω-cm Si(B): ββββ ≅≅≅≅ 0.286 cm/GW; αααα = 30 cm-1
for 10 Ω-cm Si(P): ββββ ≅≅≅≅ 0.193 cm/GW, αααα ≅≅≅≅ 0
More highly doped sample shows enhanced ββββ.
Further experiments to acquire nonlinear refractive index dataand full curve fitting analyses in progress.
First Measurement of SETs inLMH6624
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LMH6624 SET Test Results
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SETs in LMH6624
-0.14
-0.12
-0.1
-0.08
-0.06
-0.04
-0.02
0
0.02
0.04
-80 -60 -40 -20 0 20 40 60 80 100
Time (ns)
Am
plitu
de (V
)
Position 1
-0.25
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
-80 -60 -40 -20 0 20 40 60 80
Time (ns)
Am
plitu
de (V
)
Position 2
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
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0.4
-80 -60 -40 -20 0 20 40 60 80
Time (ns)
Am
plitu
de (V
)
Position 3
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.2
-80 -60 -40 -20 0 20 40 60 80
Time (ns)
Am
plitu
de (V
)
Position 7
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Summary
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