High-Speed Quantum Efficiency
Measurements in Research and Manufacturing
Mountain View, California
Beaverton, Oregon
Quantum Efficiency
Silicon
ARC
Si
ARC thickness
Front Surface Quality
Bulk Lifetime
Back Surface Quality
CIGS
ZnO
CdS
Same Info, plus:
CIGS
CdS thickness
CIGS bandgap
itop = ∫ QE (λ ) • S (λ ) dλ
Multijunction
Same Info, plus:
Cell Current Matching
?
=
ibottom = ∫ ...
Traditional QE Machines
$
$
$
$
.
1 in 100,000
Monochromator
Filter Wheel
1:100,000
Strength
Weakness
Resolution
Brightness
Brightness
Filter Degradation
Typical measurement time: ~5 minutes
FlashQE Development History
Young et al
Prototype
Tau Science
Commercial Dev
2005
2008
2011
2014
4
FlashQE- Technology
Typical Measurement Time: ~1 second
Solid State Lightsource:
Cell Current = f(λ1, λ2, …)
• All wavelengths measured simultaneously
• Solid State lightsource >20,000 hr lifetime
• Active feedback
FlashQE Configurations: Mapping
R&D Applications
•Small Spot Configuration
•Throughput:
•40 sites/minute
•Chuck:
•Cell
•Mini-module
•Options:
•Light Bias
•Reflectance
•Transmittance
FlashQE Configurations: Full Cell
Module for In-Line Integration
•Cell sort
•Spectral Binning
•Eliminate Spectral Mismatch Correction
•SPC
•Emitter
•BSF
•ARC
•BARC…
Example: Stability Test on c-Si
Measurement Time: 9 hours– 32,000 Repeats
Full Cell
6-σ <1%
Example: Temperature Coeff: QE(λ,Τ)
As Temp rises…
Bandgap narrows (Varshni Equation)
QE increases near gap
λ (IR)
Overlayer (Nitride) absorption redshifts
QE decreases in UV
Result
(1st
order):
λ (UV)
∆QE/∆T
λ (IR)
(UV )
+More complex behavior
Surf Recomb, Trapping
Example: QE Temp Coefficient
60 second measurement: warm sample from 25-43C
Example: Light Induced Degradation, c-Si
: #2- #1=∆EQE
1 sec
EQE #1
6 hr
Light Soak
1 sec
EQE #2
∆EQE (%)
Depth info
Si
QE Mapping: c-Si Cell
In UV, ~7% QE Enhancement at wafer edge
λ=390 nm
PixELTM
Absorption Depth: 0.1 micron
Near Term Challenges (1-3 yrs)
Improve Metrology “Time to Information”
R&D, QA labs
• Shorten turnaround time of standard
techniques.
LBIC, QE, Impurity Imaging…
• Workflow optimization
Manufacturing
• Detect specific defect types
Hotspots, µ−cracks
• SPC info to improve η
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Higher Speed is Needed
Problem: Wafer handling bottleneck in R&D, QA labs
Hot-spot
LBIC
Tau Science
Minutes
Hours
PL
Minutes
EL
Minutes
QE
10’s of Minutes
…Hours of elapsed time…
Solution: Multipurpose Tools
Tau Science
Hotspot: 400ms
PL: 100ms
MP LBIC: Minutes
FlashQE: 1sec
Complete in seconds-minutes.
Long Term Challenges (>3 yrs)
Continuing challenge of “Time to Information”
>3000 wph…
Machine Interface Standardization
• Mechanical
• FA / MES communication protocols
Balance Complexity vs. Cost
Tau Science
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Tau Science