1) Fraunhofer Institute for Mechanics of Materials IWM, Halle (Saale), Germany ... high through put solutions. - NDT with ... cracks/inclusions in ceramic material ...
Failure analysis using scanning acoustic microscopy for diagnostics of electronic devices and 3D system integration technologies Peter Czurratis2), Sebastian Brand1), Frank Altmann1), Matthias Petzold1)
1)
Fraunhofer Institute for Mechanics of Materials IWM, Halle (Saale), Germany 2) PVA Tepla Analytical Systems GmbH, Westhausen, Germany
PVA TePla Analytical Systems GmbH - Company Confidential -
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Outline • Motivation and Background • Potential of Scanning Acoustic Microscopy • Limitations and Challenges of SAM • Technical Advances in SAM • Analog pre-processing • Optimized amplification • New transducer designs • SAM in GHz-band (Resolution in the 1 µm scale)
• Results • Summary
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Motivation and Background Background - Ongoing requirements for non-destructive methods in F/A - failure localization, especially in z dimension - investigation of failure - root cause - high through put solutions - NDT with highest possible resolution Motivation - current NDT methods are be limited (not applicable in 3D integration)
- improve imaging resolution - penetration depth Why Acoustic Microscopy ? - operating non-destructively - depth specific information - high sensitive for voids and small - delaminated areas
cracks/inclusions in ceramic material
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Potential of Scanning Acoustic Microscopy
molded device
Die top -die bottom
acoustic X-section of an IC
- non-destructive investigations of opaque materials - non-destructive cross-sectioning - high axial- and lateral resolution, depending on frequency - fast 3D-imaging - information contained in time domain signals - estimation of E modulus, G modulus and Poission ratio
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Current limitations & Challenges Current limitations: - f vs. penetration: acoustic attenuation - penetration depth (lens aperture, focussing, frequency) - resolution (wavelength depending on sound velocity) -requires coupling fluid (impedance matching)
Attenuation vs. Frequency
x1; yn
x1; y1
x2; y1
x2; yn
x3; y1
x3; y n
xn; yn
xn; y1
2D-scan required PVA TePla Analytical Systems GmbH - Company Confidential -
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How to Overcome those Challenges / Limitation ? increased transmitt power, customized design
increased sensitivity of receiver chain / SNR, time corrected gain power-amplifier
T/R switch
pre-amplifier
pre-processing
analog pre-processing
∑
performance of piezo-element (sputtered)
ADC
increased sensitivity of data acquisition unit
ultrasonic transducer
ocus behavior of acoustic lenses, pplication specific solutions
coupling fluid
PC
interconnect wiring / micro-bumps
software based postprocessing
BCB
acoustic frequencies ->resolution
silicon
line - signal
PVA TePla Analytical Systems GmbH - Company Confidential -
pre-processing rf-data during scan analog ->extremely fast (real-time) HILBERT integration of signal low-noise components / increased SNR
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Technical Advances in SAM amplification –
– optimized
Acoustic Attenuation : • • • Solutions : • • •
impacts sensitivity and SNR restricts inspection of materials with high absorption / scattering decreases frequency (exponential relationship) ->directly linked to resolution
increased transmitt amplitude (amplification; transmitt power) increased receive-sensitivity decreased noise number of receiver chain
Design of optimized transmitter/receiver electronics with 20 dB increase in gain
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Technical Advances in SAM scanning times –
– reducing
simultaneously scanning 2-channel-device
fully automated SAM inspection system - Auto-Wafer-
simultaneously scanning 4-channel-device
PVA TePla Analytical Systems GmbH - Company Confidential -
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Technical Advances in SAM design –
- optimized transducer design and performance - piezo elements sputtered on lens substrate (saphire or quarz)
– transducer piezo element acoustic lens
- application specific lens design - numerical simulation of sound propagation / pressure distribution - focussing and frequency adjusted during design: acoustic impedeance net work
PVA TePla Analytical Systems GmbH - Company Confidential -
sound diffraction pattern
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Technical Advances in SAM microscopy –
– acoustic GHz-
Prototype of GHz-SAM Control unit - 600 MHz – 2 GHz - downmodulation - USB controlled Opto- Acoustic GHz Microscope - Tone-Burst excitation
Extremely fast high-resolution scanner - 60 Hz line-repetition frequency - 50 nm scan resolution - 2 mm scan field - 10 mm defocus range
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Results
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Surface Profilometry using
GHz-SAM
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Results
and axial)
Near Surface analysis with µm Resolution (lateral • • • •
Acoustic micrograph: Cr deposition on photo mask for mask repair applications
topography parametric image 3 2 1
-30
0
-40
-1
z [µm]
-50 -60
-2
-70
-3
-80 -90
optical micrograph
6 µm
V(x, z) graph 5
10
15
20 25 x [µm]
30
35
PVA TePla Analytical Systems GmbH - Company Confidential -
-4 -5
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Inspecting µ-Bump Devices using
GHz-SAM PVA TePla Analytical Systems GmbH - Company Confidential -
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Results
µ – Bumps
Acoustic Inspection through BCB mechanical key / and Si-Die
µ-Bumps
BCB (5 µm)
Silicon (800 µm) Inter connect wiring acoustic inspection
before preparation
interface to be inspected
top-die removed
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Results µm
µ – Bumps
@ 1 GHz acoustic frequency resolution 1 acoustic micrograph at -10 µm defocus; imaging of interfaces behind BCB key arrows correspond to position in X-section scan
30 µm
X-section along red marker -30 -40
20 µm
acoustic X-section recorded at increasing defocus positions (transducer stepwise moved toward sample)
z [µm]
-50
acoustic micrograph (surface in focus)
-60 -70 -80
-90 20 PVA TePla Analytical Systems GmbH - Company Confidential -
40
60
80 x [µm]
100
120
140
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Results
µ – Bumps
µm
@ 1 GHz acoustic frequency resolution 1
SEM image
µ - pillar
10 µm
SAM image 20 µm
- delaminations clearly visible - 1 µm resolution
SAM image PVA TePla Analytical Systems GmbH - Company Confidential -
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Delamination Analysis in Stacked Devices using
post-Processing in SAM PVA TePla Analytical Systems GmbH - Company Confidential -
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Software Approaches –
– Delamination Analysis in 3D integration
Problem : -
c -se ic X us t a co ( c an B-S
high sound velocity of Silicon extremely thin Si - layers Time Of Flight (TOF) shorter than pulse length interfaces cannot be separated
) tio n
Sample Die-Stack
Approach : -
structures and layer-thicknesses are known expected arrival times can be computed numerical deconvolution algorithms differential analysis (known / unknown sample) comparing echo amplitudes between adjacent interfaces
50
100
150
200
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Software Approaches –
SD2 SD4 SD6
– Delamination Analysis in 3D integration
SD1
IF 1/2 IF 2/3
SD3
IF 3/4
SD5
IF 4/5 IF 5/6
Substrate Die 5 Theoretical calculation of theDieBAI 6 depending on die thickness and acoustic impedeance for a reference sample for all interfaces
PVA TePla Analytical Systems GmbH - Company Confidential -
Die 5 Die 6
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Software Approaches –
– Delamination Analysis in 3D integration
• normal signal: reference sample without interface defects • signal with delamination or void inclusion in some interfaces
• voids and delaminations are not easily distinguished in time signal in case of conventional C-SAM detection • Solution: imaging of time-gated backscattered amplitude integral (BAI) PVA TePla Analytical Systems GmbH - Company Confidential -
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Software Approaches
– Delamination Analysis in 3D integration
–
BAI data processing 1
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• RF acquisition (500 MS/s) • Hilbert transformation • low-pass filter • sliding time gate (80 ns) • backscattered amplitude integral (BAI) (Raum et al. IEEE UFFC, 1997) t2
BAI abs hilbert Signal t1
BAI vs. gate position void
PVA TePla Analytical Systems GmbH - Company Confidential -
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Software Approaches –
– Delamination Analysis in 3D integration
Slices from top to bottom
IF 1/2
IF 2/3
TOF : 1.24 µs
IF 3/4
TOF : 1.38 µs
IF 5/6
IF 4/5
TOF : 1.42 µs
substrat
TOF : 1.52 µs
crack
TOF : 1.39 µs
TOF : 1.64 µs
Parameter : BAI PVA TePla Analytical Systems GmbH - Company Confidential -
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Summary & Conclusions Technical Advances •
ongoing improvement of SAM-equipment to push the limits
•
optimization in electronics, transducers and software-tools
•
adressing signal power, penetration depth, attenuation, resolution and frequency
•
Extending the fields of application to 3D-integrated devices
Results • delamination analysis in layered structures • µ-bump inspection • high resolution SAM inspection for thin layers • applicable in failure analysis and process control for 3D-manufacturing
Future Work •
Characterization of TSV-filling integrity PVA TePla Analytical Systems GmbH - Company Confidential -
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