300mm Bonded Wafer Metrology
Using Scanning Acoustic Microscopy
Jim McKeon, Ph.D. - Director of Technology
Josh Waldman – Product Development Manager
Sonix, Inc.
8700 Morrissette Drive
Springfield, VA 22152
tel: 703-440-0222
fax: 703-440-9512
e-mail: [email protected]
1
Ultrasonic Inspection of 3D Architectures
• 3D architectures present challenges to
conventional processing and inspection
tools
• Ultrasonic inspection is inherently a 3D
technology
• Ultrasound provides defect detection,
metrology, and monitoring for process
control
2
Comparison of Imaging Methods
• IR imaging
-Inexpensive
-Ease of Operation
-Clean room compatibility
• X-ray
-Good Resolution
- Through Transmission Technique
- Loss of resolution as
doping level increase
- Cannot penetrate through gold
-Difficult to detect air
-Single image shows all interfaces
• Scanning Acoustic Microscopy
-Can detect sub-µ air gaps
- Requires water couplant
-Good resolution
-Each interface can be imaged separately
3
IR Vs SAM Imaging
IR Image
SAM Image: Interface 1
SAM Image: Interface 2
4
Ultrasonic Inspection
Ultrasound
Ultrasound
Pulse
PulseEcho
EchoInspection
Inspection
••AAtransducer
transducerproduces
producesaahigh
high
frequency
sound
wave
which
frequency sound wave which
interacts
interactswith
withthe
thesample.
sample.
•1
–
300
MHz
•1 – 300 MHz
•A
•Achange
changein
inacoustic
acousticimpedance
impedance(Z)
(Z)
results
resultsin
insome
somesound
soundreflected
reflectedand
and
some
transmitted
some transmitted
••High
Highfrequency
frequencysound
soundwaves
wavescan
can
not
propagate
through
air.
not propagate through air.
•Air
•Airhas
hasZZ==00
Transducer
••CouplantCouplant-AAmaterial
materialused
usedto
tocarry
carry
the
high
frequency
sound
waves.
the high frequency sound waves.
•Water
•Waterisisthe
themost
mostcommon
common
couplant
couplant
H2O
Couplant
Si Wafer 1
Glass wafer
Si Wafer 2
5
SAM Capabilities
Bonded wafer
Si Wafer 1
Si Wafer 2
MEMS pressure sensor
Si Wafer
•Voiding in wafer bonding
•Bond delaminations for hermetic
seal applications (MEMS)
•Metrology for wafer pair
alignment post bonding
Glass Wafer
Alignment of bonded wafer pair
Si Wafer 1
Si Wafer 2
6
Example Images
MEMS Inspection
Bonded Wafer Voiding
7
Example Images
Patterned Wafer Voiding
Eutectic – Au compression
8
Example Images
Bumped Wafers – Bump up
Bumped Wafers – Bump down
9
A-SCAN
Initial Pulse
Front surface
Transducer
Si Wafer 1
Interface of interest
Si Wafer 2
Back surface
The raw ultrasonic data. It is the received RF signal from a single point (x,y).
10
C-Scan
Data from a specified depth over the entire scan area. (Horizontal cross-section).
11
Tomographic Acoustic MicroImaging (TAMI)
•Allows imaging of multiple interfaces at different depths with a single scan
12
Triple Stacked wafer: TAMI
TAMI Image 1
TAMI Image 3
Si Wafer 1
Glass wafer
TAMI images
Si Wafer 2
Front surface
Silicon
wafer 1Glass
13
Glass
waferSilicon
wafer 2
Determining Void Size Distribution:
Cluster Analysis
•Cluster Analysis determines void size distribution based on user-defined amplitude
and size criteria
•Void count and percentage of void area are indicated
14
Production Status Page
15
Reports
16
Process Validation
Silicon wafer 1-Glass Wafer interface
Glass-Silicon wafer 2 interface
•Circular pattern of circular voids from particulate residue from polishing?
17
Process Validation
Original process
Modified process
11.664% defect area
1.086% defect area
18
Metrology
Anodic - Cross Pattern Fiducials
100 µm
50 µm
19
Metrology
Anodic – 10µm line pairs
SOI 5 - 10µm voids
20
Metrology
Via measurement - spatial
21
Metrology
Via measurement - depth
Cu velocity = 4.66 mm/µs
22
Metrology
Wafer Thickness Measurement
Si velocity = 8.6 mm/µs
23
Metrology
Wafer Thickness Measurement
24
Challenges in Inspecting 3D Architectures
• More Layers
more reflective loss at an interface
- Signal significantly weakened at lower interfaces
• Thin layers / small features
- Greater attenuation
higher frequencies
• Internal Multiples may interfere with real echoes
• Voiding at higher interfaces
non-imageable
shadow areas at lower interfaces
• Non-air fiducials
fiducial marks
not as distinct as etched (air-filled)
25
SAM Tools
• Manual Tool
–
–
–
–
–
50mm – 300mm capability
5 – 300 MHz transducer frequencies
Void / Delam detection, Process Validation, Metrology
Recipes, Reports
SEMI S2, S8, CE
• Automated Tool
–
–
–
–
–
–
–
50mm – 200mm capability
5 – 230 MHz transducer frequencies
3 cassettes
SECS/GEM for up to 200mm
Void / Delam detection, Process Validation, Metrology
Drying
SEMI S2, S8, CE
• Automated 300mm Tool (additional requirements)
– FOUP
– SECS/GEM for 300mm
26
Summary
• Scanning Acoustic Microscopy provides
– Vertical and horizontal section views
– Detection of
• Sub micron delaminations
• Cracks
• Voids
– Auto Analysis for use in production process
control
– Metrology for fiducials, thickness measurement,
via measurement
27
Questions?