advanced mems wafer bonding enabled by high vacuum processingsemicontaiwan.org › en › sites ›...
Post on 26-Jun-2020
24 Views
Preview:
TRANSCRIPT
Advanced MEMS Wafer Bonding Enabled by
High Vacuum Processing
Markus Wimplinger Corporate Technology Development & IP Director
“The Ultimate Goal in Wafer Bonding”
Different CTE Bulk
Materials
Very High Vacuum (<-E-5mbar)
Perfect Bond Line Uniformity (<+/-5nm)
~
Electrically Conductive
(ohmic contact or p/n junction)
Optically
Transparent
High (Bulk Equivalent)
Bond Strength
EVG® ComBond® - High Vacuum Bonding
Applic
ations f
or
Hig
h V
acuum
E
ncapsula
tion b
y W
afe
r B
ondin
g
Gyroscopes
Microbolometers
Thermally Isolated Devices Such as Atomic Clocks
Other?
EVG® ComBond® - High Vacuum Bonding
Re
quirem
ents
for
Hig
h V
acuum
E
ncapsula
tion b
y W
afe
r B
ondin
g
Effective Bake-Out Process
Dual Temperature Bake-Out
Getter Activation
Alignment in Vacuum
Formation of Hermetic Seal
EVG® ComBond® - High Vacuum Bonding
Wafers are baked out prior to aligning and clamping.
Open faced
Wafers will have a minimum of 8 mm free space above them.
Wafers stay in vacuum until bonding is completed
This increased spacing and temperature as compared to traditional
wafer bonding; where the wafers are aligned, separated with spacers
(50 µm – 500 μm) and clamped in ambient atmosphere; results in
improved desorption of water molecules from the surface of the
wafers.
Conceptual drawing of
bake out module
EVG® ComBond® - High Vacuum Bonding
• Improved getter activation due to separate preprocessing of top and
bottom wafer.
– Getter wafer can be activated at a high temperature
– Other wafer can be baked out at lower temperature if required.
EVG® ComBond® - High Vacuum Bonding
• Because of the modular tool configuration, custom
preprocessing modules can be developed and added
without redesigning the tool
• Examples:
– Reducing atmosphere; such as forming gas
– Connection to a non EVG module
– Special customer requirements
Bonding Methods Supported by EVG® ComBond®
Bonding processes other than the
yellow highlighted processes would be
supported as well, but ComBond®
typically does not offer a unique value
proposition
EVG® ComBond®
Process Flow or Direct bonding with ComBond® Activation
High Vacuum
EVG® ComBond®
Process Results: Si – Si Wafer Bonding
Pre-Bonding Surface Characterization:
Topography AFM Measurements
p-type Si (100) Rq = 0.147 nm
p-type Si (100)
Rq = 0.092 nm p-type Si (100) Rq = 0.18 nm
p-type Si (100)
Rq = 0.066 nm
Recipe 1 Recipe 2 Recipe 3 As received
Rq < 0.5 nm for all samples / recipes
Low microroughness profiles are preserved during activation.
EVG® ComBond®
Process Results: Si – Si Wafer Bonding
Bonding Trials Overview
Q.-Y. Tong and U. Gösele, in
Semiconductor Wafer Bonding:
Science and Technology, p. 118,
John Wiley And Sons, Inc., New
York (1999).
Reproducibly achieved bond energy ≈ bulk fracture energy without any thermal
treatment before, during or after processing.
Latest results
EVG® ComBond®
Process Results: Si – Si Wafer Bonding
HR-TEM Measurements
sample #1- medium energy
EVG® ComBond®
Process Results: Si – Si Wafer Bonding
HR-TEM image reveals an
amorphous layer of 2.6 nm
thickness in the bond interface.
Oxygen signal
Oxide-free!
Si/Si bond interface
EVG® ComBond®
Process Results: Si – Si Wafer Bonding
• EDXS was performed on 3 rectangular areas.
• Spectra show the interface is most likely not composed
of SiOx.
• O and C signals have nearly the same peak intensity,
regardless at which position the spectra were taken.
• This indicates O and C contamination is due rather to
sample preparation.
keV
1
keV
2
keV
3
EDXS Measurements
EVG® ComBond®
Process Results: Si – Si Wafer Bonding
Bonding Interface
Characterization: Uniformity C-SAM / Maszara Test
High quality bond interface
Maximum bond strength
without thermal annealing
EVG® ComBond®
Process Results: Si – Si Wafer Bonding
Bonding Interface
Characterization: Structural HR-TEM
Influence of activation power on amorphous layer thickness in
a nutshell:
High power Low power Very low power
Metal Thermo-Compression Wafer Bonding
Tem
pera
ture
Time
High melting
material
High melting
material
Metals have typically oxides on the
surfaces which can prevent perfect
bonding
Oxide
Polycrystalline
Metal
Metal Thermo-Compression Wafer Bonding:
Oxide Removal
High melting
material
High melting
material
Oxide removal by either wet
chemical, forming gas (to
enable bonding for e.g. Cu-Cu
bonding) of ComBond® for
any oxidized surface
Noble metals as e.g. Au have
no oxide formation and can
be bonded directly
Oxide free
surface
Metal Thermo-Compression : Step 1 – Contacting
Tem
pera
ture
Time
Wafers are aligned and brought into
contact
Flat surfaces needed to optimize
contact between the wafers
No grain growth
over the interface
Metal Thermo-Compression : Step 2 – Heating
Tem
pera
ture
Time
Solid-Solid Process
No liquid face at process temperature
Sill interface between the wafers as
the no grain growth over the interface
starts
Started grain growth
over the interface
Metal Thermo-Compression : Step 3 – Isothermal
Annealing
Tem
pera
ture
Time
Grains newly formed
and no more interface
Initial
interface
When the process is finished no more interface
can be detected and bulk strength is obtained
Al-Al bonding results using conventional bonding processes
Left to Right: increasing temperature 400 °C – 550 °C, ∆ = 50 °C, 60 kN
→ decreasing SAM signal with increasing bond temperature
→ increasing bond interface quality with rising bond temperature
400 °C 450 °C 500 °C 550 °C
Al-Al
EVG® ComBond®
Process Results: ComBond Al-Al Wafer Bonding
EVG® ComBond®
ComBond Platform – High Vacuum Wafer Bonding Cluster Tool
Bake
Module
ComBond
Activation
Module
(CAM)
Bond
Module
Vacuum Align
Module
Load
Locks
and
Handling
Cluster
Align & Contact
< 1µm & < 10kN
EVG® ComBond®
ComBond Platform – High Vacuum Wafer Bonding Cluster Tool
Bake
Module
ComBond
Activation
Module
(CAM)
Load
Locks
and
Handling
Cluster Removes
Surface
Contaminants
< 450°C
Removes
Native
Oxides
Bond
< 500 °C
< 100 kN
All Handling
and Modules
at
< 9E-8 mbar
EVG® ComBond®
ComBond Modules – Vacuum Align Module (VAM)
Vacuum Align Module VAM Technical Data
F2F Alignment
Back Side Alignment BSA
RIR Alignment
< 1µm
< 1µm
< 1µm
Piston force Up to 10 kN
Throughput 12 wph
Wafer Substrate 150 mm, 200 mm BSA
200 mm F2F
150 mm, 200 mm F2F with RIR
Wafer stack height < 4 mm
• Alignment Wafers Sizes
• Face to Face (200mm)
• BS Alignment (150mm & 200mm)
• RIR Alignment (150mm & 200mm)
• Force up to 10 kN
• Enhanced vacuum level of < 9 x 10-8 mbar
• Clamp mechanism to fix aligned wafer pair for wafer transfer
Summary & Conclusions
Different CTE Bulk
Materials
Very High Vacuum (<-E-5mbar)
Perfect Bond Line Uniformity (<+/-5nm)
~
Electrically Conductive
(ohmic contact or p/n junction)
Optically
Transparent
High (Bulk Equivalent)
Bond Strength
Thank you for your attention!
Please visit our booth #606 / 4F
top related