Anodisches Niedertemperatur

(Anodisches) Niedertemperatur-Waferbonden
für mikrosystemtechnische Anwendungen
Mario Baum
Fraunhofer-Institut
für Elektronische Nanosysteme ENAS
Jörg Frömel, Chenping Jia, Marco Haubold,
Dirk Wünsch, Jörg Bräuer, Karla Hiller, Maik Wiemer
Page 1
Fraunhofer ENAS
Überblick
 Vorstellung Fraunhofer ENAS
 Anodisches Bonden – Einsatz
 Prozesstemperatur als Forschungsschwerpunkt
 Anodisches Niedertemperatur-Waferbonden
 Feldunterstütztes Direktbonden
 Niedertemperatur-Direktbonden
 Reaktives Bonden von Glas bei Raumtemperatur
 Zusammenfassung
Page 2
Fraunhofer ENAS
Fraunhofer Institute for Electronic Nano Systems
Systems integration by using
micro and nano technologies
 MEMS/NEMS design
 Development of MEMS/NEMS
 MEMS/NEMS test
 System packaging/wafer bonding
International Offices:
Since 2001 / 2005 Tokyo/Sendai-Japan
 Back-end of Line technologies for
micro and nano electronics
 Process and equipment simulation
Since 2002
Shanghai-China
 Micro and nano reliability
Since 2007
Manaus-Brazil
 Printed functionalities
 Advanced system engineering
Page 3
Fraunhofer ENAS
Smart Systems Campus Chemnitz
Lightweight Structures Engineering
3D-Micromac AG
Start-up-building
Fraunhofer ENAS
Institute of Physics and
Center for Microtechnologies at the CUT
Page 4
Fraunhofer ENAS
Fraunhofer ENAS / ZfM: A historical perspective and trends
Applications
Wafer Bonding / MEMS Packaging
Interposer
Integration
MOEMS
MEMS
GEMAC
Inclination Sensor
Fabry-Perot
Filter
LITEF High Prec.
Accelerometer
X-Fab
Embedded
Interconnects
* IZM
MDI
* ZfM
Anodic Wafer
Bonding
Silicon Fusion
Wafer Bonding
1994
Glass Frit
Wafer Bonding
1996
Page 5
Fraunhofer ENAS
1998
2000
Adhesive
Wafer
Bonding
BDRIE
Technology
2002
* ENAS
2D AIM
low g
sensor
E&H
Pressure
Sensor
Eutectic
Wafer
Bonding
Smart System
Integration
2004
3D Integration
Thin film
Encapsulation
Nano
Structures &
Effects
Functional
Substrates
bond
frame
Nano Effects
for Wafer
Bonding
Laser Assisted
Wafer Bonding
Thermo Compression
Wafer Bonding
Technologies
2006
2008
2010
Fraunhofer ENAS / ZfM: Wafer bonding portfolio
Page 6
Fraunhofer ENAS
Anodisches Bonden - Einsatz
Joining of glass (borosilicate) and silicon substrates without intermediate layers or
silicon materials with sputtered thin glass layers.
Inclination sensor
Technology steps:
Gyroscope sensor
 Joining of starting materials
 Heating of the substrates
 Applying of an electrostatic field
 Cooling of the substrates
Materials:
 Silicon
 Borosilicate glasses e.g. borofloat, pyrex, SD2
 Intermediate layers like SiO2, Si3N4, Al
Typical parameters:
 Temperature between 250°C and 510°C
 Voltage between 50 and 2000 V
Page 7
Fraunhofer ENAS
Micro mirror
Aktiv Sensor
GmbH
Pressure
sensor
Anodisches Bonden - Einsatz
The BDRIE technology flow for inertial sensors
Cross section of the glass – Si – glass
variant
Active structure
glass
Si
glass
Contact hole with metallisation
Example: Vibration sensor
Page 8
Fraunhofer ENAS
Anodisches Bonden - Einsatz
The BDRIE technology flow for inertial sensors 1
Glass (400 µm thickness) with
sandblasted holes
Si 300 µm, with etched cavities on
the bottom side
Anodic bonding
Page 9
Fraunhofer ENAS
Anodisches Bonden - Einsatz
The BDRIE technology flow for inertial sensors 2
Thinning of the Si wafer (grinding
and polishing) down to 50 µm
thickness of the active layer
Dry etching of Si
Page 10
Fraunhofer ENAS
Anodisches Bonden - Einsatz
The BDRIE technology flow for inertial sensors 3
Glass (500 µm thickness)
Wet etching of a cavity
Anodic bonding with active wafer
Metal deposition for through
contacts
Issue: edges of the holes
must be smooth and free of
defects for successful thinlayer metallization
Page 11
Fraunhofer ENAS
Examples of holes and fabricated MEMS structures
Sand blasted
holes, view
on bond side
SEM of
hole in
glass-Si
compound
Page 12
Fraunhofer ENAS
Example of inertial MEMS with
metallized through holes
Forschungsschwerpunkt
Anodisches Niedertemperatur-Waferbonden
 Gehäuseausführung als Dreifachstapel Glas – Glas – Silizium
 1. Bondinterface Glas – Glas
 Direktbonden (oberhalb 210°C)
 2. Bondinterface Glas – Silizium  Anodisches Bonden (bei 210°C)
 Elektrische Kontaktierung z.B. mittels vertikalen TSVs
Metallisiertes TSV zur Kontaktierung
Strukturiertes Siliziumsubstrat
MEMS
Glasverbund mit Kavität
Schematische Darstellung der umhausten Struktur
Page 13
Fraunhofer ENAS
Forschungsschwerpunkt
Anodisches Niedertemperatur-Waferbonden
 Fertigungstechnologie:
1. Sandstrahlprozess zur Perforation
2. Direktbonden nach Vorbehandlung
3. Temperung bei 400°C
Gefertigte Perforation (links) / direkt gebondete Wafer (rechts)
Page 14
Fraunhofer ENAS
Prozessablauf Deckelfertigung
Forschungsschwerpunkt
Anodisches Niedertemperatur-Waferbonden
 Technologie:
 Nutzung der vorhandenen Aluminium Leiterbahnen als Bondschicht
 Interface Al-Glas erlaubt das Absenken der Prozesstemperatur während
dem anodischen Bonden
 Ausreichende Bondfestigkeit bleibt erhalten
Fakten:
 SUSS MicroTec SB8e Substratbonder
 Prozesstemperatur 210°C
 Grenzwert 200°C
 Bondspannung 800V
 Max. Strom 1,1 mA
 Kontaktierungsfenster im Oxid zur
Anschluss des Al an das Substrat
Page 15
Fraunhofer ENAS
Forschungsschwerpunkt
Anodisches Niedertemperatur-Waferbonden
Testchips für die elektrische
Charakterisierung sowie
Hermetizitätsuntersuchungen
Page 16
Fraunhofer ENAS
Umhauste HF Schalter auf Waferlevel
Forschungsschwerpunkt
Anodisches Niedertemperatur-Waferbonden
 Test des Al-Glas Interface nach
Bond @ 210°C mittels Mikro-Chevrontest
 Bruch des Glaschips als überwiegender
Fehlermechanismus
Max. Zugkraft
Mittelwert
12,3 N
Standardabweichung
2,2 N
Anzahl getesteter Chips
Aluminium = Bondfläche
Bruch im Glaschip
Resultat nach Chevrontest  Bruch des Glaschips
Page 17
Fraunhofer ENAS
12
Forschungsschwerpunkt
Anodisches Niedertemperatur-Waferbonden
 Weitere Verringerung der Bondtemperatur untersucht
 Mithilfe von Zwischenschichten (Al) eine signifikante
Minimierung erreicht
 Bondfestigkeit zeigt hohe Werte bei 150 °C
Bondtemperatur
Page 18
Fraunhofer ENAS
Forschungsschwerpunkt
Anodisches Niedertemperatur-Waferbonden
Dependence of fracture toughness
from bond temperature
Bonding of borosilicate
glass to silicon:
• Fracture toughness
heavily depend on
bonding temperature
• Main mechanism of
bonding is oxidation
at interface
Page 19
Fraunhofer ENAS
Forschungsschwerpunkt
Anodisches Niedertemperatur-Waferbonden
Dependence of fracture toughness
from bond temperature
Adding of thin metal
layer in between the
interface:
• Oxidation is much
easier than silicon
• Fracture toughness
dependence on
bonding temperature
very low
Hata,S.; Froemel,J.; Gessner,T.; The improvement of the bonding strength of low temperature
anodic bonding; Japan Institute of Electronics Packaging; The 19th JIEP Annual Meeting;
(2005)
Page 20
Fraunhofer ENAS
Forschungsschwerpunkt
Field Assisted Direct Bonding
 Anodic bonding : 300 V and
300…400°C
 Back grinding of glass wafer to
ca. 20 µm thickness
 Surface and layer quality is
better than after sputtering
 2nd bonding: field assisted:
150°C and 100 V
Page 21
Fraunhofer ENAS
Field Assisted Direct Bonding
Process parameters

Substrate 1: 4-inch Si, p-(100),
200µm thickness

Substrate 2: 4-inch glass,
Borofloat, 500µm

Temperature: start from120°C,
step up to 150°C

Bias voltage: start from 200V, shift
gradually to 2000V at a pace of
200 ~ 300V

Tool force: constant 300N

All experiments performed under
vacuum
Page 22
Fraunhofer ENAS
Field Assisted Direct Bonding
Bonding quality inspection - IR imaging
150°C, 120V
Page 23
Fraunhofer ENAS
150°C, 100V
Result Summary

A wafer bond was reached at 100 V and 150 °C

The shear strength of the joined wafer pair is greater than the flexural
strength of 200µm thick Si plate – break out

Migration current is significantly lower than normal AB process
(60…250µA max. vs. 10mA)

Temperature is the major factor for this bonding, voltage the second

Further steps: characterization of the strength and transfer to patterned
wafers
Page 24
Fraunhofer ENAS
Forschungsschwerpunkt
Oberflächenaktiviertes Direktbonden
Bonding partners:
 Borosilicate glass – 4”, thickness 500 µm,
CTE 3.25 ppm/K
 Silicon – 4”, thickness 525 µm, CTE 2.3 ppm/K
Results:
 Tensile force of 5 N - Activated specimen is more than
two times higher than the strength of the reference
 Bond strength of this wafer stack is as high as a
conventionally anodic bonded Si/glass wafer stack
 Bond strength of the bonded interface is comparable to
the bulk material
Process Parameter:
 Pre-Treatment: CMP and RCA-procedure
 Optimal process gas: O2dH2O (humid oxygen)
 Annealing: 250°C, 6h, air
Page 25
Fraunhofer ENAS
Forschungsschwerpunkt
Reaktives Raumtemperaturbonden
Page 26
Fraunhofer ENAS
Forschungsschwerpunkt
Reaktives Raumtemperaturbonden
Adv antages :
 Localized heating
 Stress-free bonding
 Bonding of heterogeneous materials (Si-metal, Si-ceramic...)
 Integration of new materials (Optical layers, bio-sensitive layers...)
 Very fast  large area bonding / wafer bonding within several ms
 Room-temperature metallic bonding
 No special surface preparation needed (“just” wetting layer)
 Bonding at different atmospheres possible
 Different bonding geometries possible
Page 27
Fraunhofer ENAS
Conclusion
 Our motivation is decreasing the process temperature
for wafer bonding techniques, optimizing the overall
parameters and minimizing the thermal influence to the
devices.
 As an independent research organization we are able to
offer individual services for companies doing R&D.
 We see future trends in an increasing functionality in
one system with decreasing size.
 Smart System Integration covers all aspects of research:




Materials
Technologies
Packaging
Equipment
Page 28
Fraunhofer ENAS
Source: Fraunhofer ENAS
Thank you for your kind attention!
Fraunhofer ENAS
Dept. System Packaging
Mario Baum
Technologie Campus 3
D-09126 Chemnitz
Phone: +49 - 371 – 45 00 12 61
Fax:
+49 - 371 – 45 00 13 61
E-mail: [email protected]
http://www.enas.fraunhofer.de
Page 29
Fraunhofer ENAS

Download Report