[l-17] packaging schemes for mems

8/7/2019 [L-17] Packaging Schemes for MEMS

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6/17/2004 Liwei Lin, University of California at Berkeley 1

Packaging Schemes for MEMS

Liwei Lin

Associate Professor, Department of Mechanical EngineeringCo-Director, Berkeley Sensor and Actuator CenterUniversity of California at Berkeley


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Presentation Outlinel MEMS Products & the Role of Packagingl Microelectronics Packagingl MEMS Packaging Issuesl MEMS Packaging Approaches

Integrated microfabrication processes

Water bonding processesl Summary


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IC and MEMS Packagingl IC Packaging

well-developed (dicing, wire bonding ...) 30% to 95% of the whole manufacturing cost

l MEMS Packaging specially designed packaging processes difficult due to moving structures, chemicals ... the most expensive process in

micromachining


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Existing MEMS ProductsDevice Year Units Sale Comment

(M) (M)Blood Pressure 1998 20 22 price drop, sale flatAuto MAP 2000 52 400 price droppingAuto Accelerom. 2002 100 ~400 price droppingAuto Gyro 2002 20 ~200 newer marketInk-Jet Head 2002 470 8,400 huge marketDisk-Drive Head 2002 1,500 12,000 huge marketHead Positioner 2002 400 ~800 new marketDisplays 2000 1 300 High chip costValves 2005 1~2 100 small market


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Example: MEMS Pressure Sensorsl Automobiles

MAP

Barometric pressure Fuel-tank pressure Turbo-boost pressure Tire pressure

l Human body Blood pressure, Heart, brain, uterus Typically on catheter or probe tip

l Industrial Applications Food processing, HVAC


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Example: MEMS Accelerometerl Automobiles

Airbags, Side airbags,Headlight leveling

l Military Trajectory control,

Impact sensing l Consumer

Joystick, virtual reality l Industrial

Vibration monitoring such as bearing l Environmental - Seismic monitoring


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Current MEMS CompaniesCompany Products (principal) MicromachiningLucas Novasensor Pressure (piezoresistive) bulkDelphi(Delco) Pressure (piezoresistive) bulk

gyro (capacitive) surfaceEG&G IC Sensor Pressure (piezoresistive) bulkFoxboro/ICT Pressure (piezoresistive) bulkHoneywell flow (thermal) bulk+surface

IR image (thermal-resis.) surfaceAnalog Device accelerometer (capacitive) surfaceMotorola accelerometer (capacitive) surfaceRobert Bosch accel. + gyro (capacitive) surfaceTexas Instrument display (electrostatic) surfaceOMM optical switch (electrostatic) surfaceRedwood microsys. Valve (thermal) bulkTiNi Alloy Valve (thermal) bulk + surface


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MEMS Optical Switch CompaniesCompany Products (status)Optical Micro-Machines (OMM) 2-D (16 x 16) - shippingSercalo 1-D and 2-D (4x4) - shipping

Onix 2-D (8x8) - magneticAgilent 2-D (32x32) - bubbleNortel/Xros 3D (1152 x 1152) - patentLucent 3D (256x256)Corning/IntellisenseJDS Uniphase/Cronos(MCNC) C Speed

Tellium/Astarte MEMXAdvanced Integrated Photonics (AIP) Optical SwitchTransparent Optical MEMS Nayna NetworksIntegrated Micromachines Inc. (IMMI) Litton Poly-ScientificBoston Micromachines Corp. LolonCalient Networks/Kionix Light Connect


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Summary MEMS Marketl Todays MEMS Market

Pressure sensors

Accelerometers Ink-jet printer heads Disk-drive heads

l Tomorrows High growth MEMS Market

Yaw-rate sensors Displays Bioanalysis Optical Switch RF Filters


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MEMS Device Cost AnalysisDie $0.45Trimmed circuit on ceramic board $1.10Board in plastic arterial line $10.00Billed to patient $300.00Vertical integration for greater profit !


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Microelectronics Packagingl Electronic Package Hierarchy

Chip Module (1st level) Card (2nd level) Board (3rd level) Gate (4th level)


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Package Encapsulationl Protection from corrosion, mechanical damagel Moisture is one of the major sources of corrosion


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Example of Corrosionl Migrated-gold resistive shorts in the presence of

moisture and chlorine

Shumka and Piety, Migrated-Gold Resistive Shorts in Microelectronics,13th Ann. Proc. Rel. Phys. Symp., pp.193-98, 1975


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Hermetic Seal (MIL-STD-883)l A seal that will indefinitely prevent the entry of

moisture and other contaminants into the cavity

In practice such seals are non existent Smaller gas molecules will enter the cavity over time

by diffusion or permeation and reach equilibrium


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Water Penetrationl Absence of an explicit relationship between device

life and moisture levell Hermetic packages probably have much lower leak rate

than the specifications allow (moisture absorbed on thewalls of leakage path )


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Types of Hermetic Packagingl The permeability to moisture of Glasses,

Ceramics and Metals is orders ofmagnitude lower than plastic materials

Metal package harshest conditions, 80% of all metal packages are

welded, with the remaining being soldered

Ceramic package Solder glass seal by high-lead-content vitreous or

de-vitrifying glasses at 400 oC Hard glass seal by high-melting borosilicate glass at

1100 oC


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Soldering and Brazingl Soldering

Tin-Lead solder (indium and

silver are sometimes addedto improve the fatiguestrength)

Tin-Lead oxidizes easily andshould be stored in nitrogen

l

Brazing Eutectic Au-Sn (80:20) at 280

- 350 oC for stronger, morecorrosion-resistant seal andthe use of flux can beavoided


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Weldingl Most popular method in high-reliability packagesl High-current pulses produce local heating 1000-1500 oCl Can accommodate greater deviations from flatnessl Electrode, e-beam and laser can be used as energy sources


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Glass Sealingl Device passivation to against moisture and

contaminantl Hermetic glass-to-metal seals or glass-ceramic seall Chemical inertness, oxidation resistance, electrical

insulation, impermeability to moisture and othergasses, wide choice of thermal characteristics

l Disadvantages: low strength and brittlenessl Soft glass sealing are made by lead-zinc-borate

glasses below 420 oC ->low water content, goodchemical durability, thermal expansion closelymatched to that of the ceramic

l Water is absorbed on glass network and may getreleased into the sealed cavity


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MEMS Packaging Issues

l Key Issues Free standing

microstructures Hermetic sealing Temperature sensitive

microelectronics

l MEMS Accelerometer Example: Surface-

MicromachinedAccelerometers byAnalog Devices, Inc.

ADXL50 by Analog Devices, Inc.


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Example Resonant Gyroscopel MEMS Gyroscope

Example: surface-micromachinedvibration gyroscope byDraper Lab


microstructures Hermetic sealing Vacuum encapsulation

Drapers vibration micro gyroscope


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Example Pressure Sensorl Pressure Sensor

Example: bulk-micromachinedpressure sensor byMotorola Inc.

l Key Issues Exposure to external

pressure source Housing for harsh

environment Interface coating

Motorolas MEMS-based pressure sensor


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Example Optical MEMSl Optical MEMS

Example: surface-

micromachined DMDby Texas Instrumentl Key Issues

Free standingmicrostructures

Hermetic sealing Temperature sensitive

microelectronics

DMD

ProjectedImage

Lamp

ColorWheel

ProjectionOptics

TIs DMD TM Chip for Projection Display


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Example Microfluidicsl Microfluidics

Example: diffusion-

based sensor byMicronics Inc.l Key Issues

Micro-to-Macrointerconnector

Good sealing Temperature sensitive

materials

Micronics Inc.s T sensor


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Example BioMEMSl BioMEMS

Example: Lab-on-a-chip

by Caliper Inc.l Key Issues

Micro-to-Macrointerconnector(capillary tubes?)

Good sealing Temperature sensitive

materialsCalipers lab-on-a-chip


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Example RF MEMSl MEMS Relay

Example:

micromachined RFrelay by Omron with aneedle (1 billionoperation, 0.5 msec)

l Key Issues

Free standingmicrostructures Hermetic sealing Vacuum

encapsulation ? Omrons MEMS RF relay


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Wafer-Level Approachl To adopt IC packaging

processes as much as

possiblel To protect MEMS

devices and follow ICpackaging processes

l

Encapsulations (caps)are required


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MEMS Encapsulation Processesl Integrated MEMS Encapsulation Processes

Guckel (1984) reactive gas sealing

Ikeda (1988) epitaxial deposition Lin (1993) LPCVD deposition Smith (1996) CMP + film deposition

l Wafer Bonding Processes Anodic bonding (1969) SOI, pressure sensors ... Fusion bonding (??) pressure sensors Eutectic bonding (??) assembly, packaging ...


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Example:LPCVD Packaging Process

l Example: Surface-

micromachined microelectromechanicalfilters

Lin, Howe and Pisano, JMEMS,Vol. 7, pp. 286-294, 1998

Beam length 150 mBeam width 2 mBeam thickness 2 mSuspension 2 mResonance 18 kHzQuality factor 30 in air

Lin et. al., Microelectromechanical Filters for Signal Processing,IEEE/ASME J. of Microelectromechanical Systems, Vol. 7, pp.286-294, 1998


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LPCVD Encapsulation Process (1)

(a) Standard surface-micromachining process

(b) Additional thick PSGdeposition to defineencapsulation regions

(c) Additional thin PSG

deposition to defineetch channels


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(d) Nitride shell deposition;etch hole definition

(e) Removal of all sacrificialPSG inside the shell;supercritical CO 2 drying;global LPCVD sealing


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Fabrication/Measurement ResultsSEM Microphoto Measured Spectrum, Q = 2200


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Fabrication Results

Overhanging microresonator thin coating of silicon nitride


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Reactive Gas Sealing Process

(a) Construct polysiliconshell on top of device

Cavity

Polysilicon

Substrate

Sealed Cavity

Thermal Oxide

Substrate

(b) Reactive gas seal @>900 oC(Oxidation to consumethe gas inside the cavity)

Si + O 2 --> SiO 2

Guckel et. al., Planar Processed Polysilicon Sealed Cavities for PressureTransducer Arrays, IEDM, pp. 223-225, 1984


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Epitaxial Deposition and Sealing

Ikeda et. al., Silicon Pressure Sensor Integrates Resonant Strain GaugeOn Diaphragm, Sensors and Actuators, A21, pp.146-150, 1990


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CMP and Thin Film Deposition

(a) MEMS microstructure isfabricated in a trench,sealed and flattened

(b) Conventional CMOS processis conducted

Smith et. al., Characterization of the Embedded Micromechanical Device ApproachTo the Monolithic Integration of MEMS with CMOS, SPIE, Vol. 2879, 1996

Silicon Substrate

Embedded MEMSMicrostructure

Silicon Substrate

CMOS


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Permeable Polysilicon Window(a) PSG Deposition

Nitride deposition and patterning

Thin polysilicon deposition

(b) HF etching to remove PSG

Lebovitz et. al., Permeable Polysilicon Etch-Access Windows for MicroshellFabrication, Transducers95, pp. 224-227, 1995

Silicon Substrate

Silicon Substrate

Silicon Substrate

(c) LPCVD nitride deposition andsealing

PSG Polysilicon Nitride


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Wafer Bonding Processesl Anodic Bonding

Temperature @~450 oC, voltage @~1000 volts Silicon (metal) to glass

l Fusion Bonding Temperature @~1000 oC Silicon to silicon (glass, oxide)

l Eutectic Bonding Silicon to metal (silicon-to-gold @~363 oC)


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Anodic Bondingl Sodium-rich glass (e.g. Corning #7740 -

Pyrex)l Operation temperature is well below the

melting temperature of glass for 5 ~ 10minutes

l Surface roughness < 1 ml Native oxide on Si must be thinner than

0.2 ml Bonding temperature below 450 oC or the

thermal properties of materials begin todeviate seriously

Wallis and Pomerantz, Field Assisted Glass-Metal Sealing,J. of Applied Physics, Vol. 40, pp. 3946-3949, 1969


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Anodic Bonding Temperaturel Bonding temperature > 280 oC --> Si under tensionl Bonding temperature < 280 oC --> Si under

compression


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Anodic Bonding Mechanisml At elevated temperature, sodium migrates toward

the cathode and leaves a space charge region anda high electrical field between the glass and silicon

l Electrostatic force pull silicon and glass intointimate contact

l Covalent bondsare formed

Anode

SiliconGlass

Cathode_

+Vdc


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Anodic Bonding Modificationsl Ti mesh bias electrode is deposited over glass for

faster bonding 1l Si dioxide and aluminum are used as intermediate

layer to screen the underlying silicon from harm fromthe high electrical field 2

l Sputtered or evaporated borosilicate glass (4 to 7 umthick) are used as intermediate layers for bonding 3,4

l

Sputtered Corning #7570 glass has been reported toprovide bonding within 10 mins with 30 to 60 Volts 5

1Ito et al., A Rapid Selective Anodic Bonding Method,Transducers95, pp.277-280, 1995

2Sander., A Bipolar-Compatible Monolithic Capacitive Pressure Sensor, Tech. Report No. G558-10,Stanford Univ. 1980.

3Brooks and Donovan., Low Temperature Electrostatic Si-To-Si Seal Using Sputtered Borosilicate Glass,J. of Electrochem. Soc., Vol. 119, pp.545-546, 1972

4Krause et al., Silicon to Silicon Anodic Bonding Using Evaporated Glass, Transducers95, pp228-231, 1995,5Esashi et al., Low Temperature Silicon to Silicon Bonding with Intermediate Lowe Melting Point Glass,Sensors and Actuators, Vol. A23, pp.931-934, 1990,


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Silicon Fusion Bonding (SFB)l Chemical reaction between OH-groups (native or

grown oxide)l

In an oxidizing ambient at temperatures greater than800 oC, higher temperature (>1000 oC is necessary toget voidless bonds)

l Surface roughness less than 4 nml Wafers must undergo hydration (soaking the wafers in

a H 2O2-H2SO 4 mixture, diluted H 2SO 4, boiling nitric acidor oxygen plasma) to create hydrophilic top layerconsisting O-H bonds

l Bonding systems: Si + Oxidized Si wafer, tow OxidizedSi wafer, two bare Si wafers, Si + Si with a thin layer ( H 2O + Si-O-Si 1

1Shimbo et al., Silicon-to-Silicon Direct Bonding Method,J. of Appl. Phys., Vol. 60, pp.2987-2989, 1986


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Silicon Fusion Bonding Variationsl Transformation from Silanol bonds to Siloxane bondsl Silanol groups may get hydrogen bonding at room

temperaturel Bond strength after various annealing temperatures 1

< 300 oC, --> bond strength remains the same as spontaneousbond

300 oC - 800 oC --> voids can be formed (possibly due to watermolecules)

> 800 oC --> bond strength increases to about the fracturestrength of single crystal silicon of 10 to 20 MPa (at 1000 oC)

l Low temperature bonding processes have beenreported

< 150 oC for 10 to 400 hr 2 Energetic particle bombardment (argon at 1.5 keV) 3

1Schmidt., Silicon Wafer Bonding for Micromechanical Devices,Solid-State Sensor and Actuator Workshop, pp.127-130, 1994.

2Tong et al., Low Temperature Direct Wafer Bonding, J. of Microelectromechanical Systems, Vol. 3, pp. 29-35, 1994.3Suga et al., A Novel Approach to Assembly and Interconnection for MEMS , MEMS95, pp.413-418, 1995


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Eutectic Bondingl Au-Si eutectic bonding takes place at a temperature of

363 oCl Many other bonding systems


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Wafer-Wafer Transferl Wafer-to-wafer transfer by HEXSIL and Si-Au eutectic

bonding

Cohen et al.,Wafer-to-Wafer Transfer of Microstructures for Vacuum Packaging,Solid-State Sensor and Actuator Workshop, pp.32-35, 1996..


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Organic Polymer Bonding

l Advantages: Low bonding temperature No metal ions Elastic property of polymer can reduce bonding stress

l Disadvantages: Not a good material for hermetic sealing High vapor pressure Poor mechanical properties

l Examples: UV-curable encapsulant resins Thick ultraviolet photoresists such as polyimides, AZ-4000,

and SU-8


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Higher Level Packaging

l L0 (encapsulating a microstructure)l L1(chip carrier)l Protection of silicon die and electrical leads

Vapor-deposited organizes (e.g., parylene) Silicon gel coating over the die A plastic or ceramic cap for particle and handling protection (TO-8) A welded-on nickel cap with pressure port


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Chip Carrier Example


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Self-Assemblyl Assembly of micromechanical devices is a big

challengel Self-assembly provides an alternative way to

either manual or automated assemblyl Example: fluidic self-assembly

Yeh and Smith,,Fluidic Self-Assembly of Microstructures and Its ApplicationTo the Integration of GaAs on Si, MEMS94, pp.279-284, 1994


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Summaryl The importance of MEMS packaging in

MEMS commercialization is briefedl MEMS packaging issues are discussedl MEMS packaging approaches are

introduced Integrated processes Wafer-bonding processes


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Acknowledgementl Some market information are adopted from

Dr. Kirk Williams, UC Extension MEMS Class

Note, May 29 June 1, 2001


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Special Packaging Schemes

Liwei LinAssociate Professor, Department of Mechanical EngineeringCo-Director, Berkeley Sensor and Actuator CenterUniversity of California at Berkeley


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Presentation Outlinel Introductionl New Packaging Processes

Localized Eutectic, Fusion and Solder Bonding Localized CVD Bonding Localized Nanosecond Laser Bonding RTP (Rapid Thermal Processing) Bonding Localized Ultrasonic Bonding Localized Inductive Heating and Bonding

l Summary and Acknowledgementl Wrap-up & Discussions


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MEMS Packaging Issues


microstructures Temperature sensitive

microelectronics

l Example: Surface-MicromachinedAccelerometers byAnalog Devices, Inc.

ADXL50 by Analog Devices, Inc.


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Approach

l To adopt IC packagingprocesses as much as

possiblel To protect MEMSdevices and follow ICpackaging processes

l

Encapsulations (caps)are required


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MEMS Encapsulation Processesl Integrated MEMS Encapsulation Processes

Guckel (1984) reactive gas sealing Ikeda (1988) epitaxial deposition Lin (1993) LPCVD deposition Smith (1996) CMP + film deposition

l Wafer Bonding Processes Anodic bonding (1969) SOI, pressure sensors ...

Fusion bonding (??) pressure sensors Eutectic bonding (??) assembly, packaging ...


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(a) Standard surface-micromachining process

(b) Additional thick PSGdeposition to defineencapsulation regions

(c) Additional thin PSGdeposition to defineetch channels


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(d) Nitride shell deposition;etch hole definition

(e) Removal of all sacrificialPSG inside the shell;supercritical CO 2 drying;global LPCVD sealing


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Fabrication/Measurement ResultsSEM Microphoto Measured Spectrum, Q = 2200


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Fabrication Results Overhanging microresonator thin coating of silicon nitride

NSF CAREER A d Di i i f El i l & C i i S 5/98 4/2002


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MEMS Post-Packagingl MEMS Packaging Processes

Integrated Processes

Highly process dependent , not versatile Not suitable for post-processing

Wafer Bonding Processes Need high temperature which may damage

microelectronics or temperature sensitive MEMS materials

Require very smooth and flat surfacesl Localized Heating & Bonding Processes

Localized Eutectic, Fusion bonding and others

NSF CAREER Award, Division of Electrical & Communication Systems, 5/98-4/2002Rated No. 1 in the panel

DARPA BAA98 43 MTO/MEMS P 5/98 4/2001


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Massively Parallel Post-Packaging

DARPA BAA98-43, MTO/MEMS Program, 5/98 - 4/2001

Innovative Approach Industrial Participants

- Analog Devices Inc.- Motorola Inc.- Delco Electronics Corp.- Honeywell Inc.- Ford Motor Company

- SiTek Inc....

US patent, No. 6,232,150, May 15, 2001


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Rationale: Localized Heating High temperature is confined Temperature is controllable

Lin Cheng and Najafi Japanese Journal of Applied Physics Vol 11B pp 1412 1414 1998


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Localized Eutectic Bonding Conventional oven, Si-Aueutectic bonding - uniformity??

Localized eutectic bondingexcellent bonding strength

Lin, Cheng and Najafi, Japanese Journal of Applied Physics, Vol. 11B, pp. 1412-1414, 1998

Surface +

Cheng Lin and Najafi IEEE/ASME J of MEMS Vol 9 pp 3 8 2000


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Localized Fusion Bonding Silicon-to-glass fusion

bonding - heater disappeared After HF dipping

excellent bonding result

Cheng, Lin and Najafi, IEEE/ASME J. of MEMS, Vol. 9, pp. 3-8, 2000

Surface +

Cheng Lin and Najafi IEEE/ASME J of MEMS Vol 10 pp 392 399 2001


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Localized Solder Bonding

Surface +

Indium solder as intermediatelayer - Al Dew Point Sensor

Before Bonding

After Bonding

Cheng, Lin and Najafi, IEEE/ASME J. of MEMS, Vol. 10, pp. 392-399, 2001

Cheng Hsu Lin Najafi and Nguyen MEMS01 pp 18 21 2001


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Localized Vacuum Encapsulation

Cheng, Hsu, Lin, Najafi and Nguyen, MEMS 01, pp. 18-21, 2001

Surface +

Vacuum encapsulated combresonator under a glass cap

0

3000

6000

9000

12000

0 4 8 12 16 20 24

Weeks

Q factor

Long-term testing under thevacuum packaged cavity

0

3000

6000

9000

12000

0 7 14 21 28 35 42 49 56 63 70

Weeks

Q factor

Cheng Hsu Lin Najafi and Nguyen MEMS01 pp 18-21 2001


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Vacuum Level and Outgas

Cheng, Hsu, Lin, Najafi and Nguyen, MEMS 01, pp. 18-21, 2001

Surface +

Q factor vs. Pressure

0

2000

4000

6000

8000

10000

12000

0.0001 0.01 1 100 10000

Torr

Q factor

BeforeAnnealing

AfterAnnealing

BeforeAnnealingwith higher Q

Quality factor vs. pressure

-75

-65

-55

-45

97 101 105 109

Frequency [KHz]

Transmission[dB]

Q~25

Q~500

Ti/Au Coating

Ti/Au coating to reduce outgas

Cheng Hsu Lin Najafi and Nguyen MEMS01 pp 18-21 2001


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Wafer-Level Processing

Cheng, Hsu, Lin, Najafi and Nguyen, MEMS 01, pp. 18 21, 2001

Surface +

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 2000 4000 6000

Gas Resident Time (sec)

Ca

vity Pressure (torr)

Gas resident time Wafer-level packaging scheme

He Lin and Cheng Transducers99 pp 1312-1215 1999


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Temperature distributionon a microheater

Localized CVD Process

He, Lin and Cheng, Transducers 99, pp.1312 1215, 1999

Surface +

Experimental result

Surface-reaction limiteddeposition process

Lin, IEEE Trans. on Advanced Packaging, Vol. 23, pp. 608-616, 2000


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Localized CVD Bonding

Surface +

Lin, IEEE Trans. on Advanced Packaging, Vol. 23, pp. 608 616, 2000

Device Substrate (Si)

Packaging Cap (Si)

Oxide

PolysiliconMicroheater

(a)

PolysiliconInterconnection

(b)

Selective CVD Polysilicon

Device Substrate (Si)

Packaging Cap (Si)

Device Substrate Cap Substrate

Joachim and Lin, ASME MEMS Symposium, MEMS-Vol. 1, pp.37-42, 1999


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Localized CVD Trimming

Joachim and Lin, ASME MEMS Symposium, MEMS Vol. 1, pp.37 42, 1999

Surface +

Localized CVD for selective trimming 1.5 x 1 x 100 m 3 with 0.7 mA input current for 20 min non-uniform deposition --> surface reaction limited

Su and Lin, MEMS01


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Plastic Bonding and Liquid

Encapsulationl Plastics to Silicon, to Glass

and to Plastics bonding

,

Surface +

l Direct encapsulationof liquid

Kim and Lin, MEMS02, pp. 415-418, 2002


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Ultrasonic Bonding and Sealing

, , pp ,

u Lateral vibration setup for ultrasonic bonding

Horn

PiezoelectricActuator

Guide-Slider

DieHolder

Load

Fixture

Control Unit

Native AlOxide

Al

Al

Al

Al

BeforeBonding

AfterBonding

Si Chip

Glass Cover

Au/Al (0.6, 1 m)In/Al (5 m)



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Hermetic Sealing Results (In/Au)l Hermetic sealing with

indium/gold bonding

BondingRing

ColoredLiquid

Air

ColoredLiquid

Spread Indium

Air

, , pp ,

l Spreading caused byexcessive force



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Ultrasonic Bonding Parametersl Both In/Au and Al/Al bonding systems have

been successfully demonstrated

pp

Parameters In/Au Al/AlPower supply

output 20~25 Watts 30~50 Watts

Bonding time 0.8~1.8 sec 1.5~4.0 sec

Pressure 9.2~15.4 MPa 20.8~40.1 MPaVibration amplitude 0.8~1.5 m 0.8~1.5 mTotal bonding area

on one chip 1.59~2.12 mm2 1.59~2.12 mm 2

Cao and Lin, HH02, to appear, 2002


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Selective Induction Bondingl This method has great potential for wafer-level

selective packaging processesl The bonding time can be very fast and the heating

zone can be well confined by remote heating source

Sample

CoilSubstrate

Platform

Substrate

SolderRing

Glass tometalbonding

Glass to glassbondng

10m

50m

Luo and Lin, Transducers01


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Nanosecond Laser Welding

Bondingresults

Mask

Mask

Patterns

which

pre-define

Bondingareas

u Ultrafast bonding, Restricted heating zone,Parallel packaging

Surface +

Chiao and Lin, Sensors and Actuators, Vol. 91A, pp. 404-408, 2001


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Low thermal mass Ramp up- 100 oC/sec Cool down- 50 oC/sec( 1000-400 oC ) Low thermal budget

( D x t is small )

Wafer-level process

Lamp

Thermal Radiation

Device Wafer

Cap Wafer

RTP Wafer-Level Bonding



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Fabrication & Packaging Processes

InterconnectionLines

Sealing Ring width-100-250 m

Comb-driveResonator

Sealing area-450x450~1000x1000 m2

Bump



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RTP Bonding (Al to Glass or Nitride)u RTP (Rapid Thermal Processing) for deviceencapsulations (750 oC for 10 seconds)

Surface +



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Bonding Results - Bond Strength

l Forcefully break thebond Glass fracture strength 270 MPa*

* M. K. Keshavan et.al, J. of Mat. Sci, v15, p839-44, 1980

Chiao and Lin, Transducers01


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Accelerated Hermeticity Testing

l MIL-STD-883E method1014.10 gross and fine leaktests for 60 packages

l Pass Helium leak test withrate < 5x10 -8 atm-cc/secl Autoclave chamber 2.7atm

130 oC 100% RH steam for864 hrs

l 90% confidence 0.017year in harsh environmentwhich is in equivalent toabout 50 years in normalusage

l Lognormal Distribution --failure process

, t in hours

Surface +

Chiao and Lin, Transducers01


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Life Time Prediction

l Overestimate AFl

Package formed by Al-Nitride bonding does notaging as much as plasticdip and anodically bondedsilicon-glass package*W.D. Brown. Advanced electronic packaging.

IEEE Press, 1999.

Normal Usage(years)

W=150 mA=1000x1000 m 2

270W=200 m

A=1000x1000 m2

300W=100 mA=450x450 m 2

1700W=200 m

A=450x450 m 2

W=Bonding widthA=Area

50

, Ea=0.9, n=3*=3000

Acceleration Factor

1min in autoclave 3000minsunder normal usage

Chiao and Lin, Hilton Head02


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l Pre-bake the wafers at 300C invacuum for various periods

l Bonding at 750 oC for 10 seconds

RTP Vacuum Packaging



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Vacuum Packaging Results

l A comb-resonator is vacuumpackaged

l Quality Factor~ 1800 200l Pressure inside the package ~

200mTorr

0

500

1000

1500

2000

0 4 12

200

400

1800

Time of Pre-Baking in Vacuum ( hours)

Quality Factor

l Quality factor increases withthe pre-baking time



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Long-Term and Accelerated Tests Autoclave chamber 2.7atm,

130 oC/100% RH steam Q stays at 200 for 24 hours

0.2

0.4

0.6

0.8

1

24.56 24.58 24.6 24.62 24.64 24.66 24.68 24.7

Before autoclaveAfter autoclave for 24 hours

Frequency ( KHz )

Normalized A

mplitude

l Long-term testing up to 4 weeksl Q stays 1800 200l Frequency drift is within 0.13%

1000

1500

2000

2500

18.59

18.6

18.61

18.62

18.63

18.64

1 2 3 4

Q Factor

Resonant Frequency

Weeks

Quality Factor

R es onant F r equenc y ( K H z )


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Summary

l Special packaging schemes are discussedl Localized Thermal Bonding Processes

Localized Eutectic, Fusion and Solder Bonding

Localized CVD & Nanosecond laser Bonding Localized ultrasonic bonding & inductive heating

l Rapid Thermal Bonding Process RTP silicon nitride-to-aluminum bonding Accelerated hermeticity tests

l Two vacuum post-packaging methods aredemonstrated Localized solder bonding RTP bonding


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Acknowledgement

l Students & Post-docs Y.T. Cheng, J.B. Kim, M. Chiao, Y.C. Su &

A. Cao Cheng Luo, G.H. He

l Univ. of Michigan Electronics Lab &UC Berkeley Microfabrication Lab

l NSF CAREER AWARDl DARPA/MTO/MEMS Program


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Wrap-up & Discussions

l There is plenty of room at the bottom!!l Packaging is the key for commercial

productsl Discussions:

Packaging foundry?? Packaging design house?? Packaging IP?? More packaging possibilities??

[l-17] packaging schemes for mems

Documents