au-sn slid bonding empc2009 presentation

8/10/2019 Au-Sn SLID Bonding EMPC2009 Presentation

1/17

Au

Sn SLID Bonding: Fluxless Bonding with HighTemperature Stability, to Above 350 oC

Au

Sn SLID Bonding:Fluxless Bonding withHigh Temperature Stability,

to Above 350 o C

Knut E. Aasmundtveit 1, Kaiying W

ang 1, Nils Hoivik 1, Joachim M. Graff 2,and Anders Elfving 3

1 Vestfold University College, Norway2SINTEF Materials and Chemistry, Norway

3SensoNor Technologies, Norway


2/17


3/17

Au


Au Sn bonding Traditional use of Au Sn bonding: eutectic composition

80 wt% Au / 20 wt% SnEstablished processUsed for

Optoelectronic devicesHermetic sealing of cavities

3D integration Properties of eutectic Au Sn bonding

Melting/ solidification temperature: 278 oCHigher than common lead-free solders (~220 oC)and traditional Pb Sn solder (183 oC)

Oxidation resistant (high Au content)Fluxless bonding possible


4/17

Au


Progress of diffusion reaction

Sn

Cu

Liquid

SLID bonding Solid-Liquid InterDiffusion

Cu Sn SLID exampleProcessing at ~ 250-300 oC (Sn melts)Interdiffusion createsintermetalliccompounds (IMC)

Cu6Sn5 ()(intermediate phase)Cu3Sn ( )(final, stable phase)

Final bond:

Cu / Cu 3Sn / Cu layeredstructureSolid phase up to 700 oC(much higher than processtemperature!) After A. Munding, Univ. Of Ulm


5/17

Au


SLID bonding Solid-Liquid InterDiffusion

Resists high temperatures

High-T applicationsEngine controlOil/ gas extractionGeothermal energyEtc

High T during processingGetter activation for vacuumcavities: ~ 350 oC

Resists repeated processingtemperature

Bondline of IMC does notmelt at bonding temperatureSuccessive chip stacking (3D integration)Interconnects/ seal rings in separateprocesses possible

SensorBAR

TX

C

Source: SINTEF

100 or 150mm MEMS

200 mm

300mm CMOS

Interconnects Through vias


6/17

Au


Alternatives for Au Sn bonding Eutectic: 80 wt% Au

Melting point 278oC

Soldering technique (melting/solidification same T)Eutectic structure:

AuSn ( d)

Au5Sn ( z ) Sn-rich eutectic: 10 wt% Au

Melting point 217 oCSimilar to standardLead-free solder

Eutectic structure:Sn

AuSn 2 () or AuSn 4 ()

SLID: Different possibleIMCs, melting points:

Au 5Sn ( z/ z ),up to 519 oCAuSn ( d) (419 oC)AuSn 2 ( ) (308 oC)AuSn 4 ( ) (252 oC)


7/17

Au


Previously presented: AuSn 2 ( )

Electoplated Au / Sn layersBonded at 280 oCBond structure:

Au / AuSn 2 / Au AuSn 2 melts at 308 oC

Alternatives for Au Sn bonding

High-temperature IMCs:d or z/ z

Au / IMC / Au

K. Wang et al: ESTC 2008, Greenwich, UK


8/17

Au


Previously presented: AuSn 2 ( )

High-temperature IMCs:d or z / z

Au / IMC / AuAuSn ( d):

Melts at 419 oC

Au-Sn interdiffusion during aging d + Au converts to eutectic

structure over time? lower melting point?

Au 5Sn ( z / z) :Melting temperature up to 519 oC

Au-Sn interdiffusion is notexpected to give phasetransformations

Alternatives for Au Sn bonding

z/ z phase:

Preferred option forhigh-temperaturestable bonds!!


9/17

Au


Sample preparation Metallization

Wafers with Au seed layer:Si wafers w/ 300 nm oxide layerTiW (60 nm) / Au (100 nm): sputtered

Patterning (photoresist AZ4562)Bonding frames (rectangular, 200m width)

Electroplating Au: Cyanide solution, 5.4 mA/cm 2, 60-65 oCSn: Sulphate solution, 10 mA/cm 2, RT

Layer structure:Sample 1: Single layer Au

4.0 mSample 2: Multilayer Au / Sn / Au

4.0 m / 2.0 m / 0.1 mTop Au layer for oxidation protection

Experimental procedure

Au

Au

Sn Au

Si + SiO 2 + TiW

Si + SiO 2 + TiW

(0.1 m + 4.0 m)

(0.1 m + 4.0 m)

0.1 m

2.0 m

Overall Sn content:8 wt% Sn (13 at% Sn)

Surplus of Au relativeto Au 5Sn-phase


10/17

Au


Sample preparation Bonding

Electroplated samples are aged Ambient conditions 12 months Au Sn interdiffusion alloy

Two-step bondingPick-and-place at RT

Bonding in vacuum chamberBonding temperature 350 oCTypical getter activation temperatureBonding time varied


Au

Au

Sn Au

Si + SiO 2 + TiW

Si + SiO 2 + TiW

(0.1 m + 4.0 m)

(0.1 m + 4.0 m

0.1 m

2.0 m

Force

250 o C

RT

5 min

5

min.

5 min.

10 min.

20 min.

30 min.

RTRTRTRT

350 o C

5 min.


11/17

Au


Bond integrity

Die shear (room temperature)Delvotek 5000

Bond strength at elevated temperaturesExperiment 1: Hot plate

Bonded pairs in recesses on hot plate

Pushing uppermost chip (force ~ 2 N)Looking for delamination (bondline material melting)Test temperature range: RT-380 oCTested for samples of all bonding times

Experiment 2: Oven

Shear force ~ 5 NOven temperature 300 oC, 325 oC, 350 oC, 375 oC, 400 oCTested for samples bonded 20 min and 30 min


F

Bond interface


12/17

Au


Microscopy of cross-sections

Cross-sections made of samples of each bonding timeInvestigated with

Optical microscopyScanning Electron MicroscopyEnergy Dispersive X-ray Spectroscopy (EDS)



13/17

Au


Multilayered sample prior to bonding

Cross-section, Phase determination by EDSAu Sn interdiffusion in aged sample

The bonding performed is:Au layer to Au / AuSn ( d) dual layer

Results

AuSn ( d-phase)

Si

Au

7 m Au

Au

AuSn ( )

Si + SiO 2 + TiW

Si + SiO 2 + TiW

Force


14/17

Au


Bonded sample, cross-section

Single phase intermetallic, homogenous throughout the bondlineMetal structure Au / IMC / Au: Similar to Cu Sn SLIDAll samples are similar (independent of bonding time)Intermetallic identified to be Au 5 Sn

EDS: Renders ~10 at% SnPossible Au-rich phases at RT: Au (


15/17

Au


Bond integrity

Room temperature:> 60 MPa

Elevated temperature, hot plate:No delamination observed for any sampleMelting temperature > 380 oC

Elevated temperature, ovenOne sample survives 400 oC, no delaminationOne sample delaminates at 375 oC

Survives 350 oC

Results


16/17


17/17

Au


Acknowledgements Funding by RCN (Research Council of Norway),

BIA project No 174320, 3DHMNS 3D Heterogeneous Micro Nano Systems

Laboratory assistance:Tormod Vinsand, Vestfold University College

Finn M. Reinhardsen, Vestfold University College

au-sn slid bonding empc2009 presentation

Documents