Design BEoL and 3 D TSV structures –A joint of FEA for reliability of BEoL and 3‐D TSV...

March 17, 2011 • Santa Clara, California

Design for reliability of BEoL and 3‐D TSV structures – A joint effort of FEA and innovative experimental techniques

Jürgen Auersperg1, D. Vogel1, M.U. Lehr3, M. Grillberger3, J. Oswald3, S. Rzepka1, B. Michel1,2

1 Fraunhofer Institute for Electronic Nano Systems ENAS, Germany2 l h f f l b l d2Micro Materials Center at Fraunhofer Institute for Reliability and Microintegration IZM, Germany

4GLOBALFOUNDRIES Dresden Module One LLC & Co. KG, Dresden, Germany

Micro Materials Center ChemnitzHeads: Prof. B. Michel and

Dr. Sven Rzepka

Outline

Motivation

Multi‐level FE modeling of CPI

Multi‐failure evaluation for Near‐Chip‐Edge and Near‐Bump Cracks in BEoL

Role of Initial Stresses

TSV –damage and delamination investigation

Required experimentsRequired experiments

Summary and Outlook

Jürgen Auersperg D Vogel M U LehrJürgen Auersperg, D. Vogel, M.U. Lehr, M. Grillberger, J. Oswald, S. Rzepka, B. Michel Micro Materials Center Chemnitz

Heads: Prof. B. Michel andDr. Sven Rzepka

Task – Heterogeneous Integration ‐ Packaging

Bridging the gap between chip and application

Bump side

Transistor side

<10 µm

Jürgen Auersperg D Vogel M U Lehr

nm, µmNanostructures

cm, mApplications

Jürgen Auersperg, D. Vogel, M.U. Lehr, M. Grillberger, J. Oswald, S. Rzepka, B. Michel Micro Materials Center Chemnitz


Multiscale – why? Geometry

Packaged microprocessor(eight symmetric model

Packaged microprocessor(10 – 40 mm size) PI layerNi layerBEoL stack region

HMT solderUnderfill

Bump side

HMT solder

Soldermask

LJT solder

gap<10

BEoL‐stack(5 – 10 µm size)


Boardpad

LJT solder

Transistor side

µm

Solder interconnect with BEoL‐stack(50 – 80 µm size)

Feature sizes: some nm!



Multiscale – why? Geometry

Bridge 40 mm to sub‐nm forBridge 40 mm to sub nm for Chip Packaging Interaction investigations of

a BEoL structure

Structural details: sub ‐ nm



Multiscale – why? Structure

Nano lawn for interconnect formation

Can these materials longer be modeled as homogeneous

materials?materials?

Atomistic level modeling

Molecular dynamics


Low‐k dielectrics (nano‐porous) Polymer: 23 H2O for 98 °C/ 100 RH



Multiscale ‐Molecular Dynamics – Two Ways used Structure

The way I:

1. Modeling of the molecular structure

2. Homogenization in a unit cell

3. Use it directly inside a Macro‐model,a FE‐Model for instancea FE Model for instance

The way II:

Finite Element Region

1. Modeling of the molecular structure

2. Simulations towards extraction of key‐properties (YOUNG’s modulus CTEFinite Element Region

Crack Tip Molecular Dynamics Region

properties (YOUNG s modulus, CTE, diffusion coefficients)

3. Use these properties inside a Macro‐d l FE M d l f i


model, a FE‐Model for instance

Polymer: 23 H2O for 98 °C/ 100 RHJürgen Auersperg, D. Vogel, M.U. Lehr, M. Grillberger, J. Oswald, S. Rzepka, B. Michel Micro Materials Center Chemnitz


M i i

Moisture Diffusion in Epoxy by Molecular Dynamics StructureMotivation:

Understand diffusion phenomena as structure‐property correlation for reliability prediction

Method

Materials: Epoxy with sev. chem. composition Exp: measure diffusion D & saturation S

Varied parameters = Arrow:

increasing polarity and chain lenght

Exp: measure diffusion D & saturation S Sim: molecular dynamics

Result:

Polymer: 23 H2O for 98 °C/ 100 RH

2.0x10-6

2.5x10-6

3.0x10-6

2/s)1.50E-007

2.00E-007

2.50E-007

m^2

/s)

oeff.

oeff.

D and S are strong functions of (as tested) ‐ density, ‐ polarity, h l h

0 0

5.0x10-7

1.0x10-6

1.5x10-6

D (c

m^

0 00E 000

5.00E-008

1.00E-007

D (c

mDiff co

Diff co

‐ chain length, ‐ stoichiometry, ‐ temperature

Sim & Exp show correct tendencies


Molecular Dynamics 98°C/100RH0.0

Experiment:98°C/100RH0.00E+000

SimExp98 °C/ 100 rh

Sim & Exp show correct tendencies

Quantitative Results need correct 3D network representation of epoxy resins



E.D. Dermitzaki, J. Bauer, B. Wunderle, B. Michel

Multiscale – Finite Element Techniques ‐ Substructuring Continuum

Multi‐level Substructuring 256xSubstructuring 256x

3

24 1



Multiscale – Finite Element Techniques – Submodeling Continuum

256x

Multi‐level Submodeling 256x

2Submodeling

31 4



Multi‐failure Evaluationf


Dr. Sven Rzepka

2nd Failure‐Mode – Risk for Die‐Cracking, Cracking of Substrates, …

Stress field with stress singularity

r1Smooth bending w/o singularities in stresses/strains

Stress field with well known stress singularity 1stresses/strains singularity r1

Cl i l t th h th G li d t i t it F t h i

Well known angle from anisotropic etching, for instance


Classical strength hypothesesmax. surface stress evaluation Weibull‐plots

Generalized stress intensity factor (gSIF) A‐factor …

Fracture mechanics: K‐factor (SIF), J‐integral, energy release rate (ERR) …



3rd Failure‐Mode – Delamination at Materials Interfaces

20µm

rrKi iyyxx 2/)( 0 Hutchinson et al.

1992

xyyy forarandforar

exp2

2exp2 *

00


Mixed Mode Situation 2



Cohesive Zone Modeling – Drawbacks and Challenges CZM

DCB specimen with crack propagation under continuous displacement controlled opening ! CZM‐Models have to handle and

deliver damage parameters (damage progress per(damage progress per cycle/time)

CZM with damage options


Subjects of current research!



XFEM ‐Mesh Independent Crack Propagation XFEM

FEM shape functions

FEM unknowns

Discontinuousenrichment functions

XFEM unknowns

FEMdisplacement

XFEMHeaviside enrichmentdisplacement

all nodesHeaviside enrichmentsubset of nodes

Crack crossing an element Crack tip in an element



BEoL Stack of an IC – Cracking/Delamination ‐ Locations and Impacts

Near-chip-edge cracks under Chip Package Interaction (CPI)

Crack stop structure

Near-bump cracking during reflow(NBC)

Leadfree Copper Pillars



Chip Package Interaction (CPI)

Near-chip-edge cracks


Dr. Sven Rzepka

BEoL Stack of an IC – Near‐Bump‐Cracks – Region of Interest NBC

LID adhesive

Packaged FE‐model(eight symmetric model)

LID adhesive

TIM1

Die

Underfill

PI layerNi layerBEoL stack region

Board

Soldermask

HMT solderUnderfill

Soldermask

LJT solder

gap


Boardpad



3D BEoL Stack Part‐model – Submodeling with Substructures NBC

Substructure

Finite elelement characteristic size in BEoL‐stack

Substructure region

< nm

Replacement of the finest (1x) structures b s perelements (repeatedl sed) leads

Substructure region

by superelements (repeatedly used) leads to a dramatically reduced model size(by factor 3),


complete model(with and without element edges)

vias andmetal traces



3d Local Model of a BEoL Part – Crack Introduced ‐ SubModeling NBC

Global model

Submodel

Initial crack



3d Local Model of a BEoL Part – SubModel Placing and Orientation NBC

Submodel driving nodes



Multiscale –Substructure & Submodeling of a BEoL stack of an IC NBC

Mode II(In‐Plane Shear)

Mode III(Out‐of‐Plane Shear)



Multiscale –Substructure & Submodeling of a BEoL stack of an IC NBC

C k d i i f l h k fCrack driving force along the crack front

Results:

• Find most critical places with

• Material interface delamination


Material interface delaminationand/or

• Cohesive fracture of material



BEoL Stack of an IC – Die Edge Cracking ‐ Interface Fracture Mechanics CPI

max. norm. ERR vs Crack Length

1,20

1,40max. norm. ERR vs Crack Length

1,20

1,40

Chip corner0 60

0,80

1,00

orm

. G

0 60

0,80

1,00

orm

. G

C k t t t0,20

0,40

0,60n

margin 51 µm to crack-stop-structure


w/o crack stop structure0,20

0,40

0,60n



w/o crack stop structure


Margin

Crack stop structure0,00

0 20 40 60 80 100 120crack length [µm]

w/o crack-stop-structure0,00

0 20 40 60 80 100 120crack length [µm]

w/o crack-stop-structure



BEoL Stack of an IC – Die Edge Cracking ‐ Interface Fracture Mechanics CPI

• 10 bimaterial interface paths +

• 4 cohesive crack paths in ULK

Max. ERR in diff. Crack Paths, 40 µm Crack Length marg 100

2,9

3Max. ERR in diff. Crack Paths, 40 µm Crack Length marg 100

2,9

3

2,7

2,8

en. G

2,7

2,8

en. G Chip corner

2 4

2,5

2,6ge

2 4

2,5

2,6ge

C k t t t

Path


2,3

2,4

1 2 3 4 5 6 7 8 9 10path2,3

2,4

1 2 3 4 5 6 7 8 9 10pathMargin

Crack stop structure



NBC

Reflow Process Dependent f pNear‐Bump‐Cracks in BEoL

Leadfree


Dr. Sven Rzepka

3d Global‐Local Model Simulations – Stress States NBC

Peeling Stresses at 0 °C (under CPI) Peeling Stresses at RT (end of reflow)

Chip center Chip center

Chip centerChip center


Avoid worst case: white spots in SAM



Cooling Down from Soldering – Reflow Profiles NBC

Aggressive cooling l

Highlead Leadfreeslope

Some studies have shown Mohanty, R., Apell, M. C., Burke, fl lthat an aggressive cooling

slope can provide optimal diffusion of material and fine eutectic grain

R.: Reflow Process Control Monitoring, and Data Logging, URL: http://www.emsnow.com/cnt/files/White%20Papers/speedReflo


fine eutectic grain structures

es/White%20Papers/speedReflowProcessControl.pdf



FE‐Modeling of the Soldering Process – Reflow Profile Modification NBC

Temperature vs. Time

200

250

300Leadfree profileLeadfree profile 02Highlead profileHighled profile 02

Temperature vs. Time

200

250

300Leadfree profileLeadfree profile 02Highlead profileHighled profile 02

Highest G for Leadfree Soldering

Stress relaxation of the solder joints

50

100

150

200 Highled profile 02Highled profile 03

50

100

150

200 Highled profile 02Highled profile 03

Stress relaxation of the solder joints

0

50

0 400 800 1200 1600 20000

50

0 400 800 1200 1600 2000

C li dCooling down period discussed here



Crack and Damage Initiation/Propagation Investigation NBC

Problems:Material/Interface propertiesIntegration Stability/Controlability

Damage

Damage propagation investigation in order to find highest damage risk locationsg g

XFEM


XFEM in order to find crack starting locations and paths



Chip Package Interaction and Initial Stressesp g

From Manufacturing Processes


Dr. Sven Rzepka

Local Residual Stress Measurement ‐ Approaches ‐

Electron Back Scattered Diffraction(EBSD) based method deformation of Kikuchi diffraction pattern as measure of stressas measure of stress

determines stress tensor comp.

Residual StressesStresses

Raman Spectroscopy uses shift of Raman

Stress Release Technique (fibDAC)

uses shift of Raman bands due to stress

TERS effect with potential to obtain resolution beyond 100


Stress Release Technique (fibDAC) utilizing deformation field after trench

milling by FIB

resolution beyond 100 nm

D Vogel A GollhardtJürgen Auersperg, D. Vogel, M.U. Lehr, M. Grillberger, J. Oswald, S. Rzepka, B. Michel Micro Materials Center Chemnitz


D. Vogel, A. Gollhardt

Local stress measurement concept – stress relief by FIB milling (fibDAC)

Material removalby

FIB feature milling

Stress relief, i.e.deformation

nearby milling pattern

Quantifying d f i fi ld b

Solution of the mechanical stress relief Displacement deformation field by

Digital ImageCorrelation (DIC)

mechanical stress relief problem by

Finite Element Analysis(FEA)

Displacement field fitting


Stress values

D Vogel A GollhardtJürgen Auersperg, D. Vogel, M.U. Lehr, M. Grillberger, J. Oswald, S. Rzepka, B. Michel Micro Materials Center Chemnitz


D. Vogel, A. Gollhardt

Near‐Bump Cracks in BEoL – Taking Initial Stresses into Account

During whole processing w/o and with initial stresses

Crack Paths 6 and 14 with ULK vs. Gen3

1,00000

1,2max. ERR for all Steps at the Crack Front

With initial stresses

0,662850,8

1

G

0,22349 0 18113

0,44671 0,432920,4

0,6

gen.

,0,12081

0,181130,10560

0

0,2

Path 6 Path 6 Path 14 Path 14 Path 6 Path 6 Path 14 Path 14


Path 6 ULK

Path 6 Gen3

Path 14 ULK

Path 14 Gen3

Path 6 ULK is

Path 6 Gen3 is

Path 14 ULK is

Path 14 Gen3 is



3D I t ti TSV d BE L3D‐Integration – TSV and BEoL

Cracking/Delamination risks during BEoL‐manufacturing on top of TSVs?


Dr. Sven Rzepka

TSV and BEoL‐structure

Protrusion



TSV and BEoL‐structure ‐ Possible Failure Mode – Delamination

Protrusion



TSV and BEoL‐structure ‐ Possible Failure Mode – Delamination

Protrusion Assumtions:• Initial delamination between TSV and barrier• Initial stresses in TSV and introduced step by stepInitial stresses in TSV and introduced step by step during BEoL‐processing

• Partly delaminated BEoL• Cracks in BEoL



TSV and BEoL‐structure – Delamination Investigation

Changing stress traction direction

Strong dependence on stress free assumptions

Crack flanks partly in

stress free assumptions


contact – negative Jint



Sequential Build Up – Cohesive Zone Modeling – BEoL to MOL Delamination

Measure for interface

Cohesive zone elements introduced between MOL and BEoL – damaging during thermal loading delamination of initially undamaged material interface

Measure for interface loading (BEoL removed for better demonstration

Interface totally damaged atInterface totally damaged at distance ‘d’

d

TSV Define CZM‐properties:


Silicon Tn, Ts, Tt, GI, GII, GIII, En, Es, Et (all are estimated here!)



and BEoL‐structure ‐ Possible Failure Mode – Damaging of Copper

Define damage ‐


properties:pl, ‐p/q, rate, Gc, …)all are estimated here!)



M t i l P t D t i tiMaterial Property Determination

Size Dependent Material Behavior


Dr. Sven Rzepka

Material Behavior ‐Measure Required Properties

Dynamical‐Mechanical Analysis (DMA) Thermomechanical Analysis (TMA) Creep data eval. (Solder)

Temp.dep. creep data (Epoxy) Stress relaxation data (Epoxy) Poisson’s ratio eval.Temp.dep. creep data (Epoxy) Stress relaxation data (Epoxy) Poisson s ratio eval.



H. Walter, J. Auersperg

Nanoindentation in low‐K DielectricsBump side

BEoL stack

7 µm

Thin layers

Chip side

7 µm

For TSV:

800

1000

1200

1400

SimN] 800

1000

1200

1400

SimN]

F, uF, u • Initial yield stress• Hardening behavior

200

400

600

MeasurementE=145, sy=1600-10000Experiment

Sim

Forc

e [µ

200

400

600

MeasurementE=145, sy=1600-10000Experiment

Sim

Forc

e [µ

Intenter

Thin Layer

S b t t

Intenter

Thin Layer

S b t t

a de g be a o

-200

00 20 40 60 80

Distance [nm]

-200

00 20 40 60 80

Distance [nm]

SubstrateSubstrate

Experiment Simulation Agreement


Parameter – extraction only possible by coupled Sim & Exp



Raul Mrosko, Saskia Huber, O. Wittler

TSV Copper – YOUNGs Modulus by nano‐Indentation

46,405

P13 Messung 3

d e m o d e m o d e m o d e m o d e m od e m o d e m o d e m o d e m o d e m o

120

140

P13 Messung 3

46,400

)

d e m o d e m o d e m o d e m o d e m o




80

100

Er(G

Pa)

46,395

Y(m

m)





82 275 82 270 82 265 82 26040

60

46390

d e m o d e m o d e m o d e m o d e m od e m o d e m o d e m o d e m o d e m o

-82,275 -82,270 -82,265 -82,260

X(mm)

-82,275 -82,270 -82,265 -82,26046,390

X(mm)



Copper Material Behavior– Properties Necessary

Necessary to know:

• Young's‐modulus dep. On Temperature

• Initial yield stressInitial yield stress

• Hardening vs. plastic strains

• Regarding TSV: initial stress state

Xi Liu, Qiao Chen, Pradeep Dixit, Ritwik Chatterjee, Rao R. Tummala, and Suresh K. Sitaraman, Failure Mechanisms and Optimum Design for Electroplated Copper Through‐Silicon Vias(TSV), 2009 Electronic Components and Technology

fConference, pp. 624 ‐ 629



Size Effects and Damage in Thin Metallic Films during Nano‐Indentation

Meso‐mechanics Homogeneous

• Strain gradient plasticity

• Higher order stress theories

Dislocation movementDislocation movement restrictions inside boundaries

D. Gross, A. Trondl:Numerical Simulation of Size Effects and Damage in Thin Metallic Films during Nano‐


Indentation,Proc. ICF 12, Ottawa, CA, 2009, Paper on CD: fin00457.pdf



D d F t T h Ch t i tiDamage and Fracture Toughness Characterization

Size Dependent Material Behavior


Dr. Sven Rzepka

Interface Fracture Toughness Tests

P

Pull‐off test schematic of substrate, interface and pull stud

Modified CT‐specimen Peel test


Pull‐out test Brazilian disk specimen Superlayer adhesion test

A.A. Volinsky et al. / Acta Materialia 50 (2002) 441–466



Interface Fracture Toughness Tests ‐ Bending

Asymmetric Double Cantilever Beam Brazil‐Nut‐Sandwich

Single Leg BendingSymmetric Double Cantilever Beam

4‐point bending

Asymmetric DCB

Asymmetric End‐Notched FlexureEnd‐Notched Flexure

Mill H 2000

Double Cantilever BeamCenter Cracked Beam


Sundaraman, Sitaraman 1997Yeung, Lam, Yuen 2000

Miller, Ho 2000



Mode Separation/Evaluation – Critical ERR and Phase Angle

failure regionregion

Measured fracture toughness

Calculated crack loading



Mode Separation/Evaluation – Critical ERR and Phase Angle

2sin11 ICc GG

With (a further material/interface parameter) is a function of temperature and moisture concentration

G() i i i i

Gc

failure i G() initiation

G()no initiation

region


K. Liechti, Adhesion Measurements Relative to Electronic Packaging, Proc. 4th Annual Topical Conference On Reliability, October 30 - November 1, 2000

Hutchinson and Suo, "Mixed Mode Cracking in Layered Materials", Advances in Applied Mechanics, Vol. 29, pp. 63-191



Nano‐Indentation for Interface Fracture Toughness Evaluation

• Nanoindentation for “measuring“ Young’s modulus and hardness

• Nanoindentation for “measuring“ fracture toughness

• Nanoindentation for “measuring“ interfacial fracture toughness (adhesion) – Conical and wedge indentersBuckling

For instance:


For instance:E.E. Gdoutos, A. Volinsky, Interfacial Fracture Toughness of Thin Films, Tutorial AC‐Conf., June 6, 2005M. R. Begley, D. R. Mumm, A. G. Evan, J. W. Hutchinson, Analysis of a Wedge Impression Test for Measuring the Interface Toughness Between Films/Coatings and Ductile Substrates, Acta mater. 48 (2000) 3211‐3220



St St t D t i ti /V ifi tiStress State Determination/Verification

Fitting modeling assumption with experimental results


Dr. Sven Rzepka

TSV ‐ Stresses near the Surface – vs. Raman‐Spectroscopy

zz rz

rr


M. Hecker, GlobalFoundries, Dresden



Surface vs. Midd‐Stress rr

Surface - rr

Middle -


Middle - rr



Summary

M ltil l FE d lli f k i BE L St kt Multilevel FE‐modelling of cracks in BEoL‐Struktures

For Chip Package Interaction and

fl l df b i Reflow ‐ leadfree bumping

Goal: Reliability enhancement

Utilizing fracture mechanics concepts (cohesive and adhesive) and/or

Damage mechanics approaches



What we need

Intensive experimental work necessary for

Evaluation of residual stresses from manufacturing,

Evaluation of the material behavior (constitutive, size dependent)

Characterization of the damage behavior of materials

Characterization of strength/toughness properties (fracture mechanics characterization) of materials and materials interfaces

Verification of simulation results

Extensive simulation work necessary

Huge simulation models and computing resources


Theoretical work – delamination und fracture (CZM, XFEM), materials behavior (SGPM)



What we Need for Helpful Simulation Results

Residual stress characterization

Damage and fracture characterization

Material behavior and property characterization


Simulation results verification



Th k Y f Y Att ti !Thank You for Your Attention!


Dr. Sven Rzepka

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Design BEoL and 3 D TSV structures –A joint of FEA for reliability of BEoL and 3‐D TSV...

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