Modeling Material Plastic and Viscous Flow Effects in TSV ...

Aditya Karmarkar1, Xiaopeng Xu1, Karim El Sayed1

Wei Guo2, Geert Van der Plas2, Stefaan Van Huylenbroeck2,

Mario Gonzalez2, Philippe Absil2, Eric Beyne2

1Synopsys, Inc., Mountain View, California, USA

2IMEC, Kapeldreef 75, Leuven, Belgium

June 1, 2016

Modeling Material Plastic and Viscous

Flow Effects in TSV-middle and Backside

TSV-last Processes

14th International Conference on Reliability and Stress-Related Phenomena in

Nanoelectronics – Experiment and Simulation

© 2016 Synopsys, Inc. 2

Agenda

Introduction

Material model characterization

TSV stress effects on performance and reliability

Summary


Introduction: TSV integration

ULK

ULK

TSV

V0 V0

M1

V1

M2

X-section of TSV advanced CMOS technology integration

• 3D IC with TSV: provides high integration density; allows heterogeneous integration, improves system performance

• Integration options

Cu

Si

W. Guo, et al

IMEC/Synopsys

ECTC 2015


TSV-middle Integration Sample Flow

• TSV-middle: via processed after FEOL and before BEOL

• High thermal budget is expected

FEOL process

TSV etching

TSV liner/Barrier

TSV platting

420oC 1h annealing

TSV CMP

BEOL process

......Backside process

Stacking

350oC SiCN Dep.

320oC ULK Dep.

400oC UV Cure

400oC APF Dep.

350oC SiOC/DARC Dep.400oC SiN Dep.

......

TSV-middle process BEOL process


TSV-last Integration Sample Flow

• TSV-last: via processed after FEOL and BEOL

• No high T budget is expected

Temporary carrier wafer

Thinned

Device waferBEOL

Stacking


Material Options

ULK

ULK

TSV

V0 V0

M1

V1

M2

Silicon: anisotropic elasticity

Liner:

visco-

elasticity

Copper:

elastic-

plasticity


TSV Integration Considerations

ULK

ULK

TSV

• How TSV integration process and material

options affect FEOL and BEOL

• Capabilities for analysis and optimization

V0 V0

M1

V1

M2

Source: GlobalFoundries, ECTC 2015

FEOL performance

BEOL performance

and reliability


Agenda

Introduction



Summary


Copper Elastic-Plasticity Behavior

• Experimental Biaxial stress response of Cu film under thermal cycling

C. Okoro, et al., "Impact of the electrodeposition chemistry

used for TSV filling on the microstructural and thermo-

mechanical response of Cu," Journal of Materials Science,

vol. 46, no. 11, pp. 3868 - 3882, June 2011.

Thermal Cycles


Nonlinear Plasticity with Isotropic and

Kinematic Hardening

• Isotropic hardening

–Exponential hardening

–New yield stress:

𝜎𝑦 = 𝜎𝑦0 + 𝑅 1 − 𝑒𝑥𝑝 −𝑏𝛼–Material parameters:

– Initial yield stress (𝜎𝑦0)

– R

– b

• Kinematic hardening

–Nonlinear hardening

–Back stress:

ሶ𝑞𝑖𝑗 = 𝐻𝑘𝑖𝑛𝑛𝑖𝑗 −23𝐻𝑘𝑁𝐿𝑞𝑖𝑗 ሶ𝛼

–Material parameters:

– Hkin (𝐻𝑘𝑖𝑛)

– HNLkin (𝐻𝑘𝑁𝐿)

ε

σ

σaσb

σcσd

oHiso


Elastic-Plasticity Model Calibration for Copper

• Incremental plasticity model with nonlinear hardening can match

measured data from thermal cycles

Thermal Cycle 1

Cycle 2 Cycle 3

Cu stress highly depends on the

thermal history of integration flow.

W. Guo, et al, IMEC/Synopsys, ECTC 2015


Dieletrics Visco-Elasticity Behavior

0

10

20

30

40

50

60

70

80

0 20 40 60 80 100 120 140

Szz (M

Pa)

Temperature (C)

strain = 0.4%

strain = 0.8%

strain = 1.2%

1.0E+06

1.0E+08

1.0E+10

1.0E+12

1.0E+14

200 400 600 800 1000

Vis

co

sit

y (P

ois

e)

Temperature (K)

• Stress relaxation at elevated temperatures

Liner stress highly depends on the

thermal history of integration flow.


Nonlinear Visco-Elasticity Model with

Stress Relaxation and Strain Creep

CreepRelaxation


Visco-Elasticity Model Calibration for Liner


1st and 2nd Order Piezo-Resistance Models

[001] Surface nMOS [001] Surface pMOS

Piezo coefficients depend on

crystal orientation, carrier type

and stress magnitude

D1

D2

D3

HoleElectron

Band structure calculation

Sum of FinFET

stress + TSV stress

is in the nonlinear

range. Linear

approximation works

for low stress


Agenda

Introduction



Summary


Test Case Descriptions

•Impact on FEOL performance–TSV middle versus TSV last

–Plastic flow and viscous flow

•Impact on BEOL performance

– TSV-middle versus TSV-last

– Plastic flow and viscous flow

•Impact on BEOL Stress in TSV-last–M1 at TSV center versus M1 at TSV edge



TSV Structures

M1 at the center of the TSV

M1 at the edge of the TSV

Liner structure near

active silicon

Cu

ULK

M1

ESL

Si

ULK

M1

Liner

Si

ULK

Liner

Cu

BEOL

ESL

• Liner is modeled with

visco-elasticity

• Copper is model with

elastic-plasticity

LayoutProcess

Simulation

TSV 5x50 um

15 nm


Global and Local Models

Center

Edge

TSV

TSV Liner

ESL

ESL

Dielectric

Dielectric

BEOL

BEOL

V0

M1

V0

M1

Local_1

BEOL

Si

TSV

Liner

Half

TS

V

Pit

ch

Y

X

Global

M1 Pitch

M1

Height

V0

Height

M1 Width

V0 Width

TSV 5x50 um

ESL 15 nm

Local_2


SRadial (Pa)

TSV Impact on FEOL: TSV induced in-plane stress

• TSV-last induces lower stress due to lower thermal budget

TSV-LastTSV-Middle

SHoop (Pa)

TSV

TSV TSV

TSV

W. Guo, et al

IMEC/Synopsys

ECTC 2015


Impact on FEOL: Stress induced mobility change

• Device mobility change calculated for (100)/<110>TSV-LastTSV-Middle

Mobility (%)N type

P type

N type

P type

TSVsYY

sZZ

TSV

TSV TSV

W. Guo, et al

IMEC/Synopsys

ECTC 2015


Impact on FEOL Stress induced mobility change

• Lower via-last stress affects less on mobility

• Impact on NFET is smaller compare to PFET

-20

-10

0

10

20

30

40

0 2 4 6 8 10

Mob

ilit

y C

ha

ng

e (%

)

Distance along z-axis (mm)

TSV Last NFETTSV Last PFETTSV Middle NFETTSV Middle PFET

-40

-30

-20

-10

0

10

20

0 2 4 6 8 10

Mob

ilit

y C

ha

ng

e (%

)

Distance along y-axis (mm)

TSV Last NFETTSV Last PFETTSV Middle NFETTSV Middle PFET

TSV TSV

W. Guo, et al

IMEC/Synopsys

ECTC 2015


Syy with Plastic or Plastic+Viscous FlowPlastic + viscous flow, TSV Middle

Plastic flow, TSV Middle

Plastic + viscous flow, TSV Last

Plastic flow, TSV Last

Y

Z


Szz with Plastic or Plastic+Viscous FlowPlastic + viscous flow, TSV Middle

Plastic flow, TSV Middle

Plastic + viscous flow, TSV Last

Plastic flow, TSV Last

Y

Z


TSV Pumping: TSV-middle vs TSV-lastM1 resistance change for TSV-middle process

• TSV pumping for

TSV-middle due to

high T BEOL

• 33% M1 resistance

increases due to

TSV plastic flow

• Additional 12% M1

resistance increase

due to viscous flow

• No TSV pumping for

TSV-last due to

lower T budget

W. Guo, et al IMEC/Synopsys, ECTC 2015









–Plastic and viscous flow versus no flow


BEOL Hydrostatic Stress in TSV-lastPlastic + viscous flow, Center

No flow, Center

Plastic + viscous flow, Edge

No flow, Edge

Y

X


Dielectric 1st Principal Stress in TSV-lastPlastic + viscous flow, Center

No flow, Center

Plastic + viscous flow, Edge

No flow, Edge

Y

X


Summary

• Impact on FEOL performance

–TSV-middle integration introduces larger residual stresses in

active silicon compared to the TSV-last flow integration.

–Plastic and viscous flow reduce silicon stress

• Impact on BEOL performance

–TSV-middle integration results in M1 metal resistance increase

due to copper pumping

–Plastic and viscous flow increase TSV pumping

• Impact on BEOL stress

–Residual stress profiles in BEOL structures are different for TSV

middle and TSV last flows

• Ongoing work

–TSV-last long term stability and reliability

Modeling Material Plastic and Viscous Flow Effects in TSV ...

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