Institute of Applied Microelectronics and Computer Engineering

College of Computer Science and Electrical Engineering, University of Rostock Slide 1

Spezielle Anwendungen des VLSI – Entwurfs

Applied VLSI design

Phase 5

Reliability - Electromigration

Robert Mars

Institute of Applied Microelectronics and Computer Engineering

College of Computer Science and Electrical Engineering, University of Rostock

Metal wire

• Thickness fixed by process parameters

• Width can be adapted by designer

Slide 2

width

height

length

Institute of Applied Microelectronics and Computer Engineering

College of Computer Science and Electrical Engineering, University of Rostock

Metal reliabilityBlacks´s Equation: lifetime of an interconnect scales with and

Source: ITRS (International Technology Roadmap for Semiconductors) 2011

Slide 3

2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025 20260

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

Year

Cu

rre

nt

de

ns

ity

(M

A/c

m²)

Institute of Applied Microelectronics and Computer Engineering

College of Computer Science and Electrical Engineering, University of Rostock

Metal reliability

Slide 4

Growth of voids

Increase in current density

Increase in temperature

Increase in Joule heating

Institute of Applied Microelectronics and Computer Engineering

College of Computer Science and Electrical Engineering, University of Rostock

Electromigration

• Metal ions move towards the anode• Force on ions due to electron scattering in direction of electron flow• Electric field in metal causes electrostatic force on ions• Damage caused by divergences in atomic flux

Slide 5

Institute of Applied Microelectronics and Computer Engineering

College of Computer Science and Electrical Engineering, University of Rostock

Enhancing reliability• Wire Widening

increasing cross-section area• Passivation Layer

prevent diffusion, better dissipation of joule heat• Gold Metallizations

very high activation energy• Alloying of Metallization

addition of Ti-Si or Cu to Al• Deposition Techniques

i.e. MTTF smaller for Sputtering than electron-beam deposition• Wire length

if wire is shorter than Blech length mechanical stress compensates material flow

Slide 6

Institute of Applied Microelectronics and Computer Engineering

College of Computer Science and Electrical Engineering, University of Rostock

Thank you for your attention

Slide 7

Institute of Applied Microelectronics and Computer Engineering

College of Computer Science and Electrical Engineering, University of Rostock

Quellen

• http://www.synopsys.com/Tools/Verification/CapsuleModule/CustomSim-RA-wp.pdf

• http://www.doitpoms.ac.uk/tlplib/electromigration/index.php• http://www.ece.mtu.edu/faculty/goel/EE-4271/Web-Interconnects.pdf

Slide 8

Institute of Applied Microelectronics and Computer Engineering

College of Computer Science and Electrical Engineering, University of Rostock

Stresses

Slide 9

Institute of Applied Microelectronics and Computer Engineering

College of Computer Science and Electrical Engineering, University of Rostock

Jmax Calculation

Quelle: http://www.itrs.net/Links/2011ITRS/2011Chapters/2011Interconnect.pdf

Slide 10

Institute of Applied Microelectronics and Computer Engineering

College of Computer Science and Electrical Engineering, University of Rostock

Blech length

– activation volume (m³)

– hydrostatic component of mechanical stress (kg m-1 s-2)

– electromigration force, which causes atomic migration

- effective valence (represents the sign and the magnitude of the momentum exchange)

– resistivity (

Slide 11