eufanet workshop – esref 2012 finding opens : ebc technique

EUFANET Workshop – ESREF 2012

Finding opens : EBC technique

Sylvain Dudit - STMicroelectronics Crolles

Antoine Reverdy – Sector Technologies

Introduction – Problem statement

• Finding opens at die level is a challenge which is gets even more complex with technology node progress

• Global fault isolation techniques can provide useful data, but rarely a direct pointing of open failures.

• Node becoming smaller and interconnects more complex, precise localization matters even more to be able to find the physical defect

• We will present the Electron Beam Altered Current (EBAC) techniques as an interesting and accurate mean of detecting/confirming opens inside back end of die.

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Outline

• Problem statement

• Analysis flow and EBC techniques vs technology node

• EBAC/RCI technique overview

• Case study 1 : back end test structures

• Case study 2 : real case on 32nm Product

• Conclusion/Perspectives

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Flow : >45nm technology node 4

Electrical fail

Global Fault Isolation techniques(LIT, EMMI, OBIRCh, SDL ,LVx, TFI, VC, etc)

Timing Analysis(if suitable)

Physical Analysis(mainly SEM X-section)

• Gates are in polySi,• Density and dimensions allow SEM analysis (X-section),• PA can be done from a GFI tool

Flow : <32nm technology node 5

Electrical fail

Global Fault Isolation techniques(LIT, EMMI, OBIRCh, SDL ,LVx, TFI, etc)

Timing Analysis (if suitable)

Physical Analysis (mainly TEM)

EBAC/RCI technique

• Gates are metal with lowK dielectric with complex interconnects,• Density and dimensions force TEM analysis• PA can NOT be done from a GFI localization• EBAC refines GFI localization• PA can be done from an EBAC result

EBAC Techniques overview 6

Ligne métallique

Via

Isolant

Ligne métalliqueinférieure

Défaut résistif

Charge

injectée

Faisceau d’électrons

amplificateur Image SEM

Pointe

EBAC

R2 R1

FlottantFlottant

Amplificateur EBC

R1R1R1R1

Faisceau e-

e-e-e-e-e-e-e-

EBAC

R2 R1

FlottantFlottant

R1R1R1R1

Amplificateur EBC

e-

Faisceau e-

e-

Faisceau e-

e-e- e- e- e- e-

RCI

EBC Result

M4

M3

M2

M1

Active

EBC @ M4 level

Short

M5

M5

Open du to M5 polishing

1st Case studySample #1• 45nm technology

• Specific test structure between for back-end validation (design perform in strong collaboration between test / EFA / design / progress team for quick and reliable analysis)

• Electrical diagnostics : open on M1 /Poly structure col235, row 25

• Traditional FA technique used for fail localization : Charge contrast

• For physical analysis : X-section

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1rst Case studySample #2

• Same test chip used on : 28nm

• Electrical diagnostics : open on M1 /M2 structure col178, row 5

• Same approach for EFA by voltage contrast for fail localization

• Results : not conclusive.

• Need to try EBAC

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1rst Case studySample #2

• EBAC technique allows a failure localization when the voltage contrast is not conclusive

• No evident problem found on SEM view

• TEM analysis mandatory for a conclusive analysis

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1rst Case studySample #3

• But EBAC results being dependant of defect nature, it may not detect the failure.

• So RCI ( 2 needles EBAC) is to be tried out

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• Same test chip used on : 28nm

• Electrical diagnostics : open on M1 /M2 structure col703, row 297

• New problematic : EBAC localization not conclusive

1rst Case studySample #3

• The RCI approach allows a failure localization when the standard EBC contrast is not conclusive

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1 2 3

Defect localized

1 2 3

1rst Case studySample #3

• Physical analysis :• X-section + SEM observation : no evident defect found

• TEM results : Missing Salicide that explain the resistive open

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2nd Case study

• Context : Yield loss on a complex SOC product

• Techno : 45nm

• Context :

• Yield loss of 12% with a center/edge dependancy

• Scan failures

• Wafer map pink cells are parts to analyze

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2nd Case study Context

• ATPG ( like Tetramax) provided suspects for this analysis.

• Most burried suspect nets are at M2 level

• Direct EBC test at M4 level to discriminate suspects

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Philippe Larré 2477

• At M3 level, an open M2 has been detected with EBC technique.

• The cross-section shows an etching/photo problem at M2 level.

The EBC signal should have been highlighted up to this point

Cross section

2nd Case study Results 15

Conclusion - Perspectives

• EBAC is an effective and useful technique for finding opens :• It shows the fail location within SEM accuracy

• It allows direct TEM analysis

• Backside EBAC is an emerging and promising technique

• But EBAC has its limitations :• EBAC needs often to remove the top metal layers and therefore can be considered

as destructive.

• EBAC needs an initial fail hypothesis

• EBAC analysis needs CAD data to be interpreted

• Choice between EBAC or RCI is defect dependent

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Acknowledgments

• We would like to thank for all the support provided :

• Solenn Lelievre – STMicroelectronics Crolles

• Philippe Larre – STMicroelectronics Crolles

• Heloise Tupin – STMicroelectronics Crolles

• Michel Vallet – STMicroelectronics Crolles

• Jean-Philippe Roux – Sector Technologies

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