EUFANET Workshop – ESREF 2012 Finding opens : EBC technique
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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.
2
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
3
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
7
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
8
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
13
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
16
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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