InSitu Deformation of Copper Pillars

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In-Situ Deformation of Copper Pillars

• Vinay Sriram
• March 14th 2008

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Outline

• Motivation
• Experimental Approach
• Deformation Characteristics Single Crystal Cu,
  Nanotwinned Cu Pillars
• Summary

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Motivation
M8 M7 M6 M5 M4 M3 M2 M1
Dual Damascene Demonstrator F Galliard et al
Microelectronic Engg 83 (2006) 2309
Actual Via, Line Dimensions Diameter 100300nm
Length 200400nm Test Mechanical Strength
65nm Generation Cu Interconnects Dimensions
scaled 0.7x from 90nm
http//www.intel.com/technology/architecture-silic
on/65nm-technology/index.htm
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New Ways to Test
Pioneering work by M. Uchic et al demonstrate
that micro compression tests of pillar structures
fabricated by FIB show strong size effect which
is related to diameter of the pillars. This
technique has been extended to the electron
transparent range by A. Minor et al.
Uchic, Nix, Science 305 (2004) Shan, Minor, Nat
Mat, (2007)
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In situ Compression Tests
Static images Bright-field Dark-field
Diffraction Before and after Dynamics Indentat
ion Curve Post-mortem FIB lift-out
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Quantitative in situ Nanoindentation stage
Diamond indenter
Al Thin film

• Developed under a DOE SBIR Phase I and II
  proposal with Hysitron Inc. and NCEM
• Based on prior NCEM mechanical design, integrated
  Hysitron force displacement sensor, control
  electronics
• Load resolution 0.2 mN in TEM
• Displacement resolution 0.5 nm in TEM

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Experimental Approach

• Fabrication of Pillars FEI Strata 235 FIB
• Compression of Pillars
• JEOL 3010 TEM
• Hysitron PicoIndenter
• Displacement rate 1-20nm/s

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FIB Fabrication of Pillars
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Individual Pillars
Nominal Diameter 120170nm Length 300500nm
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Deformation of Single Crystal Cu Pillars
g
Defects
ZA 114
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Deformation of Single Crystal Cu Pillars
220
442
g
Defect Free
ZA 114
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Stress, Load Displacement Data
Yield Point sy 142MPa
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Extracted Images
Dislocations emanating from the tip of flat punch
cutting across
Dislocations running to the bottom of the pillar
Dislocation multiplication and interaction and
beginning of slip
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Deformation of Nanotwinned Cu Pillars
16nm
Twin
95nm
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Deformation of Nanotwinned Cu Pillars
ZA 110
23nm
115nm
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Stress, Load Displacement Data
Yield Point sy 490MPa
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Extracted Images
100 nm
Dislocation nucleation, movement of top grain
towards twin boundary s 490MPa
Bending of grain on top of twin boundary, Change
in Twin Boundary spacing s 611MPa
Dislocations cutting across, destroying the grain
on top of twin boundary s 794MPa
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Diffraction Pattern
Before Deformation ZA110
After Deformation ZA110
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Deformation Mechanism

• t vs ? twin spacing

• Cross Slip of a perfect FCC lattice dislocation
  into 2 Shockley partials. Illustration of double
  cross slip
• Process of cross slip of dislocation from bulk
  crystal 1 onto twin plane absorption
• Process of cross slip of dislocation from bulk
  crystal 1 onto slip plane in bulk crystal 2
  transmission
• Energetics of pathway of cross slip process

• Dislocation absorption by twin boundary results
  in hardening
• Absorption is followed by transmission resulting
  in change of twin spacing
• Schmid Factor 0.31 t 189MPa

Asaro. R, Kulkarni. Y Scripta Mat, 58(2008), p389
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Summary

• Provide In-Situ TEM evidence that twin boundary
  indeed strengthens pillars of 150nm diameter ,
  350nm long when compared to conventional single
  crystal copper
• Direct TEM evidence of Onset of Dislocation
  Nucleation (yielding) in Single Crystal Copper at
  a lower load and lower stress. Further hardening
  is due to dislocation interaction and
  multiplication
• Dislocation absorption across twin boundary
  results in pile up and hardening of twin boundary
• Dislocation transmission results in change of
  twin spacing
• Estimated resolved shear stress is close to that
  reported by literature

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Acknowledgements
View towards San Francisco Bay from Lawrence
Berkeley National Laboratory

• I would like to thank the staff at
• NCEM, LBL Jia Ye, Andrew Minor,
• Zhongoon Lee, Qian Zhan for all
• their help
• NCEM is supported by the Scientific User
  Facilities Division of the Basic Energy Sciences
  Division of the Office of Science, U.S.
  Department of Energy under Contract
  DE-AC02-05CH11231.

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Thank You