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3D Workshop 2011
H.B. Kor1,2, F. Infante3, P. Perdu2, C.L. Gan1 and D. Lewis4
1Nanyang Technological University (NTU), School of Materials Science & Engineering, Singapore
2CNES, Toulouse, France3Intraspec Technologies, France4Université Bordeaux 1, France
3D Current Path in Stacked Devices: Metrics and Challenges
Overview Introduction
Magnetic Current Imaging (MCI) The Simulation Approach
Theoretical Study Challenges Objective Experimental Details and the New Simulation Approach Results and Discussion
No interactions with neighbouring current lines Local interactions with neighbouring current lines Global interactions with neighbouring current lines
Conclusion Future Work
2
Introduction – 3D Technology & Challenges
3
3D technology: speed and performance Greater challenges in fault isolation and failure analysis
http://blogs.mentor.com/happyholden/blog/tag/hdi/
Advanced Fault Isolation Techniques
4
3D X-ray Computed Tomography (CT)
Technique[1]
Magnetic microscopy[1]
Time Domain Reflectometry (TDR)[1]
Scanning Acoustic Microscopy(SAM)[1]
[1] M. Pacheco et al., Advanced Fault Isolation and Failure Analysis Techniques for Future Package Technologies, Intel Technology Journal, 2005, vol. 9, pp. 337–352. [2] C.Schmidt, F. Altmann, C.Grosse, A. Linder, V. Gottschalk, Lock-in-Thermography for 3-dimensional localization of electrical defects inside complex packaged devices, 2008, ISTFA, pp. 102-107.
Lock-in Thermography
(LIT)[2]
Magnetic Microscopy Motivations
Magnetic fields are not screened by any non-ferromagnetic materials
Magnetic field analysis gives current path information
Advantages Non destructive, non invasive, contactless Can localize defects affecting current paths Proven for shorts
5
Magnetic Current Imaging (MCI): Physical Principles
A current line generates a magnetic field according to the Biot-Savart law:
A direct and indirect Fourier Transform applied to obtain a current density image
Limited resolution on complex current path: need of complementary approach based on simulation
30
4 rrldIBd
I B
6
B: net magnetic fieldI: currentµ0: permeability of free spacer: distance between current and sensor
7
The Simulation Approach[3]
Cor
rela
tion
Val
ue Iterative algorithm; current path built segment by segment Correlation is evaluated between the measurement of the magnetic
field in a x-y plane and simulation of the field on same plane Correlation has a maximum when simulated line coincides with the
real current
Cor
rela
tion
Val
ue
Simulated line Real Current
[3] F. Infante, P. Perdu and D. Lewis, “Magnetic Microscopy for 3D Devices: Defect localization with high resolution and long working distance on complex system in package”, Microelectronics Reliability, 2009, vol. 49, pp. 1169-1174.
Theoretical Study (1)
dYBB NN
20
2
8
22 )1()()()1,,(HDY
DYYXBN
(1)
(2)
Theoretical Study (2)
The least square error is found when the correlation value is maximum Position of a good fit can be biased by the presence of multiple sources
of magnetic field – Interactions with neighbours important! 9
Leas
t Squ
are
Err
or
Leas
t Squ
are
Err
or
Challenges
Simulation approach is being challenged by high density current distributions Evaluation of a current line from the
rest of the current lines is insufficient
Need to consider the effects from neighbours
10
Objective To demonstrate how a new simulation
approach can: overcome the limitations of the previous
segment by segment approach
help to determine the 3D current path flow in the case of a dense and complex stacked device with vertical connections by vias
11
Experimental Details
12
Device Under Test(Courtesy of CEA-Leti)
Test Structure
13
Experimental Details
Magnetic ac scan Magnetic ac scan Peak Profile
Overlay of optical image and current density
Current density
Where exactly are
the currents flowing??
14
Plane 1 Plane 2 - vias Plane 3
X-ray voltage: 160 kV
Current: 140 µA
Experimental Details
Thickness between top & bottom plane: 150 µm
Z = 0 µm Z = 0 µm
Z = -150 µmZ = 0 µm
Experimental Details and the New Simulation Approach
15
Hypothesized current path 1 (correct path)
MCI image Superimposed MCI and 2D x-ray
image
Hypothesized current path 2
Z = 0 µm
Z = -150 µm Z = -150 µm
Hypothesized current path 3
Results – No interactions with neighbours
16
Current Line of interest
Hypothesized Current Path 1 (Correct)
Hypothesized Current Path
2
Hypothesized Current Path
3Avg. Corr.
ValueAvg. Corr.
ValueAvg. Corr.
Value
1 0.258 0.284 0.2692 0.0592 0.0492 0.1493 0.0915 0.0805 0.101
4 0.0149 0.00314 0.06015 0.0673 0.0544 0.0531
6 0.00913 0.00263 0.00637
7 0.00735 0.0123 0.0628
Results are not conclusive In most cases, the highest correlation is
obtained for the wrong current path hypothesis
Z = 0 µm Z = 0 µm
Z = -150 µm
Z = 0 µm
1
2
Z = 0 µm
Z = -150 µm
Z = -150 µm
3
Results – Local interactions with neighbours
17
Current Line of interest
Hypothesized Current Path 1 (Correct)
Hypothesized Current Path
2
Hypothesized Current Path
3Avg. Corr.
ValueAvg. Corr.
ValueAvg. Corr.
Value
2 0.223 0.0316 0.222
3 0.0425 0.0751 0.0150
4 0.119 0.0417 0.1185 0.0766 0.0651 0.0560
6 0.0673 0.0194 0.0738
Results are still not conclusive
Z = -150 µm
Z = 0 µm
Z = 0 µm
1
Z = 0 µm2
Z = 0 µm
Z = -150 µm
Z = -150 µm
3
Results – Global interactions with neighbours
18
Hypothesized current path with the highest correlation value (i.e. current path 1) corresponds to the real current path in the chip
Current Line of interest
Hypothesized Current Path 1 (Correct)
Hypothesized Current Path
2
Hypothesized Current Path
3Avg. Corr.
ValueAvg. Corr.
ValueAvg. Corr.
Value
2 0.243 0.0606 0.228
3 0.234 0.173 0.214
4 0.248 0.101 0.228
5 0.236 0.154 0.203
6 0.244 0.103 0.243
Z = -150 µm
Z = 0 µm
Z = 0 µm
1
Z = 0 µm
2
Z = 0 µm
Z = -150 µm
Z = -150 µm
3
Conclusion Interactions of a current line with its global
neighbours have very important effects in the case of high density 3D integration
Use of the new simulation approach has enabled the determination of the exact current path flow in dense and complex 3D stacked devices with vertical connections, where the information from MCI alone is insufficient the previous simulation approach was biased by the
presence of a high number of current distributions
19
Future Work
Automation of the new simulation approach
Reduction in the time taken to generate the simulation results
Improvement on the accuracy
20
Acknowledgment
CEA-Leti Neocera The Merlion Programme
21
22
Thank you very much for your attention!
Any questions ?