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

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Experimental Details

12

Device Under Test(Courtesy of CEA-Leti)

Test Structure

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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??

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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

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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

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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

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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

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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

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Future Work

Automation of the new simulation approach

Reduction in the time taken to generate the simulation results

Improvement on the accuracy

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Acknowledgment

CEA-Leti Neocera The Merlion Programme

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Thank you very much for your attention!

Any questions ?