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The principle of Lock- in Thermography

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at Opened and Fully Packaged Single- and Multi-chip Devices

Christian Schmidt, Frank Altmann, Christian Große Fraunhofer Institute for Mechanics of Materials

Otwin Breitenstein

Max Planck Institute of Microstructure Physics

(2)

Optical Localization Techniques Workshop 26.+27.01.09 Toulouse

Overview

ƒ

The principle of Lock- in Thermography

ƒ

Defect localisation at open devices

ƒ

High resolution imaging

ƒ

Defect localisation at fully packaged devices

ƒ

Conclusion / Discussion

Optical Localization Techniques Workshop 26.+27.01.09 Toulouse

100 µm

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Detector wavelengths ranges 1-2 µm (short wave)

3 -5 μm (mid wave), 8-10 μm (long wave),

Optimal wavelength range for IR imaging near room temperture:

Mid Wave

Detector types for MW:

focal plane arrays made from:

- cadmium mercury telluride (CMT) - platinum silicide (PtSi)

- Indium antimonide (InSb)

Spectral distribution of a black body

Infrared imaging

Mid wave

Spectral sensitivity

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Optical Localization Techniques Workshop 26.+27.01.09 Toulouse

The principle of Lock-in Thermography (LIT)

What is the main difference between steady-state and Lock-in Thermography?

(5)
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Optical Localization Techniques Workshop 26.+27.01.09 Toulouse

both resulting signals are influenced by emissivity Æ base for calculating Amplitude and Phase

( ) ( ) S 0 2 S 90 2

A = ° + °

⎟ ⎟

⎜ ⎜

= ⎛ −

Φ

° °

0 90

S arctan S

Amplitude:

Phase:

Advantages phase:

no emissivity contrast

“dynamic compression” in the phase image allows detection of weak hot spots even in the closer area to strong hot spots

(7)

contains emissivity topography

single IR image, emission dominated

in-phase / 0°

best spatial resol., contains emission

out-of-phase / -90°

low spatial resol., emission dominated

amplitude image

contains emission

phase image

emission-corrected dynamic compression

0°/-90° image

better spatial res., emission-corrected

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Optical Localization Techniques Workshop 26.+27.01.09 Toulouse

Important factor of influence: the lock-in frequency fLock-In

• taking into account calculating the thermal diffussion length:

Æ Spatial resolution increases the higher the lock-in frequency is

In

f

Lock

Λ 1

~

f=1Hz f=10Hz f=30Hz

(9)

„Thermosensorik“ InSb 640XL

InSb – detector (spectral range: 1.5µm – 5 µm)

640x512 pixel, 15µm pixel pitch Æ high spatial resolution

sample excitation voltage: 0 – 50V

framerate: 100Hz (fullframe) up to 380Hz (subframes)

LiT- system used for measurements:

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Optical Localization Techniques Workshop 26.+27.01.09 Toulouse

Overview

ƒ

The principle of Lock- in Thermography

ƒ

Defect localisation at open devices

ƒ

High resolution imaging

ƒ

Defect localisation at fully packaged devices

ƒ

Conclusion / Discussion

Optical Localization Techniques Workshop 26.+27.01.09 Toulouse

100 µm

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Standard: defect localisation at open devices

Localisation of thermal active defects:

line shorts

oxide breakdowns

transistor / diode defects

latch-ups, ESD defects

IC is opened for optical access via removing the mould compound using e.g. chemical etching

Challenge:

root causes of defects can be influenced Æ e.g. metal splinter can be removed by chemical etching

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Optical Localization Techniques Workshop 26.+27.01.09 Toulouse

temperature-resolution: <100 µK

power dissipation detection limit : several µW

sensitivity about 3 orders better than for steady state mode!

lateral resolution: about 5 μm Example I: failed device with short path

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Overview

ƒ

The principle of Lock- in Thermography

ƒ

Defect localisation at open devices

ƒ

High resolution imaging

ƒ

Defect localisation at fully packaged devices

ƒ

Conclusion / Discussion

100 µm

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Optical Localization Techniques Workshop 26.+27.01.09 Toulouse

Aim: Improving the optical resolution for a more accurate localisation of defects

Problem: wavelength used: 5µm, diffraction limits the resolution

Solution: Increasing n by using different materials above object

High resolution IR imaging

NA 5 . x 0 λ

= Δ

Object θ

NA = n*sin

θ

NA…Numeric Aperture n…index of refraction

4.02 Germanium

3.43 Silicon (IR)

2.417 Diamond

1.544 Quartz

Index of refraction n Material

θ

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SIL retracted

SIL in working position

Left: Silicon - SIL in a tweezers: Dimension is around 3mm

Right: SIL in application detecting a heat spot with high spatial resolution

100 µm 100 µm

Without SIL SIL

Results using hemispheric SIL made of Silicon

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Optical Localization Techniques Workshop 26.+27.01.09 Toulouse

Example II: Lock-in thermography for defect localisation with following cross-section

Application of SIL imaging for better spatial resolution Æ smaller cross-section area

(17)

Example II: Lock-in Thermography for defect localisation with following cross-section

FIB cross-section

Barrier residues

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Optical Localization Techniques Workshop 26.+27.01.09 Toulouse

Overview

ƒ

The principle of Lock- in Thermography

ƒ

Defect localisation at open devices

ƒ

High resolution imaging

ƒ

Defect localisation at fully packaged devices

ƒ

Conclusion / Discussion

Optical Localization Techniques Workshop 26.+27.01.09 Toulouse

100 µm

(19)

3 mm

1.5 mm Hot spot

Au bond wires Example III: Short localization at a fully packaged single chip device

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Optical Localization Techniques Workshop 26.+27.01.09 Toulouse

Example IV: Defect localization at a stacked die device

first LIT- measurement was done at fully package stacked die

Result:

hot spot was obtained in the chip area Challenge:

poor spatial resolution, unknown defect depth Next step:

device opening, removal of Mold compound above the upper chip by chemical etching

Æ additional LIT measurement

Hot Spot

Thermogramm of the fully packaged device (Amplitude-picture overlaid with topography)

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Hot Spot

second LIT-measurement

Result:

hot spot was obtained in the chip area again, spatial resolution was significantly increased Challenge: silicon is IR-transparent

Ædefect depth is still unknown Next step:

Æ disconnection of the upper chip layer via removing the bondwires

Æ Third electrical / LIT-measurement

Thermogramm after opening the device (Amplitude-picture overlaid with topography)

Example IV: Defect localization at a stacked die device

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Optical Localization Techniques Workshop 26.+27.01.09 Toulouse

Hot Spot

third LIT – measurement

Result:

similar to second LIT, Short defect at the lower chip due to the fact that upper chip layer is inactive

Challenge:

procedure is time-consuming

Æ defect localization using the phase information of the LIT-measurement

Æ only one measurement necessary to detect

defect Thermogramm after disconnecting the upper chip layer (Amplitude picture overlaid with topography)

Example IV: Defect localization at a stacked die device

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Aim:

non-destructive defect localization at fully packaged complex devices

Solution: “Heat flow takes time”

Æ phase information give the opportunity determining the defect depth

Challenge:

Æheat occuring from the defect has to pass the mould compound before it can be observed by IR-detector Æ thermal spreading reduces spatial resolution

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Optical Localization Techniques Workshop 26.+27.01.09 Toulouse

former experiments at stacked die devices investigated the relationship between phase shift and defect depth (ESTC 2008, ISTFA 2008)

phase difference is base calculating a depth difference: 34° Æ 237µm

3D defect localisation using the phase information (Pidea Full Control)

phase difference

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Overview

ƒ

The principle of Lock- in Thermography

ƒ

Defect localisation at open devices

ƒ

High resolution imaging

ƒ

Defect localisation at fully packaged devices

ƒ

Conclusion / Discussion

100 µm

(26)

Optical Localization Techniques Workshop 26.+27.01.09 Toulouse

Conclusion:

Lock-in Thermography:

is a powerful method for failure localisation

Easy sample preparation and works from the front or back side of the chip

generally works at any temperatures (range is depending to the detector material)

is more sensitive in comparison to steady state methods (<100µK, µW range)

Satisfying spatial resolution for failure localisation on microelectrical devices:

5 μm (standard optics), 1.2µm (SIL)

is also usable for non-destructive failure localization in packaged devices

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Acknowledgment:

A. Lindner, Micronas GmbH, Freiburg, Germany

V. Gottschalk, ELMOS Semiconductors AG, Dortmund, Germany

J. Schulz, MELEXIS GmbH Erfurt

Stephan Martens, Infineon Regensburg

This work was supported by:

European funding project: PIDEA “FULL CONTROL”

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Thank you for your attention!

Christian Schmidt, Frank Altmann, Christian Große Fraunhofer Institute for Mechanics of Materials

Otwin Breitenstein

Max Planck Institute of Microstructure Physics

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