Defect Localization Using Modulated-Thermal Laser Stimulation and Phase-Shift Imaging Method A. Reverdya, P. Perduc, M. de la Bardonniea, H. Murrayb, P. Poiriera aNXP

Semiconductors, bLaMIPS, cCNES 1

Purpose • Defect localization : last step before destructive analysis (Physical characterization) – Additional informations on the defect localization could improve the localization efficiency

• Experimental studies show that TLS spots can be difficult to interpret – Could M-TLS be a solution to improve TLS signature interpretation? – Case study: Could M-TLS be a solution to distinguish artifacts from real signatures?

2

Outline • M-TLS acquisitions and phase-shift imaging • A solution to access additional information: Application on a 65nm non defective test structure • A solution for a better interpretation of TLS signature: Application on a 45nm defective structure • Conclusions

3

Modulated-TLS principle • Requirement: modulated laser source Study of the M-TLS signal time dependence ΔR (t ) = Ù Thermal Time Constant (TTC)

Magnitude (A. U.)

•

ρ 0 .L S

.α TCR .ΔT (t )

1

TLS signal

0

-1 0

10

Laser stimulation 20 30 40 Time (µs)

50

4

Practical access to the Time dependency • Requirements: – Compatible with TLS configuration (laser scan) – Access to magnitude and phase-shift (Ù time dependency) information

Transposition in the Frequency domain τstruct

0.3

Laser modulation

TLS signal

0 0

40 60 80 Time (µs)

0

10

30

50

70

90

30

50

70

90

Frequency (kHz)

150

τenv 20

Magnitude (A. U.)

1

Frequency domain

100

Phase (deg.)

Magnitude (A. U.)

Time domain

0

-150

10

Frequency(kHz)

5

M-TLS acquisition flow Scanner

Laser modulation

Treatment flow & Image reconstruction (R, φ) External acquisition

V

ΔI(t)

X, Y: In-phase & out-ofphase components

Magnitude (A. U.)

0.8

Phase-shift (deg.) -35

0.6

-40

0.4

-45

0.2

-50

0

-55

Acquisition of both magnitude and phase-shift information during a single scan 6

Outline • M-TLS acquisitions and phase-shift imaging • A solution to access additional information: Application on a 65nm non defective test structure • A solution for a better interpretation of TLS signature: Application on a 45nm defective structure • Conclusions

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Application: structure description • Study of a matrix of embedded

copper lines, 65 nm technology: – Metal layers: • M5 => M1 – Widths: • 1100nm • 740 nm • 480 nm • Min width (110 or 90 nm)

Studied line

Objective: Objective apply phase-shift detection analysis to discriminate each test structure 8

-34 -40 -46 • •

1st harmonic phase-shift (deg.)

Layer n°2

Layer n°3

Layer n°4

Layer n°5

µm

Metal layer influence (LDE)

µm

Good discrimination level between 2 consecutive metal layers Deeper the line, quicker the TLS response Resistance of the thermal path through the silicon substrate TTC Phase-shift 9

µm

3rd harmonic phaseshift (deg.)

1100 nm

740 nm

480 nm

110 nm*

µm

Line width influence (LDE)

-90 -100 -110 •

Line width information available: Wider the line, slower the TLS response

•

Line width

heat capacity

TTC

phase-shift 10

Outline • M-TLS acquisitions and phase-shift imaging • A solution to access additional information: Application on a 65nm non defective test structure • A solution for a better interpretation of TLS signature: Application on a 45nm defective structure • Conclusions

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Electromigration case study • Structure description – EM test structure, CMOS 45nm, V2M3 copper line – Specific design for copper 70 µm migration detection: • Extrusion lines • Measurement lines 10 µm

– Line width: 70nm – Line pitch: 70nm – EM test: • 10mA/µm² at 300°C • Stop criteria 1% of resistance increase

Studied line

Extrusion lines

Measuremen t Lines 12

Standard TLS approach • Classical OBIRCH analysis – OBIRCH spot located at center – Same result on several dies – No defect found

• Conclusion:

Reflected image

OBIRCH image, 150mV, 50x obj.

– This specific signature results from surrounding changes TLS ARTEFACT

SEM image along the line (X-section) 13

M-TLS study (artifact area) • Magnitude image

1

µm

Same artifact is present (as expected) Shape and value variation

Mag. A.U.

M-TLS, magnitude image 2

Phase (deg.)

µm M-TLS, phase-shift image

• Phase-shift image µm

Shape variation BUT same value along the line

µm

• Convincing quantitative values Regular value (1)

Spot value (2)

Mag.

0.18

0.39

Phase

-35.8°

-35.9°

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Phase-shift analysis interest • The artefact (magnitude image) is not visible on the phase-shift image M-TLS phase-shift analysis appears as a relevant and unique method to identify this kind of artifact resulting from surrounding interaction

• What is the phase shift signature on a real defective area? 15

M-TLS study (defective area) Magnitude • Resistance increase Ù voiding formation • Via areas are preferential elocations for voiding

Anode signature

Mag. A.U.

• Comparison of M-TLS magnitude acquisitions Center signature

The two M-TLS signatures are similar Do they come from the same interaction? 16

M-TLS study (defective area) Phase-shift Mag. A.U.

µm M-TLS, phase-shift image

Phase (deg.)

• Small variation but visible in image mode with an appropriate treatment

1

2

µm

• Specific phase-shift signature in the via location (shape & value)

µm

M-TLS, magnitude image

µm

• More significant mean values extraction Regular value (2) Spot value (1) Mag.

0.12

0.22

Phase

-35.7°

-33.8°

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Physical Characterization

SEM image of the anode side 18

Conclusions • Phase-shift detection associated with M-TLS acquisition allows to: – Access additional information on the excited structure, like depth and structure dimensions – Improve the TLS signature interpretation Design + Additional information => Indirect improvement of the localization accuracy More information on the defect Ù More confidence on the defect localization step Better interpretation of complex TLS signature (ARTEFACT) 19

Physical interpretation • 2 possible explanations: – Multiple reflection on copper surroundings – Heat conduction in copper surroundings then heat transfer to the studied line

• 2 consequences: – Increase of energy transferred to the copper line – Indirect heating => Spatial expansion

• 1 result: – Deeper and larger OBIRCH spot signature in the “measurement lines” implementation area

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