A COMPARISON OF PREPARATION TECHNIQUES FOR CU FILLED TSV CHARACTERIZATION Frank Altmann Fraunhofer Institute for Mechanics of Materials, Halle Center for Applied Microstructure Diagnostics (CAM) 15th EUFANET Workshop 1st October @ ESREF 2014

Fraunhofer CAM is a competence center for microstructure diagnostics within Fraunhofer IWM, Halle.

Purpose 

TSV high aspect ratio (several µm diameter, >100µm depth)

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Cross sectioning required for

 Metrology (dimensions, shape, barrier/isolation uniformity)

 Grain structure analysis (EBSD)  Defect inspection (voids, sidewall delaminations, cracks)

 Failure analysis (Cu pumping, shorts in isolation, cracks)

Fraunhofer CAM is a competence center for microstructure diagnostics within Fraunhofer IWM, Halle.

Site specific cleaving LatticeGear LatticeAx 300

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Crack separates Cu plug with barrier from Si oxide isolation

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Inner structure / voids can not be accessed

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Processing time: few minutes Pro’s:

 Fast access to TSV 

Con’s:

 Additional preparation required

 Only for wafer/die samples Fraunhofer CAM is a competence center for microstructure diagnostics within Fraunhofer IWM, Halle.

Metallographic cross sectioning Struers ATM Saphir

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Embedding + Grinding and polishing with SiC and diamond suspension

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Stepwise polishing to TSV Processing time: about >8h Pro’s:

 access to multiple TSV in short time  High surface quality for EBSD 

Con’s:

 Time consuming, high effort for target preparation 230nA

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Rocking beam polishing (rbp) Processing for 100µmx100µm: about 1h Pro’s:

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Short preparation time for single TSVs High surface quality for SEM/ EBSD No pre-preparation required

Con’s:

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Curtaining, re-depositon during rbp

Fraunhofer CAM is a competence center for microstructure diagnostics within Fraunhofer IWM, Halle.

Plasma FIB cross sectioning GHZ SAM

PFIB cut at defect site

Pros for failure analysis:

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Precise PFIB cutting at single defective TSVs

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Easy navigation by FIB imaging

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option for further TEM prep

Imaging of small voids, cracks, delaminations (no smearing)

Fraunhofer CAM is a competence center for microstructure diagnostics within Fraunhofer IWM, Halle.

Plasma-FIB TEM preparation 

Pt was deposited with 15nA Xe (80µmx2µmx1µm)

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Rough milling @1.3µA (32min)

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Final polish at 230 pA (30min) at 3deg sample tilt

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Overall sample prep time: 2.5h

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Lamella thickness suitable for TEM inspection: 100nm(top) - 200 nm (bottom)

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Further improvements by optimized sample tilt and curtaining suppression required

Milling steps: 180nA (20min), 15nA (16min), 1.8nA (30min)

Cu thickness map was calculated from BSE contrast by self-made software tool

Fraunhofer CAM is a competence center for microstructure diagnostics within Fraunhofer IWM, Halle.

Laser-based cross sectioning    

precise micromachining of metals, semiconductors, ceramics and compounds using ultrashort laser pulses (“cold ablation”) Laser cutting of “bar” samples out of device High-throughput local laser thinning for cross sectioning (