high-throughput analysis of electro deposited … analysis of electro deposited copper in through...

High-Throughput Analysis of Electro

Deposited Copper in Through Silicon Vias

Ruud van den Boom & Matthew Ledwith

Atotech USA Inc., Albany, NY

Proprietary and Confidential

Outline

Through Silicon Via Metrology

TSV analysis in the development state: what are we looking for?

Cross sectioning of TSV

� Quality of the cross section

� Possible techniques

� Argon ion milling

Imaging of cross sections and the surface

� Information needed

� Advantages of imaging in 3D

Summary


Through Silicon Via Metrology

Novel techniques are being developed for TSV metrology

� Stress measurements in and around the copper

� Quality of barrier / liner / seed (uniformity / density)

� Purity of copper deposit

� Copper filling performance

Size of features falls between printed circuit boards and 2D integrated chips

� Need to find techniques with an appropriate resolution / sensitivity at a high

throughput

� Techniques used will vary between development (chips / cleaved wafers) and

production (actual products)


TSV analysis in the development state:What are we looking for?

Combination of samples

� Chips or coupons

� 200mm & 300mm wafers

� Various mask designs

Filling performance

� Bottom-up growth

� Over burden thickness / mounding

� Defects

� Protrusions3µm

5 Proprietary and Confidential

Cross sectioning of TSVs


Quality of the cross sections

Early stage:

Large voids due to seed or wetting issues

~1µm

Cleaved cross section imaged in SEM

Large voids visible in bottom

Deformations to copper from cleaving



Early stage:


~1µm

Development of new chemistry

Small voids due to plating or seed issues

~100nm

Cleaved and argon milled cross section imaged in

confocal microscope

Small plaiting voids

Good cross section for defects ≥100nm



Early stage:


~1µm



~100nm

Plating process optimized - production

Nano voids due to PVD issues

~1nm

Cleaved and FIB cleaned cross section imaged in

SEM

Nano-size defects in seed

High quality cross section, good for defects >2nm

500nm



Early stage:


~1µm



~100nm

Plating process optimized - production

Nano voids due to PVD issues

~1nm

Main focus of this work is on the development stage

Voids between 100 and 1000nm

Overburden thickness

Mounding or dimples

Extrusions found after high temperature anneals

Chips or wafers that can be cleaved


Available techniques

Focused Ion Beam & Inductively Coupled Plasma FIB

� Great precision for single via analysis

� Fast analysis possible (<30min for cleaved samples)

� 3D information available with successive cross sectioning

X-ray microscopy / tomography

� Great precision for single via analysis

� Possibly non-destructive on thinned wafers

� 3D information available with tomography

Mechanical polishing & High precision cleaving

� Low cost

� High throughput

Low energy ion milling (Ar / Xe)

� Low cost

� High throughput

� High quality cross sections


Low energy ion milling

Requirements for development stage

� High throughput (>1/h)

� Single cross section of ≥2 vias

� Quality good enough to see ≥100nm features

� Lab based instrument

� Low cost of ownership









Low energy argon ion milling

Image courtesy of Gatan, Inc.SampleBladeIon beam










� Low cost

� Capable of making wide cross sections

� Fast

500µm










� Low cost


� Fast

� Good for analyzing small defects

500µm

1µm

Ni

Cu

C contamination

and voids, ~30nm










� Low cost


� Fast


� Great to reduce FIB time

Cleaved sample, with area of interest outlined

Projected FIB time without further work: 3~4h

100µm










� Low cost


� Fast


� Great to reduce FIB time

Remove excess material with ion mill: 1~1.5h

Further processing with FIB: <1h


Imaging of TSVs


Imaging of cross sections and the surface

SEM, FIB or Optical microscopy?

YesNoNoNoSurface roughness

Low

No

Possible

25nm

High

Bench-top SEM

Yes, of surfaces

Yes, destructive

No3D imaging

High

Yes

1nm

Medium

FIB-SEM

LowMediumCost

PossiblePossibleGrain contrast

120nm1nmSpatial resolution

Confocal

MicroscopyFE-SEM

HighMediumThroughput


Confocal microscopy

High throughput

� No vacuum

� No alignments

Resolution

� Void detection

� Overburden thickness

3D analysis

� Mounding height

� Protrusion height

Olympus Lext OLS4000

Scanning laser confocal microscope


Resolution

10µm

200nm void in TSV 120nm wide damascene Cu lines in SiOx (1:1)

2µm

120 nm

130 nm

140 nm

160 nm

180 nm


3D analysis

Mounding on 5µm TSVs


3D analysis

Mounding on 5µm TSVs

� Ring shaped dimple on outside of TSV

� Depth can be measured on profile

� Profile matched FIB analysis

2µm


3D analysis

Mounding on damascene

samples

Sets of 19 damascene lines

Mounding varies from

200~300nm

250nm


3D analysis

Mounding on damascene

samples

Sets of 19 damascene lines

Z-resolution limited to ~10nm, giving issues for mounding of <20nm

Requires AFM or laser interferometry


Summary

Low energy argon milling

� High throughput

� High resolution imaging possible

� Easy to use

� Low cost

� Destructive technique

Confocal microscopy

� High throughput

� Image features ≥200nm

� Measure mounding / surface roughness

� Resolution limited to ~125nm


Acknowledgements

The authors would like to thank the following people for the useful

discussions and help:

- Drew Erwin and Chris Spence of Gatan

- Rich Poplawski and Mario Gislao of Olympus

- Miguel Rodriguez of College of Nanoscale Science & Engineering, University at Albany, SUNY


Questions?

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