MRS fall meeting 2009, Boston

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Atomic scale analysis of oxides using Laser Assisted Atom Probe Tomography

B.Mazumder,A.Vella & B.Deconihout

GPM, Université de Rouen, France

CNRS Laboratory

V. Thakare & S.B.Ogale

Physical and Materials Chemistry DivisionNational Chemical Laboratory, India

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Outline

• Motivation

• Sample preparation• Results on Oxides

A) SiO2

B) MgO

C) High K material – HfO2

• Conclusions and Perspectives

3

Continuous improvement of each

part of the MOS transistors

Dopant distribution in source/drain : dopant activation, clustering

Gate dielectric stack : dopant segregation, new materials (kigh-k)

Silicides: gate contact (lower resistivity)

Silicide

Silicide

Gate

Gateoxide

Spacer

Source

Silicide

DrainSi substrate

Channel

Gate: polysilicon (dopant distribution) or metal

Microelectronics Application

Tunnel magneto resistance

MgO

Tunnel barrier : MgO

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• APT = FIM + TOF

• Tip subjected to field F~V/R

• Tip pulsed field evaporated atom by atom

• Ions projected on a PSD

• TOF mass spectrometry

• 3D reconstruction of the atomic distribution

• Volume ~100x100x100 nm3

• Spatial Resolution - 0.2nm in depth0.5nm laterally

Position SensitiveDetector (X,Y,TOF)

Radius R<100 nm

V

L

XX

YY

3D Atom Probe

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Material analysis by Atom Probe Tomography

Addition of ultrafast laser pulsing and improved Field of View (FOV) opened a new era for APT

100x100 nm2 FOV

20x20 nm2 FOV

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1.Deposition of protection cap:Pt Ion deposition (~1µm)

2.Cut a lamella by FIB 3.“Welding” it to the

micromanipulator 4.Bringing it in contact with a

support pillar 5. Welding it and cutting a

portion of tip

Two steps for sample preparation

(a) Lift out method or Attaching Si post (b) Annular milling

Sample Preparation

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▪ Silicon posts (multilayers applications)

▪ fragments, powders,…

RIE etching process (IEMN, LAAS)

Attachment of Silicon post on Metal Tip

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Annular Milling

Rough Mill Sharpening Final

0.5-1nA,30 keV 20-100pA, 30keV few pA, minimal Ga

acceleration

electrons

ions

1 µµµµm

Si

h

d

h > 2 x d

The sample is aligned along the beam direction,the inner diameter of the circular mask and the milling current

are reduced after each milling stage.

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Laser Assisted Tomography Atom Probe

Startsignal

V0

< 20 kV

PSD

RIon

P < 10-10 Pa

T < 20-80K

tip

3 Colour box Stopsignal

R<100nm

fs laserpulse

Femtosec laser,100kHz500fs

Time of flight

UVGreen

IR

Specimen

Needle

Shape

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0P B

Courtesy M.Gillebert & F.Vurpillot

Analysis of an insulating layer SiO 2 (12nm)

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Fe, Mg, O, FeO, Au

Thin layer (4nm) of MgO

Laser Wavelength: 343nm

Temperature: 80K

Laser energy: 35- 40 nJ

Flux : Constant

SEM image

Collaboration with T. Al- KassabGottingen UniversityGermany

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190nmFe,Mg,O,FeO,Si

Thick layer (32nm) of MgO

0 10 20 30 40 50 60 700

20

40

60

80

100

Com

posi

tion

(%)

Depth (nm)

Laser Wavelength: 343nm

Temperature: 20K

Fe

Mg O

-10 -5 0 5 10 150

10

20

30

40

50

60

70

80

90

100

110C

once

ntra

tion

DistanceToMatrix

Hf O HfO Si SiO

Experimental condition

Laser Wavelength: 343nm

Temperature: 40K

Laser energy: 35- 40 nJ

Flux : Constant

Si

O

HfO

nm

Thin layer (4nm) of HfO 2

Collaboration with S. B. OgaleNational Chemical LaboratoryIndia

80 100 120 140 160 180 200 2200

100

200

300

400

500

600

Num

ber

of a

tom

s

Mass

Hf2+

HfO2+

HfO2+

2

(HfO2Si)

2+ HfO1+

2HfO1+

Thick layer (20nm) of HfO 2HfO,Si

Laser Wavelength: 343nm

Temperature: 80K

Laser energy: 83 nJComplex ions

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• Oxides can be analyzed by laser assisted Atom Probe.• However it depends on the thickness of the layer, oxides

property and strictly on sample preparation.

Conclusions

Perspectives• Analysis will be with the surface parallel to the tip axis to avoid the tip rupture.• More improvement in samplepreparation and analysis.

Oxide LayerTip axis Parallel to the surface (cross section mode)

SiO2HfO2MgO

Capping layer