mrs fall meeting 2009, boston
TRANSCRIPT
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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