1. 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 Division
National Chemical Laboratory, India
1

2. Outline
• Motivation
• Sample preparation
• Results on Oxides
A) SiO2
B) MgO
C) High K material – HfO2
• Conclusions and Perspectives
2

3. Microelectronics Application
Continuous improvement of each Tunnel magneto resistance
part of the MOS transistors
Silicide
Spacer
Gate MgO
Gate
Silicide oxide Silicide
Channel
Drain Source
Si
substrate
Dopant distribution in source/drain : dopant activation, clustering
Gate dielectric stack : dopant segregation, new materials (kigh-k)
Silicides: gate contact (lower resistivity)
Gate: polysilicon (dopant distribution) or metal
Tunnel barrier : MgO
3

4. 3D Atom Probe
Position Sensitive
Detector (X,Y,TOF)
• APT = FIM + TOF
• Tip subjected to field F~V/R
• Tip pulsed field evaporated atom by atom
Y
• Ions projected on a PSD
L
• TOF mass spectrometry
X
• 3D reconstruction of the atomic distribution
• Volume ~100x100x100 nm3
• Spatial Resolution - 0.2nm in depth
V 0.5nm laterally
Radius
4
R<100 nm

5. 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
5

6. Sample Preparation
Two steps for sample preparation
(a) Lift out method or Attaching Si post
(b) Annular milling
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
6

7. Attachment of Silicon post on Metal Tip
RIE etching process (IEMN, LAAS)
▪ Silicon posts (multilayers applications)
▪ fragments, powders,… 7

8. Annular Milling
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.
ions
electrons 1 µm
h
d
Si
Rough Mill Sharpening Final
0.5-1nA,30 keV 20-100pA, 30keV few pA, minimal Ga
h>2xd acceleration
8

9. Laser Assisted Tomography Atom Probe
R<100nm
Specimen
R
Needle Ion
tip
Shape P < 10 -10 Pa
T < 20-80K
PSD
Femtosec laser,100kHz V 0 < 20 kV
500fs
fs laser
pulse Green UV
3 Colour box Stop
IR signal
Start
signal
Time of flight
9

10. Analysis of an insulating layer SiO 2 (12nm)
P B 0
Courtesy M.Gillebert & F.Vurpillot
10

11. Thin layer (4nm) of MgO
Fe, Mg, O, FeO, Au
SEM image
Laser Wavelength: 343nm
Temperature: 80K Collaboration with
T. Al- Kassab
Gottingen University
Laser energy: 35- 40 nJ
Germany
Flux : Constant
11

12. Thick layer (32nm) of MgO
Fe,Mg,O,FeO,Si
190nm 100
Fe
80
Composition (%)
60 Mg O
40
20
0
0 10 20 30 40 50 60 70
Depth (nm)
Laser Wavelength: 343nm
Temperature: 20K
12

13. Thin layer (4nm) of HfO2
110
Hf
O
Experimental condition
100 Si HfO
Si Laser Wavelength: 343nm
90 SiO
80 Temperature: 40K
70
Concentration
60 Laser energy: 35- 40 nJ
50 O
40 Flux : Constant
30 HfO
20
10
0
-10 -5 0 5 10 15
DistanceToMatrix nm
Collaboration with
S. B. Ogale
National Chemical Laboratory
India

14. Thick layer (20nm) of HfO2
HfO,Si
2+
600 HfO
500
Number of atoms
400
300 Laser Wavelength: 343nm
Temperature: 80K
200
Complex ions Laser energy: 83 nJ
100 Hf
2+
2+
HfO2 1+
2+ 1+
HfO2
(HfO2Si) HfO
0
80 100 120 140 160 180 200 220
Mass

15. Conclusions
• 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.
SiO2 MgO HfO2
Perspectives
• Analysis will be with the surface parallel to the tip axis to
avoid the tip rupture.
Tip axis Parallel to Oxide Layer
• More improvement in sample the surface
(cross section
preparation and analysis. mode)
Capping layer 15