x-rays techniques as a powerful tool for characterisation of thin film nanostructures
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X-rays techniques as a powerful tool for characterisation of thin film nanostructures El ż bieta Dynowska. Institute of Physics Polish Academy of Sciences, al. Lotników 32/46, Warsaw, Poland [email protected]. - PowerPoint PPT PresentationTRANSCRIPT
X-rays techniques as a X-rays techniques as a powerful tool for powerful tool for characterisation characterisation
of thin film nanostructuresof thin film nanostructures
ElElżżbieta Dynowskabieta DynowskaInstitute of Physics Polish Academy of Sciences,
al. Lotników 32/46, Warsaw, Poland
Workshop on Semiconductor Processing for Photonic Devices, Sept. 30 – Oct. 2, Warsaw, Poland
1. Introduction
2. Basics General information about nanostructures What we want to know about thin layers? How to get this information?
3. Selected X-ray techniques X-ray reflectivity X-ray diffraction
4. Synchrotron radiation – new possibilities
5. Summary
OutlineOutlineOutlineOutline
x
Homoepitaxial layer – the layer and substrate are the same material (the same lattice parameters).
Heteroepitaxial layer – the layer material is different than the substrate one (different lattice parameters).
Thin layer – the dimension in the z-direction is much smaller than in the x and y, respectively.
single crystal thin layer having the
crystal structure and orientation of
single crystal substrate on which it
was grown.
x
y
z
(A) Epitaxial layerz
y
0
0
(B) Polycrystalline layers –
orientations of small crystallites are
randomly distributed with respect to
layer surface(C) Amorphous layers - lack of long-distance ordering of atoms
Lattice mismatch –
f = (alayer - asubs )/ asubs
Critical thickness hc – thickness below which the layer grows pseudomorphically the cubic unit cell
of layer material is tetragonally distorted: alz alx = aly = as (the layer is fully
strained). hc decreasing when f increasing.
Layer relaxation - alxy alz al relax = abulk
alayeras
ayax
az
What we want to know about thin layers?What we want to know about thin layers?
Crystalline state of layer/layers
(epitaxial?; polycrystalline?; amorphous? …)
crystal quality;
strain state;
defect structure;
chemical composition (in the case of ternary compounds layers);
thickness
surface and interface roughness, and so on…
How to get this information?How to get this information?
By means of X-ray techniquesBy means of X-ray techniques
Because X-ray techniques are the Because X-ray techniques are the most important, non-destructive most important, non-destructive
methods of samplemethods of sample characterizationcharacterization
Why?Why?
Selected X-ray techniqueSelected X-ray techniquess
X-ray reflectivity Small-angle regionRefraction index for X-rays n < 1: Roughness investigation
x
z
n = 1- + i
Layer thickness determination
i i
t
The distance between the adjacent interference maxima can be approximated by:
i / 2t
kIkR
kT
c
i
~10-5 in solid materials (~10-8 in air); - usually much smaller than .
2i
Si rough wafer - simulation
Example: Example: superlattice
Si/{Fe/Fe2N}x28/GaAs(001)
28 times
repeated
GaAs
Fe
Fe2N
Si cap-layer
Inte
nsi
ty
i (deg)
c0.3
(2) - superlattice period
(2) –
cap-layer
Experiment
Simulation
Results of simulation
10.4 nm
4.52nm
126.6nm
All superlattice
X-ray diffraction wide-angle region
d’hkl
Bragg’s law:
n = 2d’sin
d’/n = d
= 2d sin
Geometry of measurement
Detector
Incidentbeam
Diffractedbeam
2
/2 coupling
/2 coupling
DetectorIncidentbeam
Diffractedbeam
2’
Crystalline state of layer/phase analysis
PossibilitiesPossibilities
25 30 35 40 45 50 55 6010
100
1000
10000
100000
202
NiA
s-ty
pe
004
NiA
s-ty
pe
w 00
4sf
222
006
Al2O
3
10
2 N
iAs-
type
101 N
iAs-
type
002
NiA
s-ty
pe
w 00
2sf
111
ZnMnTe/MnTe/Al2O
3
Sample 082703A T
Zn= 225oC
Inte
nsity
(cpu
)
2 theta (deg)
35 40 45 50 55 60 650
2000
4000
6000
8000
10000
12000
MnTe hex. 00.4 k
kk
Al2O
3 substrate
00.6
MnTe hex. 00.2
Imax
= 270000 cps
Inte
nsity
[cps
]
2 theta [deg]
MnTe/Al2O3
FeK radiationCuK1 radiation
ZnMnTe/MnTe/Al2O3
24,0 24,2 24,4 24,6 24,8 25,0 25,2 25,4
100
1000
10000
ZnMnTe/MnTe/Al2O
3
Sample 082703A T
Zn= 225oC
ZnMnTe sfaleryt 111
ZnMnTe wurcyt 002
Inte
nsity
(cps
)
2 theta (deg)
Crystal quality
„Rocking curve”
Detector
32,6 32,8 33,0 33,2 33,4100
1000
10000
100000 ZnSe/GaAs 131101004 rocking curve
FWHM = 112 arcsec
ZnSeLayer
FWHM = 21 arcsec
GaAsSubstrate
Omega (deg)
Inte
nsity
(cps
)
Lattice parameter fluctuations
Mosaic structure
?
21 arcsec
112 arcsec
Strain state & defect structure
Cubic unit cell of substrate:
Cubic unit cell of layer material
Strain tetragonal deformation of cubic unit cell: Pseudomorphic
case
Partially relaxed
Relaxed
as
alayer
ayax
az
az ax = ay = asub
az ax = ay asub
axay
az
alayer
az = ax = ay = alayer
The reciprocal lattice maps
S = [100]
Reciprocal lattice:
pseudomorphic
Origin
001
002
003
004
101
100
102
200 300
201
202
P = [001]sample
The sample orientation can be described by two vectors:
P - vector which is the direction normal to the sample surface;
S – any other vector which is not parallel to the P vector and lies in the horizontal plane.
|H|102 = 1/d102
Mosaic structure
relaxedLattice
parameter fluctuations
xd00l
z
Symmetric case
dhhldz
dx
Asymmetric case
Examples In0.50Al0.50As/InP
004
224 224
004
(a) (b)
2
222
2 a
lkh
d
1 For cubic system: For tetragonal
system:2
2
2
22
2 c
l
a
kh
d
1
chemical composition
Vegard’s rule:
If AB and CB compounds having the same crystallographic system and space group create the ternary compound A1-xCxB then its lattice parameter a ACB depends linearly on x-value between the lattice parameters values of AB and CB, respectively.
aAB
aCB
abulk
x0 1
aACB
x
In the case of thin layers arelaxed must be taken for chemical composition determination from Vegard’s rule:
)/(21
)/(2
1112
1112
cc
accaa
xyzrelaxed
c12, c11 – elastic constants of layer material
28.4 28.6 28.8 29.0 29.2 29.4 29.6 29.8Omega (°)
100
1K
10K
100K
counts/s
S
1-3.x00
59.6 59.8 60.0 60.2 60.4 60.6 60.8 61.0 61.2 61.42Theta/Omega (°)
1
10
100
1K
10K
counts/s
S
1-6.x00
40 60 80 100 120 140 160 180Qx*10^4 (rlu)
4980
5000
5020
5040
5060
5080
Qz*10^4 (rlu) 1-7m.A00
1.7
3.4
6.6
12.8
24.8
48.2
93.7
181.9
353.3
686.0
1332.1
2586.7
5022.9
9753.5
18939.6
5420 5440 5460 5480 5500 5520Qx*10^4 (rlu)
6140
6150
6160
6170
6180
6190
6200
6210
6220
Qz*10^4 (rlu) 1-18m.A00
1.6
2.9
5.3
9.6
17.4
31.5
57.0
103.0
186.3
336.9
609.3
1101.9
1992.8
3604.0
6517.9
Heterostructure: ZnMnxTe/ZnMnyTe/ZnMnzTe/ZnTe/GaAs
004 rocking curveZnTex
yz
004 /2
004
335 relaxed
pseudomorphic
Ti/TiN/GaN/Al2O3 under annealing
0 200 400 600 80010
2
103
104
105
106
SIM
S s
igna
l [ c
/s ]
Time [ s ]
TiGa
N
GaN/Ti as-deposited
Time [ s ]
0 200 400 600 80010
2
103
104
105
106
TiGa
N
GaN/Ti
900oC, 30s, N
2
SIM
S s
igna
l [ c
/s ]
Towards an ohmic contactsTowards an ohmic contacts
Secondary Ion Mass Spectrometry (SIMS)
XRD
NbN/GaN/Al2O3
45 50 55 60 65 70
k
k
kkAl2O3
NbN 10.1
GaN 00.2 GaN/NbN
1000oC, 30s, N2
2 (deg)
45 50 55 60 65 700
2000
4000
6000
8000
10000
12000
14000
k
k
GaN/NbN as-deposited
kkAl
2O
3
NbN 10.1
GaN 00.2
Inte
nsi
ty [ c
ps
]
2 (deg)
0 200 400 60010
1
102
103
104
105
106
107
108
GaN/NbNas-deposited
N
Nb
Ga
SIM
S S
ignal [ c/s
]
Time [ s ]
0 200 400 60010
1
102
103
104
105
106
107
108
GaN/NbN
900oC, 30s, N2
N
Nb
Ga
SIM
S S
ignal [ c/s
]
Time [ s ]
XRD
XRD
(SIMS)
(SIMS)
30 40 50 60 70
0
50
100
150
200
250
300
pN2=5-7x10-3mbar
PRF=1.9W/cm2,
ptot.=1x10-2mbar,
400 Zn3N2
Inte
nsi
ty
2 [ deg ]
30 40 50 60 70
200
400
600
800
1000 pN2
=2.5x10-3mbar
400
Z
n3N
2
PRF=1.9W/cm2,
ptot.=1x10-2mbar,
222
Zn
3N2
440
Zn
3N2
332
Zn
3N2
321
Zn
3N2
Inte
nsi
ty
2 [ deg ]30 40 50 60 70
100
200
300
400
500
600
700
pN2
=2x10-3mbar
PRF=1.9W/cm2,
ptot.=1x10-2mbar,
Zn
400
Z
n3N
2
440
Zn
3N2
321
Zn
3N2
Inte
nsi
ty [
a.u
.]
2 [ deg ]
20% N2 Zn3N2 + Zn 25% N2 polycryst. Zn3N2
50% - 70% N2 monocryst.
30 40 50 60 700
50
100
150
200
250
300 pN2=9x10-3mbar
400 Zn3N2
PRF=1.9W/cm2,
ptot.=1x10-2mbar,
Inte
nsi
ty
2 [ deg ]
GaN, Al2O3, ZnO
N2>80% polycryst. & amorph.
Deposition of Zn3N2 by reactive rf sputtering
Zn3N2
40 45 50 55 60 95 100
200
400
600
800
1000
Zn3N
2 d=650nm on GaN
oxidation @ 600oC, 15 min. 00.4
GaN
00.4
Zn
O
00.6
Al 2O
3
00.2
Zn
O00.2
GaN
Inte
nsi
ty
2 [ deg ]
polycrystalline ZnO on sapphire and quartz
40 45 50 55 600
2000
4000
6000
8000
ZnO
2 [ deg ]
Inte
nsi
ty (
a. u
.)
100
101
002
Zn3N2(50%N2)/ZnOsput./quartz
oxidation 600oC
45 50 55 600
200
400
600
800
1000
ZnO
Zn3N
2 d=650nm on Al
2O
3
oxidation @ 600oC,
15 min.
2 (deg)
101
102
002
KK
006 Al2O
3
Inte
nsi
ty (
cps)
40 50 60 700
100
200
300
400
500
600
700
800
ZnO
Zn3N
2 d=650nm on quartz
oxidation @ 600oC, 15 min.
110 102
101
101 K
002
100
Inte
nsi
ty
2 [ deg ]
ZnO:N by oxidation of Zn3N2 microstructure
highly textured ZnO on GaN and ZnO
30 40 50 60 70 80 90
100
1000
10000
Zn
O 1
01
ZnTe:N/ZnTe/GaAs
oxidized 6000C, 20 min.
Ga
As
00
4 (
K)
Zn
O 1
03
+ T
e 1
13
Z
nT
e 0
04
(K
)
Ga
As
00
4 (
K)
Zn
Te
00
4 (
K)
Te
20
1Te
11
0T
e 1
02
Zn
O 0
02
Zn
O 1
00
Z
nT
e 0
02
(K
)
Te
10
1
Zn
Te
00
2 (
K)
Inte
nsi
ty [
a.u
.]
2 [ deg ]0 1 2 3 4 5 6 7
1018
1019
1020
1021
1022
As
Ga
TeO
Zn
Depth [ m ]
Co
nce
ntr
atio
n o
f N
an
d H
in Z
nO
[a
t/cm
3 ]
100
101
102
103
104
105
106
107
108
SIM
S S
ign
al o
f Ga
, As, Z
n, T
e, O
an
d H
[ c/s ]
ZnTe:N/ZnTe/GaAs oxidised 6000C
ZnO by oxidation of ZnTe/GaAs
Te inclusions in ZnO film
XRD(SIMS)
Synchrotron radiationSynchrotron radiation
)bandwidth%1.0)(areasourcemm()mrad(
sec/PhotonsBrilliance
22
50 55 60 65 70 75
0
2
4
6
8
10
2 =
0.3
1o
Si1-x
Gex
bottom layer
"-1" "+1"
Ge004
Si (substrate) +Si
0.95Ge
0.05 (SL
0)
004
Inte
nsity
(a.u
.)
2 (deg)
Si substrate (001)
Si, 115 nm, 780 C
Si, 10 nm, 480 C
Si, 24 nm, 450 C Si, 2nm, 250 C
Ge, 1nm, 250 C
7 times
repeated
High resolution electron microscopy (HREM) –
JEOL-4000EX (400 keV)
55 60 65 702Theta/Omega (°)
0.01
0.1
1
10
100
1K
10K
100K
1M
10M
counts/s dorby-dla jarka.Z01
Example: superlattice of self-assembled ultra-small Ge quantum dots
Experimental diffraction pattern Simulated diffraction pattern
Si
004Ge
004 2 = 0.314o
Si0.8Ge0.2
bottom layer
„-1”„-2”
C
Results: HREM XRD
superlattice period C..... 33.5 nm 33 nm,
thickness of Ge............... 1.8 nm 2.0 nm
thickness of SiGex
bottom layer..................... 6.7 nm 6.7 nm
Compositon........................ ---- x 0.2
50nm
Hasylab (Hamburg), W1.1 beamline: X’Pert Epitaxy and Smoothfit software
Acknowledgements
I would like to express my gratitude to my colleagues for their kind help:
Eliana Kaminska
Jarek Domagala
Roman Minikayev
Artem Shalimov