Transcript Prezentacja programu PowerPoint

X-rays techniques as a powerful
tool for characterisation
of thin film nanostructures
Elżbieta Dynowska
Institute of Physics Polish Academy of Sciences,
al. Lotników 32/46, Warsaw, Poland
[email protected]
Workshop on Semiconductor Processing for Photonic Devices, Sept. 30 – Oct. 2, Warsaw, Poland
Outline
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
Thin layer – the dimension in the z-direction is much
z smaller than in the x and y, respectively.
y
x
0
(A) Epitaxial layer
z
y
0
single crystal thin layer having the
crystal structure and orientation of
single crystal substrate on which it
was grown.
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).
Lattice mismatch –
f = (alayer - asubs )/ asubs
as
alayer
Critical thickness hc –
az
ax
ay
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
(B) Polycrystalline layers –
orientations of small crystallites are
randomly distributed with respect to
(C) Amorphous layers
layer surface
- lack of long-distance ordering of atoms
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?
By means of X-ray techniques
Why?
Because X-ray techniques are the
most important, non-destructive
methods of sample characterization
Selected X-ray techniques
X-ray reflectivity
Small-angle region
Refraction index for X-rays n < 1:
Roughness investigation

n = 1-  + i
 ~10-5 in solid materials (~10-8 in air);
 - usually much smaller than .
z
kI
c
kR



kT
Layer thickness determination
i
i
t
x
i
2i
Si rough wafer - simulation
The distance between the
adjacent interference
maxima can be
approximated by:
i  / 2t
Example:
superlattice
Si/{Fe/Fe2N}x28/GaAs(001)
Results of
simulation
Experiment
10.4 nm
126.6
nm
4.52nm
Simulation
Si cap-layer
Fe2N
Fe
GaAs
 (2) superlattice
period
28 times
All superlattice
repeated
c0.3
 (2) –
cap-layer
i (deg)
 X-ray diffraction
wide-angle region
Bragg’s law:
n = 2d’sin
d’/n = d



            
d’hkl
            
            
            
 = 2d sin
Geometry of measurement
Incident
beam
Diffracted
beam


’
/2 coupling
2
Incident
beam
/2 coupling
Diffracted
beam



2
Possibilities
 Crystalline state of layer/phase analysis
MnTe/Al2O3
00.6
004 NiAs-type
202 NiAs-type
002
1000
Al2O3 substrate
4000
w 004
Intensity (cpu)
6000
o
TZn= 225 C
102 NiAs-type
10000
8000
Sample 082703A
sf 222
k
006 Al2O3
00.4
MnTe hex.
00.2
Intensity [cps]
100000
ZnMnTe/MnTe/Al2O3
101 NiAs-type
10000
MnTe hex.
w 002
Imax= 270000 cps
sf 111
12000
NiAs-type
ZnMnTe/MnTe/Al2O3
100
2000
k
k
10
0
FeK radiation
40
45
50
55
60
25
65
30
35
CuK1 radiation
2 theta [deg]
10000
ZnMnTe sfaleryt 111
ZnMnTe/MnTe/Al2O3
Sample 082703A
o
TZn= 225 C
1000
100
24,0
24,2
24,4
24,6
24,8
2 theta (deg)
25,0
40
45
2 theta (deg)
ZnMnTe wurcyt 002
Intensity (cps)
35
25,2
25,4
50
55
60
 Crystal quality
„Rocking curve”
100000
ZnSe/GaAs
131101

004 rocking curve

Layer
21 arcsec
GaAs
Substrate
FWHM = 21 arcsec
FWHM = 112 arcsec
Intensity (cps)

ZnSe
112 arcsec
10000
1000
Lattice parameter fluctuations
?
Mosaic structure
100
32,6
32,8
33,0
Omega (deg)
33,2
33,4
 Strain state & defect structure
Strain  tetragonal
deformation of cubic unit cell:
az
Pseudomorphic case
Cubic unit cell of
layer material
ax
ay
az  ax = ay = asub
alayer
az
Partially relaxed
ax
Cubic unit cell
of substrate:
ay
az  ax = ay  asub
as
Relaxed
alayer
az = ax = ay = alayer
The reciprocal lattice maps
Reciprocal lattice:













sample


004

003







002
102
001
101
201


Origin
100
200
300




202

The sample orientation can be
described by two vectors:
P - vector which is the direction normal
to the sample surface;

|H|102 = 1/d102




S – any other vector which is not
parallel to the P vector and lies in the
horizontal plane.
P = [001]
S = [100]
Lattice parameter
fluctuations




Mosaic
structure

relaxed




 
pseudomorphic
Examples
In0.50Al0.50As/InP
z
004

x

d00l
004
(a)
Symmetric case
(b)
224
224


dz
dhhl
dx
Asymmetric case
For cubic system:
1
d2

h 2  k 2  l2
a2
For tetragonal system:
1
d2

h2  k2
a2

l2
c2
 chemical composition
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.
Vegard’s rule:
abulk
aCB
aACB
x
aAB
0
x
1
In the case of thin layers
arelaxed must be taken for
chemical composition
determination from Vegard’s
rule:
a relaxed 
a z  2(c12 / c11 )a xy
1  2(c12 / c11 )
c12, c11 – elastic constants of layer material
Heterostructure:
ZnMnxTe/ZnMnyTe/ZnMnzTe/ZnTe/GaAs
counts/s
1-3.x00
004 rocking curve
100K
z
y
Qz*10^4 (rlu)
1-7m.A00
1.7
5080
3.4
004
ZnTe
x
5060
6.6
12.8
24.8
48.2
93.7
10K
181.9
5040
353.3
686.0
1332.1
5020
2586.7
1K
5022.9
9753.5
18939.6
5000
100
28.4
28.6
28.8
29.0
29.2
29.4
29.6
29.8
Omega (°)
4980
40
counts/s
Qz*10^4
1-6.x00
004 /2
10K
60
80
100
120
140
160
180
Qx*10^4 (rlu)
(rlu)
1-18m.A00
6220
335
6210
relaxed
1.6
2.9
5.3
9.6
17.4
6200
31.5
1K
57.0
6190
103.0
186.3
6180
336.9
100
609.3
6170
1101.9
1992.8
6160
3604.0
pseudomorphic
10
6150
6140
1
59.6
59.8
60.0
60.2
60.4
60.6
60.8
61.0
61.2
61.4
2Theta/Omega (°)
5420
5440
5460
5480
5500
5520
Qx*10^4 (rlu)
6517.9
Towards an ohmic contacts
Ti/TiN/GaN/Al2O3 under annealing
Secondary Ion Mass Spectrometry
(SIMS)
XRD
6
6
10
10
Ti
5
Ti
Ga
5
10
N
4
10
3
10
SIMS signal [ c/s ]
SIMS signal [ c/s ]
10
N
4
10
3
10
GaN/Ti
GaN/Ti
as-deposited
o
900 C, 30s, N2
2
10
Ga
2
0
200
400
Time [ s ]
600
800
10
0
200 400 600
Time [ s ]
800
NbN/GaN/Al2O3
XRD
Intensity [ cps ]
12000
10000
GaN/NbN
as-deposited
GaN
00.2
k
8000
NbN
10.1
6000
k
4000
SIMS Signal [ c/s ]
14000
Al2O3
k
k
2000
0
45
50
55
60
65
70
10
8
10
7
10
6
10
5
10
4
10
3
10
2
10
1
(SIMS)
Ga
Nb
N
GaN/NbN
as-deposited
0
200
2 (deg)
GaN
00.2
k
NbN
10.1
k
GaN/NbN
10
8
10
7
10
6
10
5
10
4
10
3
10
2
o
1000 C, 30s, N2
SIMS Signal [ c/s ]
XRD
Al2O3
k
400
600
Time [ s ]
k
(SIMS)
Ga
Nb
N
GaN/NbN
o
900 C, 30s, N2
10
45
50
55
2 (deg)
60
65
70
1
0
200
400
Time [ s ]
600
Deposition of Zn3N2 by
reactive rf sputtering
2
pN2=2x10 mbar
-2
pN2=2.5x10 mbar
800
300
200
Zn
Intensity
400
440 Zn3N2
500
321 Zn3N2
400 Zn3N2
Intensity [a.u.]
600 ptot.=1x10 mbar,
-3
1000 PRF=1.9W/cm ,
-2
ptot.=1x10 mbar,
-3
400 Zn3N2
PRF=1.9W/cm2,
222 Zn3N2
321 Zn3N2
700
600
400
200
100
30
40
50
60
20% N2 Zn3N2 + Zn
2
400
-2
ptot.=1x10 mbar,
50
60
70
25% N2 polycryst. Zn3N2
2
Zn3N2
300
PRF=1.9W/cm ,
-2
ptot.=1x10 mbar,
250
200
-3
pN2=9x10 mbar
400 Zn3N2
Intensity
Intensity
250
40
2  [ deg ]
2  [ deg ]
300 PRF=1.9W/cm ,
30
70
440 Zn3N2
GaN, Al2O3, ZnO
332 Zn3N2
Zn3N2
200
-3
150
pN2=5-7x10 mbar
150
100
100
50
50
0
0
30
40
50
2  [ deg ]
60
70
50% - 70% N2 monocryst.
30
40
50
2  [ deg ]
60
70
N2>80% polycryst. & amorph.
ZnO:N by oxidation of Zn3N2
microstructure
800
oxidation @ 600 C,
15 min.
700
o
o
oxidation @ 600 C, 15 min.
ZnO
400
500
400
102
300
200
200
102
Intensity
ZnO
100
101 K
K
002
600
K
101
600
006 Al2O3
002
Intensity (cps)
800
Zn3N2 d=650nm on quartz
110
Zn3N2 d=650nm on Al2O3
101
1000
100
0
0
45
50
2  (deg)
55
60
40
50
2  [ deg ] 60
70
002
Zn3N2(50%N2)/ZnOsput./quartz
o
oxidation 600 C
6000
2000
100
200
ZnO
4000
101
400
00.4 GaN
oxidation @ 600 C, 15 min.
8000
Intensity (a. u.)
600
o
00.2 ZnO
Intensity
800
Zn3N2 d=650nm on GaN
00.6 Al2O3
00.2 GaN
1000
00.4 ZnO
polycrystalline ZnO on sapphire and quartz
40
45
50
55
2  [ deg ]
60
95
100
0
40
45
50
2  [ deg ]
highly textured ZnO on GaN and ZnO
55
60
ZnO by oxidation of ZnTe/GaAs
GaAs 004 (K)
0
10
10
10
10
100
30
40
50
60
2  [ deg ]
70
80
ZnTe:N/ZnTe/GaAs oxidised 600 C
22
Ga
Zn
3
Concentration of N and H in ZnO [at/cm ]
ZnTe 004 (K)
(SIMS)
ZnO 103 + Te 113
GaAs 004 (K)
ZnTe 004 (K)
ZnTe 002 (K)
oxidized 600 C, 20 min.
Te 201
1000
0
ZnO 100
ZnO 002
ZnO 101
Te 102
Te 110
Te 101
Intensity [a.u.]
10000
ZnTe:N/ZnTe/GaAs
90
10
Te
O
21
19
18
1
2
3
4
5
Depth [ m ]
Te inclusions in ZnO film
8
10
7
10
6
10
5
10
4
10
3
10
2
10
1
10
0
As
20
0
10
6
7
SIMS Signal of Ga, As, Zn, Te, O and H [ c/s ]
ZnTe 002 (K)
XRD
Synchrotron radiation
Brilliance 
Photons / sec
(mrad ) 2 (mm 2source area )(0.1% bandwidth )
Example: superlattice of self-assembled
ultra-small Ge quantum dots
Results:
Si, 24 nm, 450 C
C 7 times
thickness of Ge...............  1.8 nm
Si, 10 nm, 480 C
50nm
Si, 115 nm, 780 C
D2 = 0.31
8
Intensity (a.u.)
bottom layer.....................  6.7 nm
6.7 nm
Compositon........................
x  0.2
----
counts/s
Si (substrate)
+Si0.95Ge0.05 (SL0)
004
dorby-dla jarka
10M
D 2 = 0.314
„-1”
100K
10K
"+1"
"-1"
4
004
„-2”
004
o
bottom layer
10
Si0.8Ge0.2
1
0.1
0
bottom layer
0.01
50
55
60
65
004
100
Si1-xGex
Ge
2
1K
Si
Ge
1M
6
70
2  (deg)
Experimental diffraction pattern
2.0 nm
thickness of SiGex
High resolution electron
Si substrate (001)
microscopy (HREM) –
JEOL-4000EX (400 keV)
Hasylab (Hamburg), W1.1 beamline:
X’Pert Epitaxy and Smoothfit software
o
10
XRD
superlattice period C..... 33.5 nm 33 nm,
repeated
Si, 2nm, 250 C
Ge, 1nm, 250 C
HREM
75
55
60
65
70
2Theta/Omega (°)
Simulated diffraction pattern
Acknowledgements
I would like to express my gratitude to my
colleagues for their kind help:
Eliana Kaminska
Jarek Domagala
Roman Minikayev
Artem Shalimov