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Computational Materials Science:
Multiscale Modeling of Atomic
Layer Deposition of Thin Films
Andrey Knizhnik
Kinetic Technologies Ltd, Moscow
RRC “Kurchatov Institute”, Moscow
Challenges for ultra-thin film deposition
Deposition of films with atomic scale
precision of film thickness
Catalysis
Microelectronics
Nanotechnology
Uniform deposition in high-aspect ratio
features
пѓћ Atomic layer deposition (ALD), Suntola T 1989 Mater. Sci. Rep. 4 261
Principles of ALD technique
Self-termination of adsorption provides atomic scale
control of the film thickness and ensures uniform
coverage.
Application of ALD technique
Application of ALD for deposition of high-k metal oxide
films in microelectronics
New MOSFET structure
High-k
dielectric ZrO2, HfO2, Al2O3, La2O3, etc
Gate
Source
Drain
Zr(Hf)O2 deposition from Zr(Hf)Cl4 and
H2O:
Si
Zr(OH)/s/ + ZrCl4=ZrOZrCl3/s/ +HCl
Experiment (ZrO2 ALCVD)
ZrCl/s/ + H2O=ZrOH/s/ +HCl
пЂґFilm properties depend significantly
on film deposition conditions
пЂґ Kinetic mechanisms of film growth
are required
Low leakage current
High leakage current
Features of ALD technique
Main features of atomic layer deposition
•
•
•
•
•
•
Maximum film growth rate
Temperature dependence of film growth rate
Residual impurities in as-deposited films
Selection of precursors
Film roughness
Influence with initial support state
Maximum film growth rate of ALD technique
Geometric considerations on maximum surface coverage
- not observed
Zr(Hf)O2 deposition from
Zr(Hf)Cl4 and H2O.
Repulsion between ligands of
metal precursor results in submonolayer coverage of the
substrate. Experimental
maximum film growth rate is
about 0.5 ML/ALD cycle for
halide precursors and about
Maximum surface coverage is 0.25 ML/ALD cycle.
0.1 ML/ALD cycle for
M. Ililammi, Thin solid Films 279 (1996) 124.
organometallics.
Maximum film growth rate of ALD technique
Quantum chemical calculations of precursor on the surface
120
80
60
Quantum chemical
calculation of ZrClx
adsorption energy with
respect to gaseous species
and hydroxylated surface.
HCl/g/ is removed from
reactor by purge gas.
40
20
0
-20
-40
-60
-80
ZrCl2
ZrCl4
ZrCl4(g)
+surface
ZrCl3
2 x ZrCl2
ZrCl2
+ZrCl4
3 x ZrCl2
2 x ZrCl2
+ZrCl4
gas
-100
-120
Maximum 0.5 ML/ALD
cycle can be achieved in
agreement with
experimental data.
100% water coverage
100
kJ/mol
ZrCl4/g/ + ZrOH/s/ п‚®
ZrClx/s/ + HCl/g/
0.25 ML 0.5 ML
-140
-160
Iskandarova, et al, SPIE, 2003
Multiscale modeling of thin film deposition
Construction of chemical mechanism of film growth from
first-principles data
Simulation of
film growth by
reactor model
Comparison with
experimental data
Fitting of rate
parameters
Rate coefficients
calculation from
Statistic Theory
QC calculations
of reaction
pathway
•Rate of film growth
•Mass increment per pulse
•Adsorbed groups at the surface
•Concentration of impurities
First-principles modeling of deposition reactions
Quantum chemical simulation of ZrCl4 and H2O precursor
interactions with ZrO2 surface
(1) Hydrolysis of chemisorbed MCl2 groups
Minimum-energy pathway
H2O
5
TS
E, kcal/mol
0
-5
-10
-15
-20
Zr
Hf
Ads.complex
(2) Chemisorption of MCl4 (M = Zr, Hf) on the hydroxylated MO2 surface:
(model gas-phase reaction)
Minimum-energy pathway
ZrCl4
0
TS
E, kcal/mol
-5
-10
-15
-20
-25
-30
M.Deminsky, A. Knizhnik et al, Surf. Sci. 549 (2004) 67.
.
Zr
Ads.complex
Hf
First-principles modeling of deposition reactions
Quantum chemical simulation of Al(CH3)3 (TMA) and H2O
precursor interactions with Al2O3 surface
Y. Widjaja, C.B. Musgrave, Appl. Phys. Lett., 80,3304 (2002)
Estimation of kinetic parameters for thin film deposition
Energy profiles of the most important gas-surface reactions
ZrCl4+Zr(OH)2/s/ пѓћ Zr(OH)OZrCl3/s/+HCl
H2O+ZrCl2/s/ пѓћZrCl(OH)/s/+HCl
direct reaction
direct reaction
ZrCl4
HCl
decay to products
Zr(OH)2/s/
H2O
ZrCl(OH)/s/
Loose TS
ZrCl2/s/
Rigid TS
HCl
Zr(OH)OZrCl3/s/
ZrCl4-Zr(OH)2/s/
H2O-ZrCl2/s/
Estimation of kinetic parameters for thin film deposition
Equilibrium or Dynamics?
ZrCl
4
ZrCl
4
Zr(OH)
2/s/ /s/
Zr(OH)
2
пЃґchem
пЃґchem>> пЃґrelax
ZrCl4-Zr(OH)2/s/
ZrCl4+Zr(OH)2/s/
Zr(OH)OZrCl3/s/+HCl
HCl
Zr(OH)OZrCl3/s/
ZrCl4-Zr(OH)2/s/
Bulk
Estimation of kinetic parameters for thin film deposition
Transitional State Theory Evaluation of Reaction Rate Constants
Decomposition of the surface
complex over the potential barrier.
Decomposition of the surface complex
without the potential barrier
Transition complex is rigid.
The structure is provided by the
QC calculations.
QC calculations are not sufficient to determine
the structure of the loose transition complex.
Canonical variation transition state theory was used
to calculate rate constants.
Standard transition theory was used
to calculate rate constants
Canonical variation transition state theory was used
to calculate rate constants.
Reaction
adsorption
ka, cm3/mole s
desorbtion
kd, s–1
decay to products
kf, s–1
Zr(OH)4/s/+ZrCl4 Zr(OH)4–ZrCl4/s/
Zr(OH)3-OZrCl3/s/ + HCl.
3.3п‚ґ1012 + 1.5п‚ґ1010
T
1013.6 exp(–11623/T)
4.31010 T0.4exp(–
8258/T)
Zr(OH)2Cl2/s/+ H2O [Zr(OH)2Cl2H2O] ZrCl(OH)3/s/ + HCl.
2.7п‚ґ1013 + 1.7п‚ґ1011
T
1013.6 exp(–7570/T)
1013.8 exp(–9452/T)
Hf(OH)4/s+HfCl4 Hf(OH)4–HfCl4/s/
Hf(OH)3-OHfCl3/s/ + HCl.
6.8п‚ґ1012 + 2.6п‚ґ1010
T
1013.5exp(–5962/T)
8.11010T0.2exp(–
7352/T)
1013.8 exp(–8323/T)
1013.9exp(–7515/T)
Hf(OH)2Cl2/s + H2O [Hf(OH)2Cl2H2O] HfCl(OH)3/s/ + HCl.
2.8п‚ґ1013 +
1.35п‚ґ1011 T
Development of kinetic mechanism
Calculation of reaction constants using CARAT
Calculation of the rate
constant for the reaction
Zr(OH) + ZrCl4 in the
framework of the CARAT
module. The parameters of
the reaction, reactants, and
result: dependence of the
reaction rate on temperature.
Reactor scale modeling of thin film deposition
ZrCl4 effusion cell
T=600 0C
ZrCl4 + N2 flow
ZrCl4+Zr(OH)2/s/ пѓћ
Zr(OH)OZrCl3/s/+HCl
H2O+ZrCl2/s/ пѓћZrCl(OH)/s/+HCl
…
H 2O+ N2 flow
H2O effusion cell
T=100 0C
ALD (atomic layer
deposition)
Reactor
T=200..800 0C
Kinetic mechanism generation for thin film deposition
Kinetic mechanism for ZrO2 film deposition for CWB code
List of gas-surface reactions for description of film growth in ALD reactor.
Reactor scale modeling of thin film deposition
Macro-scale simulation of ZrO2 film ALD process
Variation of the film mass
increment during one ALD
cycle
Experimental results from
J. Aarik et al. / Thin Solid
Films 408 (2002) 97.
M.Deminsky et al, Surf. Sci. 549 (2004) 67.
Improving kinetic parameters
1.00
Hydrohylation degree,пЃў
Mass,thickness increment per cycle, a.u.
Dependence of reaction kinetic parameters on local
environment
0.83
0.67
0.50
0.33
0.17
0.00
100
200
300
400
0
500
600
T, C
Ea=25 kcal/mole;
Ea=35 kcal/mole;
Ea=45 kcal/mole;
normalized thickness;
normalized mass
Experimental data on
temperature dependence
of film growth rate can
not be fitted with given
mechanism.
The smooth experimental
temperature dependence
can be explained by
dependence of water
desorption energy from
MO2 surface on the
surface hydroxylation
degree.
Improving kinetic parameters
Quantum chemical simulation of local effects forwater
adsorption on the Zr(Hf)O2 surface
Dependence of water adsorption energy on the t-Zr(Hf)O2
(001) surface hydroxylation from DFT calculations
Surface
50% surface hydroxylation
25% surface hydroxylation
25%
50%
75%
100%
t-001
Z rO 2
D issociative
131
170(159)
111(98)
91(81)
M olecular
100
94
73
42
t-101
Z rO 2
D issociative
m -001
Z rO 2
D issociative
m -001
H fO 2
D issociative
M olecular
M olecular
M olecular
-
123
81
165(166)
90(110)
150(168)
107(124)
-
44
28
109(103)
65
91(112)
-
I. Iskandarova et al, Microelectron. Eng. 69 (2003)
587.
Reactor scale modeling of thin film deposition
Temperature dependence of ZrO2 and HfO2 film growth rate
Relative increment of ZrO2 film mass and
thickness per cycle as a function of the
process temperature
J. Aarik et al. / Thin Solid
Films 408 (2002) 97.
Relative increment of HfO2 film mass and
thickness per cycle as a function of the
process temperature
J. Aarik et al,Thin Solid Films
340 (1999) 110.
Reactor scale modeling of thin film deposition
Sensitivity analysis of kinetic mechanism of ZrO2 and HfO2 film growth
Thikness, mass increment per cycle, a.u.
1.0
0.8
0.6
thikness increment, exp.
mass increment, exp.
calc. by minimal mechanism
calc. by extended mechanism
dashed area- parameters variation for extended mechanism
0.4
0
100
200
300
400
500
600
T,C
Relative increment of ZrO2 film mass and
thickness per cycle as a function of the
process temperature
Thikness, mass increment per cycle, a.u.
1.2
1.2
1.0
0.8
0.6
thikness increment, exp.
mass increment, exp.
calc. by minimal mechanism
0.4
calc. by extended mechanism
dashed area- parameters variation for extended mechanism
0
100
200
300
400
500
600
T, C
Relative increment of HfO2 film mass and
thickness per cycle as a function of the
process temperature
The dashed areas correspond to the variation of the pre-exponential factors by one order of magnitude and the variation
of the activation energies of dehydroxylation reactions over the range В±3 kcal/mole.
Reactor scale modeling of thin film deposition
Growth rate, Coverage, a.u
Simulation of Al2O3 film growth rate from TMA and H2O
simulation results sensitivity
growth rate, experiment
AlOH covergae, experiment
AlCH covergae, experiment
growth rate, simulation
OH covergae, simulation
1.5
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
Low temperature
reduction of film growth
rate is reproduced
correctly using derived
kinetic mechanism.
300
400
500
600
Temperature, K
700
800
The dashed areas correspond to the
variation of the pre-exponential
factors by one order of magnitude and
the variation of the activation energies
of dehydroxylation reactions over the
range В±3 kcal/mole.
Reactor scale modeling of thin film deposition
Low temperature reduction of film growth rate
At low temperatures ALD precursors
are trapped in stable adsorption
complex and do not react. This
results in reduction of film growth
rate in ALD process.
ZrCl4
decay to products
Zr(OH)2/s/
HCl
Zr(OH)OZrCl3/s/
ZrCl4-Zr(OH)2/s/
Precursors with smaller deep of
potential well are required, e.g.
alkylamide Hf[N(CH3)2]4 (Musgrave
et al, MRS 2005), or plasma assisted
ALD (e.g. O3 instead of H2O).
Residual Impurities in deposited ALD film
Cl impurity in ZrO2 film
Probability of Cl atom to survive
1 ALD
cycle
2 ALD
cycle
3 ALD
cycle
Pn пЂЅ exp( пЂ­ пЃ®пЃґ
P пЂЅ P0
pulse
)
пЃ® пЂЅ k ( H 2O ) * [ H 2O ]
P пЂЅ P0 P1
Since steady-state film
growth rate is ~ 0.4
layer/cycle several ALD
cycles are required to
capture chlorine atom
P пЂЅ P0 P1 P2 => Residual chlorine
concentration should be
quite small
N ALD
cycle
P пЂЅ P0 P1 пЃ‹ Pn
=>
пЃ® пЂЅ пЃ® 0 exp( пЂ­пЃЎ пѓ— Nneib ( Zr ))
Residual Impurities in deposited ALD film
Lattice kinetic Monte Carlo modeling of ZrO2 film composition
Chemical mechanism in lattice model:
At each time step
one and only one
chemical reaction is
chosen based on it
rate and total rate of
all chemical
reactionsr l
pk пЂЅ
l
1.
2.
3.
Adsorption of MCl4 groups
Hydrolysis of M-Cl groups
Surface and bulk diffusion
k
r
i
i
j
j
Lattice kinetic Monte
Carlo model
Cl
O
Residual Impurities in deposited ALD film
Lattice kinetic Monte Carlo modeling of ZrO2 film composition
Lattice kinetic Monte Carlo model :
Temperature dependence of chlorine
atoms concentration in zirconia film
Cl
H
O
Zr
Chlorine concentration, %
3
2.5
2
1.5
1
0.5
0
150
200
250
300
350
Temperature, C
[Cl] lkMC
[Cl] exper
400
450
Roughness of ALD films
1.
Steric hindrance of metal
precursors;
2.
Small concentration of the active
sites for adsorption
(dehydroxylation of the surface).
How submonolayer coverage
influence on the film roughness?
Sub-monolayer coverage can result in increasing of
roughness of ALD films and non-uniform coverage.
ALD cycles
ALD is not atomic layer
deposition, it is sub-monolayer
deposition due to:
Diffusion of precursors on the surface
Ea = 15 kcal/mol
H
O
Zr
I
H diffusion
Ea = 20 kcal/mol
H
II
I
O
II
Zr
H atom on the ideal surface
Additional O atom on the surface
Diffusion of precursors on the surface
Initial
Zr
HfCl4 diffusion
Final
Zr
HfCl4 molecule
on the fully
hydroxylated
surface
Diffusion of precursors on the surface
Summary of precursor diffusion properties
пЃ±Diffusion of
H atoms is rather rapid
пЃ±Diffusion of
OH groups over t- and m-MO2(001) surfaces is
very slow
пЃ±Diffusion of
HfCl4 molecules over the fully hydroxylated tHfO2(001) surfaces is rapid
пЃ±Diffusion of
пЃ±Diffusion of
HfCl4 molecules over the bare surface is slow
chemically adsorbed HfCl3 molecules over the
bare surface is slow, only local relaxation of HfCl3 molecules
can take place.
Roughness of ALD films
Lattice kinetic Monte Carlo modeling of HfO2 film roughness
10
Roughness in ML
at various temperatures
8
6
Surface profile with local
relaxation at T=100 C
100 C
200 C
300 C
400 C
500 C
600 C
4
2
0
0
10
20
30
40
Film thickness, ML
50
60
Steric hindrance of precursors does not in increasing of film roughness. Only
dehyroxylation of the surface results in growth of film roughness with film thickness.
Roughness of ALD films
Nucleation kinetics of HfO2 on Si, deposited by ALD
OH groups (Si-OH and Hf-OH)
are active sites for film growth
OH OH
OH OH
M.L. Green and M. Alam.
Roughness is mainly due to non-uniform nucleation at surface with low concentration
of active adsorption cites (OH groups).
First-principles modeling of deposition reactions
Quantum chemical simulation of ZrCl4 precursor
interactions with Si(001) surface
(1) Chemisorption of MCl4 (M = Zr, Hf) as inter- and intra-dimer structures on the
hydroxylated oxidized and unoxidized Si(001) surface:
Calculated minimum-energy pathways:
20
15
10
TS2
(Si}-OH
+MCl4
15
5
TS1
0
-5
-10
-15
-20
-25
Ads. complex
{Si}-O-MCl3
oxidized Si(100) surface
-MCl2-
10
-MCl2-
E, kcal/mol
E, kcal/mol
5
TS2
20
hydroxylated unoxidized Si(100) surface
Zr, intra-dimer
Zr, inter-dimer
Hf, intra-dimer
Hf, inter-dimer
(Si}-OH
+MCl4
TS1
0
-5
-10
-15
-20
-25
{Si}-O-MCl3
Ads. complex
Zr, intra-dimer
Zr, inter-dimer
Hf, intra-dimer
Hf, inter-dimer
Conclusions
пЃ± ALD
is a promising tool for deposition of uniform ultra thin
films with atomic scale precision.
пЃ±
Steric hindrance of precursors in a ALD process reduces film
growth rate, but not increase significantly film roughness.
пЃ± Temperature
dependences are generally smooth due to
dependence of rate constants on local chemical environment.
пЃ±Low
temperature growth is restricted by formation of stable
intermediate complex.
пЃ±
More reactive precursors are needed to reduce temperature of
an ALD process – plasma enhanced ALD can be used.
пЃ±
Nucleation of the film determines mainly film roughness.
Acknowledgements
•
•
•
•
•
•
•
•
•
•
Boris Potapkin
Alexander Bagatur’yants
Elena Rykova
Alexey Gavrikov
Andrey Knizhnik
Maxim Deminsky
Ilya Polishchuk
Mikhail Nechaev
Inna Iskandarova
Elena Shulakova
•Vladimir Brodskii
•Stanislav Umanskii
•Andrey Safonov
•Dima Bazhanov
•Ivan Belov
•Ilya Mutigullin
•Anton Arkhipov
•Evgeni Burovski
•Maxim Miterev
•
•
•
•
•
•
Anatoli Korkin
Ed Hall
Marius Orlovski
Matthew Stoker
Leonardo Fonseca
Jamie Schaeffer
• Bill Johnson
• Phil Tobin
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