computational materials science: multiscale modeling of atomic layer deposition of thin films...
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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. - PowerPoint PPT PresentationTRANSCRIPT
Computational Materials Science: Computational Materials Science: Multiscale Modeling of Atomic Multiscale Modeling of Atomic Layer Deposition of Thin FilmsLayer Deposition of Thin Films
Andrey KnizhnikAndrey KnizhnikKinetic Technologies Ltd, MoscowKinetic Technologies Ltd, Moscow
RRC “Kurchatov Institute”, MoscowRRC “Kurchatov Institute”, Moscow
Challenges for ultra-thin film depositionChallenges for ultra-thin film depositionDeposition of films with atomic scale precision of film thickness
Uniform deposition in high-aspect ratio features
Catalysis
Microelectronics
Nanotechnology
Atomic layer deposition (ALD), Suntola T 1989 Mater. Sci. Rep. 4 261
Principles of ALD techniquePrinciples of ALD technique
Self-termination of adsorption provides atomic scale control of the film thickness and ensures uniform
coverage.
Si
GateSource Drain
New MOSFET structure High-k dielectric
Low leakage current High leakage current
Experiment (ZrO2 ALCVD)
Zr(Hf)O2 deposition from Zr(Hf)Cl4 and H2O:
Zr(OH)/s/ + ZrCl4=ZrOZrCl3/s/ +HCl
ZrCl/s/ + H2O=ZrOH/s/ +HCl
Film properties depend significantly on film deposition conditions Kinetic mechanisms of film growth are required
Application of ALD techniqueApplication of ALD techniqueApplication of ALD for deposition of high-k metal oxide
films in microelectronics
ZrO2, HfO2, Al2O3, La2O3, etc
• 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
Features of ALD techniqueFeatures of ALD technique
Main features of atomic layer deposition
Maximum film growth rate of ALD techniqueMaximum film growth rate of ALD technique
Maximum surface coverage is 0.25 ML/ALD cycle.
M. Ililammi, Thin solid Films 279 (1996) 124.
Geometric considerations on maximum surface coverage
Zr(Hf)O2 deposition from Zr(Hf)Cl4 and H2O.
Repulsion between ligands of metal precursor results in sub-monolayer coverage of the substrate. Experimental maximum film growth rate is about 0.5 ML/ALD cycle for halide precursors and about 0.1 ML/ALD cycle for organometallics.
- not observed
-160
-140
-120
-100
-80
-60
-40
-20
0
20
40
60
80
100
120
gas
Maximum film growth rate of ALD techniqueMaximum film growth rate of ALD technique
Quantum chemical calculations of precursor on the surface
Iskandarova, et al, SPIE, 2003
ZrCl4/g/ + ZrOH/s/ ZrClx/s/ + HCl/g/
Quantum chemical calculation of ZrClx adsorption energy with respect to gaseous species and hydroxylated surface.
HCl/g/ is removed from reactor by purge gas.
Maximum 0.5 ML/ALD cycle can be achieved in agreement with experimental data.
0.5 ML0.25 ML
QC calculations of reaction pathway
Rate coefficients calculation from Statistic Theory
Simulation of film growth by reactor model
Comparison with experimental data
Fitting of rate parameters
Multiscale modeling of thin film depositionMultiscale modeling of thin film depositionConstruction of chemical mechanism of film growth from
first-principles data
•Rate of film growth•Mass increment per pulse•Adsorbed groups at the surface•Concentration of impurities
(1) Hydrolysis of chemisorbed MCl2 groups
.
(2) Chemisorption of MCl4 (M = Zr, Hf) on the hydroxylated MO2 surface: (model gas-phase reaction)
Minimum-energy pathwayMinimum-energy pathway
Minimum-energy pathwayMinimum-energy pathway
-20
-15
-10
-5
0
5
E, k
cal/m
ol
Zr
HfAds.complex
TS
-30
-25
-20
-15
-10
-5
0
E, k
cal/m
ol
ZrHf
TS
Ads.complex
First-principles modeling of deposition reactionsFirst-principles modeling of deposition reactionsQuantum chemical simulation of ZrCl4 and H2O precursor
interactions with ZrO2 surface
M.Deminsky, A. Knizhnik et al, Surf. Sci. 549 (2004) 67.
H2O
ZrCl4
Y. Widjaja, C.B. Musgrave, Appl. Phys. Lett., 80,3304 (2002)
Quantum chemical simulation of Al(CH3)3 (TMA) and H2O precursor interactions with Al2O3 surface
First-principles modeling of deposition reactionsFirst-principles modeling of deposition reactions
ZrCl4+Zr(OH)2/s/ Zr(OH)OZrCl3/s/+HCl H2O+ZrCl2/s/ ZrCl(OH)/s/+HCl
direct reaction direct reaction
ZrCl4
Zr(OH)2/s/
ZrCl4-Zr(OH)2/s/
Zr(OH)OZrCl3/s/
HCl
adsorptiondesorption
decay to products
adsorptiondesorption
H2O
ZrCl2/s/
H2O-ZrCl2/s/
ZrCl(OH)/s/
HCl
deca
y to p
rodu
cts
Energy profiles of the most important gas-surface reactions
Estimation of kinetic parameters for thin film depositionEstimation of kinetic parameters for thin film deposition
Rigid TS
Loose TS
ZrCl4
Zr(OH)2/s/ ZrCl4-Zr(OH)2/s/
Bulk
ZrCl4
Zr(OH)2/s/
Zr(OH)OZrCl3/s/
HCl
chem
rel
ax
chem>> relax
ZrCl4+Zr(OH)2/s/ Zr(OH)OZrCl3/s/+HCl
ZrCl4-Zr(OH)2/s/
adsorptiondesorption
deca
y to
pro
duct
s
Estimation of kinetic parameters for thin film depositionEstimation of kinetic parameters for thin film deposition
Equilibrium or Dynamics?
Decomposition of the surface complex over the potential barrier.
Transition complex is rigid. The structure is provided by the QC calculations.
Decomposition of the surface complex without the potential barrier
QC calculations are not sufficient to determine the structure of the loose transition complex.Canonical variation transition state theory was usedto calculate rate constants.
Reaction adsorptionka, cm3/mole s
desorbtionkd, s–1
decay to productskf, s–1
Zr(OH)4/s/+ZrCl4 Zr(OH)4–ZrCl4/s/ Zr(OH)3-OZrCl3/s/ + HCl.
3.31012 + 1.51010 T
1013.6 exp(–11623/T) 4.31010 T0.4exp(–8258/T)
Zr(OH)2Cl2/s/+ H2O [Zr(OH)2Cl2- H2O] ZrCl(OH)3/s/ + HCl.
2.71013 + 1.71011 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.
6.81012 + 2.61010 T
1013.5exp(–5962/T) 8.11010T0.2exp(–7352/T)
Hf(OH)2Cl2/s + H2O [Hf(OH)2Cl2- H2O] HfCl(OH)3/s/ + HCl.
2.81013 + 1.351011 T
1013.8 exp(–8323/T) 1013.9exp(–7515/T)
Standard transition theory was used to calculate rate constants
Canonical variation transition state theory was usedto calculate rate constants.
Transitional State Theory Evaluation of Reaction Rate Constants
Estimation of kinetic parameters for thin film depositionEstimation of kinetic parameters for thin film deposition
Development of kinetic mechanismDevelopment of kinetic mechanismCalculation 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.
ZrCl4 effusion cellT=600 0C
H2O effusion cellT=100 0C
ZrCl4 + N2 flow
H 2O+ N2 flow
ZrCl4+Zr(OH)2/s/ Zr(OH)OZrCl3/s/+HCl H2O+ZrCl2/s/ ZrCl(OH)/s/+HCl…
ALD (atomic layer deposition)
ReactorT=200..800 0C
Reactor scale modeling of thin film depositionReactor scale modeling of thin film deposition
Kinetic mechanism for ZrO2 film deposition for CWB code
Kinetic mechanism generation for thin film depositionKinetic mechanism generation for thin film deposition
List of gas-surface reactions for description of film growth in ALD reactor.
Macro-scale simulation of ZrO2 film ALD process
Variation of the film mass increment during one ALD
cycle
Reactor scale modeling of thin film depositionReactor scale modeling of thin film deposition
Experimental results from
J. Aarik et al. / Thin Solid Films 408 (2002) 97.M.Deminsky et al, Surf. Sci. 549 (2004) 67.
100 200 300 400 500 600
0.00
0.17
0.33
0.50
0.67
0.83
1.00
Hyd
rohy
latio
n de
gree
,
Mas
s,th
ickn
ess
incr
emen
t per
cyc
le, a
.u.
T, 0C E
a=25 kcal/mole; E
a=35 kcal/mole; E
a=45 kcal/mole;
normalized thickness; normalized mass
Improving kinetic parametersImproving kinetic parameters
Dependence of reaction kinetic parameters on local environment
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.
25% surface hydroxylation
50% surface hydroxylation
Dependence of water adsorption energy on the t-Zr(Hf)O2 (001) surface hydroxylation from DFT
calculations
Quantum chemical simulation of local effects forwater adsorption on the Zr(Hf)O2 surface
I. Iskandarova et al, Microelectron. Eng. 69 (2003) 587.
Surf ace 25% 50% 75% 100%D isso ciative
M o lecular
M o lecular
M o lecular
M o lecular
D isso ciative
D isso ciative
D isso ciative
t- 001Z rO 2
t- 101Z rO 2
m -001Z rO 2
m -001H fO 2
131 170(159) 111(98) 91(81)
100 94
123
81
165(166)
90(110)
150(168)
107(124)
73 42
44
28
109(103)
65
91(112)
-
- -- -- -- -- -- -
Improving kinetic parametersImproving kinetic parameters
Relative increment of ZrO2 film mass and thickness per cycle as a function of the process temperature
Relative increment of HfO2 film mass and thickness per cycle as a function of the process temperature
Reactor scale modeling of thin film depositionReactor scale modeling of thin film deposition
Temperature dependence of ZrO2 and HfO2 film growth rate
J. Aarik et al. / Thin Solid Films 408 (2002) 97.
J. Aarik et al,Thin Solid Films 340 (1999) 110.
Relative increment of ZrO2 film mass and thickness per cycle as a function of the process temperature
Relative increment of HfO2 film mass and thickness per cycle as a function of the process temperature
0 100 200 300 400 500 600
0.4
0.6
0.8
1.0
1.2
thikness increment, exp. mass increment, exp. calc. by minimal mechanism calc. by extended mechanism
dashed area- parameters variation for extended mechanismThi
knes
s, m
ass
incr
emen
t per
cyc
le, a
.u.
T,C0 100 200 300 400 500 600
0.4
0.6
0.8
1.0
1.2
thikness increment, exp. mass increment, exp. calc. by minimal mechanism calc. by extended mechanism
dashed area- parameters variation for extended mechanismThi
knes
s, m
ass
incr
emen
t per
cyc
le, a
.u.
T, C
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 ±3 kcal/mole.
Sensitivity analysis of kinetic mechanism of ZrO2 and HfO2 film growth
Reactor scale modeling of thin film depositionReactor scale modeling of thin film deposition
Simulation of Al2O3 film growth rate from TMA and H2O
Reactor scale modeling of thin film depositionReactor scale modeling of thin film deposition
Low temperature reduction of film growth rate is reproduced correctly using derived kinetic mechanism.
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 ±3 kcal/mole.
ZrCl4
Zr(OH)2/s/
ZrCl4-Zr(OH)2/s/
Zr(OH)OZrCl3/s/
HCl
adsorptiondesorption
decay to products
Reactor scale modeling of thin film depositionReactor 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.
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).
10PPP
0PP
nPPPP 10
1 ALD cycle
2 ALD cycle
3 ALD cycle
N ALD cycle
210 PPPP
)exp( pulsenP ][*)( 22 OHOHk
Since steady-state film growth rate is ~ 0.4 layer/cycle several ALD cycles are required to capture chlorine atom
=> Residual chlorine concentration should be quite small
))(exp(0 ZrNneib =>
Probability of Cl atom to survive:
Cl impurity in ZrO2 film
Residual Impurities in deposited ALD filmResidual Impurities in deposited ALD film
At each time step one and only one chemical reaction is chosen based on it rate and total rate of all chemical reactions
i j
ij
lkl
k rrp
Chemical mechanism in lattice model:1. Adsorption of MCl4 groups2. Hydrolysis of M-Cl groups3. Surface and bulk diffusion
Lattice kinetic Monte Carlo model
ClO
Lattice kinetic Monte Carlo modeling of ZrO2 film composition
Residual Impurities in deposited ALD filmResidual 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
OZr
H
Cl
Residual Impurities in deposited ALD filmResidual Impurities in deposited ALD film
Roughness of ALD filmsRoughness of ALD films
ALD is not atomic layer deposition, it is sub-monolayer deposition due to:
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?
ALD
cycles
Sub-monolayer coverage can result in increasing of roughness of ALD films and non-uniform coverage.
Ea = 15 kcal/mol Ea = 20 kcal/mol
H atom on the ideal surface Additional O atom on the surface
I II I II
Diffusion of precursors on the surfaceDiffusion of precursors on the surface
H diffusionO
ZrO
Zr
H H
HfCl4 diffusion
HfCl4 molecule on the fully
hydroxylated surface
Initial Final
Diffusion of precursors on the surfaceDiffusion of precursors on the surface
Zr Zr
Diffusion of H atoms is rather rapid
Diffusion of OH groups over t- and m-MO2(001) surfaces is very slow
Diffusion of HfCl4 molecules over the fully hydroxylated t-HfO2(001) surfaces is rapid
Diffusion of HfCl4 molecules over the bare surface is slow
Diffusion of chemically adsorbed HfCl3 molecules over the bare surface is slow, only local relaxation of HfCl3 molecules can take place.
Diffusion of precursors on the surfaceDiffusion of precursors on the surface
Summary of precursor diffusion properties
0 10 20 30 40 50 600
2
4
6
8
10
Film thickness, ML
100 C 200 C 300 C 400 C 500 C 600 C
Roughness in MLat various temperatures
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.
Lattice kinetic Monte Carlo modeling of HfO2 film roughness
Roughness of ALD filmsRoughness of ALD films
Surface profile with local relaxation at T=100 C
Roughness of ALD filmsRoughness of ALD films
Roughness is mainly due to non-uniform nucleation at surface with low concentration of active adsorption cites (OH groups).
Nucleation kinetics of HfO2 on Si, deposited by ALD
OH groups (Si-OH and Hf-OH) are active sites for film growth
OH OH OHOH
M.L. Green and M. Alam.
(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:
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-5
0
5
10
15
20
E, k
cal/m
ol
Zr, intra-dimerZr, inter-dimerHf, intra-dimerHf, inter-dimer
oxidized Si(100) surface
(Si}-OH +MCl4
Ads. complex
TS1
TS2-MCl2-
{Si}-O-MCl3
-25
-20
-15
-10
-5
0
5
10
15
20
E, k
cal/m
ol
Zr, intra-dimerZr, inter-dimerHf, intra-dimerHf, inter-dimer
hydroxylated unoxidized Si(100) surface
(Si}-OH +MCl4 TS1
Ads. complex {Si}-O-MCl3
TS2 -MCl2-
First-principles modeling of deposition reactionsFirst-principles modeling of deposition reactionsQuantum chemical simulation of ZrCl4 precursor
interactions with Si(001) surface
ConclusionsConclusions
ALD is a promising tool for deposition of uniform ultra thin films with atomic scale precision.
Steric hindrance of precursors in a ALD process reduces film growth rate, but not increase significantly film roughness.
Temperature dependences are generally smooth due to dependence of rate constants on local chemical environment.
Low temperature growth is restricted by formation of stable intermediate complex.
More reactive precursors are needed to reduce temperature of an ALD process – plasma enhanced ALD can be used.
Nucleation of the film determines mainly film roughness.
AcknowledgementsAcknowledgements
• 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