Computational Materials Science: Multiscale Modeling of Atomic Layer Deposition of Thin Films...

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.

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

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

HfAds.complex

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.

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

Zr(OH)2/s/

ZrCl4-Zr(OH)2/s/

Zr(OH)OZrCl3/s/

adsorptiondesorption

decay to products

ZrCl2/s/

H2O-ZrCl2/s/

ZrCl(OH)/s/

y to p

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

Zr(OH)2/s/ ZrCl4-Zr(OH)2/s/

Zr(OH)2/s/

Zr(OH)OZrCl3/s/

chem>> relax

ZrCl4+Zr(OH)2/s/ Zr(OH)OZrCl3/s/+HCl

ZrCl4-Zr(OH)2/s/

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

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

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

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

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

165(166)

90(110)

150(168)

107(124)

109(103)

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

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

thikness increment, exp. mass increment, exp. calc. by minimal mechanism calc. by extended mechanism

dashed area- parameters variation for extended mechanismThi

T,C0 100 200 300 400 500 600

thikness increment, exp. mass increment, exp. calc. by minimal mechanism calc. by extended mechanism

dashed area- parameters variation for extended mechanismThi

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

Simulation of Al2O3 film growth rate from TMA and H2O

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.

Zr(OH)2/s/

ZrCl4-Zr(OH)2/s/

Zr(OH)OZrCl3/s/

decay to products

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).

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

Chemical mechanism in lattice model:1. Adsorption of MCl4 groups2. Hydrolysis of M-Cl groups3. Surface and bulk diffusion

Lattice kinetic Monte Carlo model

Lattice kinetic Monte Carlo modeling of ZrO2 film composition

Lattice kinetic Monte Carlo model :Temperature dependence of chlorine atoms concentration in zirconia 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?

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

HfCl4 diffusion

HfCl4 molecule on the fully

hydroxylated surface

Initial Final

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.

Summary of precursor diffusion properties

0 10 20 30 40 50 600

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

Surface profile with local relaxation at T=100 C

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:

Zr, intra-dimerZr, inter-dimerHf, intra-dimerHf, inter-dimer

oxidized Si(100) surface

(Si}-OH +MCl4

Ads. complex

TS2-MCl2-

{Si}-O-MCl3

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

Computational Materials Science: Multiscale Modeling of Atomic Layer Deposition of Thin Films...

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