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Computational Materials Science: Multiscale Modeling of Atomic Layer Deposition of Thin Films Andrey Knizhnik Kinetic T

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.

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Computational Materials Science: Multiscale Modeling of Atomic Layer Deposition of Thin Films Andrey Knizhnik Kinetic T

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  1. Computational Materials Science: Multiscale Modeling of Atomic Layer Deposition of Thin Films Andrey Knizhnik Kinetic Technologies Ltd, Moscow RRC “Kurchatov Institute”, Moscow

  2. 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  Atomic layer deposition (ALD), SuntolaT 1989Mater. Sci. Rep. 4261

  3. Principles of ALD technique Self-termination of adsorption provides atomic scale control of the film thickness and ensures uniform coverage.

  4. Application of ALD technique New MOSFET structure High-k dielectric Gate Source Drain Si Low leakage current High leakage current Application of ALD for deposition of high-k metal oxide films in microelectronics ZrO2, HfO2, Al2O3, La2O3, etc • 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 Experiment (ZrO2 ALCVD)

  5. 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

  6. 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 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. Maximum surface coverage is 0.25 ML/ALD cycle. M. Ililammi, Thin solid Films 279 (1996) 124.

  7. Maximum film growth rate of ALD technique Quantum chemical calculations of precursor on the surface 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. 0.25 ML 0.5 ML Iskandarova, et al, SPIE, 2003

  8. Multiscale modeling of thin film deposition Construction of chemical mechanism of film growth from first-principles data Simulation of film growth by reactor model 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 Comparison with experimental data Fitting of rate parameters

  9. 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 (2) Chemisorption of MCl4 (M = Zr, Hf) on the hydroxylated MO2 surface: (model gas-phase reaction) Minimum-energy pathway ZrCl4 M.Deminsky, A. Knizhnik et al, Surf. Sci. 549 (2004) 67. .

  10. 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)

  11. Estimation of kinetic parameters for thin film deposition ZrCl4 decay to products Zr(OH)2/s/ desorption adsorption HCl Zr(OH)OZrCl3/s/ ZrCl4-Zr(OH)2/s/ Energy profiles of the most important gas-surface reactions ZrCl4+Zr(OH)2/s/  Zr(OH)OZrCl3/s/+HCl H2O+ZrCl2/s/ ZrCl(OH)/s/+HCl direct reaction direct reaction HCl decay to products H2O ZrCl(OH)/s/ Loose TS desorption ZrCl2/s/ adsorption Rigid TS H2O-ZrCl2/s/

  12. Estimation of kinetic parameters for thin film deposition Equilibrium or Dynamics? ZrCl4 ZrCl4 chem chem>> relax Zr(OH)2/s/ Zr(OH)2/s/ ZrCl4-Zr(OH)2/s/ ZrCl4+Zr(OH)2/s/ Zr(OH)OZrCl3/s/+HCl relax HCl desorption adsorption decay to products Zr(OH)OZrCl3/s/ ZrCl4-Zr(OH)2/s/ Bulk

  13. 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 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. Transition complex is rigid. The structure is provided by the QC calculations. Canonical variation transition state theory was used to calculate rate constants. Standard transition theory was used to calculate rate constants

  14. Development of kinetic mechanism Calculation of reaction constants using CARAT Calculation of the rate constant forthe reaction Zr(OH) + ZrCl4in the framework of the CARAT module. The parametersof the reaction, reactants, and result: dependence of the reaction rate on temperature.

  15. Reactor scale modeling of thin film deposition ZrCl4 effusion cell T=600 0C ZrCl4 + N2 flow ALD (atomic layer deposition) Reactor T=200..800 0C ZrCl4+Zr(OH)2/s/  Zr(OH)OZrCl3/s/+HCl H2O+ZrCl2/s/ ZrCl(OH)/s/+HCl … H 2O+ N2 flow H2O effusion cell T=100 0C

  16. 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.

  17. 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.

  18. Improving 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.

  19. 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 50% surface hydroxylation I. Iskandarova et al, Microelectron.Eng. 69 (2003) 587. 25% surface hydroxylation

  20. Reactor scale modeling of thin film deposition Temperature dependence of ZrO2 and HfO2 film growth rate Relative increment of HfO2 film mass and thickness per cycle as a function of the process temperature 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. J. Aarik et al,Thin Solid Films 340 (1999) 110.

  21. Reactor scale modeling of thin film deposition Sensitivity analysis of kinetic mechanism of ZrO2 and HfO2 film growth Relative increment of HfO2 film mass and thickness per cycle as a function of the process temperature Relative increment of ZrO2 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 ±3 kcal/mole.

  22. Reactor scale modeling of thin film deposition 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.

  23. Reactor scale modeling of thin film deposition ZrCl4 decay to products Zr(OH)2/s/ desorption adsorption HCl Zr(OH)OZrCl3/s/ ZrCl4-Zr(OH)2/s/ 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).

  24. Residual Impurities in deposited ALD film Cl impurity in ZrO2 film Probability of Cl atom to survive: 1 ALD cycle 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 2 ALD cycle 3 ALD cycle N ALD cycle =>

  25. At each time step one and only one chemical reaction is chosen based on it rate and total rate of all chemical reactions Residual Impurities in deposited ALD film Lattice kinetic Monte Carlo modeling of ZrO2 film composition • Chemical mechanism in lattice model: • Adsorption of MCl4 groups • Hydrolysis of M-Cl groups • Surface and bulk diffusion Cl O Lattice kinetic Monte Carlo model

  26. Residual Impurities in deposited ALD film Cl H O Zr Lattice kinetic Monte Carlo modeling of ZrO2 film composition Lattice kinetic Monte Carlo model : Temperature dependence of chlorine atoms concentration in zirconia film

  27. Roughness of ALD films ALD cycles • ALD is not atomic layer deposition, it is sub-monolayer deposition due to: • Steric hindrance of metal precursors; • 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.

  28. Diffusion of precursors on the surface Ea = 15 kcal/mol Ea = 20 kcal/mol I II I II Additional O atom on the surface H atom on the ideal surface H diffusion H H O Zr O Zr

  29. Diffusion of precursors on the surface Final Initial HfCl4 diffusion Zr Zr HfCl4 molecule on the fully hydroxylated surface

  30. Diffusion of precursors on the surface Summary of precursor diffusion properties • 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.

  31. [1]Ref. [5] gives an unreasonable value of the threshold (more than 90 kcal/mol), which we think is in error. Instead, we use the difference between initial and final state (17 – 26 kcal/mol), like our lowest estimation. [2]Formally this reaction describes the formation of a bulk phase. But the formula AlO(OH)2(S) presumes that the surface complex still consists of AlO and 2(OH), so that this “virtual reaction” was introduced in order to have formation of a bulk phase in the model. To avoid any effect on the overall mechanism rate, we assumed the largest possible rate coefficient for this reaction. [i] HIKE deliverable D3.1 (Oct 2002). Roughness of ALD films Reaction Rate constant k(T)=A*Tn*exp(-EA/RT source A n EA. -covrage 12 Al(CH3)3+ –OH/s/ –OH–Al(CH3)3/s/ 1.610-11 cm3/s 0 0 [6],[5] 13 –OH–Al(CH3)3/s/Al(CH3)3+–OH/s/ 3.11013 0 13.9 [6],[5] 14 –OH–Al(CH3)3/s/–AlO–(CH3)2/s/+CH4 51011 1/s 0 11.94 [[i]],[6] 15 –OAl(CH3)2/s/+CH4–OH–Al(CH3)3/s/ 1.610-11 cm3/s 0 67.0 [11] 16 –OAl (CH3)2/s/+–OH/s/–O2–AlCH3/s/+CH4 0.01 cm2/s 0 18 [6],[5][1] 17 –AlO2–CH3/s/+CH4OAl(CH3)2/s/+–OH/s/ 10-13 cm3/s 0 25.0 [6],[5] 18 –AlO–(CH3)2/s/+H2O–AlO–H2O–(CH3)2/s/ 1.610-10 cm3/s 0 0 [6],[5] 19 –AlO–H2O–(CH3)2/s/–AlO–(CH3)2/s/+H2O 1014 1/s 0 13.0 [6],[5] 20 –AlO–H2O–(CH3)2/s/–AlO–OH–CH3/S/+CH4 21011 1/s 0 15.0 [6] 21 –AlO–OH–CH3/s/+CH4–AlO–H2O–(CH3)2/s/ 1.610-19 K–3cm3/s 3 36.0 [6] 22 –AlO–OH–CH3/s/+H2O–AlO–OH–CH3–H2O/s/ 1.610-10 cm3/s 0 0 [6],[5] 23 –AlO–OH–CH3–H2O/s/–AlO–OH–CH3/s/+H2O 1014 1/s 0 17.0 [6],[5] 24 –AlO–OH–CH3–H2O/s/–AlO–(OH)2/s/+CH4 21011 1/s 0 15.0 [6],[5] 25 –AlO–(OH)2/s/+CH4–AlO–OH–CH3–H2O/s/ 1.610-19 K–3cm3/s 3 34.0 [6] 26 –AlO–(OH)2/s/–AlO/B/+OH/s/+OH/s/ 1010 1/s 0 0 Est.[2] 27 –AlO2–CH3/s/+H2O–AlO2–CH3H2O/s/ 1.610-10 cm3/s 0 0 [6],[5] 28 –AlO2–CH3–H2O/s/–AlO2–CH3/s/+H2O 1014 1/s 0 17.0 [6],[5] 29 –AlO2–CH3–H2O/s/–AlO2–OH/s/+CH4 21011 1/s 0 17.0 [6] 30 –AlO2–OH/s/+CH4–AlO2–CH3–H2O/s/ 1.610-19K–3cm3/s 3 34.0 [6] 31 –AlO2–OH/s/ –AlO2/B/+OH/s/ 1010 1/s 0 0 Est.2 32 –OH/s/+–OH/s–O/s/+H2O 0.01[6] cm2/s 0 56-38* [6],[12] 33 –O/s/+H2O=>–OH/s/+–OH/s/ 10-11 cm3/s 0 0 [6] Lattice kinetic Monte Carlo modeling of HfO2 film roughness Surface profile with local relaxation at T=100 C 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.

  32. Roughness of ALD films OH groups (Si-OH and Hf-OH) are active sites for film growth OH OH OH OH Nucleation kinetics of HfO2 on Si, deposited by ALD 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).

  33. 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:

  34. Conclusions • 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.

  35. Acknowledgements • Anatoli Korkin • Ed Hall • Marius Orlovski • Matthew Stoker • Leonardo Fonseca • Jamie Schaeffer • Bill Johnson • Phil Tobin • 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

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