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1 Development of Multi-scale Methodology of High-k oxides Growth.

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Presentation on theme: "1 Development of Multi-scale Methodology of High-k oxides Growth."— Presentation transcript:

1 1 Development of Multi-scale Methodology of High-k oxides Growth

2 2 Outline PART 1: Introduction and context PART 2: First principles investigations of possible growth mechanisms PART 3: Lattice based kinetic Monte-Carlo algorithm (HfO 2 ) PART 4: Exploitation, validation and results

3 3 PART 1 Introduction and context High-k oxides: Why? How? Methodology: available approaches overview Multi-scale strategy Our goal: first predictive and generic kMC tool for high-k oxides deposition (ALD first steps, kinetics, process optimization…)

4 Cfontexte: Croissance doxyde à fortes permitivité (high-k) MiniaturisationNanotechnologie Nouvelles filières Nouveaux matériaux 4 Enjeu majeur de la modélisation et de la simulation: Simulation des structures dinterfaces

5 Why high-k oxides ? MOSFET evolution: scaling Production year Etching width Gate oxide thickness nm4 – 5 nm nm3 – 4 nm nm2 – 3 nm nm2 – 3 nm nm< 1.5 nm nm< 0.9 nm nm< 0.7 nm Intel Corp. Enjeu majeur de la modélisation et de la simulation: Simulation des structures dinterfaces ITRS

6 6 Problem: high leakage current through the gate. A solution: use a gate oxide of greater permittivity than SiO 2. Oxidek SiO 2 3,9 Al 2 O 3 ~ 9,8 ZrO 2 ~25 HfO 2 ~35 Why high-k oxides ? To extend Moores Law Intel Corp.

7 Les oxydes minces État actuel: Limite physique de loxyde du silicium SiO 2 Oxydes candidats Problèmes spécifiques: Stabilité vis-à-vis du silicium Nature et contrôle de la couche dinterface Stabilité de la microstructure Mener un travail de recherche en amont Nouveaux procédés du dépôt Contrôle à léchelle nanométrique Caractérisation structurale et électrique Coupler: recherches expérimentale & théorique 7

8 8 High-k oxides implementation into microelectronics Materials properties considerations -High permittivity -Sufficient band offset (to minimize leakage) -Low fix charges density (for reliable threshold voltage) -Low interface states density (to keep an acceptable mobility in the channel) -Low dopant diffusivity (to keep them in the electrode or the channel) -Limitation of SiO 2 regrowth (which would reduce the capacitance) -Amorphous phase or at least few grain boundaries (to minimize leakage) Process considerations -Known solution for the gate electrode -High-k oxide deposition process compatibility (with other materials, with industrial needs) -High-k oxide (itself) compatibility with other CMOS processes (e.g. crystallization problems, dopant diffusivity) -Reproducibility -Reliability

9 9 High-k oxides implementation into microelectronics Process choice: Atomic Layer Deposition (ALD) Phase 1 : Precursor pulse Phase 2 : Precursor purge Phase 3 : Water pulse Phase 4 : Water purge (…)

10 10 Methodology: available approaches overview Available experimental data: IR spectroscopy, X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), low energy ion scattering (LEIS)… + Macroscopic simulations: feature scale and reactor scale.

11 Oxydes de grille : Stratégie Notre but : la description des mécanismes physico-chimiques principaux aux échèles nano et meso du dépôt par ALD Plusieurs millions datomes Nanoscopique Ab initio / DFT / DM Mesoscopique MCC Macroscopique Expérimentation Morphologie, Composition Taux de croissance… Expérimentation Technologie… Mécanismes réactionnels structures géométriques & électroniques… Dizaines datomes LALD implique des systèmes à états multiples, hors équilibre, des dynamiques non linéaires (par bifurcations). La complexité du problème exige une stratégie multi- échelle. 11

12 12 PART 2 Ab initio Calculations of reaction paths during the initial stage of ALD growth of HfO 2 Approach: cluster-based DFT *Reactions between the precursors and hydroxylated surface: 1) Decomposition of HfCl 4 on the surface 2) Hydrolysis *Particle formation and Chlore Contamination mechanisms

13 Apport de la Modélisation depuis 2002 Mécanismes de base : Addition des ligands à la surface – Musgrave, Elliott, Gavartin, Raghavachari, J eloaica Addition des ligands à la surface – Musgrave, Elliott, Gavartin, Raghavachari, J eloaica Echange des ligands avec la surface – Musgrave, Jeloaica, Dkhissi Echange des ligands avec la surface – Musgrave, Jeloaica, Dkhissi Hydrolyse – Musgrave, Elliott, Jeloaica, Dkhissi Hydrolyse – Musgrave, Elliott, Jeloaica, Dkhissi Effets de coopérativité – Jeloaica, Dkhissi Effets de coopérativité – Jeloaica, Dkhissi Contamination/Diffusion (Cl, C, N, H…) - Musgrave, Jeloaica, Dkhissi (non publié) Contamination/Diffusion (Cl, C, N, H…) - Musgrave, Jeloaica, Dkhissi (non publié) Diffusion de lOxygène dans le substrat – non publié Diffusion de lOxygène dans le substrat – non publié Les groupes OH sont considérés les sites actifs principaux de la surface (exp.) Les groupes OH sont considérés les sites actifs principaux de la surface (exp.)

14 14 DFT : elementary mechanisms Single bond on SiO 2 Initial reaction pathway and associated barriers in the case of Hf-based precursor exposure on SiO2/Si(100) - Incorporation is an endothermic reaction - HCl stays on the surface => purge phase {SiO 2 }-OH + HfCl 4 {SiO 2 }-O-HfCl 3 + HCl

15 - Desorption is as favourable as the first bond formation - Both bond formation are endothermic reaction - Dense structure of the oxide {SiO 2 }-(OH) 2 + HfCl 4 {SiO 2 }-O 2 -HfCl 2 + 2HCl, ,02eV -0,40eV -0,25eV 0,23eV 0,12eV -0,50eV 0,29eV DFT : elementary mechanisms Double bond on SiO 2 15

16 DFT : hydrolyse d'une liaison Hf--Cl DFT : hydrolyse d'une liaison Hf--Cl {SiO 2 }-O-HfCl 3 + H 2 O {SiO 2 }-O-HfCl 2 (OH) + HCl - La désorption de l'eau est plus favorable que hydrolyse - Hydrolyse est une réaction endothermique 16 DFT : elementary mechanisms

17 17 Hydrolysis, solvatation effect DFT : elementary mechanisms

18 18 DFT : elementary mechanisms Chlore contamination

19 A. DKHISSI, size structure Particle formation: M n O 2n 19 DFT : elementary mechanisms

20 20 PART 3 Lattice based kinetic Monte-Carlo algorithm (HfO 2 ) Preliminary considerations: space and time scales Lattice based model: how the atomistic configuration is described Temporal dynamics: how the atomistic configuration changes Elementary mechanisms: some examples

21 21 Preliminary considerations: Space scale: Crystallographic considerations

22 22 Preliminary considerations: Time scale: simulation algorithm choice TIME CONTINUOUS KINETIC MONTE-CARLO Attainable phenomenon duration: second Realistic evolution Monte-Carlo steps have time meaning

23 23 Lattice based model Merging different structures into one framework Conventional HfO 2 cell on substrateDiscrete locating model Si (layer k=1) Hf (k=2 and even layers) Ionic oxygen (k + 1/2) Hf (k=3 and odd layers) 2D cell

24 24 Other aspects: strands, contaminants… Lattice based model Example: non-crystalline HfCl 3 group, bound to the substrate via one oxygen atom. Non-crystalline aspects: -Non-crystalline Hf -Non-crystalline O -OH strands -Cl strands -HCl contamination -H 2 O

25 25 Substrate initialization (example) Lattice based model Si (100) layer (k=1) + User defined OH and siloxane distributions (random) = Large variety of available substrates

26 26 Zhuravlev model for substrate initialization Lattice based model From the Monte-Carlo point of view, OH density is the percentage of sites that have an OH

27 27 Temporal dynamics Mechanisms and events (definitions) Mechanism = elementary reaction mechanism with associated activation barrier E Site = one cell within the lattice, located by (i,j,k) indexes and containing occupation fields (can be empty) Event = Mechanism + Site, (depending on the local occupation, can be possible or not, thus must be filtered)

28 28 where Z is a random number between 0 and 1 Maxwell-Boltzmann statistics derived acceptance for arrival mechanisms (1-precursor and 2-water): kMC: Temporal Dynamics Events occurrence times calculation Occurrence time of event « mechanism m on site (i,j,k) » : Arrhenius law derived acceptance with attempt frequency ν for all other mechanisms:

29 29 Summary: the kinetic Monte-Carlo cycle Occurrence times calculation and comparison Atomistic configuration change Events filtering Occurrence of the event of smallest occurrence time Temporal dynamics

30 30 ALD cycle + kMC cycle Phase 1 : Precursor Pulse - duration T1 - temperature Th1 -pressure P1 Phase 2 : Precursor Purge - duration T2 - temperature Th2 Phase 3 : Water Pulse - duration T3 - temperature Th3 - pressure P3 Phase 4 : Water Purge - duration T4 - temperature Th4 As the kMC cycle works, ALD parameters change periodically: Temporal dynamics

31 31 Mechanisms (some examples) HfCl 4 adsorption (from DFT) E = 0 eV ΔE = eV

32 32 Mechanisms (some examples) Dissociative chemisorption (from DFT) E = 0.88 eV ΔE = 0.26 eV

33 33 Mechanisms (some examples) Densification mechanisms purpose

34 34 Mechanisms (some examples) Densification: interlayer non-cryst./cryst. (from kMC)

35 35 Mechanisms (some examples) Densification: multilayer non-cryst./tree (from kMC)

36 36 Mechanisms: complete list 01 MeCl4 adsorption 02 H2O adsorption 03 MeCl4 Desorption 04 HCl Production 05 H2O Desorption 06 Hydrolysis 07 HCl Recombination 08 HCl Desorption 09 Dens. Inter_CI_1N_cOH-iOH (all k) 10 Dens. Inter_CI_1N_cOH-iCl (all k) 11 Dens. Inter_CI_1N_cCl-iOH (all k) 12 Dens. Inter_CI_2N_cOH-iOH (all k not2) 13 Dens. Inter_CI_2N_cOH-iCl (all k not2) 14 Dens. Inter_CI_2N_cCl-iOH (all k not2) 15 Dens. Intra_CI_1N_cOH-iOH (k=2) 16 Dens. Intra_CI_1N_cOH-iCl (k=2) 17 Dens. Intra_CI_1N_cCl-iOH (k=2) 18 Dens. Intra_CC_1N_cOH-cOH (k=2) 19 Dens. Intra_CC_1N_cOH-cCl (k=2) 20 Dens. Intra_CC_2N_cOH-cOH (k=2) 21 Dens. Intra_CC_2N_cOH-cCl (k=2) 22 Dens. Bridge_TI_2N_tOH-iOH (k=2) 23 Dens. Bridge_TI_2N_tOH-iCl (k=2) 24 Dens. Bridge_TI_2N_tCl-iOH (k=2) 25 Dens. Bridge_TI_3N_tOH-iOH (k=2) 26 Dens. Bridge_TI_3N_tOH-iCl (k=2) 27 Dens. Bridge_TI_3N_tCl-iOH (k=2) 28 Dens. Bridge_TC_3N_tOH-cOH (k=2) 29 Dens. Bridge_TC_3N_tOH-cCl (k=2) 30 Dens. Bridge_TC_3N_tCl-cOH (k=2) 31 Dens. Bridge_TC_4N_tOH-cOH 32 Dens. Bridge_TC_4N_tOH-cCl 33 Dens. Bridge_TC_4N_tCl-cOH 34 Dens. Bridge_TT_3N_tOH-tOH (k=2) 35 Dens. Bridge_TT_3N_tOH-tCl (k=2) 36 Dens. Bridge_TT_4N_tOH-tOH 37 Dens. Bridge_TT_4N_tOH-tCl 38 Dens. Bridge_TT_5N_tOH-tOH 39 Dens. Bridge_TT_5N_tOH-tCl 40 Siloxane Bridge Opening Suggested by… -DFT studies -kMC investigation -Experiments

37 37 PART 4 Exploitation, validation and results Hikad simulation platform ALD first steps Growth kinetics

38 38 Hikad simulation platform Main features HfO 2, ZrO 2 and TiO2 ALD ALD thermodynamic parameters (link with experimental data) Start from an existing atomistic configuration file (Recovery option) Initial substrate atomistic configuration customization Feedback options (log file + automatic configuration/graphic files export) Back up option Evolutivity Steric restriction switch (for big precursors) Mechanisms activation energies Performance Huge substrates compared to ab initio or DFT Up to events Improved events filtering (SmartFilter option) Shortcuts method preventing fast flip back events (SmartEvents option) Computation effectiveness analysis Analysis Simulation data analysis, even during simulation job Easy and fast browsing through events using bookmarks (find event, ALD phase, ALD cycle...) Atomistic configuration visualisation using AtomEye Snapshots (jpeg, ps or png formats) Configuration analysis (substrate, coverage, coordination...) Batch processing

39 39 ALD first steps Coverage vs. substrate initialization

40 40 Coverage vs. substrate initialization ALD first steps One precursor pulse phase: 100ms, 1.33mbar, 300°C Best start substrates: 50% and Random on dimers

41 41 Early densifications barrier fit ALD first steps One precursor pulse phase: 90% OH, 200ms, 1.33mbar, 300°C Criteria: 90% OH => 80% coverage (exp.) => Densifications barriers: 1.5 eV

42 42 Coverage vs. Deposition temperature ALD first steps Precursor pulse phase: 50ms, 1.33mbar + purge -Low temperatures: chemisorptions cant occur -High temperatures: poor OH density => Optimal temperature: 300°C

43 43 Surface saturation ALD first steps One precursor pulse phase: 1.33mbar, 300°C Saturation: 48% coverage for a 90ms long pulse

44 44 Growth kinetics Coverage for 10 ALD cycles Pulse phases: 1.33mbar, 300°C + purges Fast first cycle, then slow growth… 73% coverage saturation = simulation artefact

45 45 End configuration Growth kinetics -First layer will never be full nor dense: bridge densifications needed -Hard to achieve 100% substrate coverage, waiting for SiOSi openings -Blocking states are visible (trees)

46 Growth kinetics: speeds Transient regimeSteady state regime V t,exp = 7E+13 Hf/cm²/cycle (TXRF)V s,exp = 12E+13 Hf/cm²/cycle (TXRF) Hard to obtain a reliable and stable growth speed because of blocking effect Steady state regime simulations suffer less 46

47 Growth kinetics: conclusions ALD cycle Transient regime (V t ) Waiting for siloxane bridges openings until full SiO 2 coverage. Steady state regime (V s >V t ) HfO 2 growth onto HfO x (OH) y (more OH) Amount of deposited Hf atoms 1 st cycle Fast initial Si-OH sites saturation 47

48 48 Conclusion Original methodology: - Multi-scale strategy - First predictive tool at these space and time scales for high-k oxides growth - Generic method: MeO 2 oxides (changing barriers), other precursors (using steric restriction switch) Validation and first encouraging results: - Substrate preparation dependence - Optimal growth temperature - Surface saturation - Activation barriers calibration (densifications) - Growth kinetics: hard substrate coverage, but blocking effect

49 49 Perspectives… First: - Reduce blocking effect with new densification mechanisms - Add migration mechanisms, and lateral growth mechanisms to obtain complete substrate coverage and maybe grain boundaries - Study coordination evolution and crystallisation Next: - Simulate thermal annealing (migrations, crystallisation…) - Dopant migration - Standardisation

50 50 Electronic structure of poly(9,9-dioctyfluorene) in the pristine and reduced state The electronic structure of the conjugated polymer poly(9,9-dioctylfluorene) and the charge storage mechanism upon doping with lithium atoms have been studied using a combined experimental-theoretical approach. Experimentally, the density of states in the valence band region was measured using ultraviolet photoelectron spectroscopy, and the spectra interpreted with the help of the results of ab-initio calculations

51 51 Chemical structures of PFO, LPPP and PPP

52 UPS spectra of the valence band region of PFO: The He II radiation (white dots) and synchrotron radiation (black dots) spectra are compared with the theoretical DOVS. The bottom panel shows the corresponding VEH band structure. He UPS spectrum showing the two lowest binding energy features of pristine PFO. 52 Excellent agreement between theory and experiment Electronic structure of poly(9,9-dioctyfluorene) in the pristine state

53 VEH theoretical band structures of PFO, LPPP, and PPP. Comparison of the He I UPS spectra of PFO with PPP and LPPP: experimental spectra and theoretical DOVS 53 Comparison between PFO with PPP and LPPP

54 54

55 Comparison of the VEH theoretical simulations with the experimental results 55 Electronic structure of poly(9,9-dioctyfluorene) in the reduced state UPS spectra illustrating the doping-induced changes in the valence band region of PFO as a function of Li deposition. Starting from the bottom spectrum ~corresponding to the pristine polymer!, succeeding spectra correspond to increases in lithium deposition. The overall changes in the VB region are displayed in the left panel. The right-hand side provides a magnification of the region close to the Fermi energy.


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