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Development of Multi-scale Methodology of High-k oxides

Growth

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OutlinePART 1:

Introduction and context

PART 2:First principles investigations of possible growth mechanisms

PART 3:

Lattice based kinetic Monte-Carlo algorithm (HfO2)

PART 4:Exploitation, validation and results

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PART 1Introduction 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…)

Cfontexte: Croissance d’oxyde à fortes permitivité (high-k)

Miniaturisation Nanotechnologie

Nouvelles filières

Nouveaux matériaux

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Enjeu majeur de la modélisation et de la simulation:Simulation des structures d’interfaces

Why high-k oxides ?

MOSFET evolution: “scaling”

Production year

Etching width

Gate oxide

thickness

1997 250 nm 4 – 5 nm

1999 180 nm 3 – 4 nm

2001 150 nm 2 – 3 nm

2002 130 nm 2 – 3 nm

2004 90 nm < 1.5 nm

2007 65 nm < 0.9 nm

2010 45 nm < 0.7 nm Intel Corp.

Enjeu majeur de la modélisation et de la simulation:Simulation des structures d’interfaces

ITRS 2004

5

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Problem: high leakage current through the gate.

A solution: use a gate oxide of greater permittivity than SiO2.

Oxide k

SiO2 3,9

Al2O3 ~ 9,8

ZrO2 ~25

HfO2 ~35

0k SC

t

Why high-k oxides ?

To extend Moore’s Law

Intel Corp.

Les oxydes minces 

État actuel: Limite physique de l’oxyde du silicium SiO2

•Oxydes candidats Problèmes spécifiques: Stabilité vis-à-vis du silicium Nature et contrôle de la couche d’interface Stabilité de la microstructure

Mener un travail de recherche en amont

Nouveaux procédés du dépôt

Contrôle à l’échelle nanométrique

Caractérisation structurale et électrique

Coupler: recherches expérimentale & théorique

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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 SiO2 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

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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

(…)

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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.

Oxydes de grille : Oxydes de grille : StratégieStratégie

Notre but : la description des mécanismes physico-chimiques principaux aux échèles nano et meso du dépôt par ALD

Plusieurs millions d’atomes

NanoscopiqueAb initio / DFT / DM

MesoscopiqueMCC

MacroscopiqueExpérimentation

Morphologie, Composition Taux de croissance…

Expérimentation Technologie…

Mécanismes réactionnels structures géométriques &

électroniques…

Dizaines d’atomes

L’ALD implique des systèmes à états multiples, hors équilibre, des dynamiques non linéaires (par bifurcations). La complexité du problème exige une stratégie multi-échelle.

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PART 2

Ab initio Calculations of reaction paths during the initial stage of ALD growth of HfO2

Approach: cluster-based DFT

*Reactions between the precursors and hydroxylated surface:

1) Decomposition of HfCl4 on the surface

2) Hydrolysis

*Particle formation and Chlore Contamination mechanisms

Apport de la Modélisation depuis 2002Apport de la Modélisation depuis 2002

Mécanismes de base :Mécanismes de base :

Addition des ligands à la surface – Addition des ligands à la surface – Musgrave, Musgrave, Elliott, Gavartin,Elliott, Gavartin, Raghavachari, JRaghavachari, Jeloaicaeloaica Echange des ligands avec la surface – Echange des ligands avec la surface – Musgrave, Jeloaica, DkhissiMusgrave, Jeloaica, Dkhissi Hydrolyse – Hydrolyse – Musgrave, Musgrave, Elliott, Jeloaica, DkhissiElliott, Jeloaica, Dkhissi Effets de coopérativité – Jeloaica, Effets de coopérativité – Jeloaica, DkhissiDkhissi Contamination/Diffusion (Cl, C, N, H…) - Contamination/Diffusion (Cl, C, N, H…) - Musgrave, Jeloaica, Dkhissi (non publié)Musgrave, Jeloaica, Dkhissi (non publié) Diffusion de l’Oxygène dans le substrat – Diffusion de l’Oxygène dans le substrat – non publiénon 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.)

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DFT : elementary mechanisms Single bond on SiO2

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{SiO2}-OH + HfCl4 {SiO2}-O-HfCl3 + HCl

- Desorption is as favourable as the first bond formation - Both bond formation are endothermic reaction- Dense structure of the oxide

{SiO2}-(OH)2 + HfCl4 {SiO2}-O2-HfCl2 + 2HCl,

0.50

0.53

0.150.52

0.17

0,02eV

-0,40eV

-0,25eV

0,23eV0,12eV

-0,50eV

0,29eV

DFT : elementary mechanisms Double bond on SiO2

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• DFT : hydrolyse d'une liaison Hf--ClDFT : hydrolyse d'une liaison Hf--Cl

0.619

0.12

0.916

{SiO2}-O-HfCl3 + H2O {SiO2}-O-HfCl2(OH) + HCl

- La désorption de l'eau est plus favorable que hydrolyse

- Hydrolyse est une réaction endothermique

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DFT : elementary mechanisms

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Hydrolysis, solvatation effect

DFT : elementary mechanisms

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DFT : elementary mechanisms Chlore contamination

A. DKHISSI , Adkissi@laas.fr

size

stru

cture

Particle formation: MParticle formation: MnnOO22nn

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DFT : elementary mechanisms

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PART 3

Lattice based kinetic Monte-Carlo algorithm (HfO2)

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

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Preliminary considerations:

Space scale: Crystallographic considerations

≈ ≈

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Preliminary considerations:

Time scale: simulation algorithm choice

TIME CONTINUOUS KINETIC MONTE-CARLO

Attainable phenomenon duration: second

Realistic evolution

Monte-Carlo steps have time meaning

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Lattice based model Merging different structures into one framework

Conventional HfO2 cell on substrate Discrete 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

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Other aspects: strands, contaminants…

Lattice based model

Example: non-crystalline HfCl3 group, bound to the substrate via one oxygen atom. Non-crystalline aspects:

-Non-crystalline Hf

-Non-crystalline O

-OH strands

-Cl strands

-HCl contamination

-H2O

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Substrate initialization (example)

Lattice based model

Si (100) layer (k=1)

+

User defined OH and siloxane distributions

(random)

=

Large variety of available substrates

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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

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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”)

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m

m,k,j,i

ZlogT

where Z is a random number between 0 and 1

Tk

Eexp.

B

mm

Maxwell-Boltzmann statistics derivedacceptance for arrival mechanisms

(1-precursor and 2-water):

T.M

S.P.Cst

2,1

2,1

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:

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Summary: the kinetic Monte-Carlo cycle

Occurrence timescalculation

and comparison

Atomisticconfiguration

change

Events filtering

Occurrence of the event of smallest occurrence time

Temporal dynamics

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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

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Mechanisms (some examples) HfCl4 adsorption (from DFT)

E≠ = 0 eV

ΔE = -0.48 eV

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Mechanisms (some examples) Dissociative chemisorption (from DFT)

E≠ = 0.88 eV

ΔE = 0.26 eV

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Mechanisms (some examples) Densification mechanisms purpose

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

kMC)

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

kMC)

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Mechanisms: complete list01 MeCl4 adsorption02 H2O adsorption03 MeCl4 Desorption04 HCl Production05 H2O Desorption06 Hydrolysis07 HCl Recombination08 HCl Desorption09 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-cOH32 Dens. Bridge_TC_4N_tOH-cCl33 Dens. Bridge_TC_4N_tCl-cOH34 Dens. Bridge_TT_3N_tOH-tOH (k=2)35 Dens. Bridge_TT_3N_tOH-tCl (k=2)36 Dens. Bridge_TT_4N_tOH-tOH37 Dens. Bridge_TT_4N_tOH-tCl38 Dens. Bridge_TT_5N_tOH-tOH39 Dens. Bridge_TT_5N_tOH-tCl40 Siloxane Bridge Opening

Suggested by…-DFT studies-kMC investigation-Experiments

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PART 4

Exploitation, validation and results

Hikad simulation platform ALD first steps Growth kinetics

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Hikad simulation platform Main features• HfO2, ZrO2 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 1015 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

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ALD first steps Coverage vs. substrate initialization

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Coverage vs. substrate initialization

ALD first steps

One precursor pulse phase:100ms, 1.33mbar, 300°C

Best start substrates: 50% and Random on dimers

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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

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Coverage vs. Deposition temperature

ALD first steps

Precursor pulse phase:50ms, 1.33mbar + purge

-Low temperatures: chemisorptions can’t occur-High temperatures: poor OH density=> Optimal temperature: 300°C

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Surface saturation

ALD first steps

One precursor pulse phase:1.33mbar, 300°C

Saturation: 48% coverage for a 90ms long pulse

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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

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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”)

Growth kinetics: speeds

Transient regime Steady state regime

Vt,exp = 7E+13 Hf/cm²/cycle (TXRF) Vs,exp = 12E+13 Hf/cm²/cycle (TXRF)

Hard to obtain a reliable and stable growth speed because of blocking effectSteady state regime simulations suffer less

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Growth kinetics: conclusions

ALD cycle

Transient regime (Vt)

“Waiting” for siloxane bridges openings until full SiO2

coverage.

Steady state regime (Vs>Vt)

HfO2 growth onto HfOx(OH)y (more OH)

Am

ount

of

depo

site

d H

f at

oms

1st cycle

Fast initial Si-OH sites saturation

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Conclusion

Original methodology:- Multi-scale strategy- First predictive tool at these space and time scales for high-k oxides growth

- Generic method: MeO2 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”

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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

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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

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Chemical structures of PFO, LPPP and PPP

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.

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Excellent agreement between theory and experiment

Electronic structure of poly(9,9-dioctyfluorene) in the pristine state

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

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Comparison between PFO with PPP and LPPP

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Comparison of the VEH theoretical simulations with the experimental results

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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.