Transcript Why high-k oxides

Development of Multi-scale
Methodology of High-k oxides
Growth
1
Outline
PART 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
2
PART 1
Introduction and context
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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…)
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Cfontexte: Croissance d’oxyde à fortes permitivité (high-k)
Miniaturisation
Nanotechnologie
Nouvelles filières
Nouveaux matériaux
Enjeu majeur de la modélisation et de la simulation:
Simulation des structures d’interfaces
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Why high-k oxides ?

MOSFET evolution: “scaling”
ITRS 2004
Production
year
Intel Corp.
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
Enjeu majeur de la modélisation et de la simulation:
Simulation des structures d’interfaces
5
Why high-k oxides ?

To extend Moore’s Law
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
C 
k  0S
t
Intel Corp.
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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
7
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.
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Oxydes de grille : Stratégie
L’ALD implique des systèmes à états multiples, hors équilibre, des dynamiques non
linéaires (par bifurcations). La complexité du problème exige une stratégie multiéchelle.
Nanoscopique
Mesoscopique
Macroscopique
Ab initio / DFT / DM
MCC
Expérimentation
Dizaines d’atomes
Plusieurs millions d’atomes
Morphologie, Composition
Taux de croissance…
Expérimentation
Technologie…
Mécanismes réactionnels
structures géométriques &
électroniques…
Notre but : la description des mécanismes physico-chimiques principaux aux
échèles nano et meso du dépôt par ALD
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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
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Apport de la Modélisation depuis 2002

Les groupes OH sont considérés les sites actifs principaux de la surface (exp.)
Mécanismes de base :
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Addition des ligands à la surface – Musgrave, Elliott, Gavartin, Raghavachari, Jeloaica
Echange des ligands avec la surface – Musgrave, Jeloaica, Dkhissi
Hydrolyse – Musgrave, Elliott, Jeloaica, Dkhissi
Effets de coopérativité – Jeloaica, Dkhissi
Contamination/Diffusion (Cl, C, N, H…) - Musgrave, Jeloaica, Dkhissi (non publié)
Diffusion de l’Oxygène dans le substrat – non publié
DFT : elementary mechanisms
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Single bond on SiO2
- Incorporation is an endothermic reaction
- HCl stays on the surface => purge phase
{SiO2}-OH + HfCl4  {SiO2}-O-HfCl3 + HCl
Initial reaction pathway and associated barriers in the case of Hf-based
precursor exposure on SiO2/Si(100)
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DFT : elementary mechanisms

Double bond on SiO2
{SiO2}-(OH)2 + HfCl4  {SiO2}-O2-HfCl2 + 2HCl,
0,29eV
0.17
0,23eV
0,12eV
0.53
0,02eV
0.50
-0,25eV
0.52
0.15
-0,40eV
-0,50eV
- Desorption is as favourable as the first bond formation
- Both bond formation are endothermic reaction
- Dense structure of the oxide
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DFT : elementary mechanisms
•
DFT : hydrolyse d'une liaison Hf--Cl
{SiO2}-O-HfCl3 + H2O  {SiO2}-O-HfCl2(OH) + HCl
0.12
0.619
0.916
- 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
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DFT : elementary mechanisms
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Chlore contamination
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DFT : elementary mechanisms
structure
Particle formation: MnO2n
size
A. DKHISSI , [email protected]
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PART 3
Lattice based kinetic Monte-Carlo algorithm (HfO2)
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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:
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Space scale: Crystallographic considerations
≈
≈
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Preliminary considerations:
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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
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Merging different structures into one framework
Conventional HfO2 cell on substrate
Discrete locating model
2D cell
Si (layer k=1)
Hf (k=2 and even layers)
Ionic oxygen (k + 1/2)
Hf (k=3 and odd layers)
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Lattice based model
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Other aspects: strands, contaminants…
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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Lattice based model
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Substrate initialization (example)
Si (100) layer (k=1)
+
User defined OH and
siloxane distributions
(random)
=
Large variety of
available substrates
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Lattice based model
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Zhuravlev model for substrate initialization
From the Monte-Carlo point
of view, OH density is the
percentage of sites that
have an OH
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Temporal dynamics
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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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kMC: Temporal Dynamics
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Events occurrence times calculation
Occurrence time of event « mechanism m on site (i,j,k) » :
T i , j, k , m 
 log  Z 
m
where Z is a random number between 0 and 1
Maxwell-Boltzmann statistics derived
acceptance for arrival mechanisms
(1-precursor and 2-water):
 1, 2 
Cst .P .S
M 1, 2 .T
Arrhenius law derived acceptance with
attempt frequency ν
for all other mechanisms:
m
 E m 

  . exp  

k
T
B


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Temporal dynamics
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Summary: the kinetic Monte-Carlo cycle
Events filtering
Occurrence times
calculation
and comparison
Occurrence of the event of
smallest occurrence time
Atomistic
configuration
change
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Temporal dynamics
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ALD cycle + kMC cycle
As the kMC cycle works, ALD parameters change periodically:
Phase 1 : Precursor Pulse
- duration T1
- temperature Th1
-pressure P1
Phase 4 : Water Purge
- duration T4
- temperature Th4
Phase 2 : Precursor Purge
- duration T2
- temperature Th2
Phase 3 : Water Pulse
- duration T3
- temperature Th3
- pressure P3
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Mechanisms (some examples)
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HfCl4 adsorption (from DFT)
E≠ = 0 eV
ΔE = -0.48 eV
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Mechanisms (some examples)
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Dissociative chemisorption (from DFT)
E≠ = 0.88 eV
ΔE = 0.26 eV
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Mechanisms (some examples)
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Densification mechanisms purpose
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Mechanisms (some examples)
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Densification: interlayer non-cryst./cryst. (from
kMC)
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Mechanisms (some examples)
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Densification: multilayer non-cryst./tree (from
kMC)
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Mechanisms: complete list
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
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MeCl4 adsorption
H2O adsorption
MeCl4 Desorption
HCl Production
H2O Desorption
Hydrolysis
HCl Recombination
HCl Desorption
Dens. Inter_CI_1N_cOH-iOH (all k)
Dens. Inter_CI_1N_cOH-iCl (all k)
Dens. Inter_CI_1N_cCl-iOH (all k)
Dens. Inter_CI_2N_cOH-iOH (all k not2)
Dens. Inter_CI_2N_cOH-iCl (all k not2)
Dens. Inter_CI_2N_cCl-iOH (all k not2)
Dens. Intra_CI_1N_cOH-iOH (k=2)
Dens. Intra_CI_1N_cOH-iCl (k=2)
Dens. Intra_CI_1N_cCl-iOH (k=2)
Dens. Intra_CC_1N_cOH-cOH (k=2)
Dens. Intra_CC_1N_cOH-cCl (k=2)
Dens. Intra_CC_2N_cOH-cOH (k=2)
Dens. Intra_CC_2N_cOH-cCl (k=2)
Dens. Bridge_TI_2N_tOH-iOH (k=2)
Dens. Bridge_TI_2N_tOH-iCl (k=2)
Dens. Bridge_TI_2N_tCl-iOH (k=2)
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33
34
35
36
37
38
39
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Dens. Bridge_TI_3N_tOH-iOH
Dens. Bridge_TI_3N_tOH-iCl
Dens. Bridge_TI_3N_tCl-iOH
Dens. Bridge_TC_3N_tOH-cOH
Dens. Bridge_TC_3N_tOH-cCl
Dens. Bridge_TC_3N_tCl-cOH
Dens. Bridge_TC_4N_tOH-cOH
Dens. Bridge_TC_4N_tOH-cCl
Dens. Bridge_TC_4N_tCl-cOH
Dens. Bridge_TT_3N_tOH-tOH
Dens. Bridge_TT_3N_tOH-tCl
Dens. Bridge_TT_4N_tOH-tOH
Dens. Bridge_TT_4N_tOH-tCl
Dens. Bridge_TT_5N_tOH-tOH
Dens. Bridge_TT_5N_tOH-tCl
Siloxane Bridge Opening
(k=2)
(k=2)
(k=2)
(k=2)
(k=2)
(k=2)
(k=2)
(k=2)
Suggested by…
-DFT studies
-kMC investigation
-Experiments
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PART 4
Exploitation, validation and results
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Hikad simulation platform
ALD first steps
Growth kinetics
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Hikad simulation platform
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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...)
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Batch processing
ALD first steps
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Coverage vs. substrate initialization
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ALD first steps
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Coverage vs. substrate initialization
One precursor pulse phase:
100ms, 1.33mbar, 300°C
Best start substrates: 50% and Random on dimers
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ALD first steps

Early densifications barrier fit
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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ALD first steps
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Coverage vs. Deposition temperature
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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ALD first steps
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Surface saturation
One precursor pulse phase:
1.33mbar, 300°C
Saturation: 48% coverage for a 90ms long pulse
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Growth kinetics
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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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Growth kinetics
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End configuration
-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”)
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Growth kinetics: speeds
Hard to obtain a reliable and stable growth speed because of blocking effect
Steady state regime simulations suffer less
Transient regime
Vt,exp = 7E+13 Hf/cm²/cycle (TXRF)
Steady state regime
Vs,exp = 12E+13 Hf/cm²/cycle (TXRF)
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Amount of deposited Hf atoms
Growth kinetics: conclusions
1st cycle
Fast initial Si-OH
sites saturation
Steady state regime
(Vs>Vt)
Transient regime (Vt)
HfO2 growth onto HfOx(OH)y
(more OH)
“Waiting” for siloxane bridges
openings until full SiO2
coverage.
ALD cycle
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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”
48
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
49
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
50
Chemical structures of PFO, LPPP and PPP
51
Electronic structure of poly(9,9-dioctyfluorene)
in the pristine state
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.
Excellent agreement between theory and experiment
52
Comparison between PFO with PPP and LPPP
Comparison of the He I UPS spectra of PFO with PPP and LPPP:
experimental spectra and theoretical DOVS
VEH theoretical band structures of PFO, LPPP, and PPP .
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Electronic structure of poly(9,9-dioctyfluorene)
in the reduced state
Comparison of the VEH theoretical simulations
with the experimental results
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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