1
Eric GarfunkelDepartments of Chemistry and PhysicsRutgers UniversityPiscataway, NJ
Key interactions:Gustafsson, Bartynski, Chabal – Rutgers Gennadi Bersuker – Sematech Rich Haight, Supratik Guha – IBM
Other collaborators: M. Green – NIST; E. Gusev - Qualcomm; W. Tsai – Intel; J. Chambers, H. Niimi – TI
Advanced Gate Stacks and Substrate Engineering
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SiO2 Monolayer?
Metal Electrode
High-κ Dielectric
Source DrainPost-Si?
Barrier?
10-20nm
CMOS transistor ~2010?
Goal: develop understanding of interaction of radiation with CMOS materials
2hφ1hφ
2eφ 1eφ
C ∝ Aε/d
EOT - effective oxide thickness
New materials: metal electrodes, high-K dielectrics, semiconducting substrates
Electronic structure, defects, mobility, reliability, failureLook for specific physical and chemical signatures of
radiation induced defects – create atomic picture of defects
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Rutgers CMOS Materials Analysis
Scanning probe microscopy – topography, surface damage, electrical defectsIon scattering: RBS, MEIS, NRA, ERD – composition, crystallinity, depth profiles, H/DDirect, inverse and internal photoemission –electronic structure, band alignment, defectsFTIR, XRD, TEMElectrical – IV, CVGrowth – ALD, CVD, PVD
Use high resolution characterization methods to: i. Determine composition, structure and electronic properties
gate stacks that use new (post-Si) materials ii. Help determine physical and chemical nature of radiation
induced defects
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Results
Generated thin films with high-K dielectrics (HfO2) and metal gate electrodes (Al, Ru).Performed ion scattering, photoemission, internal and inverse photoemission on selected systems.Had samples irradiated by Vanderbilt group (Feldman), as well as at Rutgers.Performed conductive tip SPM measurements of defects on selected systems
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75 80 85 90 95
×5
depth
Zr
SiO
Scat
tere
d Yi
eld
(a.u
.)
Proton Energy (keV)
ZrO2
(ZrO2)x(SiO2)y
Si(100)
~100 keV p+
depth profile
0 10 20 30 40 50 60 700.0
0.5
1.0
1.5
2.0
MEIS depth profiling
Si
ZrO2.04
Zr
O
Con
cent
ratio
n
Depth (Å)
Sensitivity:≈ 10+12 atoms/cm2 (Hf, Zr)≈ 10+14 atoms/cm2 (C, N)Accuracy for determining total amounts:≈ 5% absolute (Hf, Zr, O), ≈ 2% relative≈ 10% absolute (C, N)Depth resolution: (need density)≈ 3 Å near surface≈ 8 Å at depth of 40 Å
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Nitride barrier monolayers to minimize diffusion
• Nitride barrier layers helpful to slow O, Si and dopant diffusion, as well as silicate formation and other interface reactions.
• Nitridation also raises crystallization temperature.
75 80 85 90 950
100
200
300
400
500
600
700
×2
0Å
0ÅN O
Si
Hf
Yie
ldEnergy (keV)
ONitride barrier layers?
Si
SiO2
MOx
Si
0 10 20 30 40 50
0.0
0.2
0.4
0.6
950oC 800oC
700oC610oC
Com
posi
tion
Depth [Å]
as is
500oC
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105 110 115
HfO2
18O
16O
Yie
ld (a
.u.)
H+ energy (keV)
Si
105 110 115
HfO2SiO2
18ON
16O
Yie
ld (a
.u.)
H+ energy (keV)
Si
x = 0% 33% 50%
105 110 115
(HfO2)2SiO2
18ON
16O
Yiel
d (a
.u.)
H+ energy (keV)
Si
HfO2(SiO2)x re-oxidation in 18O: 500°C, 10-2 Torr, 30 min
Isotope reactions and diffusion in silicatesRelation between composition and O incorporation
• strong exchange reaction even at 500°C: 16O loss, with same total O conc.• no change in width of 16O and Si peaks (no formation of interfacial oxide)• exchange rate decreases with increase of SiO2 fraction x• 50:50 mix of SiO2:HfO2 is enough to suppress oxygen exchange (in this case)
Rutgers/Sematech
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Exchange and growth T-dependence
0 500 600 700 800 900 10000
3
6
9
12
Oxy
gen
in H
f sili
cate
laye
r [at
oms/
cm2 ]
Tx [C]
O18 O16 O sum
0 500 600 700 800 900 10000
3
6
9
12
Inte
rfaci
al o
xyge
n co
ncen
tratio
n [a
tom
s/cm
2 ]
Tx [C]
O18 O16 O sum
• Due to exchange reactions, the 18O in (HfO2)2(SiO2) layers increases, 16O decreases, with the total oxygen content constant.
• There is higher 16O density at the interface (16O/18O >1) at Tx=500-700oC (oxygen or vacancy exchange mechanism)
• Interface 16O/18O changes at Tx≥800oC due to (a) higher 18O equilibrium concentration(b) opening of direct paths through (HfO2)2(SiO2)
SiOxNy
Si
(HfO2)2(SiO2)
0.8 1.0 1.20.1
1
10
Inte
rfaci
al O
[x
1015
ato
ms/
cm2 ]
1000/T [K-1]
Hf2SiO6/SiOxNy
SiO2
SiOxNy
Interaction of metal overlayers with dielectric
As-deposited amorphous HfO2 film has small amount of interfacial SiO2 (~6-7Å) and excess of oxygen (~HfO2.07)Deposited Ti forms uniform layer, no strong intermixing with HfO2; Oxygen concentration in Ti layer is small (TiOx, x<0.10)
After UHV anneal at 300oC for 15 min:Lowering and broadening of Ti peakHf and Si peak shift and O peak change
⇒ Ti layer oxidation
100 104 108 112 116 120 124 1280
600
1200
1800
2400
Yie
ld
Energy [keV]
as deposited 15 min UHV anneal 300oC Hf
Ti
Si
O
surfint
x10
Si (100)
HfO2.07
SiO2
27Å
6ÅTi
RT
27Å
7Å 300oC
UHVSi (100)
HfO2
SiO2
Ti
Si (100)
HfO1.9
HfSiOx
TiOx
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Interface chemical stability: Heats of oxide formation of most stable oxides and XPS results demonstrating interface reactivity
Surf. Sci. 333 (1995) 845; Surf Sci. Rep, 27, 1997
coun
ts
464 460 456 452
Binding Energy [eV]
2Å Fe
2Å Cu
XPS Ti2pbefore and aftermetal deposition
7Å Hf
2Å Cr
-ΔH formation in kJ per mol O
Metal
<0 Au
0 - 50 Ag, Pt
50 - 100 Pd
100 - 150 Rh
150 - 200 Ru, Cu
200 - 250 Re, Co, Ni, Pb
250 - 300 Fe, Mo, Sn, W, Ge
300 - 350 Rb, Cs, Zn
350 - 400 K, Cr, Nb, Mn
400 – 450 Na, V
450 – 500 Si
500 - 550 Ti, U, Ba, Zr
550 - 600 Al, Sr, Hf, Ce, La
600 - 650 Sm, Mg, Th, Ca, Sc, Y
w/Hf
Cr
Fe
Cu
Ti peak before metallization
Rel
ativ
e ox
ygen
affi
nity
of
ove
rlaye
r met
al
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76 80 84 88 92 96
F
As
Si
O
C
Scat
tere
d in
tens
ity (a
. u.)
Energy (keV)
MEIS spectra of low energy dopant implants: ultrashallow junctions
0 10 20 30 40 50 60 701E20
1E21
1E22
As c
once
ntra
tion
(cm
-3)
Depth (Å)
Depth profile derived from the As MEIS peakDepth profile of As in Si from a low
energy implant (1kV, ~1015 As/cm2)
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Arsenic (As) behavior in SIMOX vs. bulk-Si
Interaction of As with vacancies following higher E implants…
After annealing:
• Si interstitials remain in bulk-Si, but NOT in SIMOX
• excess vacancies annihilate Si interstitials in SIMOX
• SIMOX crystal quality is excellent, especially for RTA
0.0
0.5
1.0
1.5
2.0
2.5
75 80 85 90 95 1000.0
0.5
1.0
1.5
2.0
2.5
O
Si
As
RTA 1000ºC/10s
SIMOX Si
Cou
nts
FA 950ºC/15min
SIMOX Si
Energy (keV)
Si interstitials
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Alternative Channel MaterialsMobility improves by straining Si, but CMOS scaling demands further improvements….try other semiconductors!Key challenge for alternative channel materials is the dielectric – need low interface and bulk defect concentration Also need high Ion/Ioff ratio, appropriate integration, high thermal stability, appropriate band alignment with no Ef pinning, etc.Ge and SiGe studied extensively for years - IBM, Intel…III-V compound semiconductors now being seriously considered for CMOS –Motorola/Freescale, Agere, Intel, IBM, IMEC…
from IBM
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HfOxHfOx/Ge (ALD and MOCVD)/Ge (ALD and MOCVD)Film properties very Film properties very gowthgowth dependentdependent
80 84 88 92 960
1000
2000
Cl
Yie
ld
Energy [keV]
Experiment Total Spc Hf Ge O Cl
Hf
OCl
Ge76 78 80 86 88 90
200
300
400 O
Yie
ld
H+ Energy [keV]
ALD little interfacial GeOx (within sensitivity of the measurements)some Cl accumulation at the interfacesome epitaxial growth
MOCVD HfGe and HfGeOx intermixing (condition dependent)surface Ge (supressed by Ge nitridation)
92 94 96 980
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30
HfO2/Ge ALD (31Å), HF etch MOCVD, HF etch MOCVD (20Å), N pasv
Hf
Ge
Gesurf
H+ Y
ield
Energy [keV]
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HfO2 on GaAs: MEIS and TEM comparison
No etch
HF etch
w/Agere
• TEM and MEIS results are consistent;• native oxide ≈ 20 Å;• As:Ga ≈ 0.17, (Ga+As):O ≈ 1.04
GaAsa-C
HfO2
Ga-rich oxide
GaAsa-C
HfO2
Ga-rich oxide
TEM* MEIS
O Hf
O Hf
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Electronic structure in multilayer stacks
• Band edge energies determined in many ways – elec. and optical spec.• Can we use spectroscopies to (i) measure energies and LDOS more
precisely, (ii) determine interface dipoles and band alignment, and (iii) use interface engineering to control effective work function…
+ -
ΔφCBM
ΔVin
ΔφVBM
φ Metal
SiHigh-κMetal
Vin Si
ECBM Si
Eg SiEVBM SiEVBM Hi-κ
ECBM Hi-κ
Eg Hi-κ
Vin Hi-κ
ΔVM-Hiκ
- +
DO
S
Si High-k Metal
EF
Band edges
DefectStates?
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Inverse Photoemission (Unoccupied States)e- e-
Photoemission (Occupied States)
e-
e-
e-e-
Experimental tools to examine electronic structure
EF
CL
VB
CBEF
VB
Core Level
CBElectron Counts
Ele
ctro
nE
nerg
y
EVBM
Pho
ton
Ene
rgy
# of Photons
ECBMEF
EF
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Thicker oxides may charge - use care!
Underlying silicon states visibles
UPS InvPE
HfO2/SiO2/Si
Hf 5dO2p
3.8 ± 0.1eV
2.2 ± 0.1eV
Gap = 6 ± 0.2 eV
Band tail statesDefects states
Single chamber measurments
Direct Gap Determination
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Band offsets with Si for HfxSi1-xO2
*
HfO2 Hf0.55Si0.45O2 SiO2
Band offsets with Si for HfxSi1-xO2
*Ef position correctedto account for the Si doping
*
Si1.4 1.5
3.43.4
3.4
4.4
1.8
3.2 3.8
1.5
4.3
3.5
Experiments Model
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n-type Si
p-type Si p-type Si
Metal or poly-Si
Dielectric
SiO2 HfxSi1-xO2 HfO2
Oxide/semiconductor and metal/oxide interfaces
Ru Al
Workfunction 5.2 eV 4.2 eV
Chemistry Low Reactivity~ Noble Metal
High ReactivityStable Oxide
Metal electrode
Dielectric
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Energy shifts upon metallization
VB, CB and core levels are shifting the same wayby the same amount
VB
CB
Hf4f
Al/Hf0.55Si0.45O2
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Metal interaction with the substrate
Si
SiO2
HfO2
Ru
Ru 4p
Hf 5p
No oxidation of ruthenium Oxidation of Aluminium Formation of a Al2O3 layer
Si
SiO2
HfO2
AlAl O2 3
Al 2p
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Al/HfO2/GeOx/Ge
GeGeOx
AlAl2O3
Hf
Ge
GeOx
Al
Al2O3
Ge
HfO2
HfO2
Hf4f and VB shift
Interfacial oxidereduction at 300 K
No significantreductionof HfO2 in Hf4f
3 Å Al10 Å Al
Clean surface
3 Å Al10 Å Al
Clean surface3 Å Al10 Å Al
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Internal Photoemission (IntPES)
EcEF
EV
φM/Ox
metal semiconductor
EF
high-κ
a
c
b
EcEF
EV
φSi/Ox
metal semiconductor
EF
high-κ(a) Ec(Hiκ)-EF(met.) e-IntPES; (b) photo-excitation; optical band gap; (c) Ec(sc)-Ev (Hiκ) h-IntPES
Arc lamp Monochromator
Chopper
Lock-in amplifier
I-V Source Measure
Unit
Probe station
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IntPES: Al / HfO2 / GeNegative Bias on Ge, ΦGe/ HfO2 : ~3.1 eV
2 3 4 5 6
Y1/2 (A
U)
Photon Energy (eV)
-0.05V -0.075V -0.1V -0.125V
0.14 0.16 0.18 0.20 0.22 0.242.76
2.78
2.80
2.82
2.84
2.86
2.88
Bar
rier H
eigh
t (eV
)
E1/2 (MVcm-1)1/2
HfO2/Ge Barrier Height
2.75 3.00 3.25 3.50
Y1/2 (A
U)
Photon Energy (eV)
Ec
EF
EV
φbarrier
metal semiconductor
EF
high-κ
ΦGe~3.1 eV
EF
Al HfO2 Ge
EC
EV
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Scanning probe measurements of topography and dielectric properties
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tapping mode current image
AFM and current image of unirradiated HfxSiyOz/Si film
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Left: tapping mode Right: current image
AFM and current image of irradiated HfO2/Si filmflux is ~2x1015 H+/cm2 H+~100keV
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AFM images of HfO2/SiON/SiBefore (a) and after (b) radiation exposure ~1015 ~
200keV He2+
(a) (b)
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Conductive Tip AFM Image and I-V Behavior of a Ru/HfO2/Si Stack
-6 -4 -2 0 2 4 6
1
10
100
log[
I(pA
)]
Bias (V)0.2 0.4
-6
-4
-2
0
ln(I/
V2 )
1/V-4 -2 0 2 4
-2
-1
0
1
2
I (pA
)
Bias (V)
For simple F-N tunneling with an electron effective mass of 0.18, the HfO2/Si conduction band barrier height is 1.4eV
Image physical and spectroscopic behavior of radiation induced defects
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PlansGeneration broader range of films and devices with high-K dielectrics (HfO2) and metal gate electrodes (Al, Ru, Pt).Interface engineering: SiOxNy (vary thickness and composition)Expand physical measurements of defects created by high energy photons and ions using SPM and TEMCorrelate physical measurement results with electrical methods. Develop quantitative understanding of behavior as a function of particle, fluence and energy.Monitor H/D concentration and profiles, and effects on defect generation (by radiation) and passivation.Determine if radiation induced behavior changes with new channelmaterials (e.g., Ge, InGaAs), strain, or SOIExplore effects of processing and growth on radiation behavior.Correlate with first principles theory.