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

5

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

6

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

7

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

15

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

18

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

22

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

27

tapping mode current image

AFM and current image of unirradiated HfxSiyOz/Si film

28

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.