Radiation Effects on Emerging Electronic Materials and Devices

Leonard C. FeldmanVanderbilt University

Department of Physics and AstronomyVanderbilt Institute on Nanoscale Science and Engineering

June 14/15, 2007

Radiation Effects in Emerging Materials

Overview

Topics of Interest

Basic radiation interaction with electronic materials-review, educational, modifications at the nanoscale

Alternate Dielectrics and Gate Stacks-in all aspects-growth, spectroscopy, radiation effects

SiGe devices and other “alternate substrates” (Ge, InGaAs, SiC)

Strained silicon

Basic radiation interaction with electronic materials-

review, educational, modifications at the nanoscale

Tutorials and review:

Interaction of x-rays with MOS devices occurs primarily via the generation of (photo) electrons in the metal and the underlying silicon.

The energetic electrons (<= 10 KeV) create electron hole pairs in the dielectric which may be trapped by “processing” defects.

The dielectric is too thin to incur any substantial direct defect production by the primary radiation.

The outgoing electrons are too low in energy for direct displacements, but create further secondarys, and possibly defects, through bond breaking leading eventually to e-h pair production.

Gate

oxid

eSi

met

al

MOS Schematic

MAJOR POINT FROM THE PREVIOUIS CONSIDERATIONS

“Processing defects”, defects from the imperfection of the grown dielectric, are the primary trapping centers

-nanocrystalline HfO2

-HfO2/SiO2 interface

-classic defects such as oxygen vacancies, etc

-Hf penetration into the SiO2 layer and its interaction with H

“Processing defects”, defects from the imperfection of the grown dielectric,

are the primary trapping centers

even for the higher atomic number, physically thicker HfO2

Number of Hf atoms versus distance from interface

1 nm

Single Hf atoms inside SiO2 interlayer

interface2 Å

4 Å

distance (Å)

Basic radiation interaction with electronic materials-

modifications at the nanoscale

Nanoscale:

Basic theory of e-h pair production, particularly ε, the average energy required for e-h pair creation, is based on bulk concepts, including bulk density of states.

The nanoscale thicknesses, and the new understanding of nanoscale effects calls for re-examination of these concepts.

Gate

oxid

eSi

met

al

MOS Schematic

ΔV=Q/C=Ne {(dE/dx) tox/ε} /C

ε= average energy/e-h pair

Ne= number of electrons penetrating the dielectric

ε vs. Egε= 2.6Eg + K

Shockley-Klein

Rutgers CMOS Materials Analysis

Surface/interface analysis:• Ion scattering: RBS, MEIS, NRA, ERD –

composition, crystallinity, depth profiles, H/D• Direct, inverse and internal photoemission –

electronic structure, band alignment, defects• Scanning probe microscopy – topography,

surface damage, electrical defects

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

SiO2 Monolayer?

Metal Electrode

High-κ Dielectric

Source DrainGe, III-V

Barrier?

10nm

CMOS gate ~2010?

Materials stability, band alignment and defects in CMOS nanoelectronics

L. Goncharova, S. Rangan, O. Celik, C.L. Hsueh, R.A. Bartynski, T. Gustafsson and E. Garfunkel

Departments of Chemistry and Physics, and

Institute for Advanced Materials, Devices and Nanoelectronics

Rutgers University, Piscataway, NJ

Collaboration: Vanderbilt, Sematech, NIST, IMEC, IBM, Intel, Bell Labs, NCSU, Penn State, Stanford, UT-Dallas, UT-Austin, Albany.…

2h

1h

2e 1e

DO

S

Si High-k Metal

EFBand edge states

Defects

Defects in the post-Si era:Al/HfO2/InxGa1-xAs

• Surface passivation and composition of interfacial layer• High-K deposition• Post-deposition annealing• Metal gate effects• “Normal” and radiation induced defects – nature and evolution

100 104 108116 120 124 1280

2

4

6 ox - In0.5

Ga0.5

As

S-pass In0.5

Ga0.5

As

Nor

mal

ized

Yie

ld

Energy [keV]

CO

S

InGaAs

104 108 112 116 120 124 128

Yie

ld

Energy [keV]

O

S

Hf

InGa As

x5

Eo=130.5keV

Incident angle = 0o <100>

Scattering angle = 125.3o <111>HfO2

5Å InGaOx

InGaAs(001)

S2-

Al

length scales of order and defects in nano-crystalline and non-crystalline Hf-based gate dielectrics

Gerry Lucovsky

students and post doc: S. Lee, JP Long, H Seo and LB Fleming

collaborators: J Whitten, D Aspnes, Jan Luning (SSRL), G. Bersuker and P Lysaght (Sematech)

objective: determine the effect of different length scales of order for nano- and non-crystalline Hf based dielectrics on pre-existing

intrinsic defects, and then on radiation (X-ray) induced defects

approach

i) prepare NCSU samples by plasma-CVD

ii) determine electronic structure, Hf d-state relative energies, by near edge X-ray absorption, soft X-ray photoelectron

spectroscopy, and vis-VUV spectroscopic ellipsometry using symmetry adopted linear combinations (SALC-FA Cotton) of

atomic states as a guideline

iii) study electrical properties in MOSCAPs and compare electrical and X-ray stress

significant resultslength scale, coh - coherent Hf d– O p-bond inter-PUC coupling

0 0.5 1 1.5 2 2.5 3 3.5 40.98

1

1.02

1.04

1.06

1.08

1.1

1.12

length scales, s

bond-lengths, bond-angles0.15-0.35 nm

rings ofbonded atoms

0.4 - 0.6 nm

chemical bondingself-organizations

0.6 to 0.8 nm

non-crystallinethin films

nano-crystallinethin films type I

tphys

<2 nmTproc

< 700oC

type IItphys

>3 nmTproc

>/=700oC

phase-separated

Hf silicates80% HfO2

Hf Si oxynitrides

phase-sep. silicates and type I

coh ~ 2 nm or < 5 PUCsno J-T splittings

and band-tail defects

2

2.5

3

3.5

4

4.5

5

5.5

530 531 532 533 534 535

HfO2

6 nmOK1

abs

orp

tio

n (

arb

. un

its)

x-ray photon energy (eV)

5d3/2

Eg

900oC

700oC

500oC

300oC

slope1.4

slope1.0

type II coh > 3 nm or > 6 PUCs

J-T splittings anddiscrete band-edge

defects

asymmetric h/e trapping +/- defects X-ray stress

0.5

1

1.5

2

2.5

3

3.5

4

4.5

4.5 5 5.5 6 6.5 7 7.5 8

exp

silo

n 2

( 2

)

photon energy (eV)

HfO2

900oC anneal

Eg

Hf 5d3/2

Eg

Hf 5d3/2

2 band edgedefect states

J-T splitting 1.2 eV

1000

104

105

106

2 4 6 8 10 12 14

cou

nti

ng

rat

e (

arb

un

its

)

energy (eV)

Ti Si oxynitridesas-deposited

SXPS60 eV

16% Si3N4

40% Si3N4

occupieddefects

hole traps

Hf Si oxynitrides- high Si3N4 %

no inter-group Hf d-O p-bonding

no phase-separation, but only for small range of compositions

very low tunneling, ~12 (to 16-18)

positive charge defects - X-ray stress HfO2 and Hf silicates

both positive/negative charged defects

1.6

2

2.4

2.8

3.2

3.6

4

4.4

530 535 540 545

2 nm HfO2

as-deposited

2 nm HfO2

800oC anneal

5d3/2Eg

5d5/2T2g

6s 6pA1g T1u

O K1 edgeGe (100)

(a)

abso

rption (arb. u

nits)

X-ray photon energy (eV)

2

2.5

3

3.5

4

4.5

5

530 535 540 545

5d3/2Eg

5d5/2T2g

6 nm HfO2

800oC anneal

6s 6pA1g T1u

6 nm HfO2

as-deposited

O K1 edgeGe (100)

(b)

abso

rption (arb. u

nits)

X-ray photon energy (eV)

1.6

2

2.4

2.8

3.2

3.6

4

4.4

530 535 540 545

2 nm HfO2

as-deposited

2 nm HfO2

800oC anneal

5d3/2Eg

5d5/2T2g

6s 6pA1g T1u

O K1 edgeGe (100)

(a)

abso

rption (arb. u

nits)

X-ray photon energy (eV)

2

2.5

3

3.5

4

4.5

5

530 535 540 545

5d3/2Eg

5d5/2T2g

6 nm HfO2

800oC anneal

6s 6pA1g T1u

6 nm HfO2

as-deposited

O K1 edgeGe (100)

(b)

abso

rption (arb. u

nits)

X-ray photon energy (eV)

Si substrate Ge substrate

SiON GeN/GeO

HfO2 or TiO2 HfO2 or TiO2

Si substrate Ge substrate

SiON GeN/GeO

HfO2 or TiO2 HfO2 or TiO2

O K1 525-555 eV X-rays

resonant photoemission for O-Hf, O-Ti anti-bonding states

N K1 395-425 eV X-rays

resonant photoemission for Ge-N, Si-N anti-bonding states

Si substrate Ge substrate

SiON GeN/GeO

HfO2 or TiO2 HfO2 or TiO2

Si substrate Ge substrate

SiON GeN/GeO

HfO2 or TiO2 HfO2 or TiO2

Si substrate Ge substrate

SiON GeN/GeO

HfO2 or TiO2 HfO2 or TiO2

Si substrate Ge substrate

SiON GeN/GeO

HfO2 or TiO2 HfO2 or TiO2

O K1 525-555 eV X-rays

resonant photoemission for O-Hf, O-Ti anti-bonding states

N K1 395-425 eV X-rays

resonant photoemission for Ge-N, Si-N anti-bonding states

direct bonding HfO2 : Ge(100)

electricals being studied and measurements extended to Ge(111)

0.136

0.138

0.14

0.142

0.144

0.146

395 400 405 410 415

abso

rpti

on

(a

rb.

un

its

)

X-ray photon energy (eV)

N K1 edgeGe (100)

(a)

3

3.1

3.2

3.3

3.4

3.5

3.6

395 400 405 410 415

2 nm HfO2

800oC anneal

6 nm HfO2

800oC annealab

sorp

tio

n (

arb

. un

its)

X-ray photon energy (eV)

N K1 edgeGe (100)

(b)

GeO and GeN removed during anneal resonant X-rays reveal buried interface

2.5

3

3.5

4

4.5

5

5.5

530 535 540 545

6s 6p5d5/2

T2g

5d5/2

Eg

O K1 edge6 nm HfO2

abso

rpti

on

(a

rb.

un

its

)X-ray photon energy (eV)

SiON-Si

900oC

Ge

800oC

substrate specific -bonds SiON interface/Ge-direct

HfO2 sample details

• State-of-the-art samples, SEMATECH, Inc.

• 65 nm technology node

• nMOSFETs with W/L = 10m/0.2m

• tphys = 7.5 nm and 3.0 nm

(EOT = 1.2 nm and 0.5 nm)

• SiO2 interlayer (~ 8Å)

HfO2 based nMOSFET

Gate

p-substrate

p-well

Source Drain Body

n+ n+ p+

Samples Experimental

• 10 keV X-rays, RT irradiation

• Function of dose

• Function of bias

• Characterization done using

I-V measurements

HfO2 total dose results

tphys = 7.5

nm

tphys = 3.0

nm• Thinner dielectric traps significantly less charge

S. K. Dixit et al., “ Radiation induced charge trapping in ultra-thin HfO2 based MOSFETs”, accepted for NSREC 2007

• nMOSFETs with W/L = 10m/0.2m

n-MOSFET cross-section

Carrier injection from tunneling Si- surface condition dependent Both electron and hole trapping observed Predominant bulk hole trapping (radiation) Zero bias - radiation induced trapping

SiO2 p-SiEC

EV

Ef

Ei

HfO2TiN

HfO2/TiN

HfO2 results

Hafnium silicates

Crystallization introduces defects and shallow traps at the grain boundaries

Radiation response expected to be better for silicates

Limitations of HfO2:

HfO2 - low thermal budget ~ 500°C

Nanocrystalline HfO2 formed during

PMA

Dopant penetration is an issueNeed for HfSiO: Increased thermal budget to ~ 1000°C

Reduction in dielectric constant

RBS & CV of HfSiO/SiO2/p-Si films

Total dielectric thickness from RBS: ~10 to 11nm

Physical characterization Electrical characterization

Total dielectric thickness from CV: ~12nm

E0 = 1.4 MeV 4He

E1 = KE0

Results

• Initial results confirm the trend (… Hf r)

RBS results C-V results

TID Response of Hf0.6 and Hf0.3 Films

Devices prepared by RPECVD; EOT ~ 4 nm

Two dielectric films: Hf0.6 (containing crystalline HfO2) Hf0.3 (amorphous)

Electron trapping observed in the Hf0.6 film under large positive bias

Probable explanation:

e-trapping at nanocrystalline grain boundaries

TID Response Comparison to Previous Hf Silicate Films

TID-induced charge trapping improved compared to previous Hf silicate devices [J. A. Felix et al., IEEE Trans. Nucl. Sci., vol. 49, pp. 3191-3196, 2002]

∆Not ~ factor of 17 smaller at 1 Mrad

Reduced charge trapping indicates superior HfSiON film qualities and improvements in processing techniques

Facilities at Vanderbilt

Physical and Electrical characterization• Ion beam characterization using RBS, PIXE, channeling studies

• C-V measurements

• I-V measurements

• 10 keV X-ray source (in-situ bias and irradiations)

• 2 kV Van de Graaff electrostatic accelerator

• Low dose rate Ce source

Radiation sources

Future upgrades• In-situ biased ion irradiations using H, He and Ne beams

• Low-temp (up to 7K) ion irradiations using a cryostat

Other facilities• Thermal oxidation and gate metal deposition facilities

• Delta Oven furnace for high temp biased anneals

• Wire bonder for packaging wafer level devices

Biased irradiations and anneals

Irradiation (-2V) RT Annealing (0V)

• Partial recovery observed with a 0V annealing gate bias

• No additional voltage shifts observed for time scales of up to 13 hours indicating the existence of residual positive charge in the oxide

Radiation Effects in SiGe DevicesJohn D. Cressler and Team

• Investigation of the Best Path to RHBD in Bulk SiGe HBT Technologies• First Cryogenic Temperature (77K) Proton Experiment of SEU in Bulk SiGe HBTs • Investigation of Radiation Effects in both Bulk C-SiGe HBTs and SiGe HBTs on SOI • Investigation of Radiation Effects in both SiGe nMODFETs and SiGe pMODFETs

Bulk SiGe HBTs C-SiGe HBTs (npn + pnp) SiGe p/n-MODFETs

S. K. Dixit et al., “ Radiation induced charge trapping in ultra-thin HfO2 based MOSFETs”, accepted for NSREC 2007

Voltage Stress and Biased Irradiation

Hole injection saturatesafter an hour

Simultaneous injection + irradiationis even worse

MURI meeting June’07

S. K. Dixit et al., “ Radiation induced charge trapping in ultra-thin HfO2 based MOSFETs”, accepted for NSREC 2007

CVS and biased irradiation

Simultaneous injection + irradiation

is even worse

SiO2

p-Si

EC

EV

Ef

Ei

HfO2TiN

HfO2/TiN

Hole injection- 2V bias stress

Accumulation

Hole injection saturatesafter an hour

S. K. Dixit et al., “ Radiation induced charge trapping in ultra-thin HfO2 based MOSFETs”, accepted for NSREC 2007

CVS and biased irradiation

Electron injection saturates

Simultaneous stress + irradiationhole trapping dominates with dose

SiO2

p-Si

EC

EV

Ef

Ei

HfO2

TiN

HfO2/TiN

Electron injection+ 2V bias stress

Inversion