Hf impurities in Si/SiO2/HfO2 stacks

Klaus van Benthem2

Sergey Rashkeev1,2,4

Stephen Pennycook2,1

(1) Vanderbilt University, Department of Physics & Astronomy(2) Oak Ridge National Laboratory

(3) Vanderbilt University, Department of Electrical Engineering & Computer Science

(4) Present address: Idaho National Laboratory

SUPPORT: AFOSR and DOE

Apostolos Marinopoulos1

Xing Zhou3

Sasha Batyrev1

Ronald Schrimpf3

Daniel Fleetwood3

Sokrates Pantelides1,2

• Stray Hf atoms in SiO2 interlayer (Oak Ridge National Lab)

(van Benthem and Pennycook)

Hf atoms inside SiO2

Silicon SiO2 HfO2

0.8 nm

• Electrical measurements under switched-bias annealing after irradiation and constant-voltage stress (Vanderbilt)

SiO2 interlayer formation duringpost-deposition annealing

Constant-voltage stress (CVS) and irradiation (10 keV X-rays)

Oscillations of interface-trapdensity by switching bias

applied to Si/SiOxNy/HfO2 stacks

(Zhou, Schrimpf, Fleetwood)

H+ reactions at near-interface region

Pb centers

@ 25o – 150o C

H+

H+

Si SiSi

Hf

H+

suboxide

Si-sub

SiO2

HfO2

bond

H

NEGATIVE BIAS

H+

H+

Si SiSi

Hf

H+

suboxide

Si-sub

SiO2

HfO2

bond

H

NEGATIVE BIAS

Number of Hf atoms versus distance from interface

1 nm

Single Hf atoms inside SiO2 interlayer

interface2 Å

4 Å

distance (Å)

substitutional Hf: localized perturbationperfect structure

interstitial Hf rebonding

E(int) = E(sub) + 4 eV

HIGH-ENERGYSTATES !

SUBSTITUTIONAL IMPURITIES

SUBSTITUTIONAL IMPURITIES

1.4 eV penaltyfor segregation

Tu & Tersoff 2000

quartz

Ordering of Si planes

No particular crystalline polymorph

Hf atoms: markers

Constant-voltage stress (CVS) and irradiation (10 keV X-rays)

Oscillations of interface-trapdensity by switching bias

applied to Si/SiOxNy/HfO2 stacks

(Zhou, Schrimpf, Fleetwood)

H+ reactions at near-interface region

Pb centers

@ 25o – 150o C

H+

H+

Si SiSi

Hf

H+

suboxide

Si-sub

SiO2

HfO2

bond

H

NEGATIVE BIAS

H+

H+

Si SiSi

Hf

H+

suboxide

Si-sub

SiO2

HfO2

bond

H

NEGATIVE BIAS

Passivated Pb-center

Hole capture

Proton motion in the presence of interface defects at Si/SiO2

Suboxide bond

Depassivation

Proton trapping at bond center

BARRIER > 2.2 eV

+

+

Passivated Pb-center

Hole capture

Hafnium substitutional defect near Si/SiO2

Hf-suboxide bond

Depassivation

H+ near bond center

BARRIER ~ 1.1 eV

+

+

CONCLUSIONSCONCLUSIONS

Presence of Hf in SiO2 interlayer: important in near-interface reactions of Hydrogen

Can explain observed oscillations of interface trap density

Hf lowers the barrier for H+ shuttling

H+

H+

Si SiSi

Hf

H+

suboxide

Si-sub

SiO2

HfO2

bond

H

NEGATIVE BIAS

N B T S

H+ MOTION AND INTERACTION WITH INTERFACE DEFECTS

H+

H+

Si SiSi

Hf

H+

suboxide

Si-sub

SiO2

HfO2

bond

H

NEGATIVE BIAS

Pb centers

N B T S

H+

H+

Si Si

-

Si

Hf

H+

suboxide

(1) (2) (3) (4)

Si-sub

SiOxNy

HfO2+

bond

H

(a)

MECHANISMS FOR ELECTRON EXCHANGE AND H+ MOTION

NEGATIVE BIAS

• HfO2 deposition on Si

• annealing at 950o C

Z-contrast image

No Hafnium atom observed to segregate

Silicon HfO2

formation of SiO2 interlayer

SiO2

Single Hafnium atoms inside SiO2 interlayer

0.8 nm

(van Benthem and Pennycook)

Switched-bias annealing after constant-voltage stress

Enhanced magnitude/reversibility of interface-trap charge

MOS capacitors with high-κ gate dielectric

Al / HfO2+SiOxNy / Si