novel dielectrics for advanced semiconductor devices

Cristiano Krug and Gerry Lucovsky

Department of Physics North Carolina State University

outline

band edge states - nanocrystalline HfO2 and ZrO2 theory and experiment inherent limitations

engineering solutions

band edge states - non-crystalline Zr and Hf silicate alloys theory and experiment inherent limitations

engineering solutions

novel device structure experimental result

proposed device structures

research plan

band edge states nanocrystalline HfO2 and ZrO2

theory and experiment

inherent limitations

engineering solutions

theory -- crystal field and Jahn-Teller term-splittings model calculation - ZrO2 band edge d-

statestwo issues

can XAS detect mixtures of

tetragonal and monoclinic nano-

crystallites?

and

can mixtures account for range of defect state energies

in electrical measurements ?

-0.5

0

0.5

1

1.5

2

rea

ltiv

e e

ner

gy

(e

V)

C-FJ-T

tetra.J-T

mono.J-T

mono.z-gb x-gb

sphericallysymmetric

Eg

T2gJ-T - orthorhombic

monoclinicC-F cubic

-0.2

-0.1

0

0.1

0.2

0.3

0.4

531 532 533 534 535 536 537 538 539

photon energy (eV)d

eri

vati

ve a

bs

orp

tio

n (

arb

. u

nit

s)

ZrO2

O K1 edgereactive

evaporation

Eg (2) T2g (3) Eg (2) T2g (4+)

as-deposited MO-RPECVD films by IR are

monoclinic similar result for ZrO2

multiple features in T2g region are indicative of mixture of

monoclinic and tetragonal by XRD

nano-crystallite grains - different for different processing Stefan Zollner’s results at Freescale - XRD and SE

theory -- crystal field and Jahn-Teller term-splittings model calculation - ZrO2 band edge d-

statescan XAS detect

mixtures of tetragonal and

monoclinic nano-crystallites?

YES

model predicts at least 4 features in

T2g band

observed for reactive

evaporation, but not for MO-RPECVD-0.5

0

0.5

1

1.5

2

rea

ltiv

e e

ner

gy

(e

V)

C-FJ-T

tetra.J-T

mono.J-T

mono.z-gb x-gb

sphericallysymmetric

Eg

T2gJ-T - orthorhombic

monoclinicC-F cubic

0

500

1000

1500

2000

2500

3000

3500

4000

4.5 5 5.5 6 6.5

ZrO2

V.V. Afanase'vA. Stesmans

photon energy (eV)

[ph

oto

con

du

ctiv

ity]

1/2

(arb

. u

nit

s)

Eg band edgefeature

band edge"defect state"

model calculations indicate band edge defect state is associated with a Jahn-Teller distortion at internal grain boundary and is intrinsic to nano-crystalline thin films

104

105

106

5 5.5 6 6.5 7 7.5 8 8.5 9

ab

sorp

tio

n c

on

sta

nt

(cm

-1)

photon energy (eV)

Eg (2 features)

band edge"defect state"

T2g (1 of

3 features)

nc-ZrO2

B. Rogers,S. Zollner

-bonded d*-states/defects at conduction band edge in absorption constant (2) andconductivity (PC)

onset of strong optical absorption - lowest Eg state -

optical band

gap

optical band

gap

Z . Yu et al., APL 80, 1975 (2002),

in Chap 3.4 - High-K dielectrics, M. Houssa

(ed), IOP, 2004.

localized band edge J-T d*-states inherent asymmetry in transport and trapping

including BTI’s

trap depth 0.5-0.8 eV, same state PC

and band edge abs.

trapping/Frenkel-Poole transport

tunneling but not F-P x'port

crystal field and Jahn-Teller term-splittings model calculation using Zr and O atomic states

can mixtures account for range of defect state energies

in electrical measurements ?

YES

3x energy scale ~ 0.5 - 0.8 eV

-0.5

0

0.5

1

1.5

2

rea

ltiv

e e

ner

gy

(e

V)

C-FJ-T

tetra.J-T

mono.J-T

mono.z-gb x-gb

sphericallysymmetric

Eg

T2g

-0.5

0

0.5

1

1.5

2

rea

ltiv

e e

ner

gy

(e

V)

C-FJ-T

tetra.J-T

mono.J-T

mono.z-gb x-gb

sphericallysymmetric

Eg

T2gJ-T - orthorhombic

monoclinicC-F cubic

engineering solutions

NEC solution limit applied bias so that injection into

band edge defect states is not possible

modify band tail states by alloying with divalent (MgO) or trivalent oxides (Y2O3)

e.g. Y2O3 in cubic zirconia introduces vacancies random distribution gives cubic structure and eliminates J-T term

splittings, but evidence for absorption associated with excitations to/from midgap state issue: is this state electrically active ?

study has just been undertaken

VUV spectroscopic ellipsometry and UV-VIS

transmission

term-spitting removed - but new absorption band at ~4.1 eV

sub-band-gap absorption - O vacancies

Jahn-Teller term-split d-states of nc-ZrO2 not in Y-Zr-O, but edge

broadened

0

50

100

150

200

3.5 4 4.5

, ab

so

rpti

on

co

nst

ant

(cm

-1)

photon energy (eV)

ZrO2-9.5%Y2O3

"cubic zirconia"ZrO2-9.5%Y2O3

cubic zirconia

4.1 eV

0

1

2

3

4

5

6

7

5 5.5 6 6.5 7 7.5 8 8.5 9

A

ima

gin

ary

par

t o

f d

iele

ctr

ic c

on

sta

nt

(2)

photon energy (eV)

bulk x'tal-90.5% ZrO2

9.5% Y2O3

6.3 eV

5.3 eV

0

2

4

6

8

5 5.5 6 6.5 7 7.5 8 8.5 9

ima

gin

ary

par

t o

f d

iele

ctri

c c

on

sta

nt

(2)

Eg (2 features)

T2g (1st feature)

nc-ZrO2

photon energy (eV)

nanocrystalline ZrO2

5.7 eV

6.2 eV

7.0 eV

8.5 eV

outline

band edge states non-crystalline Zr and Hf silicate alloys

theory and experiment

inherent limitations

engineering solutions

IR results - GB Rayner - PhD thesis, NCSU

Si-O-1 group shoulder ~ 950 cm-1

grows with increasing x in

as-films deposited

changes continuously with annealing in inert

ambient, Ar

SiO2 features at 1068, 810 and 450 cm-1 sharpen up

with increasing Tann

chemical phase separation “non-crystalline” by XRD, but, x=0.23 nano-crystalline by TEM

and EXAFS

4 0 06 0 08 0 01 0 0 012 0 01 40 01 6 0 0

W a v e n u m b e rs (cm -1)

Ab

sorb

ance

(a

.u.)

1 0 1 8 2 6 3 4 4 2 5 0 5 8 6 6

2 (D eg re es )

Co

un

ts (

a.u

.)

a s d e p .

6 0 0 °C

8 0 0 °C

7 0 0 °C

9 0 0 °C

a s d e p .

6 0 0 °C

7 0 0 °C

8 0 0 °C

9 0 0 °C

x = 0 .1 0 1 0 6 6

8 1 0

4 5 0

4 0 06 0 08 0 01 0 0 012 0 01 40 01 6 0 0

W a v e n u m b e rs (cm -1)

Ab

sorb

ance

(a

.u.)

1 0 1 8 2 6 3 4 4 2 5 0 5 8 6 6

2 (D eg re es )

Co

un

ts (

a.u

.)

a s d e p .

6 0 0 °C

8 0 0 °C

7 0 0 °C

9 0 0 °C

a s d e p .

6 0 0 °C

7 0 0 °C

8 0 0 °C

9 0 0 °C

x = 0 .1 0 1 0 6 6

8 1 0

4 5 0

1 0 1 8 2 6 3 4 4 2 5 0 5 8 6 6

2 (D eg re es )

Co

un

ts (

a.u

.)

a s d e p .

6 0 0 °C

8 0 0 °C

7 0 0 °C

9 0 0 °C

a s d e p .

6 0 0 °C

7 0 0 °C

8 0 0 °C

9 0 0 °C

x = 0 .1 0 1 0 6 6

8 1 0

4 5 0

4 0 06 0 08 0 01 0 0 012 0 01 40 01 6 0 0

W a v e n u m b e rs (cm -1)

Ab

sorb

ance

(a.

u.)

F ig u re 3 .7 T h e (a ) IR a b s o rp t io n s p e c tra a n d (b ) X R D re s u lts o f x = 0 .2 3 a llo y a s a fu n c t io n o f a n n e a lin g te m p e ra tu re u p to 9 0 0 C .

1 0 1 8 2 6 3 4 4 2 5 0 5 8 6 6

2 (D eg re es )

Co

un

ts (

a.u

.)

x = 0 .2 3

a s d e p .

6 0 0 °C

7 0 0 °C

8 0 0 °C

9 0 0 °C

9 0 0 °C

a s d e p .

6 0 0 °C

7 0 0 °C

8 0 0 °C

1 0 6 8

8 1 0

4 5 0

(a )

(b )

4 0 06 0 08 0 01 0 0 012 0 01 40 01 6 0 0

W a v e n u m b e rs (cm -1)

Ab

sorb

ance

(a.

u.)

F ig u re 3 .7 T h e (a ) IR a b s o rp t io n s p e c tra a n d (b ) X R D re s u lts o f x = 0 .2 3 a llo y a s a fu n c t io n o f a n n e a lin g te m p e ra tu re u p to 9 0 0 C .

1 0 1 8 2 6 3 4 4 2 5 0 5 8 6 6

2 (D eg re es )

Co

un

ts (

a.u

.)

x = 0 .2 3

a s d e p .

6 0 0 °C

7 0 0 °C

8 0 0 °C

9 0 0 °C

9 0 0 °C

a s d e p .

6 0 0 °C

7 0 0 °C

8 0 0 °C

1 0 6 8

8 1 0

4 5 0

(a )

(b )

4 0 06 0 08 0 01 0 0 012 0 01 40 01 6 0 0

W a v e n u m b e rs (cm -1)

Ab

sorb

ance

(a

.u.)

1 0 1 8 2 6 3 4 4 2 5 0 5 8 6 6

2 (D eg re es )

Co

un

ts (

a.u

.)

a s d e p .

6 0 0 °C

8 0 0 °C

7 0 0 °C

9 0 0 °C

a s d e p .

6 0 0 °C

7 0 0 °C

8 0 0 °C

9 0 0 °C

x = 0 .1 0 1 0 6 6

8 1 0

4 5 0

4 0 06 0 08 0 01 0 0 012 0 01 40 01 6 0 0

W a v e n u m b e rs (cm -1)

Ab

sorb

ance

(a

.u.)

1 0 1 8 2 6 3 4 4 2 5 0 5 8 6 6

2 (D eg re es )

Co

un

ts (

a.u

.)

a s d e p .

6 0 0 °C

8 0 0 °C

7 0 0 °C

9 0 0 °C

a s d e p .

6 0 0 °C

7 0 0 °C

8 0 0 °C

9 0 0 °C

x = 0 .1 0 1 0 6 6

8 1 0

4 5 0

1 0 1 8 2 6 3 4 4 2 5 0 5 8 6 6

2 (D eg re es )

Co

un

ts (

a.u

.)

a s d e p .

6 0 0 °C

8 0 0 °C

7 0 0 °C

9 0 0 °C

a s d e p .

6 0 0 °C

7 0 0 °C

8 0 0 °C

9 0 0 °C

x = 0 .1 0 1 0 6 6

8 1 0

4 5 0

4 0 06 0 08 0 01 0 0 012 0 01 40 01 6 0 0

W a v e n u m b e rs (cm -1)

Ab

sorb

ance

(a.

u.)

F ig u re 3 .7 T h e (a ) IR a b s o rp t io n s p e c tra a n d (b ) X R D re s u lts o f x = 0 .2 3 a llo y a s a fu n c t io n o f a n n e a lin g te m p e ra tu re u p to 9 0 0 C .

1 0 1 8 2 6 3 4 4 2 5 0 5 8 6 6

2 (D eg re es )

Co

un

ts (

a.u

.)

x = 0 .2 3

a s d e p .

6 0 0 °C

7 0 0 °C

8 0 0 °C

9 0 0 °C

9 0 0 °C

a s d e p .

6 0 0 °C

7 0 0 °C

8 0 0 °C

1 0 6 8

8 1 0

4 5 0

(a )

(b )

4 0 06 0 08 0 01 0 0 012 0 01 40 01 6 0 0

W a v e n u m b e rs (cm -1)

Ab

sorb

ance

(a.

u.)

F ig u re 3 .7 T h e (a ) IR a b s o rp t io n s p e c tra a n d (b ) X R D re s u lts o f x = 0 .2 3 a llo y a s a fu n c t io n o f a n n e a lin g te m p e ra tu re u p to 9 0 0 C .

1 0 1 8 2 6 3 4 4 2 5 0 5 8 6 6

2 (D eg re es )

Co

un

ts (

a.u

.)

x = 0 .2 3

a s d e p .

6 0 0 °C

7 0 0 °C

8 0 0 °C

9 0 0 °C

9 0 0 °C

a s d e p .

6 0 0 °C

7 0 0 °C

8 0 0 °C

1 0 6 8

8 1 0

4 5 0

(a )

(b )

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0

Radius (Angstroms)

Fourier Transform

(a.u.)

x ~ 0.25

As Dep.

900°C

Zr–O

Zr–Zr

(a)

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0

Radius (Angstroms)

Fourier Transform

(a.u.)

x ~ 0.25

As Dep.

900°C

Zr–O

Zr–Zr

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0

Radius (Angstroms)

Fourier Transform

(a.u.)

x ~ 0.25

As Dep.

900°C

Zr–O

Zr–Zr

(a)

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0

Radius (Angstroms)Fourier Transform

(a.u.)

x ~ 0.55

As Dep.

900°C

Zr–O Zr–Zr

(b)

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0

Radius (Angstroms)Fourier Transform

(a.u.)

x ~ 0.55

As Dep.

900°C

Zr–O Zr–Zr

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0

Radius (Angstroms)Fourier Transform

(a.u.)

x ~ 0.55

As Dep.

900°C

Zr–O Zr–Zr

(b)

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0

Radius (Angstroms)

Fourier Transform

(a.u.)

x ~ 0.25

As Dep.

900°C

Zr–O

Zr–Zr

(a)

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0

Radius (Angstroms)

Fourier Transform

(a.u.)

x ~ 0.25

As Dep.

900°C

Zr–O

Zr–Zr

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0

Radius (Angstroms)

Fourier Transform

(a.u.)

x ~ 0.25

As Dep.

900°C

Zr–O

Zr–Zr

(a)

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0

Radius (Angstroms)Fourier Transform

(a.u.)

x ~ 0.55

As Dep.

900°C

Zr–O Zr–Zr

(b)

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0

Radius (Angstroms)Fourier Transform

(a.u.)

x ~ 0.55

As Dep.

900°C

Zr–O Zr–Zr

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0

Radius (Angstroms)Fourier Transform

(a.u.)

x ~ 0.55

As Dep.

900°C

Zr–O Zr–Zr

(b)

1 0 1 8 2 6 3 4 4 2 5 0 5 8 6 6

2 (D e g re e s )

Co

un

ts (

a.u

.)

As D e p .

6 0 0 o C

9 0 0 o C

8 0 0 o C

7 0 0 o C

(a )x = 0 .2 3

1 0 1 8 2 6 3 4 4 2 5 0 5 8 6 6

2 (D e g re e s )

Co

un

ts (

a.u

.)

( b )

As D e p .

6 0 0 oC

7 0 0 oC

8 0 0 oC

9 0 0 oC

te t rag o n a lZ rO 2

x = 0 .5

comparison of extended x-ray absorption fine structure and x-ray diffraction

crystallite size

difference for x ~ 0.25 and

x ~ 0.5

from HRTEM

x~0.25, ~3 nm

x~0.5, ~10 nm

chemical phase separation (CPS) in Zr silicate and ZrSiON alloys after 900°C annealing

doubly degenerate Eg feature in non-crystalline Zr silicate alloys independent of alloy composition

after 900°C anneal, chemical phase separation and crystallization Eg narrowed/shifted 0.5 eV in Zr silicate, asymmetric in

ZrSiON

6

8

10

12

14

16

18

530 532 534 536 538 540photon energy (eV)

abso

rpti

on

(ar

b. u

nit

s)

Zr silicate alloys

x = 35% ZrO2 non-crystalline

x = 60%ZrO2

phase-separated

non-crystalline

E~0.5 eV

n-c

0

1

2

3

4

530 532 534 536 538 540

Zr, Si oxynitride~20% ZrO2

900oC anneal

Zr 4d*

derivativeabsorption

Si 3s* (Si-O)

photon energy (eV)

abso

rpti

on

(ar

b. u

nit

s)

SiO2

CPS

i) metal ions, Na1+, Ca2+, Y3+,

Zr4+, etc.. disrupt network converting bridging Si-O-Si to

terminal Si-O1- group

ii) number of terminal groups valence of metal ion, 1 for Na, 2 for Ca, 3 for Y and 4 for Zr

iii) connectedness of network defined by shared corners,

Cs between SiO4/2 units

iv) Cs = 4 perfect 3 D network, Cs= 1,0 completely

disrupted mixture of SinOm molecular ions and metal

ions

statistical/mean field disruption of SiO2 network 1:1 representation of silicate alloys

0

1

2

3

4

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

(CaO)x(SiO2)1-x

(ZrO2)x(SiO2)1-x

(NaO1/2)x(SiO2)1-x

(YO3/2)x(SiO2)1-x

corn

ers

sh

are

d/S

i ato

m

alloy composition, x

rate of network disruption increases with valence of metal ion when normalized on a per/atom basis

for x > xo for Cs = 0, silicate is “inverted” and SinOm are minority species

xo

cs = 0

cs

1500 1200 900 600 300

1100C

1000C

900C

as dep.

[a]

abso

rpti

on

(a.

u.)

wave number (cm-1)538 536 534 532 530 528

[b]

sig

nal

leve

l (a.

u.)

O 1s core state energy (eV)

1000C

900C

as dep.

538 536 534 532 530 528

[b]

sig

nal

leve

l (a.

u.)

O 1s core state energy (eV)

1000C

900C

as dep.

(SiO2)0.4(Si3N4)0.25(ZrO2)0.35

pseudo-ternary (SiO2)1-x-y(Si3N4)y(ZrO2)x alloys remote plasma enhanced chemical vapor deposition

as-deposited amorphous alloy – significant Si oxynitride bonding

after anneal at 1000°C – chemical phase separation into SiO2, nanocrystalline ZrO2 with N-bonding

pseudo-ternary (SiO2)1-x-y(Si3N4)y(ZrO2)x alloys remote plasma enhanced chemical vapor deposition

(SiO2)0.3(Si3N4)0.4(ZrO2)0.3

as-deposited amorphous alloy – significant Si oxynitride bonding

after anneal at 1000°C – no chemical phase separation and self-organization encapsulating ZrSiO4

bonding groups

viable engineering solution, k~9-10, EOT to 0.7-0.8 nm

538 536 534 532 530 528

[d]

sig

nal

str

eng

th (

a.u

.)O 1s core level energy (eV)

900C

as dep.

1000C

538 536 534 532 530 528

[d]

sig

nal

str

eng

th (

a.u

.)O 1s core level energy (eV)

900C

as dep.

1000C

1500 1200 900 600 300

1100C

1000C

900C

as dep.

[c]

abso

rption (a.

u.)

wave number (cm-1)

novel device structures (one example)

experimental results for Ge-SiO2

no preoxidation C-V is as good as the best discussed by

Saraswat of Stanford Univ. at Workshop on Future Electronics

2005

two approaches

i) 15 oxidation followed by plasma nitridation

ii) grow 3-5 atomic layers of pseudo-morphic Si on Ge and

oxidize surgically to prevent Ge-O bond formation use on-line

AES

this worked in mid-late 80's, but was not followed-up

Ge – direct deposition of SiO2 with & without pre-oxidation, 0.5-0.6 nm

same as RPAO step for GaN

pre-oxidation of Ge leads to an

increase in Dit, but a decrease in negative fixed charge – next step

interface nitridation!

-Qf

Dit

~Vfb

0.4 -cm n-type - Al

research plans

device testing - ZrO2-Y2O3 and atomically engineered ZrSiON alloys

nitrided Ge interfaces - two approaches

nano-scale vertical p-n junctions (~25 nm diameter!) a precursor to vertical MOS devices

(SRC patent application in process)