ALD high-k and higher-k integration on GaAs Ozhan Koybasi 1), Min Xu 1), Yiqun Liu 2), Jun-Jieh Wang 2),

Roy G. Gordon 2), and Peide D. Ye 1)*

1) School of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana, U.S.A.

2) Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts, U.S.A.

*Email: yep@purdue.edu

Silicon-based CMOS devices with traditional structures are approaching fundamental physical limits. Researchers are looking for ways to continue the trend of scaling by using alternative materials such as Ge and III-V compound semiconductors that could out-perform Si-based CMOS. Although significant progress is made on InGaAs MOSFETs with ALD high-k dielectrics (Al2O3, HfO2, HfAlO, and ZrO2), GaAs MOSFETs remain a big challenge, mostly showing minuscule drain currents. In this paper, we report on the strong dependence of the electrical properties on different GaAs surface orientations. (111)A Ga polar surface is much more forgiving in terms of Fermi-level pinning for n-channel GaAs MOSFET as shown in Fig.1, compared to (100) Ga-As non-polar surface. It might be directly related with ALD surface chemistry and could be explained by the trap neutral level model. In order to further scale down the equivalent oxide thickness (EOT) of dielectrics, the integration of ALD higher-k (LaLuO3) on GaAs was systematically studied. The precursors lanthanum tris(N,N'-diisopropylformidinate), and lutetium tris(N,N'-diethylformamidinate) reacted with water vapor at 350 oC. The dielectric structures are shown in Fig.2. Fig. 3 shows multi-frequency CV characteristics on n-type and p-type MOS capacitors on GaAs (100) surface with 2 nm Al2O3/8 nm LaLuO3/2nm Al2O3 as composite dielectric (structure A in Fig. 2). The observed frequency dispersion at accumulation capacitance is comparable to that of pure ALD Al2O3. Meanwhile, LaLuO3 with k = 25 to 30 provides a significant advantage in capacitance values. The work verifies the potential to integrate ALD higher-k dielectrics on III-V and deliver 1-2 nm EOT dielectrics by ALD for aggressively scaled ultimate CMOS technology.

0.0 0.5 1.0 1.5 2.00

2

4

6

8

10

12

14

16ALD Al2O3 (8nm)/GaAs (111)A VGS from 0V to 5.5Vin steps of 0.5VLCH=0.75 µ µ µ µm

Dra

in C

urre

nt I D

S(m

A/m

m)

Drain Voltage VDS(V)

Figure 1 I-V characteristics of an NMOSFET on GaAs (111)A surface with 8nm ALD Al2O3 as gate dielectric.

GaAs n-type or p-type(100) or (111)A

8nm LaLuO3

2nm Al O2 3

2nm Al O2 3

GaAs n-type or p-type(100) or (111)A

8nm LaLuO3

2nm Al O2 3

GaAs n-type or p-type(100) or (111)A

8nm LaLuO3

2nm Al O2 3

GaAs n-type or p-type(100) or (111)A

8nm LaLuO3

(A) (B) (C) (D)

Figure 2 Four LaLuO3 higher-k dielectric structures on GaAs.

-5 -4 -3 -2 -1 0 1 2 3 41.00E-011

2.00E-011

3.00E-011

4.00E-011

5.00E-011

6.00E-011

7.00E-011

8.00E-011

p-GaAs(100) substratePDA@600oC,30s

500Hz 10KHz 100KHz

As-deposited 500Hz 10KHz 100KHz

Cap

acita

nce

(F)

Gate Voltage (V)-4 -3 -2 -1 0 1 2 3 4 5

0.00E+000

1.00E-011

2.00E-011

3.00E-011

4.00E-011

5.00E-011

6.00E-011

7.00E-011

8.00E-011

n-GaAs(100) substratePDA@600oC,30s

500Hz 10KHz 100KHz

As-deposited 500Hz 10KHz 100KHz

Cap

acita

nce

(F)

Gate Voltage (V)

Figure 3 Multi-frequency CV of p-type and n-type GaAs MOS capacitors with the process splits of as-grown and 600oC post -deposition anneal (PDA). The diameter of the capacitors is 100μm.

AL

Dhi

ghA

LD

high

kkan

dhi

gher

and

high

erkk

inte

grat

ion

onin

tegr

atio

non

GaA

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choo

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lect

rical

and

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pute

r Eng

inee

ring,

fp

gg,

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ue U

nive

rsity

2. D

epar

tmen

t of C

hem

istry

and

Che

mic

al B

iolo

gy,

Har

vard

Uni

vers

ity

Pete

r’s G

roup

, Sch

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f EC

E Th

e 39

thIE

EE S

ISC

2008

.12.

11

y

Ye’s

Gro

up, E

CE

ALD

200

97.

20.

200

9

Out

line

Out

line

Mot

ivat

ion

Mot

ivat

ion

Brie

f res

ults

on

ALD

Al 2O

3/GaA

s(11

1)A

MO

SFET

ALD

Hig

her-

kLa

LuO

3de

posi

tion

proc

ess

ALD

Hig

her-

kLa

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3on

GaA

s(11

1)A

and

(100

)sur

face

sA

LDH

ighe

rk

LaLu

O3

onG

aAs(

111)

Aan

d(1

00)s

urfa

ces

---4

diff

eren

t MIS

stru

ctur

es a

re u

sed

to in

vest

igat

e

Sum

mar

y

Pete

r’s G

roup

, Sch

ool o

f EC

E Th

e 39

thIE

EE S

ISC

2008

.12.

11

Mot

ivat

ion

Mot

ivat

ion

1.Tr

aditi

onal

III-

V: h

igh

freq

uenc

y an

d/or

hig

h po

wer

app

licat

ions

; N

ew II

I-V

thru

st: h

igh

perf

orm

ance

logi

c ap

plic

atio

nsSi

bd

CM

OS

lii

ib

di

2015

Siba

sed

CM

OS

scal

ing

is g

oing

to b

e en

din

2015

.Fo

r 22

nm

tech

nolo

gy n

ode

beyo

nd, i

t req

uire

s no

vel c

hann

el m

ater

ials

such

asI

II-V

and

hig

h-k

2.T

he a

dvan

tage

of I

II-V

as c

hann

el m

ater

ials

is h

igh

elec

tron

mob

ility

.

3.A

dvan

tage

ofA

LD

high

-k:

3.

Adv

anta

geof

AL

Dhi

ghk:

---c

omm

erci

al A

LD

tool

s are

ava

ilabl

e--

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D se

lf-cl

eani

ng e

ffec

t on

III-

V

---s

i gni

fican

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gres

s on

III-

V M

OSF

ET

gp

gin

the

past

3-5

yea

rs u

sing

AL

D--

-eas

y tr

ansf

er to

Si C

MO

S pl

atfo

rmS

iIn

0.53

Ga 0

.47A

sIn

As

InS

bS

ist

rain

ed S

ibu

lk G

eG

aAs

GaA

sG

aNG

aNIn

PIn

PIn

0.53

Ga 0

.47A

sIn

As

InS

b

Si M

OS

FET

(Inte

l)

Pete

r’s G

roup

, Sch

ool o

f EC

E Th

e 39

thIE

EE S

ISC

2008

.12.

11

μe40

01,

000

3,90

08,

500

8,50

01,

250

1,25

05,

400

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08,

000

20,0

0030

,000

μ h16

024

01,

800

300

500

800

E g(e

V)

1.1

1.1

0.66

1.42

1.42

3.4

3.4

1.35

1.35

0.72

0.36

0.18

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01,

000

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08,

000

20,0

0030

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μ h16

024

01,

800

400

400

850

850

200

200

300

500

800

E g(e

V)

1.1

1.1

0.66

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0.18

Inve

rsio

n G

aAs M

OSF

ET

: A H

isto

rica

l Dile

mm

a In

vers

ion

GaA

s MO

SFE

T: A

His

tori

cal D

ilem

ma

Mos

t of i

nver

sion

GaA

s NM

OSF

ETs h

ave

min

uscu

le d

rain

cur

rent

( <

1 m

A/m

m).

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enet

alSo

lidSt

ate

Elec

troni

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1751

(199

7)-F

.Ren

etal

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tate

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troni

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1(1

997)

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uan

et a

l. A

ppl.

Phys

. Let

t. 88

, 263

518

(200

6)

-D. S

hahr

jerd

i et a

l. A

ppl.

Phys

. Let

t. 92

, 203

505

(200

8)

-any

man

y ot

hers

in 7

0s a

nd 8

0s.

New

Sol

utio

n : o

ur r

esul

ts o

n G

aAs(

111)

A(n

ext s

lide)

Alte

rnat

ives

:

(1) I

n-ric

h In

GaA

s (se

e re

cent

wor

k by

Pur

due,

Inte

l, IB

M, N

THU

, UC

SB…

)

Pote

ntia

liss

ue:n

arro

wba

ndga

pm

ater

ial

band

-to-b

and

tunn

elin

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tent

iali

ssue

:nar

row

band

gap

mat

eria

l,ba

ndto

band

tunn

elin

g,…

(2) S

i int

erfa

cial

con

trol l

ayer

or S

iH4

pass

ivat

ion

on G

aAs (

see

rece

nt w

ork

by U

T A

ustin

, Int

el, S

UN

Y A

lban

y, IB

M, N

US,

UT

Dal

las,…

.)

ili

ddii

lSiO

iO

ii

hi

l

Pete

r’s G

roup

, Sch

ool o

f EC

E Th

e 39

thIE

EE S

ISC

2008

.12.

11

Pote

ntia

liss

ue:a

dditi

onal

SiO

2in

crea

ses E

OT,

inve

rsio

n m

echa

nism

unc

lear

,…

Inve

rsio

n N

MO

SFE

T o

n G

aAs(

111)

A w

ith A

l 2O3

45

(A/m)

VG

S 0

~4V

in s

teps

of 0

.5V

x 10

-4

GaA

s(10

0)Lg

=4m

123

ain Current IDS

Lg4

m

GaA

s (1

00)

(111

)A G

a po

lar

(100

) Ga-

As

un-p

olar

0.0

0.5

1.0

1.5

2.0

0

Dra

Dra

in V

olta

ge V

DS (V

)

I DS=3

.5x1

0-4

A/

mX

100,

000

Exp

lain

ed b

y an

em

piric

al m

odel

Bas

ed o

n tra

p ne

utra

l lev

el s

hift

243036

tIDS (A/m)

VG

S 0

~4V

in s

teps

of

0.5V

GaA

s(11

1)A

Lg=4

m

GaA

s(1

11)A

00

05

10

15

20

061218

Drain Current

GaA

s(1

11)A

Pete

r’s G

roup

, Sch

ool o

f EC

E Th

e 39

thIE

EE S

ISC

2008

.12.

11[*

M. X

u et

al,

AP

L, 9

4, 2

1210

4, 2

009]

[* W

.E.S

pice

et a

l, JV

ST,

16(

5), 1

979]

0.0

0.5

1.0

1.5

2.0

D

rain

Vol

tag

e V

DS

(V

)

D

I DS=3

0 A

/m

Hig

her

Hig

her--

kkon

GaA

s for

EO

T sc

alin

gon

GaA

s for

EO

T sc

alin

g

Furth

er a

pplic

atio

n lim

ited

due

to th

e sm

all k

valu

e (8

~9) o

f Al 2O

3

Impl

emen

tatio

n of

hig

her-k

gate

die

lect

ric L

aLuO

3w

ith k

=24~

26!!!

Que

stio

ns:

Que

stio

ns:

How

to in

tegr

ate

high

er-k

LaL

uO3

on G

aAs

or II

I-V ?

Is it

feas

ible

to in

tegr

ate

LaLu

O3

dire

ctly

on

GaA

s ?

Pete

r’s G

roup

, Sch

ool o

f EC

E Th

e 39

thIE

EE S

ISC

2008

.12.

11

Hig

her

Hig

her--

kkdi

elec

tric

dep

ositi

on p

roce

ssdi

elec

tric

dep

ositi

on p

roce

ss

H2O

FurnaceHeater

FurnaceHeater

N2

Pump

Lu

La

120

o C115

o C

Diti

MO

pre

curs

ors

Oxi

dant

Bub

bler

tem

p.D

epos

ition

tem

p.La

2O3

: Lu 2

O3

La(a

md)

3Lu

(am

d)3

DI H

2O12

0oC

for L

a11

5oC

for L

u35

0o C

1:1

Pete

r’s G

roup

, Sch

ool o

f EC

E Th

e 39

thIE

EE S

ISC

2008

.12.

11[*

pro

vide

d by

Y. L

iu in

Pro

f. R

oy G

ordo

n’s

grou

p at

Har

vard

]

Req

uire

men

ts fo

r hi

gher

Req

uire

men

ts fo

r hi

gher

--kkin

tegr

atio

nin

tegr

atio

n

Hig

her-k

Met

al E

lect

rode

Com

patib

le?

Com

patib

le?

(4)

GaA

s

Diff

eren

t MIS

stru

ctur

es to

be

stud

ied

each

stru

ctur

e sp

lits

into

two:

• as-

depo

site

d

• PD

A@

600o

C,3

0s in

N2

8nm

LaLu

O

2nm

Al 2O

3

Ni G

ate

8nm

LaLu

O

Ni G

ate

2nm

Al 2O

3

Ni G

ate

8nm

LaL

uO3

2nm

Al 2O

3

GaA

s(11

1)A

or(1

00)

8nm

LaL

uO3

2nm

Al 2O

3

GaA

s(11

1)A

or(1

00)

8nm

LaL

uO3

2nm

Al 2O

3

GaA

s(11

1)A

or(1

00)

Pete

r’s G

roup

, Sch

ool o

f EC

E Th

e 39

thIE

EE S

ISC

2008

.12.

11

GaA

s(11

1)A

or (1

00)

GaA

s(11

1)A

or (1

00)

GaA

s(11

1)A

or (1

00)

(1)

(2)

(3)

CC--V

cha

ract

eris

tics o

n p

V c

hara

cter

istic

s on

p--ty

pe G

aAs

type

GaA

s

200

160

200

w/ P

DA a

s-de

posi

ted

(pF)

2nm

Al 2O

3

Ni G

ate

Fi

80120

citance

8nm

LaL

uO3

23

2nm

Al 2O

3

Freq

uenc

ies:

50

0Hz

10K

Hz

100K

Hz

-5-4

-3-2

-10

12

34

40

Capac

GaA

s(11

1)A

or (1

00)

Cap

acita

nce

incr

ease

d af

ter a

nnea

ling

due

to w

ater

-ads

orpt

ive

prop

erty

of L

a-ba

sed

diel

ectri

c

54

32

10

12

34

Gat

e Vo

ltage

(V)

diel

ectri

cA

ll p-

type

GaA

s MO

S C

Vs a

re “

good

-look

ing”

with

less

freq

uenc

y-di

sper

sion

at

accu

mul

atio

n, w

hich

incl

udes

(100

), (1

11)A

with

Al 2O

3, H

fO2,

HfA

lO a

nd L

LO.

Pete

r’s G

roup

, Sch

ool o

f EC

E Th

e 39

thIE

EE S

ISC

2008

.12.

11

It re

late

s with

ALD

“se

lf-cl

eani

ng e

ffect

” on

As 2

O3,

As 2

O5,…

(se

e Fr

ank

et a

l. 20

05,

Hua

ng e

t al.

2005

, Hin

kle

et a

l. 20

07, a

nd o

ther

s) a

nd lo

wer

hal

f ban

d-ga

p of

GaA

s has

less

pr

oble

m.

CC--V

cha

ract

eris

tics o

n St

ruct

ure

(1)

V c

hara

cter

istic

s on

Stru

ctur

e (1

)16

0

/PD

A

80120

160

w/P

DA

as-

depo

site

d

ance (pF)

NiG

ate

-4-3

-2-1

01

23

45

040

Capacita

Gat

eVo

ltage

(V)

8nm

LaL

uO3

2nm

Al 2O

3

Ni G

ate

n-G

aAs(

100)

Freq

uenc

ies:

50

0Hz

Gat

eVo

ltage

(V)

120

160

w/ P

DA

as-

depo

site

d

ce (pF)

2nm

Al 2O

3

GaA

s(11

1)A

or (1

00)

500H

z10

KH

z10

0KH

z

4080120

Capacitanc

EOT:

~3.

3nm

n-G

aAs(

111)

A

Freq

uenc

y di

sper

sion

on

(111

)A is

bet

ter t

han

that

on

(100

)

-4-3

-2-1

01

23

45

40

Gat

e Vo

ltage

(V)

()

Pete

r’s G

roup

, Sch

ool o

f EC

E Th

e 39

thIE

EE S

ISC

2008

.12.

11

Low

er D

ital

ong

uppe

r hal

f ban

d-ga

p of

GaA

s(11

1)A

EO

T~3.

3nm

,kva

lue

is e

xtra

cted

to b

e ~2

4

CC--V

cha

ract

eris

tics o

n St

ruct

ure

(2)

V c

hara

cter

istic

s on

Stru

ctur

e (2

)

120

160

200

w/ P

DA

as-

depo

site

d

ance (pF)

-4-3

-2-1

01

23

45

04080

Capacita

8nm

LaLu

O3

Ni G

ate

n-G

aAs(

100)

160

200

240

w/ P

DA

as-

depo

site

d

e (pF)

Gat

e Vo

ltage

(V)

8nm

LaL

uO3

2nm

Al 2O

3

GaA

s(11

1)A

or (1

00)

4080120

160

Capacitance

EOT:

~2.

3nm

()

()

n-G

aAs(

111)

A

Cap

acita

nce

incr

ease

d as

exp

ecte

d an

d EO

T sc

aled

dow

n to

2.3

nm

-4-3

-2-1

01

23

45

CG

ate

Volta

ge (V

)

nG

aAs(

111)

A

Pete

r’s G

roup

, Sch

ool o

f EC

E Th

e 39

thIE

EE S

ISC

2008

.12.

11

Exac

tly d

ue to

the

rem

oval

of A

l 2O3

capp

ing

laye

r of 1

nm E

OT

No

addi

tiona

l int

erfa

ce la

yer i

ntro

duce

d by

met

al/h

ighe

r-kdi

rect

con

tact

CC--V

cha

ract

eris

tics o

n St

ruct

ure

(3)

V c

hara

cter

istic

s on

Stru

ctur

e (3

)

NiG

ate

NiG

ate

8nm

LaL

uO3

2nm

AlO

Ni G

ate

8nm

LaL

uO3

2nm

Al 2O

3

Ni G

ate

2nm

Al 2O

3

GaA

s(11

1)A

or (1

00)

3

GaA

s(11

1)A

or (1

00)

160

200

240

280

w/ P

DA a

s-de

posi

ted

e (pF)

160

200

240

w/ P

DA a

s-de

posi

ted

ce (pF)4080120

160

apacitanc

4080120

Capacitancn-

GaA

s(11

1)A

n-G

aAs(

111)

A

-4-3

-2-1

01

23

45

40

C

Gat

e Vo

ltage

(V)

Surp

risin

gly,

cap

acita

nce

didn

’t ob

viou

sly

incr

ease

d af

ter a

nnea

ling

-4-3

-2-1

01

23

45

40C

Gat

e Vo

ltage

(V)

nG

aAs(

111)

An

GaA

s(11

1)A

Pete

r’s G

roup

, Sch

ool o

f EC

E Th

e 39

thIE

EE S

ISC

2008

.12.

11

Som

e in

terf

acia

l lay

er m

ay b

e in

trodu

ced

at h

ighe

r-k/G

aAs i

nter

face

Will

this

ext

ra-la

yer i

nflu

ence

the

inte

rfac

e qu

ality

?

Inte

rfac

e Tr

ap D

ensi

ty o

n G

aAs(

111)

AIn

terf

ace

Trap

Den

sity

on

GaA

s(11

1)A

253035

Al 2O

3/n-G

aAs(

111)

A (c

ontro

l) A

l 2O3/L

aLuO

3/n-G

aAs(

111)

A (3

)Al

O/L

aLuO

/AlO

/n-G

aAs(

111)

A(1

)

V-1)

152025

Al2O

3/LaL

uO3/A

l 2O3/n

GaA

s(11

1)A

(1)

2 cm-2eV

0510 it(x1012

(1~3

)X10

11

0.6

0.8

1.0

1.2

0

Di

E-E v

(eV)

Dit

was

ext

ract

ed b

y H

F-LF

met

hod

(3) a

lmos

t has

the

sam

e D

itas

the

cont

rol s

ampl

e, b

ut h

as h

ighe

r Dit

to th

e E C

edge

Pete

r’s G

roup

, Sch

ool o

f EC

E Th

e 39

thIE

EE S

ISC

2008

.12.

11

Surp

risin

gly

even

with

Al 2O

3IC

L, (1

) has

hig

her D

itth

an (3

)

Pure

hig

her

Pure

hig

her--

kkdi

rect

on

GaA

sdi

rect

on

GaA

s

No

reas

onab

le C

-V

char

acte

ristic

obta

ined

!!!ch

arac

teris

tic o

btai

ned

!!!

Hig

her-k

Met

al E

lect

rode

GaA

s

Pos

sibl

e P

robl

ems:

Two

inte

rface

s sh

ows

good

qua

lity

resp

ectiv

ely,

Why

doe

sn’t

it w

ork

with

pur

e hi

gher

-kdi

rect

on

GaA

s? S

mal

l con

duct

ion

band

offs

et ?

?

Furth

erin

vest

igat

ion

need

ed!!!

Pete

r’s G

roup

, Sch

ool o

f EC

E Th

e 39

thIE

EE S

ISC

2008

.12.

11

Furth

er in

vest

igat

ion

need

ed !!

!

Sum

mar

ySu

mm

ary

Inve

rsio

n N

MO

SFET

is re

aliz

ed b

y in

tegr

atio

n of

ALD

Al 2O

3on

GaA

s(11

1)A

Hig

her-k

LaLu

O3

isfir

stde

mon

stra

ted

tobe

inte

grat

edon

GaA

sH

ighe

rkLa

LuO

3is

first

dem

onst

rate

dto

bein

tegr

ated

onG

aAs

---m

etal

/LaL

uO3

inte

rfac

e qu

ite st

able

---A

l 2O3/L

aLuO

3/GaA

s has

com

para

ble

inte

rfac

e as

Al 2O

3/GaA

s2

33

23

---A

l 2O3/L

aLuO

3/GaA

s int

erfa

ce m

ay in

trodu

ce a

dditi

onal

laye

r afte

r PD

A

Furth

er st

udy

on m

etal

/LaL

uO3/G

aAs i

s nee

ded

We

ackn

owle

dge

the

valu

able

dis

cuss

ions

and

on-

goin

g co

llabo

ratio

n w

ith

Prof

. R.M

. Wal

lace

’s g

roup

at U

T D

alla

s. Th

e w

ork

is p

artly

supp

orte

d by

NSF

, SR

C F

CR

P M

SD C

ente

r, an

d D

oD A

RO

.

Pete

r’s G

roup

, Sch

ool o

f EC

E Th

e 39

thIE

EE S

ISC

2008

.12.

11