Pri

nci

ple

s o

f A

tom

ic L

aye

r

De

po

siti

on

De

po

siti

on

J P

rov

ine

10

.27

.20

10

(sp

eci

al t

ha

nks

to G

an

esh

Su

nd

ara

ma

nd

Pro

f. F

ritz

Pri

nz)

Met

ho

ds

for

Dep

osi

tin

g Th

in F

ilms

Me

tho

dA

LDM

BE

CV

DS

pu

tte

rE

vap

or

PLD

Th

ick

ne

ss U

nif

orm

ity

go

od

fair

go

od

go

od

fair

fair

Fil

m D

en

sity

go

od

go

od

go

od

go

od

fair

go

od

Ste

p C

ove

rag

eg

oo

dp

oo

rva

rie

sp

oo

rp

oo

rp

oo

r

Inte

rfa

ce Q

ua

lity

go

od

go

od

vari

es

po

or

go

od

vari

es

Low

Te

mp

. D

ep

osi

tio

ng

oo

dg

oo

dva

rie

sg

oo

dg

oo

dg

oo

d

De

po

siti

on

Ra

tefa

irfa

irg

oo

dg

oo

dg

oo

dg

oo

d

Ind

ust

ria

l Ap

pli

cab

ilit

yva

rie

sva

rie

sg

oo

dg

oo

dg

oo

dp

oo

r

Tri-methyl

aluminum

Al(CH3)3(g)

CH

HH H

Al

Methyl group

(CH3)

ALD

Exa

mp

le C

ycle

fo

r A

l 2O

3 D

epo

siti

on

In a

ir H

2O

vapor

is a

dsorb

ed o

n m

ost surf

aces, f

orm

ing a

hyd

roxyl

gro

up.

With s

ilic

on this

form

s: S

i-O

-H (s

)

After

pla

cin

g the s

ubstr

ate

in the r

eacto

r, T

rim

eth

ylA

lum

inum

(TM

A) is

puls

ed into

th

e reaction c

ham

ber.

H O

Substrate surface (e.g. Si)

CH

H

H

H

Al

Reaction of

TMA with OH

Methane reaction

product CH4

H

HH

HHC

C

ALD

Cycle

for

Al 2O

3

Al(CH3)3 (g)+ : Si-O-H (s)

:Si-O-Al(CH3)2(s)+ CH4

Trimethylaluminum(TMA) reacts with the adsorbed hydroxyl groups,

producing methane as the reaction product

O

Substrate surface (e.g. Si)

CHH

Al

Excess TMA

Methane reaction

product CH4

HHC

ALD

Cyc

le f

or

Al 2

O3

Al

O

TrimethylAluminum (TMA) reacts with the adsorbed hydroxyl groups,

until the surface is passivated. TMA does not react with itself, terminating the

reaction to one layer. This causes the perfect uniformity of ALD.

The excess TMA is pumped away with the methane reaction product.

Substrate surface (e.g. Si)

CHH

Al

H2O

HHCO

HH

ALD

Cyc

le f

or

Al 2

O3

Al

O

After the TMA and methane reaction product is pumped away,

water vapor (H2O) is pulsed into the reaction chamber.

H Al

OO

Al

Al

New hydroxyl group

Oxygen bridges

Methane reaction product

Methane reaction

product

ALD

Cyc

le f

or

Al 2

O3

2 H

2O

(g)+ :Si-O-Al(CH3)2(s)

:Si-O-Al(OH)2(s)+ 2 CH4

O

H2O reacts with the dangling methyl groups on the new surface forming aluminum-

oxygen (Al-O) bridges and hydroxyl surface groups, waiting for a new TMA pulse.

Again metaneis the reaction product.

Al

H Al

OO

O

Al

Al

ALD

Cyc

le f

or

Al 2

O3

O

The reaction product methane is pumped away. Excess H

2O vapor does not react with

the hydroxyl surface groups, again causing perfect passivationto one atomic layer.

Al

HH

H

OO

OO

OAl

Al

Al

OO

OO

OAl

Al

Al

OO

OO

O

ALD

Cyc

le f

or

Al 2

O3

One TMA and one H

2O vapor pulse form one cycle. Here three cycles are shown, with

approximately 1 Angstrom per cycle. Each cycle including pulsing and pumping takes e.g. 3 sec.

O

Al

Al

Al

OO

OO

Al(CH3)3 (g)+ :Al-O-H (s)

:Al-O-Al(CH3)2(s)+ CH4

2 H

2O

(g)+ :O-Al(CH3)2(s)

:Al-O-Al(OH)2(s)+ 2 CH4

Two reaction steps in each cycle:

Ma

in C

om

po

ne

nts

of

an

ALD

Sys

tem

Ch

am

be

r

Ma

in V

acu

um

Va

lve

Ca

rrie

r G

as

Lin

e

(Va

po

r D

raw

)

ALD

Ma

nif

old P

recu

rso

r C

yli

nd

ers

ALD

Pu

lse

Va

lve

s

Ma

in V

acu

um

Va

lve

Pro

cess

Va

cuu

m i

n 1

00

-

10

00

mT

ra

ng

e

Ad

van

tag

es

of

ALD

U

niq

ue C

hem

istr

y D

rive

n P

rocess

Self-saturating reactions with surface

Thermal decomposition of precursor not-allowed

Low temperature and low stress

(molecular self assembly)

Excellent adhesion

20

0

30

0

40

0

50

0

60

0

Film Thickness ()

Gro

wth

Rate

per

Cyc

le

C

onfo

rmal C

oating

Perfect 3D conformality: no line of sight issues

Ultra high aspect ratio (>2,000:1)

Large area thickness u

niform

ityand s

cala

bility

C

hallengin

g S

ubstr

ate

s

Gentle deposition process for sensitive substrates

(i.e. biomaterials, plastics)

Coats challenging substrates (teflon, graphene

gold)

0

10

0

02

00

40

06

00

Film Thickness ()

Num

ber of C

ycle

s

Typical ALD processes have a growth

rate between 0.5-1.5 per cycle

Dis

ad

van

tag

es

of

ALD

U

niq

ue, C

hem

istr

y D

rive

n P

rocess

Not every material possible

Precursors can limit process due to reactivity / availability

Process limited by activation energy

No thermal decomposition of precursor allowed

C

onfo

rmal C

oating

Deposition can be comparably slow: cycles tim

es of 1 second to >1

minute depending on substrate and temperature

Removal of excess precursor and by-products is required

C

hallengin

g S

ubstr

ate

s

Functionalizationsteps may be required

ALD

W

ind

ow

Co

nd

en

sati

on

lim

ite

dD

eco

mp

osi

tio

n l

imit

ed

Gro

wth

Rat

e

/cyc

le

Ea

ch A

LD p

roce

ssh

as

an

id

ea

l p

roce

ss

win

do

w

in w

hic

h g

row

th i

s sa

tura

ted

at

a

mo

no

laye

r o

f fi

lm.

ALD

Win

do

wTe

mp

erat

ure

De

sorp

tio

n l

imit

ed

Act

iva

tio

n e

ne

rgy l

imit

ed

/c

ycle

Sa

tura

tio

n

Leve

l

Go

od

ALD

pre

curs

ors

ne

ed

to

ha

ve t

he

fo

llo

win

g c

ha

ract

eri

stic

s:

1.

Vo

lati

lity

Va

po

r p

ress

ure

(>

0.1

Torr

at

T