Principles of Atomic Layer Deposition-EE412
description
Transcript of Principles of Atomic Layer Deposition-EE412
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Pri
nci
ple
s o
f A
tom
ic L
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r
De
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siti
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De
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J P
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ine
10
.27
.20
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nd
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ma
nd
Pro
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ritz
Pri
nz)
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Met
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ds
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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)
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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.
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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:
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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
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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
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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