presentation 7 thin film
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Historical Development and Basic Concepts
Two main de osition methods are used toda :1. Chemical Vapor Deposition (CVD) 2. Physical Vapor Deposition (PVD)
- APCVD, LPCVD, PECVD, HDPCVD - evaporation, sputter deposition
Chemical Vapor Deposition (CVD)
Quartz reaction chamberRF induction (heating) coils
Exhaust scrubber
Furnace - with resistance heaters
Standup wafers
Silicon wafersGraphite susceptor
vent
VaccumPumpSiH 4 + O 2SiO 2 + 2H2
H2Ar
H2+PH3
H2+B2H6
HCl4 H2
SiCl 4 + 2H2 Si + 4HCl
Gas controland
sequencerSiH 4
O2
Source GasesAPCVD - Atmospheric Pressure CVD
LPCVD - Low Pressure CVD
30-250 Pa
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Chemical Vapor Deposition
12 6
7
Gas stream
Susceptor
Wafer
3 4 5
1. Transport of reactants to the deposition region.
*2. Transport of reactants from the main gas stream through the boundary.
*3. Adsorption of reactants on the wafer surface.
*4. Surface reactions, including: chemical decomposition or reaction,
surface migration to attachment sites (kinks and ledges); site
incorporation; and other surface reactions (emission and redepositionfor example).
*5. Desorption of byproducts.
. .
7. Transport of byproducts away from the deposition region.
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= =D
g
=
Chemical Vapor Deposition
S S S g
g S g g S
JS = Jg
J k h N
rowt ate v =
N
=
kS + hg N
Mass Transfer Limited : v hgg
Nfor kS >> hg
Nwhere N is the number of atoms per22 -3Surface Reaction Limited : v kS
Nfor hg >> kS
for the case of epitaxial Sideposition)
Exam le: Calculate the de osition rate for a CVD s stem h =1.0 cm/s k =10
cm/s, Ptotal= 760 torr, Psi=1 torr, T=1000oC.
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CVD Calculation( ) ( ) ( ) ( )
24
o
42
C1200atProcessDepositionReversible
gasHClsolidSigasHgasSiCl ++
ks term withks = k0exp(-Ea/kT)
ale) ReactionEtchingCompeting
SurfaceCleantoUsedbecanStreamInputinHCl
G G =
Net growth velocity
(lo
gsc ) ) )
24
SilaneofionDecompositPyrolytic-eAlternativ
2 gasSiClsolidSigasSiCl +
Reactioncontrolled
Mass transfercontrolled Mixed
2
600
42 HSiSiH C
o
+
The surface term is Arrhenius
with EA depending on the
.single crystal silicon deposition).
hG is constant (diffusion
through boundary layer).
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Epitaxial Growth
ReactionEtchinCom etinC1200atProcessDe ositionReversibleo
( ) ( ) ( )gasSiClsolidSigasSiCl24
2 +( ) ( ) ( ) ( )
SurfaceCleantoUsedbecanStreamInputinHCl
4224
gasHClsolidSigasHgasSiCl ++
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Epitaxial Growth
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RateGrowthEpitaxial Growth
ep epos on o en one a g o
get high quality single crystal growth.
hG controlled. horizontal reactorconfiguration.
+== g
gS
gSS
NhkNv
hG
corresponds to diffusion through a
boundary layer of thickness .
>>gS
g
ghk
Nhv for
:LimitedTransferMassS
= g
g
D
h
But typically is notS
along a surface.
special geometry isrequired for uniform
deposition.
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Epitaxial Growth
DV
=e
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Epitaxial Growth
u o op ng Out-diffusion
Pattern Shift During EpitaxialGrowth Over an n+ Buried Layer.
Pattern is Both Shifted andDistorted in Shape
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Epitaxial Growth
apor ase p axy 0.1-10 m/min
Liquid Phase Epitaxy (LPE) Compound Semiconductors . .
Molecular Beam Epitaxy (MBE) ompoun em con uc ors 0.001-0.3 m/min, 400-900oC, Pvac=10
-8 Pa
III-V Compound Semiconductors GaAs, InP, GaInAs, InAs
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CVD Polysilicon Deposition
25-150 Pa
Thermal Decomposition of Silane 100% Silane
20-30% Silane in Nitrogen
SiH600o C Si + 2H
100-200 /min at 600-650o C
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)500-(300AluminumoverDioxideSiliconofDeposition C
CVD Silicon Dioxide Deposition
LPCVDorPressurecAtmospheri-SiODopedPhosphous
577T2
2
o
2224++ CHSiOOSiH
ionMetallizatPrior toeTemperaturHigher
625425223
++ HOPOPH
SiO2 containing 6-8% phosphoruswill soften and flow at 1000-1100o C.
222
900atReactionlaneDichlorosi
22222
o
+++ HClNSiOONHSiCl
C
P-glass reflow can be used to
smooth surface topology.
( ) byproducts+SiOOCSi
C750-650TEOSofionDecompositLPCVD
2452
o
H
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CVD Silicon Nitride Deposition
Oxidation Mask for Recessed Oxidation
Final Passivation Layer Over Die Surface
Silane Reaction with Ammonia - 700 - 900oCat Atmospheric Pressure
3SiH4 + 4NH3 Si3N4 +12H2
Dichlorosilane Reaction - LPCVD at 700 - 800o C
2 2 3 3 4 2
Plasma Reaction of Silane with Nitrogen
4 + 2 + 2
Plasma Reaction of Silane with Ammonia (Argon Plasma)
SiH4 + NH3 SiNH+ 3H2
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Plasma Enhanced CVD (PECVD)
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Plasma Enhanced CVD (PECVD)
RF ower in ut
Electrode
Electrode
Wafers
Plasma
Gas outlet, pump
Heater
Gas inletSiH O
Non-thermal energy to enhance processes at lower temperatures. Plasma consists of electrons, ionized molecules, neutral molecules, neutral and
- , . Free radicals are electrically neutral species that have incomplete bonding andare extremely reactive. (e.g. SiO, SiH3, F)
The net result from the fragmentation, the free radicals, and the ion bombardmentis that the surface processes and deposition occur at much lower temperature
than in non-plasma systems.
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Plasma Enhanced CVD (PECVD)
A radio frequency (13.56MHz) voltage isapplied between the two electrodes causes
gas molecules, leading sustainable plasma
at lower pressure than dc plasma.
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Chemical Vapor Deposition
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-
CVD Metal Deposition
FWWF 3,
26
6
+
HFWHWF
WF
63
HydrogenwithofReduction-Tungsten
26
6
++
HClMHMCl 10252
HydrogenithReaction wLPCVD-TiandTaMo,
25 ++
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Physical Vapor Deposition
Definitions of Vacuum Regimes:
1.) Rough Vacuum: ~0.1-760 torr2.) Medium Vacuum: ~ 0.1 to 10-4 torr
~ -8 -4.4.) Ultrahigh Vacuum: < 10-8 torr
Molecular flow regime: gas densityu v y w, w u -
molecule collisions occur andmolecule-chamber wall collisionsdominate the flow process (moleculesare held back by walls)
Mean Free Path (MFP)
At room temperature, is 78 um for 1 torr (typical plasma process pressure) and
7.8106 meters for 110-11 torr (typical Molecular Beam Epitaxy systems).
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Kinetic Theory of Gas
Avera e velocit of as molecule:
m
kTzyx
2===
At RT, is 60 m for 100 Pa (sputter, Argon)and 60 meters for 110-4 Pa Eva oration .
ean ree a
Molecule Flux
PkTnn x 22 P
kTmmn
222===
kTn =
Mass Evaporation Rate
TP
kmP
kTmR
ME 22
==
A
T
P
k
mR
ML
2
=
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Physical Vapor Deposition(a) Filament Evaporation with Loops of
Wire Hanging from a Heated Filament
(b) Electron Beam is Focused on MetalCharge by a Magnetic Field
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Filament & Electron Beam Eva oration
Physical Vapor Deposition
2
coscos
r
=
coscos2
=r
G ML AT
P
k
mR
ML2
=
coscos2
22
=rTk
G
r
or2coscos ==
APm
42
2
0
2rTk
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Example: An evaporator is used to deposit aluminum. The aluminum charge ismaintained at a uniform temperature of 1100oC. If the evaporator planetary has a
42
2
0
2r
A
T
P
k
mG
=
,rate of aluminum?
27)( =Alm22 6.197854.0 cmRA
crucible==
3
/2700)( mkgAl =
torrAlP3101)( =
APm=
10022.6/)/(027.0
42
2323
23
2
0
2
molkg
rTk
=
)4.0(4
00196.0
1373
760/101325100.1
.
2
23
m
m
min
A8.17102.9 11
o
s
m==
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Shadowin and Ste Covera e Problems
Physical Vapor Deposition
Reason: Low Pressure Vacuum Deposition in which the Mean Free
a s arge. Solution:(a) High Pressure: smaller mean free path.
ea e wa er: o ac a e sur ace us on, amp(c) Rotate the wafer: continuously rotate the hemispherical cage
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S utterin
Physical Vapor Deposition_
Al target
Dark spaceor sheath
Al
Ar+
Al
Aro
-
Ar+
e-
O
Negative glow
r
Ar+
e-
e-
Wafer surface
Al Al
Al
Uses plasma to sputter target, dislodging atoms which then deposit on
wafers to form film.
- - .
Better at depositing alloys and compounds than evaporation.
The plasma contains equal numbers of positive argon ions and electrons
as well as neutral argon atoms.
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DC S utterin
Physical Vapor Deposition Most of voltage drop of the system
CathodeAnode
_
(V c)
Wafers(due to applied DC voltage, Vc)occurs over cathode sheath.
Argon plasma, ornegative glow
Cathodeglow
Cathodedark spaceor sheath
Anode sheath
sputtering yield, Y, defined as the
number of atoms or molecules
ejected from the target per incident
V
oltage
+
-
0Distance
V p0
on. s a unc on o e energy
and mass of ions, target material,
and incident angle.
V c
Ark+ ions are accelerated across
charged cathode, striking thatelectrode (the target) and
sputtering off atoms (e.g. Al). These
travel through plasma and deposit
on wafers sitting on anode.
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Thin Film DepositionStep Coverage
0.5
1.0
1.5
2.0a)
0.5
1.0
1.5
2.0
microns
c)
microns-2.0 -1.0 0.0 1.0 2.
-0.5
0.0
.i
microns-2.0 -1.0 0.0 1.0 2.0
-0.5
0.0
1.0
1.5
2.0
1.0
1.5
2.0
1.0
1.5
2.0
-1.00 1.000.0-0.5
0.0
0.5microns
-1.00 1.000.0-0.5
0.0
0.5microns
-1.00 1.000.0-0.5
0.0
0.5microns
Intrinsic Stress
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Deposition
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