presentation 7 thin film

7/27/2019 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

=


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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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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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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-

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


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


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

presentation 7 thin film

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