Chemical Vapor Deposition

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Introduction to Chemical Vapor Deposition

A) Chemical Vapor DepositionCVD TypesCVD UsesCVD Process

General CVD Reactor ConceptGeneral CVD Process Advantages General CVD Process Applications

B) Dealing with Engineering Science of CVD ReactionsTransport Processes

Laminar Flow Boundary Layer ConceptOther Susceptor to Flow Axis Options

ThermodynamicsReaction Kinetics

C) Operational OverviewPolycrystaline SiliconSilicon DioxideNitride Films

LPCVDAPCVD

PECVD

Chemical Vapor DepositionCurrent Options

Atmospheric Pressure CVD

Plasma Enhanced CVD

Low Pressure CVD

CVD

Silicon Nitride

Silicon dioxide PolycrystallineSilicon

Epitaxial LayersCustomized Surfaces

Insulator Conductors

Barriers

Chemical Vapor DepositionCVD Applications

Arrival FlowRate

Substrate

Input Flow Rate

r = Growth Rate of Filmg

rg

Surface Reaction Rate

Gro

wth

Rate

Film

Chemical Vapor DepositionCVD Process

Surface Reaction

CVD Reactor Concept

Reaction Chamber

Susceptor

Controlled Thermal Environment

Controlled Pressure Environment

Film Surface

Hydrogen Carrier Gas

With additional film significant containing gas components

General CVD Process Advantages

Excellent Step CoverageLarge Throughput (100 A/min film growth)Low Temperature Processing (450 to 1000 C)Applicable to any Vaporization Source Technology(Laser CVD for direct Writing)

General CVD Process Applications

Epitaxial FilmsEnhance performance of Discreet and Integrated Bipolar DevicesAllow Fabrication of RAM’s and CMOS in Bulk Substrate

DielectricsInsulation between Conducting LayersDiffusion and Ion Implant MasksCapping Dopant FilmsExtracting ImpuritiesPassivation to Protect Structures from

ImpuritiesMoistureScratches

Polysilicon ConductorsGate ElectrodesConductors for Multilevel MetalizationsContacts for Shallow Junction Devices

B) Dealing with Engineering Science of CVD Reactions

Transport Processes

Thermodynamics

Reaction Kinetics

Transport Processes

Turbulent Flow No, to Many Particles.

Molecular Flow No, to Low a Throughput

Laminar Flow ( Only One Left, Make Do)

Set Conditions For Laminar Flow ( Low Reynolds Number Value)

R = D V ( )

Reynolds NumberLinear Velocity

Tube Diameter

# µ

Gas Density

Gas Viscosity

Laminar Flow Conditions

Diameter and velocity in tens of cm and cm/s will give Reynolds numbers in laminar flow regime

R = 1.76 x 10 5

Growth( D /R) (1/ T )

1.67

( T/ y ) (Z) P)

Boundary Layer Thickness

Reagent Partial Pressure

Reagent’s Gas Phase Coefficient of Thermal Diffusion

0.33

Susceptor

Input Reactant Gas Flow

Boundary layer develops along susceptor flow axis

X1

X2

X3

X4

Graphic Exaggerated for Visual Effect

Velocity Gradient Profiles at Discrete Points along Flow Axis

1 2 3X

4X X X

Un

der

dev

elop

ed

flow

pat

tern

at

this

p

osit

ion

alo

ng

susc

epto

r

Dis

tan

ce A

bov

e S

usc

epto

r

Trends in GradientsVelocity Values

Increase Along Susceptor Increase Above Susceptor

Temperature Values Increase Along SusceptorDecrease Above Susceptor

Reactant Concentration ValueDecrease Along SusceptorIncrease Above Susceptor

Velocity Gradient Profiles at Discrete Points along Flow Axis

1 2 3X

4X X X

Un

der

dev

elop

ed

flow

pat

tern

at

this

p

osit

ion

alo

ng

susc

epto

r

Other Susceptor to Flow Axis Options

Design Factors Include Flow Direction and Wafer Angle

A) Input gas flow

B) Input gas flow

C) Input gas flow

D) Input gas flow

E) Input gas flow

ThermodynamicsCVD Phase Diagram

Give range of input conditions for CVD that could produce specific condensed phases.Presented as Function of Temperature or Pressure vs Mole Fraction.

Boron codeposit only in High Boron Mole Fractions in input stream

Boron codeposition favored at higher pressures.1200 oC

1000 oC

1400 oC

Reactant Gas Mole Fraction

B/(Ti + B)

0.01 Atm 1.0 Atm

0.6

TiB 2 Phase

H/HCl = 0.95

Use Graphic for Educational Value Only7 th Conference on CVD 1979K.E. Spear

Electrochemical Society Vol 79

TiB

2 & B

Ph

ase

BCl 3/CH 4 = 4

Use Graphic for Educational Value Only

J. Electrochem. Soc. 123 ,136, 1976Bernard Ducarroir

10 -4 10 -3 10 -2 10 -1 10 -0

10 -4

10 -3

10 -2

10 -1

Partial Pressure for Methane

B4 C + C

B4 C

B4 C + B

B

CarbonVapor

1600 0 C

1.0 Atm

Boron-Carbon CVD Phase Diagrams

1 0 0 0 oC

9 0 0 oC

11 0 0 oC

Inp u t R e ac tan t G a s M o le F ra ctio nS i / (S i + V )

0 .6H /H C l = 0 .9 5

U se G raph ic for E du cation al V alu e O n ly7 t h C o n fe re n c e o n C V D 1 9 7 9K .E . S p e a r

Electrochem ical S ociety V ol 79

1 2 0 0 oC

VCl2

VCl2 + V5Si3

V5Si3

P = 0.25 atm

Vanadium-Silicon-Hydrogen-Chloride CVD Phase Diagrams

Vanadium-Silicon-Hydrogen-Chloride CVD Phase DiagramComposition ratios for input gases of VCl 4 /SiCl4 /H2 are not equilibrium values

Transport Processes vs Thermodynamics

Task: Make a V5 Si3 film.

Procedure: From CVD Phase Diagram for a 900 oC deposition, an input gas molefraction of 0.20 can be used.

Problem: As V5 Si3 forms on surface, actual reagent gas Si mole fraction consumedat surface is higher (0.375) than the input reactant gas ratio supplied(0.20). Thus Si at surface is depleted, more Vanadium is available at thesurface and actual equilibrium shifts to production of V3Si.

Procedure: Hold temperature constant but shift the input gas mole fraction to 0.5.

Problem: As V5 Si3 forms on surface, actual reagent vanadium gas mole fractionconsumed (0.625) is higher than the input gas mole fraction for vanadium. Thus Vanadium at surface is depleted, more Silicon is available at thesurface and actual equilibrium shifts to production of VSi2.

Reaction Kinetics

Use Graphic for Educational Value Only

124, 790 (1979)Besmann ,J. Electrochem. Soc.

1/T (x 10 / K)

5.0 6.0 7.0 8.0 9.0

1.0

10.0

Titanium Diboron Deposition Arrhenius Plot

P = 0.263 Atm.Input flow Rate = 462 cc /min

B/(B + Ti) = 0.66

Cl/(Cl + H) = 0.33

Input GasesTiCl 4

BCl 3

H2

Reaction Temperatures (2000 K to 1000 K)

-1

Use Graphic for Educational Value Only

Arrhenius Rate Profiles

1/T

1.0

10.0

(a)(f)

Lower Surface TemperaturesHigher Surface Reaction Rates

Use Graphic for Educational Value Only

Partial Pressure Reactant Gas

1.0

10.0

Arrhenius Isotherms

(a)

(f)Surface Reaction Limiting Growth Rate

1 / T

Best Fit Model Behavior based

Operational Line for Deposition at Higher Pressure

rg1

On 5 Calibration Runs

1/ T 2

rg2

Desired GrowthRate

New Operating Temperature

1/ T1

Current Operating Temperature

Current Growth Rate

ln (rg2

/ rg1

) (q act /k ) (T 2 T

1/ T2T1)

C) Operational Overviews

Polycrystalline Silicon (Polysilicon)

Four popular ways to alter pressure.

Change gas flow rate but keep pumping speed constant.

Change pumping speed with constant flow rate

Change reacting gas or carrier gas with other held constant

Change both gases but keep there ratio constant.

ConsiderationsTemperature

Pressure (LPCVD)

Si

H

HH H

Si Si

25 PA to 130 PA

100% Silane

25 PA to 130 PA

20% to 30% Silane

At high temperatures get gas phase reactions that produce rough, looselyadhering deposits and poor uniformity.At low temperatures deposition rates are to slow for industrial situations.

Zone heating rear of furnace up to 15 C hotter. (Better film uniformity)o

Si

APCVD

575 to 650

Toxic ( 1 Atm but 90% N2 )PyrophoricHigh Exposure Limit

Co

LPCVD575 to 650 C

o

Silicon dioxide

Low Temperature

Loose adhering deposits on side walls of reactor. ( Particles that cancontaminate the film.

At high silane pressures allows for gas phase reactions. ( Promotesparticle contamination and hazy films)

Fair step coverage

Low film density ( 2. 0 g/cm 3 )

Deposition rate complex function of Oxygen concentration

Easy chemical reaction. ( Low activation energy, 0.4 ev (10 kcal/mole) )

Film depends on gas phase transport of material to surface

Low temperature allows production of films that will serve asinsulation between aluminum levels in device.

Si

H

HH H

SiO2

(Oxidation)

400 - 450 CO2

Films Contain Hydrogen as

Silanol (SiOH)Hydride (SiH)

Or Water

Amorphous Structure of SiO4 Tetrahedra

Si

H

HH H

SiO 2

NO

650 to 750 C

SiO

CC

H

H

H

HO OC

H

H

C

H

H

OCH2CH3

CH2CH3

Silane Tetraethoxysilane

TEOS

SiO 2

650 to 750 C(LPCVD)

30 PA to 250 PA

100 to 1000 std. cc / min

Medium Temperature

S i

C l

HC l H

S iO 2

(N 2O )

85 0 to 9 00 C

D ic h lo ro s ila n e

LPCVD

Nitrous Oxide

High Temperature

Nonlinear pressure dependence that is function of wafer position.

Small amounts of Chlorine in films that tends to cause cracking in a poly layer)

Reagent depletion problems

Phosphorus doping is difficult. ( The phosphorus oxides are volatile at highdeposition temperatures.)

Excellent Uniformity

Except for epi and parallel plate processes both sides of wafer are coated.

EquipmentFurnace with or without vacuum capabilityPlasma Chamber

CVD is Crucial to Fabrication of IC's, Especially MOSFETS

(The Bottom Line)

Pad Silicon Dioxide

First Monolayerof Silicon Nitride

Si

Cl

Cl

N

HH

Precursor

NH Si Cl

H Cl

H

Cl

Cl Cl

H

H

N

HHH

Si

Cl

Cl H

HSi

Cl

Cl HH