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Chemical Vapor Deposition. This presentation is partially animated. Only use the control panel at the bottom of screen to review what you have seen. When using your mouse, make sure you click only when it is within the light blue frame that surrounds each slide. - PowerPoint PPT Presentation
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Chemical Vapor Deposition
This presentation is partially animated. Only use the control panel at the bottom of screen to review what you have seen. When using your mouse, make sure you click only when it is within the light blue frame that surrounds each slide.
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