epitaxy deposition.ppt

epitaxy

1. Epitaxial Deposition
MANIT BHOPAL
1
MEMS
ABHISHEK SINGH
222116611

2. 2
Epitaxy
ThetermEpitaxycomesfromthe
Greekwordmeaning‘ordered
upon’.
Epitaxymeansthegrowthofa
singlecrystalfilmontopofa
crystallinesubstrate.
Formostthinfilmapplications
(hardandsoftcoatings,optical
coatings,protectivecoatings)itis
oflittleimportance.
However,forsemiconductorthin
filmtechnologyitiscrucial.

3. 3
Homoepitaxy:
The film and the substrate are the same material.
Often used in Si on Si growth (A on A)
Epitaxiallygrown layers are purer than the substrate and can be doped
independently of it.
Types of Epitaxy
Heteroepitaxy:
Film and substrate are different materials.(Growth of AlAson Si or GaAs
on Si).
Trying to grow a layer of a different material on top of a substrate leads to
unmatched lattice parameters.
This will cause strained or relaxed growth and can lead to interfacial
defects.
Suchdeviationsfromnormalwouldleadtochangesintheelectronic,
optic,thermalandmechanicalpropertiesofthefilms.
Allows for optoelectronic structures and band gap engineered devices.

4. 4
Ordered, crystalline growth
Epitaxial growth
Epitaxial Growth
NOT epitaxial
HighQualityFilm(1μmorless
thickness)depositedonahigh
qualitysubstrate.
Toensurehighcrystallinequality,
thelatticeparametersofthethin
layershouldmatchwiththatofthe
substrate(tominimizestrain).

5. 5
WhileSiisnottheidealmaterialfromanelectronicandopticalpointofview,its
abundance,easeofprocessingandavailabilityofagoodnativeoxidehavemadeit
thebackboneofsemiconductorindustry.
CombiningSisubstrateswithcompoundsemiconductorfilmswouldenablehigher
optoelectronicfunctionalityandhigherspeeds.However,thereareseverelattice
mismatchandchemicalcompatibilityissuesbetweenSiandmostIII-Valloysthat
precludedirectgrowth.
Metal-SemiconductorHetero-epitaxy:Metal-semiconductorstructuresareusedfor
contactapplications.Whilenotessential,epitaxialgrowthallowsincreasedelectron
mobilitythroughajunction.
Epitaxialgrowthisusefulforapplicationsthatplacestringentdemandsona
depositedlayer:
High purity, Low defect density, Abrupt interfaces, Controlled doping profiles
High repeatability and uniformity, Safe, efficient operation
Can create clean, fresh surface for device fabrication
Why Epitaxial Growth

6. 6
Engineered wafers
Clean, flat layer on top of less ideal
Si substrate
On top of SOI structures
Ex.: Silicon on sapphire
Higher purity layer on lower quality
substrate (SiC)
In CMOS structures
Layers of different doping
Ex. p
-
layer on top of p
+
substrate to
avoid latch-up
Why Epitaxial Growth
Tomakelayerwhichisnotavailableinnature
VeryimportantinIII-Vsemiconductorproduction
BipolarTransistor(Neededtoproduceburiedlayer)
III-VDevices(Interfacequalitykey,Hetero-junction
BipolarTransistor,LED,Laser).

7. 7
Steps:
Absorptionofadatoms
Surfacediffusion
Crystalgrowth
Evaporationofadatoms
Parameters:
Growthtemperature
Growthpressure
Flowamountofreactants
Substrateandtreatment
Epitaxial Growth Steps & Parameters

8. 8
Scheme of Epitaxial Deposition

9. 9
Epitaxial Deposition Techniques
Epitaxialgrowthcanbeperformedattemperatures
considerablybelowthemeltingpointofthesubstratecrystal.
Avarietyofmethodsareusedtoprovidetheappropriate
atomstothesurfaceofthegrowinglayer.
VaporPhaseEpitaxy/Chemicalvapordeposition(grown
fromVapor)
Liquidphaseepitaxy(grownfromaMelt)
Molecularbeamepitaxy(anevaporationoftheelementsin
aVacuum)
Withthiswiderangeofepitaxialgrowthtechniques,itis
possibletogrowavarietyofcrystalsfordeviceapplications,
havingpropertiesspecificallydesignedfortheelectronicand
optoelectronicdevicebeingmade.

10. 10
Liquid Phase Epitaxy
Reactants are dissolved in a molten solvent at high temperature
Substrate dipped into solution while the temperature is held
constant
Example: SiGeon Si
Bismuth used as solvent
Temperature held at 800°C
High quality layer
Molecular Beam Epitaxy
Very promising technique
Beams created by evaporating solid source in UHV
Not ideal for large area layers or abrupt interfaces
Thermodynamic driving force relatively very low
Epitaxial Deposition Techniques

11. 11
MOMBE---meanswhenMetelOrganicSourceusedforMBE
Sputtering---thelayerqualityisverypoor.Thusitisusedformaking
contactwiththehelpofmetalrelatedsource.
HVPE---HydrideVaporPhaseEpitaxy
PulselaserDeposition(PLD)
ReactiveEvaporation
ElectronBeamPlasmaTechnique
SolvothermalMethod
Epitaxial Deposition Techniques
*Advantages,Disadvantages,andApplicationsofallthese
techniquesareverymuchimportant.Pleasecollectallthe
information……………….

12. 12
Techniques Strengths Weaknesses
LPE (liguid phase epitaxy)Simple, High purity Scale economies Inflexible,
Non-uniformity
HVPE( hydride vapor
phase epitaxy)
Well developed Large scale No Al alloys Complex
process/reactor control difficult,
Hazardous sources
MBE Simple process, Uniform,
Abrupt interface In-situ
monitoring
As/P alloy difficult, Expensive ,
Low throughput
MOCVD/OMVPE/OMCVD
MOVPE
Most flexible, Large scale
production Abrupt interface
Simple reactor, High purity,
selective in situ monitoring
Expensive sources Most
parameters to control Accurately
Hazardous precursors
Overview of Epitaxy Techniques