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Thin Film Deposition at NUFAB
CVD, ALD and Beyond
John Ciraldo and William Mohr
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Introduction
Northwestern University Micro/Nano Fabrication Facility
6000 foot Class-100 cleanroom
4 Bays:
Characterization
Lithography
Wet Bench Processing
Etch & Deposition
Staff of 6 scientist & engineers
Full process & development support
Located on ground floor of Tech F-wing
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Thin Film Deposition
PVD
Physical Vapor Deposition
Thermal Evap., MBE, e-Beam Evap., Sputter, PLD…
CVD
Chemical Vapor Deposition
PECVD,LPCVD,MWCVD, MOCVD…
Some other stuff
ALD, spin coating, electroplating…
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PVD vs CVD Physical Vapor Deposition (PVD) relies
on physical processes to vaporize solid materials
Chemical Vapor Deposition utilizes reactions between one or more precursors and in-situ gases Precipitate is deposited on substrate
CVD tends to be associated with higher temperature depositions and higher depositions rates
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Thermal Chamber is evacuated to high vacuum
Source material typically placed in W crucible
Source material is heated to sublimation, allowing for deposition
Reasonably good step coverage Can be controlled somewhat through
geometry
Spitting is possible for some materials
Deposition can be quite fast
Poor process tunability
Materials limited by thermal properties
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Evaporation
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Thermal Evap Denton Vacuum Explorer 14
Accommodates wafer sizes up to 6”
Substrate heating up to 200°C
Three 200kVA shielded sources
Recipes proved for:
Multiple metals, high rate Cu and Au
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At NUFAB
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Molecular Beam Special case of thermal evaporation
where Knudson (effusion) cells are
used and throw distance is typically
increased
Generally limited to epitaxy
Performed at UHV
Not available at NUFAB
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Epitaxy (MBE)
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E-Beam Special case of evaporation where the
source is heated by an e- beam
Generally line-of-sight coverage
Efficient use of source materials
Well suited for lift-off processes
Not ideal for 3D structures
Compound materials may decompose
under high temperatures
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Evaporation
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E-Beam AJA ATC-2036-E System
Accommodates substrates up to 6”
6 pockets for source material, 2 user
configurable
Water-cooled, rotatable substrate holder
Substrate heating to 200°C
Staff-provided processes
Al, Ni, Cr, Au, Ag, Mo, Ti, W…
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Evaporation
At NUFAB
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Sputtering Physical erosion via ion bombardment
Comes in many ‘flavors’
RF, DC, Pulsed-DC, HiPIMS…
Suitable for most solid materials
Generally good conformality
Somewhat process tunable
Provides challenges for lift-off
Processes are highly tunable
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Sputtering Plasma ignition via electrical excitation and
mechanical interactions
Ions, typically argon, are accelerated
towards the target material
Near the target, the ions are ‘steered’ by a
strong magnetic field
Upon ion collision, atoms are ejected from
target, with some depositing on substrate
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How does it work?
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Sputtering Plasma ignition via electrical excitation and
mechanical interactions
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How does it work?
DC RF Pulsed DC HiPIMS
Metals √ √ √ -
Dielectrics X √ √ -
Reactive √ √ √ √
Deposition Rate √ X √ -
Density - - - √
Smoothness - - - √
Ease of Use √√ √ X XX
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Sputtering
NUFAB has two sputtering systems Both systems:
AJA Orion 8 systems
Up to 8” substrate (4” above 350 °C)
Up to 850°C Substrate heating
RF substrate biasing
+/- 2% thickness uniformity
Sputter I is ‘workhorse’ most flexibility in allowed materials
RF, DC, Pulsed DC and HiPIMS capabilities
User installed targets
Sputter II is high purity system RF, DC and Pulsed DC capabilities
Staff installed targets
Recently added gold and platinum sources
Staff-written processes: Ultra fast, multiple source processes for Cu and reactive
SiO2
ITO, Bi, Fe, Au, Pt…
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NUFAB Capabilities
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Pulsed Laser Sputtering, but with lasers
Source material is ablated form target
using high-power laser pulsed
Can be prone to spitting, particulate
formation and globular depositions
Due to vapor quenching, can be used
to study metastable material phases
Not available at NUFAB
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Deposition
(PLD)
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Thin Film Deposition
PVD
Physical Vapor Deposition
Thermal Evap., MBE, e-Beam Evap., Sputter, PLD…
CVD
Chemical Vapor Deposition
PECVD,LPCVD,MWCVD, MOCVD…
Some other stuff
ALD, spin coating, electroplating…
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Chemical Vapor Deposition typically occurs due to
reactions at the substrate surface
Not a single technique, but a family of
techniques
Prone to high rate depositions for thin
and thick films
Far too many variants for a single talk
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Deposition
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Low Pressure Functionally similar to APCVD
(atmospheric pressure CVD)
Common technique for silicates
Pressures on order of 75-750 mTorr
Lower pressure dramatically improved
mass transport characteristics (slows
them)
Improved step coverage
CVD is thermally driven
Typical temperatures in the range of 600-
1100°C
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CVD (LPCVD)
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Plasma Chemical interactions induced via
electrical stimulation, rather than
thermal
Allows for significantly lower substrate
temperatures during deposition
Typical excitation is RF, but may be DC
Very fast depositions realizable
10s to 100s of nm/min possible
At very high rates, uniformity may be
sacrificed
Good conformality for structured wafers
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Enhanced CVD
(PECVD)
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LPCVD
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vs PECVD
PECVD LPCVD
Deposition Temperature Low High
Deposition Rate High Low
Wafer Capacity Low High
Substrate Damage Low None
Uniformity Good Excellent
Film Density Good Excellent
Stress Tends to be compressive
(may be adjustable)
Typically low
Sides Coated Single Double
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LPCVD Recipes for standard and low-stress
Si3N4
Both recipes stoichiometric
Dichlorosilane (SiH2Cl2) based recipes,
ammonia reducer
4” Wafer capability, with ability to load
many wafers simultaneously
25 wafers/carrier
Processing temperature: 835°C
Fully automated processes
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At NUFAB
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PECVD
STS (SPTS) LpX CVD tool
Configured for 4” substrates Small substrates easily accommodated with
carrier wafer
Equipped with loadlock and automated transfers
Fully automated processes
Silane based processes
Recipes for silicon oxide, silicon nitride and polysilicon
Typical process temperate is 300°C Can accommodate 200-400°C processes
Dual excitation sources for stress control in nitride films HF: 13..56 MHz, LF: 380kHz
Staff-Provided recipes for Low stress SiO2, low stress Si3N4, polysilicon at multiple dopant concentrations, low temp processes…
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At NUFAB
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Overview of Techniques
Conventional deposition techniques
MOCVD
ALD
Less Conventional
Parylene
Spin on Glass (SOG)
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MOCVD Overview
Metal Organic Chemical Vapor Deposition
Typically used for III-V or II-VI materials
GaN, InGaAs, AlGaAs, GaAs, InP, SiC, AlN
Homoepitaxy and heteroepitaxy
Typically used in for creating photonic and power and RF devices
Pros:
High throughput
Epitaxy
Large variety of materials
Easy to change between materials
Sharp interfaces
Good uniformity
Cons:
Expensive
Can have extremely hazardous and or expensive sources
Process needs to be closely monitored
Not at NUFAB
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MOCVD: Metal Organics
Metal Organics
Ligand
Metal
Typical Sources
Trimethyl Aluminum
Trimethyl Gallium
Triethyl Gallium
Trimethyl Indium
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Ligand
Metal
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MOCVD: Hydrides
Hydrides
Typical Sources
NH3
AsH3
PH3
SiH4
Si2H6
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MOCVD: Principal of Operation
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Carrier Gas
Hydrides
Metal Orgainics
Pump and
Exhaust system
Hydride manifold
MO manifold
Wafer
Gas Injection
Susceptor
planetary
rotation
Heater
Chamber
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MOCVD: Principal of Operation
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MOCVD: Principle of Operation
1. Metal Organics and Hydrides
Mix in reaction chamber (500 –
1200C)
2. Chemicals pyrolyze in chamber
due to heat
3. Resulting metal lands on
surface and random walks until
a step is found
4. Organic is removed through the
exhaust
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ALD Overview
Atomic Layer Deposition Typically used when:
High uniformity is required
Need to coat sidewalls of device
Very tight thickness tolerances
Typically lower temperature deposition as compared to other CVD processes
Pros: Large variety of materials
Easy to change between materials
Sharp interfaces
Good uniformity
Cons: Low throughput
Very slow
Can have extremely hazardous and or expensive sources
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ALD: Applications
Optical Antireflection
Optical filters
Photonics
Transparent Conductors
Electronics/MEMS Gate dielectrics
Gate electrodes
Diffusion barriers
DRAM
Flexible electronics
Other Nanotubes
Powders
Wear/corrosion resistant coatings
Fuel cells/catalysis
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Same precursors as MOCVD
Additional precursors are also available based on material,
temperature, cost restraints
Typical reducers for ALD
H2O
N2 plasma
O3 (Ozone)
O2 plasma
NH3
NH3 plasma
ALD: Sources
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ALD: Principle of Operation
Discrete steps
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"Thermal and Plasma-Enhanced Atomic Layer Deposition on Powders and Particles Geert Rampelberg, Véronique Cremers, Delphine
Longrie, Davy Deduytsche, Johan."
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ALD: Principle of Operation
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Carrier Gas
Oxidizer/
Reducer
Metal Organics
Pump and
Exhaust system
Oxidizer/ Reducer
manifold
MO manifold
Wafer
Plasma
Injection
Heated
chuck no
rotation
needed
Chamber
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ALD: NUFAB Capabilities
Arradiance GEMStar XT-P
Up to 6” substrates
Chamber Heats to 350C
Platten Heats up to 500C
Four slots for precursors
Can be changed by Staff with 48 hr
notice
Can create Ar, O2, H2, NH3 plasma
Mechanical rotation for coating
powders
Films currently available:
Al2O3, HfO2, TiO2, Pt, ZnO, SiO2
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Parylene: Overview
CVD process that creates biocompatible coating of devices for medical industry
Also used to protect electronics from the environment
Pros: Directly coats surfaces at room temperature with high uniformity, high repeatability, and
pinhole free
Chemically stable and biocompatible
Barrier to oxygen and moisture
Fungal resistant
Thermal mechanically stable
Electrical isolation of samples
Adheres well to most surfaces
Cons: Limited only to parylene
Must be vacuum compatible
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Parylene: NUFAB Capabilities
SCS Labcoter2 Parylene
Deposition System
Two systems: I and II
Fixture Rotation
Process parameters optimized for
Parylene C
provided by NUFAB
1g of Parylene yields ~ 1µm of film
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Parylene: Principle of Operation
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Furnace
Heats to
690C
Pump
Cold Trap
Substrate
holder
Dimer
Solid
Dimer
Gas
Monomer
Gas Polymer
Gas
distribution
Rotates
Vaporizer
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Spin On Glass (SOG): Overview
Method for depositing SiO2 without a vacuum chamber
Used for barrier layers and for electrical isolation
Biodegradable
Able to deposit at a range of thicknesses depending on spin speed and viscosity
Used in electronic industry as replacement for PECVD for electrical isolation and in medical field as biodegradable/biocompatible barrier
Silicate (e.g. Na2SiO2 + water + ethanol + acetone + isopropanol)
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Spin On Glass (SOG): Procedure
Attach substrate to spin coater
Apply SOG
Set spinner to 3000 RPMs for 40 sec
Bake at 200C for 60s
Repeat procedure for a thicker coating
Bake at 400C for 30min to solidify completly
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Spin On Glass (SOG): NUFAB Capabilities
Properties after baking for 200C for 60sec
Thicknesses: 200 nm
Index of refraction: 1.41
Properties after baking for 400C for 30min
Thickness: 170nm
Index of refraction: 1.34
Volume Resistivity 5x1013 Ωcm
Surface Resistance 2x1012 Ω/
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Review
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PVD CVD ALD Parylene Spin on Glass
Deposition
Temperature
Low High Fair Low Fair
Deposition Rate Low High Low Fair -
Substrate Damage Depends Low Depends None None
Uniformity Good Good Excellent Good Good
Film Density Good Excellent Depends Excellent Excellent
Stress Tends to be
compressive
(may be
adjustable)
Typically low Depends Low Low
Manufacturability High High Low Fair High
High Aspect Ratio
Conformality
Depends Good Excellent Good -
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