CLEANING IN A VACUUM

Outline

• Vacuum processing

• Contamination and defects

• Cleaning in a vacuum

• Vacuum qualification test

• Organic contamination

• Summary

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VACUUM PROCESSING

What is a vacuum system

• It is a large strong metal container called a

Vacuum Chamber

• In use it is completely sealed to stop any

air getting in

• The materials to be coated are put in the

chamber before it is sealed

• All the air is pumped out

• The coating is made

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What is a vacuum chamber

• A sealed container from which all the air has

been pumped out

• The pressure within a vacuum is less than

normal atmospheric pressure (10−7mbar)

• Along with the air any water or other low boiling

point materials present within the materials of

the vacuum chamber or materials placed in it

for processing will also be sucked out

• This is called outgassing

Outgassing

• Most plastics will outgas so special

plastics have to be used in vacuum.

• There is more outgassing in flexible plastic

films

• Many additives will outgas

• Unreacted chemicals in rubbers will

outgas

• Even metals can outgas under vacuum

Vacuum Format

• Sheet format

– Mainly used in the semi-conductor industry

– Has to be cleaned before it enters vacuum

• Roll to Roll format

– Currently used in wide format for food

packaging

– Increasingly used in narrow format for Hi Tech

applications such as Plastic Electronics

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R2R vacuum line

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Benefits of vacuum

• Metal melts at a lower temperature

• Coatings can be deposited more quickly

• No oxidation of coatings like aluminium or

silver as there is no oxygen

• Very thin films can be deposited

• The films are very dense as there are no

solvents or other carriers

• No air molecules so no collisions

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Vacuum Processes

• Thermal Evaporation

• Chemical Vapour Deposition (CVD)

• Physical Vapour Deposition (PVD)

• Plasma Enhanced Deposition (PE)

• Atomic Layer Deposition (ALD)

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Thermal Evaporation

• Thermal Evaporation often called vacuum

metallizing.

• Metal is melted and turns into vapour

• Resistance heating or E beam melting

• Long established relatively low technology

• Used mainly in food packaging

applications to provide an oxygen barrier

• Metal used is mainly aluminium

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Chemical Vapour Deposition(CVD)

• Different chemicals are injected into the

vacuum chamber

• They react to form a material which is

condensed onto the film surface

• They can form conductive or insulative

materials

• They can also form ceramic coatings

• Used for barrier coatings and TFT

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Physical Vapour Deposition (PVD)

• Sputtering

• A solid metal target is hit with ions which

knock particles of metal off

• The particles of metal are attracted to the

film surface by an electric field

• The most common material is ITO

• This gives a conductive surface which is

transparent

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Atomic Layer Deposition (ALD)

• Conformal Thin Films on structured

substrate- self limiting

• 2 precursors – 2 half reactions separated

by a purge cycle

• Min Film Thickness ~0.1Å

• Can be in vacuum or ambient

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Plasma Enhancing (PE)

• Plasma is a cloud of ions

• There are two used for plasma in a

vacuum

– As a pretreatment to remove organic

contamination, change the surface energy of

the film and improve adhesion

– To supply energy to improve the coating

process

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Substrates

• Polyester Terepthalate (PET)

• Polyester Napthalate (PEN)

• Polyimide

• Polypropylene (PP)

• Metal foils eg steel or aluminium

• Flexible glass

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Vacuum Applications

• ITO Films

• ITO Glass

• Barrier Films

• Plastic Electronics

• Touch Panel

• OLED/OPV

• TFT

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CONTAMINATION AND DEFECTS

Technology Drivers

• Films are getting thinner – easier to

damage by particles in the wind of the roll

• Coatings are getting thinner – even

nanoscale particles can cause pinholes

• The functional requirements on coatings

are becoming more demanding

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Issues

• Particles of contamination on substrates

cause defects in vacuum deposition

processes used in Flat Panel display

manufacturing

• Defects cause significant yield loss

• Removal of particles is essential for high

functionality and reliability

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Challenges

• Yield

– Functional Failure

• Shorts/opens

– Barrier failure

• H20 ingress

– Brittle coating fracture

– Adhesion Failure

• Cost of substrate

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Key Yield Drivers

• Contamination

– Base film contamination

• Oligomer

• Particles

– Protective Film contamination

• Removal creates static which attracts particles

– Process Generated contamination

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Where contamination comes from

• People

• Atmosphere

• Substrate

• Deposition process

• Vacuum Chamber cleaning

• Vacuum Chamber pumpdown

• Vacuum Chamber venting

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How particles cause defects 1

• The particles prevent the coating reaching

the substrate

• The particles get covered in coating

• When the substrate is moved or rewound

the particles are knocked loose from the

substrate leaving uncoated areas called

pinholes in the coating

• These pinholes affect the functionality of

the film25

How particles cause defects 2

• Particles can fall from the walls and roof of

the vacuum chamber

• If they land on the surface of the film and

the film is wound up the particles will

cause a depression or dent in the film

which will repeat for several layers

• The particles can also fracture brittle

ceramic coatings during rewind

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How particles cause defects 3

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Starry Night 1

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Starry Night 2 - Korea

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Starry Night 2 – Korea

Japanese Base Film

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CLEANING IN A VACUUM

Cleaning Technology Options

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Cleaning Issues

• No outgassing

• No decline in cleaning performance

• No impact on Surface Energy

• Be able to clean full roll without intervention

• No air, not liquids

• Must not add static

• Operate at normal drum temperatures -15°C to 100°C

• Remove particles 20nanometer to 200micron

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Typical types of particle

• Particle size from 200 microns to 20 nm

• Small particles of airborne dust and fibres

• Slitting dust

• Metal particles from deposition process

• Ceramic particles from deposition process

• Particles from roll cores

• Particles from packaging and handling

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R2R vacuum line

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Cleaning Locations

• Unwind

• Post Deposition

• Rewind

• Rewind protective Film

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Which side to clean?

cooled deposition drum cooled deposition drum

thermal expansion substrate

thermal load thermal load

As the heat load is applied the substrate

wants

to expand but is constrained by the friction

between the substrate and cooled deposition

drum

Now there is some debris preventing the

web laying flat on the surface of the drum.

There is then, locally, less cooling & the

web wants to expand. As it is already off

the surface this is easy to achieve & the

wrinkle starts.

Debris

Keep the drum & substrate clean

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Rear Side Issues

• Particle on rear of film becomes front side

contamination at rewind.

• Ceramic coating are easily fractured by

rear side particle being pressed against

deposition.

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Rear Side Issues

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Results – Metallised PET

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Additional cleaning opportunities

• Hand Cleaning of Chamber/shields etc

• Hand cleaning of roll ends prior to loading

• Hand cleaning of outer wrap of roll

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Shield Cleaning

In the R2R vacuum tool cleaning is very important for

removal of particles from the machine. This cleaning can

be done with:

• Industrial vacuum cleaner with HEPA filter

Very suited for removal of large SiN flakes around the

microwave tubes and other locations

• Tissues with IPA

Very suited for cleaning drums

• Tacky roller (Teknek)

Very suited for cleaning walls/shieldings of all the

chambers

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Cleaning results with Teknek roller

Shieldings PC1

Shieldings PC1

Backside foil LL1-

PC1 1 PC1 walls LL1 bottom

Bottom PC1Bottom PC1

1 Backside foil dirty

because of removal slit

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VACUUM QUALIFICATION TEST

Teknek Technology

• Fully certified Vacuum compatible contact

cleaning system

– Nanocleen cleaning roller

• 100% silicone free, no other free chemistry – no

outgassing

• High cleaning efficiency – unaffected by vacuum

• No change to Surface Energy

– AREF Adhesive

• 100% silicone free, no release liner – no

outgassing

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Certified Vac Compatible

• Approved by Holst Institute (Holland)

– Tested at 10-7mbar

– Outgassing verified by RGA

– Silicone free verified by

• FTIR

• Edx

• RGA

– Cleaning efficiency checked before/after

vacuum exposure

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Vacuum Test - Holst Institute

• Scud Vacuum System 032

• 2 small rollers

• 2 sheets adhesive

• Pumped down to 1E-7 mbar

• Time in vacuum 66 hours

• Each sample weighed before and after

– Nanocleen Rollers – Weight loss 0.4% *

* Adsorbed moisture

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Cleaning performance before/after

Vacuum - Holst Institute

Teknek Cleaning System Efficiency Test - Holst Institute

Vacuum Conditions Particle

Nanocleen Roller AREF Adhesive Capacity (g)

ambient ambient 0.26

ambient 1 weekend in vac (0.1 mbar) 0.25

ambient 18 hours in high vac (1e-6 mbar) 0.25

1 weekend in vac (0.1 mbar) ambient 0.26

1 weekend in vac (1e-6 mbar) ambient 0.25

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RGA Test - Holst Institute

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ORGANIC CONTAMINATION

Oligomers

• Oligomers are unreacted monomers left in

the film during manufacture

• Oligomers migrate to the surface over time

• Temperature increases the rate of

migration

• Oligomers are not dry unattached particles

• Oligomers cause pinhole defects

Additives

• Antioxidants

• Nucleation promoters

• Radical scavengers

• Surface activators

• Anti misting

• Slip agents

• Colour

• Optical brighteners

• Viscosity modifiers

• Gloss improvers

• Anti static

• Anti blocking

• Voiding agents

• Dispersion stabilisers

• Flame retardants

• Surfactants

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Questions to ask

• How wide is the substrate

• What pressure is the vacuum operating

• Are the unwind and rewind operating at

the same pressure as the deposition

• What are the maximum and minimum

temperatures within the chamber

• What length is the roll of substrate

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Benefits Summary

• Teknek technology can now

– Remove particles down to 100 nm

– From all types of substrates

– As thin as 15 microns

– In both sheet and roll format

– At speeds from 1m/min to 300m/min

– In a high vacuum environment

– Without silicone

– Gives significant yield improvements

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