CLEANING IN A VACUUM
Outline • Vacuum processing • Contamination and defects • Cleaning in a vacuum • Vacuum qualification test • Organic contamination • Summary 2
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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 5
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 −7 mbar) • 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 8
R2R vacuum line 9
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 10
Vacuum Processes • Thermal Evaporation • Chemical Vapour Deposition (CVD) • Physical Vapour Deposition (PVD) • Plasma Enhanced Deposition (PE) • Atomic Layer Deposition (ALD) 11
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 12
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 13
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 14
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 15
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 16
Substrates • Polyester Terepthalate (PET) • Polyester Napthalate (PEN) • Polyimide • Polypropylene (PP) • Metal foils eg steel or aluminium • Flexible glass 17
Vacuum Applications • ITO Films • ITO Glass • Barrier Films • Plastic Electronics • Touch Panel • OLED/OPV • TFT 18
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 20
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 21
Challenges • Yield – Functional Failure • Shorts/opens – Barrier failure • H20 ingress – Brittle coating fracture – Adhesion Failure • Cost of substrate 22
Key Yield Drivers • Contamination – Base film contamination • Oligomer • Particles – Protective Film contamination • Removal creates static which attracts particles – Process Generated contamination 23
Where contamination comes from • People • Atmosphere • Substrate • Deposition process • Vacuum Chamber cleaning • Vacuum Chamber pumpdown • Vacuum Chamber venting 24
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 film 25
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 26
How particles cause defects 3 27
Starry Night 1 28
Starry Night 2 - Korea 29
Starry Night 2 – Korea Japanese Base Film 30
CLEANING IN A VACUUM
Cleaning Technology Options 32
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 33
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 34
R2R vacuum line 35
Cleaning Locations • Unwind • Post Deposition • Rewind • Rewind protective Film 36
Which side to clean? Now there is some debris preventing the As the heat load is applied the substrate web laying flat on the surface of the drum. wants There is then, locally, less cooling & the to expand but is constrained by the friction web wants to expand. As it is already off between the substrate and cooled deposition the surface this is easy to achieve & the drum wrinkle starts. cooled deposition drum cooled deposition drum substrate thermal expansion Debris thermal load thermal load Keep the drum & substrate clean 37
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. 38
Rear Side Issues 39
Results – Metallised PET 40
Additional cleaning opportunities • Hand Cleaning of Chamber/shields etc • Hand cleaning of roll ends prior to loading • Hand cleaning of outer wrap of roll 41
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 42
Cleaning results with Teknek roller Shieldings PC1 Backside foil LL1- PC1 walls LL1 bottom PC1 1 Shieldings PC1 Bottom PC1 Bottom PC1 1 Backside foil dirty because of removal slit 43
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 45
Certified Vac Compatible • Approved by Holst Institute (Holland) – Tested at 10 -7 mbar – Outgassing verified by RGA – Silicone free verified by • FTIR • Edx • RGA – Cleaning efficiency checked before/after vacuum exposure 46
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 47
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