Clear Barriers and High Volume Productivity

Rainer Ludwig and Liz Josephson

APPLIED MATERIALS

ABSTRACT

The volume of Transparent Barrier Coating used in commercial and industrial applications is growing. The target

markets for these coatings require the delivery of stable, high quality coatings. Compared to all other vacuum web

coating processes, EB-evaporation delivers the highest coating speed and productivity.

This paper gives an update on the state of the art of technology for Transparent Barrier Coatings with EB-evaporation

and shows recent results of our work regarding improvements of coating uniformity as well as an outlook for other

applications.

INTRODUCTION

Optimum flexible packaging material should combine maximum protection of the content with minimum adverse

effects to the environment. This can be achieved for example by the use of metallized films. By providing a gauzy

Aluminum layer to the plastic film, the oxygen transmission rate ( OTR ) can be reduced by a factor of up to 100 and

in addition a light protection is provided. Other new applications require also a low OTR or water vapor transmission

rate ( WVTR ), but in addition transparency for visible light, microwavability, or the use of a metal detector for the

packed food. This requirements can be fulfilled by replacing the aluminum layer of a metallized film by an oxide

coating. Different oxides like Silicon oxide ( SiOx ), Aluminum oxide ( Al2O3 ), Magnesium oxide ( MgO ), or

mixtures of different oxides can do the job. On the other hand, different vacuum coating processes can be used to

produce oxide layers:

With sputtering, all king of oxide layers can be produced at optimum quality level. But the coating speed is only in a

low percentage range of a metallizing speed.

Plasma Enhanced Chemical Vapor Deposition ( PECVD ) was proposed already by J. Felts in 1990 [ 1 ], but this

process could not gain a wider acceptance.

The most used process nowadays is evaporation, especially electron beam ( EB ) evaporation [2,3,4 ]. This process

provides not only coating speeds similar, or even higher, than metallizing, but is also flexible for the use of different

coatings and has a high robustness. This is of special importance for the production of transparence, “ not visible”

coatings.

In the following sections, the principle of EB web coating, with main focus on how to ensure coating quality will be

given.

ELECTRON BEAM WEB COATING

Fig. 1 shows the principle of inline layer control in an EB web coater, using feed back control from inline transparency

measurement.

Fig.1: closed loop control in EB web coater

As in a Metallizer, a substrate roll is wound through a vacuum chamber from unwind reel to a rewind reel, passing a

cooled coating drum. Below the coating drum, a crucible is located, filled with the coating material. The energy, needed

for the evaporation of this material comes from an electron beam, provided by an electron beam gun.

A scanning unit, directly installed in the electron beam gun, is moving the beam on the crucible surface. The power

distribution on the crucible surface is controlled by the actual measured transparency value on the corresponding

substrate surface area.

What is important for a stable Coating Quality?

Layer Uniformity

To be really sure about the layer thickness in an actual roll, all across its widths and length, it is a must to have an

inline measurement system for a relevant layer property.

For most transparent barrier layers the measurement of the optical transparency at low wave length can be used. An

example for such a measurement unit is shown in Fig. 2

Fig. 2.: Inline layer measurement system

Light from a light source outside of the vacuum is wave length selected ( wave length range 380 nm to 1000 nm ), is

split up and transferred to multiple sensor heads across the substrate width. The substrate is moving in between the end

of the glass fibers and the sensors. The system can also measure optical density up to OD 4.

The measured values of the different heads can be used for a closed loop control with the beam scanning unit. This

control is performed, using a special, patented software [ 5 ].

Uninterrupted Coating With high-voltage sources arcing always is an issue. Even with optimized EB guns, using separate pumped beam

generator chambers and additional intermediate pumping between beam generator and process chamber, particles from

the process may reach critical areas and cause arcing. Such arcs led to a shutdown of the high voltage power supply

and can result in uncoated areas on the substrate in web running direction.

Arcing cannot be avoided to 100 % and shutdown of power supply will occur. But uncoated areas on the substrate can

be avoided, if the shut down of the power supply is short enough. Such fast switching was ensured in older type power

supplies by using high power tubes. Nowadays modular, switching type power supplies are used, which also can

minimize the voltage interruption time to be in the range of several hundred microseconds [ 6 ]. Such a power supply

is shown in fig. 3.

Fig. 3: High-Voltage Power Supply

Pinholes

Here with transparent barrier coating, there is a big advantage against metallizing. Even if pinholes are present, they are

not visible! Usually pinholes are also not critical for the barrier function, in case the coated film is laminated

afterwards. However, in case of printing directly on the coating, a invisible pinhole can become visible. For example a

pinhole in a SiOx coating below a directly printed-on barcode can create problems.

In addition to usual counteractive measures, like polished guiding rollers, with EB machines pinholes can be minimized

with an optimized beam scanning program. However, the most influencing factor is the evaporation material itself.

Electrostatic Charging of the Substrate

Coating of plastic film with insulating layers at high speed is more critical than coating with a conductive metal layer.

In electron beam web coaters we have an additional charging up by reflected electrons. For discharging of the

substrate prior leaving the coating drum, an special plasma tool has to be used.

Adhesion Adhesion of the coating to the substrate is a key issue for later on processing like laminating or retorting. Adhesion can

be influenced by inline pretreatment. A detailed description is given elsewhere [ 7 ]. Depending on the requirements, in

electron beam web coaters are used either DC driven Magnetron glow discharge tools as shown in fig. 4 or RF driven

Hollow Anodes as shown in fig. 5

Fig. 4 : DC driven TreatMag

The TreatMag [ 8 ] is used in all kind of web coaters, like, EB machines, sputter machines, capacitor web coaters and

Metallizers. By running Ar-plasma it can be used for cleaning of the substrate surface. With reactive gases like oxygen

or nitrogen, also a chemical modification of the substrate surface is possible.

Fig. 5: Two Hollow Anodes in electron beam web coater

Compared to the TreatMag, with a RF driven Hollow Anode [ 9 ], higher energetic particles can be provided to the

substrate.

Substrate Overheating

Like in Metallizers, the coating has to take place on a cooled drum. Due to the reflected electrons the substrate is

charged up during coating with the effect of better thermal contact between substrate and drum. So thermal problems

are lower compared to Metallizers.

Transparent Barrier Coating

The barrier properties, the most important layer function ,cannot be directly measured. Even offline, only limited spot

measurements, which are very time consuming, can be done. So at least an indirect method for inline indication of

barrier properties should be helpful.

For PET substrates, a correlation of barrier properties with the coating thickness is known. Fig.6 shows the dependence

of OTR with coating thickness for different coatings.

Fig. 6. OTR as function of layer thickness

For all coatings ( Al, Al2O3, SiOx ) a stable barrier function starts at a thickness of about 20 nm. For Al, the OTR

decreases further with increasing coating thickness. For Al2O3 and SiOx the OTR values stays constant with increasing

thickness. That means, provided to have stable process parameters like vacuum, web tension, substrate temperature,

layer composition, also the barrier properties should stay stable, in case a certain minimum coating thickness can be

guaranteed. This is a good basis for quality insurance of the barrier properties. Of course, also the layer thickness

cannot be measured directly inline, but there is a relationship again to the optical properties. This relationship is a direct

one to OD in case of Al. In case of oxides a relationship to the transparency is given for constant stoichiometry.

Fig. 7 shows the light transmission of 12 µm PET, uncoated and with different SiOx layers.

Fig. 7. spectral transparency of SiOx layers

In case all above marked items are handled with care ( the coating is uniform within the right thickness range, the

coating is not interrupted and the substrate is not too much charged, the substrate was not overheated and the adhesion

is good ) also the barrier value range should be stable. However, stable at what value is a question which is mainly

influenced by the substrate itself. By applying the same coating to different substrates, the OTR value can vary in the

case of 12 µm PET between more than 3 to well below 1 cm3/m2 day. For OPP the range is between 20 and several

100. In case of reactive evaporation of Al2O3, there is an additional knob which can be influenced by the machine

supplier. It could be shown, that with plasma assisted evaporation, the range of barrier values is stabilized at the lower

end. Fig. 8 shows the patented arrangement of microwave tools in the evaporation chamber of an electron beam web

coater for initiation a plasma in the evaporation cloud.

Fig. 8: Microwave driven Plasma Source near Crucible

Optical Coatings

As an example for an optical coating, a multi layer of Al, Al2O3 and thin, semitransparent Al was produced in a

TOPBEAM. Such, Fabry Perot type systems provide different colors based on interference effect as shown in Fig. 9.

Fig.9 Fabry Perot type multi layer

The thickness of the transparent middle layer is the determining factor for the color. By viewing the coating under

different angles, the light has to pass different distances between the mirrors. This causes a color shift effect. Important

for a defined color is a very precise thickness uniformity of the middle layer. This can be provided also by closed loop

control of the EB, using a inline measurement system for spectral reflectance.

Figure 10 shows samples of different Fabry Perot Type coatings, produced in a TOPBEAM.

Fig. 10 Fabry Perot Type Coatings

CONCLUSIONS

With EB web coating a proven and robust process for mass production of transparent barrier coatings is available.

Depending different on requirements, also different coatings like SiOx, Al2O3 or even oxide mixtures can be

produced.

Based on improved inline layer thickness control possibilities, even optical multi layers for security, brand protection

applications, which were in the past only subject of the much slower sputtering process can be produced.

References

1. J. Felts, “Transparent Gas Barrier Technologies”, ”, 33

rd Ann. Techn. Conf. of the SVC, 1990

2. W. Lohwasser et. al. 2 Large Scale Electron Beam Web Coating, Not only for packaging”, 43rd

Ann. Techn.

Conf. of the SVC, 362, 2000

3. T. Ohta et. al, “A Ceramic (SiO2-Al2O3 mixture) Coated Barrier Film by Electron Beam Evaporation”, 43rd

Ann. Techn. Conf. of the SVC, 368, 2000

4. P. Seserko et. al., “ Transparent Barrier Coatings by electron Beam Evaporation – An Update”, 44th

Ann.

Techn. Conf. of the SVC, 482, 2001

5. M. Bähr et. al., “ New Scan and control System (ESCOSYSTM

) for High Power Electron Beam Techniques”,

Proc. Of PSE, 1996

6. A. Thiede et. al., “ New Type of High Voltage Power Supplies for Electron Beam Web Coaters”,46th

Ann.

Techn. Conf. of the SVC, 149, 2003

7. R. Ludwig et. al., “ In Chamber Pretreatment for Vacuum Web Coaters”, 48th

Ann. Techn. Conf. of the SVC,

2005

8. G. Loebig et. al., “TreatMag, a New Tool for Inline Plasma Pre-treatment in Web Coaters for Packaging

Applications”, 41st Ann. Techn. Conf. of the SVC, 502, 1998

9. M. Geisler et. al.,“ RF Plasma Tool for Ion-Assisted Large-Scale and Sheet Processing”, 44th

Ann. Techn.

Conf. of the SVC, 482, 2001

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2006 PLACE Conference

September 17-21 Cincinnati, Ohio

Clear Barrier and High Volume Quality Production

Presented by:

Rainer LudwigSenior Manager Sales and MarketingAPPLIED MATERIALS

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Introduction

Clear Barrier and High Volume Quality Production

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Clear Barrier

• Optimum Flexible Packaging =Maximum Protection + Minimum Influence to Environment

Metallizing• Additional Requirements for the Packaging:

Transparency for visible Light, Microwaveability, Use of Metal detector.

Can be fulfilled with Oxide Coatings :Silicon oxide ( SiOx ), Aluminum oxide (Al2O3), Magnesium oxide( MgO ); Mixtures of Oxides

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Oxide Coating

Clear Barrier and High Volume QualityProduction

...how to produce an oxide coating?

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Oxide Coating

• Sputteringcan do it, but Coating Speed in the low Percentage Range of Metallization

• Plasma Enhanced Chemical Vapor Depositionproposed since 1990, but no Breakthrough

• Evaporationhighest Productivity, mostly used, especially the most powerful Evaporation Process

Electron Beam Evaporation

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Electron Beam Web CoaterChamber Cross Section similar to MetallizerMost Difference is the Coating Source

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Electron Beam Evaporation

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EB Evaporation

HV-Power Supply ( 200 / 400 kW )

Crucible withEvaporation Material

Beam Controller ESCOSYS

Robust gun with decoupled pumping

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Winding

Reversible winding system optional

Max. width: 2100 / 1100 mm

Max. roll diameter: 1.2 / 1 m

Coating Speed: up to 17 m/sec

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Coating Processes

• Direct Evaporation of OxidesSiOx, Al2O3, SiO2, MgO, ....

• Reactive EvaporationEvaporation of Aluminum + Oxygen= Aluminum Oxide on the Substrate

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Quality

Clear Barrier and High Volume Quality Production

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Layer Quality

– Layer Functions?

– How to document?

– How to produce?

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Layer Quality

Metallizing Clear Barrier Coating

Thickness: OD, eye ?Defects: Light Transmission ?Adhesion: Tape Test ?

Layer visible Is there a coating at all?

Clear Barrier: Detailed Roll Report, including all relevant Layer Functions is needed

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Layer Functions

Metallizing Clear Barrier Coating

Barrier x xLight Protection xContent visible xMicrowaveable xMetal free x

Optical - , Electrical - and Barrier Properties

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Layer Quality - Optical Properties

• Requirement: To be Transparent

Inline measurement of optical Transparency

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Layer Quality - Electrical Properties

• Requirement:Not conductive

( Always ) fulfilled for Transparent Layers

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Layer Quality - Barrier Properties

• Direct Measurement: measure the Barrier– Time consuming, no inline process

Only spot check possible

• Indirect Inline Measurement utilizing other Layer Properties?– Thickness– Optical Properties

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Barrier Properties

OTR is a function of thickness ( shown on 12 µm PET )

But no direct inline measurement of thickness possible

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Layer Quality: Optical and Barrier Properties

Most Transparent Barrier Coatings have UV-Absorption Useable for Inline Measurement as indirect

Measurement of thickness

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Layer Quality – How to Document ?

• Optical Properties, TransparentInline Measurement of Transparency

• Electrical Properties, not ConductiveInline Measurement of Transparency

Both also valid also for uncoated Substrate

• Barrier Properties- Indirect Measurement: Is a Layer present in the

right Thickness Range?Inline Measurement of Transparency in the UV Range

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Quality – How to Produce ?

Inline Measurement of Transparency in UVInline Coating Control

•Other Quality related Items:Pinholes Layer Structure Electrostatic Charging Substrate Overheating Adhesion (Substrate )....

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Layer Measurement with LMS-XL

Glass fibers from light sourceand measurement sensors

Front view of base unit

The LMS-XL is used for measurement of OD ( 0.00...4 OD ) or T. The measuring wavelengthcan be selected by a filter ( 350 nm ...1000 nm )

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Pinholes

• Not critical for Barrier in case of Laminating• Can become visible in case of direct Printing

• Process dependent. Pinholes, mainly influenced by the Evaporation Material

A Pinhole in a Transparent Coating is not visible !

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Plasma Assisted Evaporation

Microwave driven Plasma sources near Crucible

Improved Barrier Range for reactive Process Al2O3

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Adhesion

• Adhesion is key issue for later processing like Laminating or Retorting Can be influenced with inline Plasma Pretreatment

Different Tools are available:

RF Hollow Anode

DC Magnetron

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( Substrate )

• Also important for Barrier is the Substrate

• Same Coating on different Type PET ( 12 µm )OTR between < 1 and 4

• Same Coating on different Type OPPOTR between < 20 and several 100

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Electrostatic Charging

• With EB, additional Charging from reflected Electrons

Charging is bad for winding

Charging is good for Substrate Cooling

Discharging of the Substrate prior leaving the Coating Drum

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EB Web Coater – Quality related Hardware

•Substrate charging and discharging

•Plasma Pre-Treatment of Substrate

•Plasma assisted Evaporation

•Inline Measurement

•Closed Loop Control

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• TOPBEAM 2100

TOPBEAM 1100

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Top View TOPBEAM 2100

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Further Applications for EB

1.Breakthrough for EB was ME-Tape

2. Breakthrough for EB was Transparent Barrier

Based on improved Hardware / Software for highly Uniform Coatings, EB has started to take over certain applications from sputtering processes, like optical Multi - Layers

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Color Shift Multi-Layer

Middle Layer(transparent)

Top Layer (semi-transparent)

Base Layer (Mirror)

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Layer Measurement with Optoplex

Closed loop controlwith ESCOSYS

Measurement of R (lambda )with Multiple heads across web widthMax./min values indicate thethickness

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Security coatings

• Fabry Perot Filter: Al - Al2O3 - Al

Advantage:Only one Evaporation material

Different layersystems producedIn TOPBEAM

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CONCLUSIONS

• EB Web Coating offers high Process Flexibility and Coating speed

• EB Web Coaters for high Quality / high Volume Production are State of the Art in Japan and Europe since Years

• Based on recent Improvements, EB Web Coating is ready ( and already used ) for Applications with highest Requirements in Uniformity

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Thank You

PRESENTED BY

Rainer LudwigSenior Manager Sales and MarketingAPPLIED MATERIALS

Please remember to turn in your evaluation sheet...