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Large Area Coating for Glazing 3rd Vacuum Symposium

17th October 2012 Ricoh Arena - Coventry

John Oldfield

Thin Film Technology and Analytical Science Group

NSG European Technical Centre

NSG Group

• Nippon Sheet Glass founded 1918 in Osaka, Japan

• Acquired Pilkington in 2006

• One of the worlds largest producers of flat glass

• Main business areas: Architectural, Automotive, Technical Glass

• Manufacturing operations in 29 countries

• Global sales of ¥550 billion

• Sales in 130+ countries

• 29,500 employees worldwide

John Oldfield 17/10/2012

Product

17/10/2012 John Oldfield

Glass in Buildings

• Increased use of glass in modern building design along with tighter European legislation has lead to a greater focus on energy efficiency

• 40-50% of European energy usage associated with buildings (mainly heating, lighting and cooling)

• Windows account for 18-30% of a buildings heat loss – estimated that up to 80% of UK glazing is not up to current standards

• Windows energy rating scheme introduced in 2006 – all glazing (new and replacement) must be rated C or above

• This is expected to rise to A rating by 2016 – difficult to achieve with traditional (pyrolytic) low-E coatings

• Increase in demand for vacuum sputter coated glass


Product Attributes

• Thermal performance dependant on climate:

− Cool climate - Thermal insulation (high visible light transmission and solar heat gain, good heat retention)

− Warm climate - Solar control (lower visible light transmission and little solar heat gain)

• Aesthetics equally important regardless of climate

• Tailor both the colour and amount of reflection to the end use of the product


Typical Installations

Exchange Place - Edinburgh

St. Helens College


The Sputtering Process

+ -

Ar Ar+ e-

Pumps Process Gas


Typical Coating Stacks

Glass

TiO2 20nm

ZnO 5nm Ag 12 nm ITO 3 nm

SnOx 40 nm

ITO 3 nm

Glass

ZnO 5 nm Ag 9 nm

SnOx 90 nm

Ag 9 nm ITO 3 nm

SnOx 30 nm

TiO2 20nm

Low-e

Solar Control To achieve the desired properties, the

layer sequences become quite

complicated.

Critical that the coating is deposited

uniformly across the substrate


Substrate size

Standard substrate size known as the ‘Jumbo’ (6m x 3.2m)


Manufacturing


Process Targets

• For high volume production:

• Large area coating with low manning level

• High deposition rate

• Continuous coating

• Long production campaigns

− Low downtime

• High quality

− Low reject rate

• Flexibility to make different coatings from same plant configuration


Coating Plant – ESG3 (Sweden)


Plant Layout

Coating Zone Transfer

Chamber

Transfer

Chamber

Load

Lock

Washing

Machine

Inspection

Room Exit

Lock

Glass Transport Direction

Vacuum Plant S

peed

Position

Leading Edge Speed


Target Materials

• Choice of target material is important when considering plant configuration

• For example to deposit TiO2:

− Buy a TiO2 target: deposit TiO2 (sputter in Ar)

• Alternatively we can vary layer composition by introduction of different gasses to the plasma

− Buy a Ti target: deposit Ti metal (sputter in Ar)

deposit TiOx (sputter in Ar and O2)

deposit TiNx (sputter in Ar and N2)

• Reactive sputtering increases range of materials that can be deposited from one plant configuration


Flexible Plant Layout

TMP TMP

Backing Line

PSU Gas Supply Manifold

TMP

Water Cooling

Coating Issues and Solutions


Debris/Arcing

Coating voids cause by material falling off target, shielding etc onto glass

1 mm

Flakes/pinholes

Discharge marks


Coating damage due to arcing to glass

Power Supplies

• For manufacturing, DC and AC power supplies used

• DC power supply:

− Good for metallic sputtering (high deposition rate)

− Poor for reactive processes (arcing, debris – yield losses)

− Disappearing anode effect

• AC power supply:

− Much better for reactive processes

− Reduced arcing

− More stable process


Power Supplies

DC PSU AC PSU

0 V

-450 V

time time

0 V

-450 V

+450 V


N

S

N

S

S

N

Planar Targets

• Magnet array ensure most ionisation occurs close to the target

• More ionisation within this region, hence more material sputtered in this area (racetrack)

• Target erosion greater in the racetrack than elsewhere on the target

• Typical target utilisation for planar targets 20-40%


Rotatable Targets

Magnetic

Array

Water

Cooling

Cylindrical

Target

• The magnet array is stationary and the target rotates

• Majority of target surface is sputtered and kept clean

• Much better target utilisation (~80%)

• Larger effective racetrack area on target (due to rotation) – less heating per area – can apply more power


Colour Issues


Arc colour patches (banding)

Cross width colour variations

Also plate to plate colour variations – drifting of layer thicknesses over time

Regions of plate where coating is deficient in a layer where arc management system has turned target off

Caused by layer thickness variations across the plate

Effect of Layer Thickness on Colour

Glass

TiO2

ZnSnO

Ag

a*

b*


Process Monitoring

• Traversing or static spectrophotometer heads and non-contact sheet resistance – data displayed in control room

• Data also fed into optical modelling software – can model thickness of each layer across width of the plate

Transport

Direction


Rate and Stability

• Need high deposition rates for high volume production

− Rate of production can be governed by deposition rate of one layer

− Correct choice of target material and power supply

− Also correct type and number of targets

• When sputtering reactively need to work at correct point on hysteresis curve

• Can use automated methods of control - better stability

Voltage and Optical Emission Hysteresis

Metallic

Oxidic

Working point


Control of Layer Thickness: Plasma Emission Monitoring

Gas Supply Manifold

PEM

Controller

& pc

Photocell filtered for emission line of interest

Ar

Reactive gas

Fast MFC

Fast valve


Other Factors

• Glass to be coated must be reasonably fresh i.e. less than 4 weeks old

• Good quality coatings rely upon efficient glass washing

• Need to be able to store coated glass for the duration of the product shelf life without any deterioration

• Glass must be able to be transported to customer in good condition

• Glass must be able to survive processing when it reaches the customer


Summary

• Modern glazing requires complex coating stacks • They coatings have very low thicknesses but need to have

uniformity and control over large areas • Sputter coating allows deposition of thin interference coatings

from a variety of materials • Cathode and power supply design lead to stable coatings over

coating campaigns • Feedback from optical and electrical measurements allow

continuous control to stay in specification • Substrate condition and post-coating handling are very important

non-trivial factors in delivering a quality product to customers


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