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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
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Product
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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
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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
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Typical Installations
Exchange Place - Edinburgh
St. Helens College
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The Sputtering Process
+ -
Ar Ar+ e-
Pumps Process Gas
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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
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Substrate size
Standard substrate size known as the ‘Jumbo’ (6m x 3.2m)
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Manufacturing
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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
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Coating Plant – ESG3 (Sweden)
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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
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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
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Flexible Plant Layout
TMP TMP
Backing Line
PSU Gas Supply Manifold
TMP
Water Cooling
Coating Issues and Solutions
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Debris/Arcing
Coating voids cause by material falling off target, shielding etc onto glass
1 mm
Flakes/pinholes
Discharge marks
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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
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Power Supplies
DC PSU AC PSU
0 V
-450 V
time time
0 V
-450 V
+450 V
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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%
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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
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Colour Issues
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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*
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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
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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
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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
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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
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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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