As the demand for value-added products for the glass industry continues to grow, the glass industry has introduced advanced coating technologies to answer these growing market needs.

Magnetron sputtering is a vacuum coating process and one of the core methods for depositing thin films on glass. Bekaert’s technology allows customers to switch from planar to rotatable targets and offers lower cost of ownership through longer production runs, faster coating deposition and a more complete use of coating material. Bekaert has built its expertise in this field through its own sputter activity on plastic foil for window film and for industrial applications. Bekaert was the first to bring rotatable targets to the market and has developed the necessary sputter hardware to effectively use these targets on glass coating lines all over the world.
Industrial customers who execute a coating process for applications such as architectural and automotive glass (such as Low-E and solar control films, and anti-reflective coatings), display glass and photovoltaic glass can capitalize on Bekaert’s technology. Customers can also rely on Bekaert’s world-class customer support and leading research and development.

New range of rotatable sputter targets

Typical thin films and coating stacks for realising a variety of applications consist of TiO2, SiO2, Si3N4, SnO2,. These can be made by using advanced cylindrical target tubes, thus reducing the total cost of ownership and improving the ROI of glass coater operators in order to safeguard their competitiveness in the global market of today.

High Density Sn-Sputter Targets
Standard thermal sprayed Sn targets have a density of 90% of the theoretical density and an oxygen content of about 2000 ppm. Advanced thermal spray technology has resulted in the new high-density Sn target, reaching 99% of the theoretical density combined with oxygen content below 250 ppm. This new product combines the advantages of the thermal spray technology with high-density structures (See image above).
Sputter behaviour of this high-density Sn target, defined in terms of arc rate, burn-in behavior, deposition rate and I-V characteristics, shows an improved performance. Furthermore, advanced thermal spraying allows precise tuning of the grain morphology, grain orientation and material density. These flexible adjustments can be used to optimize performance to obtain specific sputter or coating characteristics, giving additional competitive advantage or cost saving to the glass coaters using this new type of target.

Thermal spray technology offers a broad range of capabilities to meet the challenging demands of sputtering targets.

• Doped materials can be produced in both stoichiometric and non-stoichiometric compositions without phase diagram constraints, allowing the glass coater operators to develop specific coatings for specific applications, not possible with classic target casting technologies.
• Nearly all materials can be sprayed, from low-melting point metals to high-melting point ceramics.
• Long-life (dog bone shaped) targets and different target lengths (up to 152”) are easily produced, helping further reduction in total cost of ownership.

TiOx targets
The production of TiOx targets is a typical example of how the strength of thermal spraying can be combined to result in a value-added target product. Firstly, the high process temperatures allow the ceramic Ti-oxide to melt. In parallel, the Ti-oxide undergoes partial reduction with the process gases, transforming it into an electrical conductive phase. Thanks to the high cooling rates the Ti-oxide remains conductive at room temperature.

The use of a Ti-oxide target instead of a pure metal Ti target drastically enhances the process stability in reactive processes without the need for a process control system like PEM. Moreover, sputter deposition speed can be improved by using Ti-oxide targets.

Si(Al) targets
SiO2 and Si3N4 thin films are sputtered starting from SiAl targets. The successful production of SiAl targets by thermal spraying takes advantage of key features of the spray process. Its inherent flexibility for target geometry not only allows a wide variety of target diameter, length, straight or dogbone target ends, but also gives the possibility to maximise the target sputter capacity by increasing the target layer thickness up to 9-13 mm. Al-dopant levels can range from 0 wt% to 19 wt% with strict control of the final chemical composition.

Advances in sputter hardware: new rotatable magnetron end blocks

Bekaert has further established itself as the leader in rotatable magnetron technology by introducing a new generation of ACV3 end blocks that integrate two advanced techniques to respond to the requirements and challenges of high power AC sputtering and the needs for improved robustness under a wide variety of operating conditions.

• An improved current transfer technique which has been incorporated into the end block in the form of a drum type slip ring to maximize the possible current density while minimizing brush wear. This concept allows extended service intervals while reaching mid frequent AC currents up to 400 A (180 kW, both AC and DC).
• An advanced water sealing technique which has been incorporated into the end block by replacing the lip seal with a mechanical seal. This mechanical seal is not sensitive to small particles in water or to sudden pressure shocks; it is self lubricating and wear resistant.

The ACV3 end blocks are the most recent additions to Bekaert’s line of proven, well-established industry-leading solutions. These new features complement the double dynamic seal for both water-atmosphere and atmosphere-vacuum with intermediate leak checking capabilities that have always been important features for avoiding catastrophic failures and proactively detecting seal break-down without the need for interrupting a running coating campaign. In addition, the new features further enhance Bekaert’s market leading end blocks which include a separately moving inner assembly within the fixed end block housing to compensate for possible non-axial movements of imperfect target tubes.

Conclusion

Magnetron sputtering is one of the most economical and results-driven processes due to advancements in technology, process and engineering. Any shortcomings of early planar magnetron sputtering techniques - for example, low target utilisation and limited sputter yield - have been overcome by the introduction of rotating cylindrical magnetrons with cylindrical target tubes

The Bekaert cylindrical magnetron with Bekaert ACV3 end blocks and Bekaert rotatable sputter targets offer the ultimate solution for maximum sputter efficiency in terms of sputter target utilization and sputter yield - which speak to the cost effective result of investing in this new technology.

Magnetron sputter deposition has become the most widely used coating technology for large area deposition on glass. In dealing in all of the end markets, be it in the architectural, automotive or display segments, magnetron sputtering will be important to your product success.

Authors:
Wilmert De Bosscher, Technology manager,
Hilde Delrue, R&D manager sputter targets

For more info:
Koen Staelens,
Product Market Manager sputter products,
Bekaert, Deinze, Belgium.
Tel: +32 9 381 61 61
Fax: +32 9 380 06 67
Email: infobac@bekaert.com
Website: