Magnetron sputtering is a vacuum coating process for depositing thin films on glass. The demand for enhanced sputter deposition for large area coating is an aspect of manufacturing through which coating specialists have realized supplementary cost reductions resulting in added competitive advantage.
Today Bekaert works with its customers to implement sputtering technologies that help them transition simply from planar to rotatable targets, which lowers their cost of ownership, increasing return on investment. Driven by progress, Bekaert was one of the first companies to bring rotatable targets to market and has developed the associated sputter hardware to effectively apply targets on glass coating lines all over the world, while providing unparalleled customer service.
A New Range of Rotatable Sputter Targets
As the market interest in vacuum coating by magnetron sputtering grows, target manufacturing is consequently expanding. Thermal spray technology the preferred technology to meet the new, challenging demands of sputtering targets as it offers a broad range of capabilities to meet these very complex manufacturing demands.
The three benefits below directly impact customers total cost of ownership:
1. Material Compositions without Constraints – doped materials can be produced in both stoichiometric and non-stoichiometric compositions without the limits of phase diagrams, allowing the operators to develop specific coatings for definite applications that can not be done using classic target casting technologies.
2. Expanded Material Spray Coverage – nearly all materials can be sprayed, from low-melting point metals to high-melting point ceramics.
3. Target Flexibility – long-life (dog-bone shaped) targets increase thickness of the material at both ends, as a result target material utilization of more than 80% can under the right circumstances be achieved with most materials and different target lengths (up to 152”) and are easily produced.
Typical thin films and coating stacks which are necessary to realize a variety of applications consist of SnO2, TiO2, SiO2 and Si3N4, amongst others. These can be completed by using advanced cylindrical target tubes which reduces the total cost of ownership while improving the operators ROI.
9mm Thick Si(Al) targets
SiO2 and Si3N4 thin films are sputtered from Si(Al) targets. The successful production of Si(Al) targets by thermal spraying takes advantage of key spray process features. Its inherent flexibility for target geometry allows a wide range of target diameter, length, straight or dogbone target ends, while maximizing target sputter capacity by increasing the target layer thickness up to 9mm. Al-dopant levels can range from 0 wt% to 19 wt% with strict controls over the final chemical composition. By changing from standard 6 mm thick targets to the new 9 mm targets (containing 50% more material), your coating cost can be reduced with up to 3% and your uptime can go up by 5% due to less target swaps.
High Density Sn-Sputter Targets
Standard thermal sprayed Sn targets have 90% of the required theoretical density with an estimated oxygen content of 2000 ppm. Advances in thermal spray technology have resulted in a new high-density Sn target, reaching more than 98% of the required theoretical density, combined with oxygen content below 250 ppm. This advance combines the benefits of thermal spray technology with high-density structures. Defined in terms of arc rate, burn-in behavior, deposition rate and I-V characteristics the sputter behavior of the high-density Sn target demonstrates superior performance. In addition, advanced thermal spraying allowed for precise tuning of the grain morphology, grain orientation and the material density. These flexible adjustments optimize performance to obtain the specific sputter or coating characteristics, creating significant cost savings to users who employ this new kind of target.
A perfect illustration of how the use of thermal spraying results in a value-added target product is the production of TiOx targets. First, the high process temperatures allow the ceramic Ti-oxide to melt. Simultaneously, the Ti-oxide undergoes partial reduction with the process gases, transforming it into the electrical conductive phase. With high cooling rates the Ti-oxide remains conductive at room temperature. The use of a Ti-oxide target drastically enhances stability during the reactive processes without requiring a feedback loop process control system, while improving sputter deposition speed.
ITO (Indium Tin Oxide) is one of the top performing TCO’s (Transparent Conductive Oxides) available to the display market. Applications manufacturers can utilize it include flat panel displays, such as LCD, PDP and OLED, which utilizes the ITO layer as a transparent electrode. Today, reactive DC magnetron sputter deposition from a planar ceramic target is the most widely deployed technique for deposition of ITO coatings on glass and plastic substrates. But in spite of its popularity, the use of planar targets, which traditionally consists of one or more tiles bonded to a metallic backing plate, has several intrinsic restrictions. Rotating cylindrical ITO targets resolve many of the limitations of planar ceramic ITO targets.
Rotating cylindrical target technology offer customers inherent advantages over planar cathodes, including:
• Larger useful target inventory and increased target material utilization, both of which lead to reduced machine down-time
• Increased process stability for reactive depositions
• Improved target cooling, increasing power density and higher deposition rate (which is explained further below)
Preliminary field tests have revealed that customers will realize that total cost of ownership can be reduced by more than 40% per square meter while doubling the utilization of targets. As targets costs continue to increase, converting to rotating cylindrical magnetrons will increase the overall return on investment even more.
Three Magnetic Keys – Thickness Uniformity, Highest Deposition and Maximized Target Utilization
More demanding sputter applications necessitate stricter thickness uniformity. The accepted standard is usually a few percentage points for a substrate width over three meters. Additionally, magnetic field strength is the most effective way (next to gas tuning) to adjust the deposition profile to obtain ideal coating uniformity. The magnetic field at the target surface must be carefully considered in order to combine the highest possible deposition rate, optimized thickness uniformity and maximized target material consumption. A higher utilization means longer target life time and more effective use of the capital spent on buying targets. Increasing utilization has an immediate impact on decreasing the total cost of ownership for customers.
To answer the three magnetic technical challenges, which are fundamental to realizing important cost and utilization benefits for customers, Bekaert introduced a new Adjustable Magnet Bar designed for large area rotating cylindrical magnetron sputtering, incorporating recent magnetic and mechanical enhancements. The complete magnet bar, which is essentially a combination of magnets on a pole piece attached to a water conduction tube, is robust, easy to handle and is qualified in an off-line measurement set-up. The new design is suitable for horizontal as well as vertical applications and offers to the customers, enhanced and more flexible tuneability of the magnetic field while optimizing target utilization. The magnet bar is critical for high performance glass coaters operating at high coating levels.
Advances in Sputter Hardware - New Rotatable Magnetron End Blocks
Bekaert has established a leadership position in rotatable magnetron technology through the introduction of their ACV3 End Blocks, which is a new generation of hardware that integrates two advanced techniques that combine to resolve the complex challenges of high power AC sputtering, improving technical performance under a wide variety of operating conditions.
• Improved Current Transfer – this innovation has been incorporated into the Bekaert ACV3 End Block through a drum type slip ring, which was specifically designed to maximize potential current density while minimizing brush wear. This allows extended service intervals while reaching mid frequent AC currents up to 400 A (180 kW, both AC and DC).
• Advanced Water Sealing – this improvement in the Bekaert ACV3 End Block has been realized by replacing the lip seal with a mechanical seal, which is resistant to small water or sudden pressure shocks, additionally the mechanical seal is self lubricating and wear resistant.
These two new features complement the double dynamic vacuum seal that is designed for both water-atmosphere and atmosphere-vacuum conditions augmented by intermediate leak checking capabilities. This is an important feature which enables users to avoid catastrophic failures by proactively detecting seal break-downs before they happen without interrupting a running coating campaign. Additionally, Bekaert can work with customers to help easily upgrade all existing end blocks to the ACV3 version.
By making the End Blocks even more robust, higher mean time between failures are reached, lowering the chance of unplanned outages and decreasing glass coater’s total cost of ownership.
Rotatable Sputter Targets & Sputter Hardware = Total Cost of Ownership Advantages and a Better Customer Experience
Magnetron sputtering is the most economical and results-driven processes available today due to remarkable R&D advancements in technology, process and engineering. The numerous shortcomings of early planar magnetron sputtering techniques including low target utilization and limited sputter yield - have been overcome by the introduction of rotating cylindrical magnetrons with cylindrical target tubes. There are three significant advantages to adopting the rotating cylindrical magnetron sputtering method instead of the planar coating method -- superior material inventory, a higher degree of utilization and increased operation time of the display coater.
The Bekaert Drop-in Cathode deployed in tandem with the company’s ACV3 End Blocks, Adjustable Magnet Bars and rotatable sputter targets offers the industry the ultimate solution for maximum sputter efficiency (improving sputter target utilization and sputter yield). Industrial customers who implement a coating process for applications like display, glass and others can benefit from Bekaert’s sputter and hardware technology advancements.
With a global presence, Bekaert works collaboratively with their customers to provide reliable solutions that help grow and expand their customer’s business. The outcome of investing in this new, innovative technology will lower the total cost of ownership and as a result better equip Bekaert’s customers to compete and prevail in a globalized marketplace.
Article published with permission of and provided by: