In in-line PVD sputtering systems, substrates are linearly passed beneath one or more sputter cathodes to obtain their thin film coating. This motion is facilitated by loading the substrates onto a carrier or pallet. Smaller systems are capable of handling only one pallet per batch run, but larger systems can handle multiple pallets by using end station pallet handlers, which send and receive pallets one after another in an ongoing convoy that pass through the transport subsystem, in a fashion wherein the tip of each follows behind the tail of the prior one.
The most common and least complicated setup is to have the cathodes and the pallets horizontal with substrates on the bottom and cathodes on top in a sputter down orientation. In this configuration, the substrates are held onto the pallets and the pallets are held onto the transport mechanism by means of gravity. The transport mechanism can just be chains that run alongside rails via the vacuum chamber.
The horizontal arrangement can be also performed in a sputter up orientation wherein substrates on top and cathodes on the bottom. However, this configuration requires mechanical means to hold the substrates in place in order to avoid their falling. This arrangement is not commonly used for single sided coating, but is sometimes used for double sided coating, where cathodes are placed both above and beneath the pallets. In this case, the pallets have appropriate openings to keep the substrates in place in order to obtain the sputter up coating on the bottom sides from the lower cathode, while simultaneously obtaining the sputter down coating on the top sides from the upper cathode. However, horizontal arrangement does have a drawback in terms of particulates that get created within the chamber. In sputter down mode, these particulates can easily get embedded in the film subsequent to their landing on the substrates. In sputter up mode, those particles do not land on the substrates, but can get re-sputtered by landing onto the targets.
Other Configurations and Features
The vertical orientation option for side sputtering provides a better particulate environment. In this case, both the pallets and the cathodes are placed in vertical position, but the deposition is lateral. However, the complexity of the tooling and transport system is substantially increased in order to hold the substrates on the pallet and keep the pallet in that orientation. This arrangement reduces the chance of particles to get landed onto either the substrate or the cathode. In any of these configurations, many different types of cathodes and power can be employed. Moreover, it also possible to accommodate optional stages such as sputter etch, heat, or ion sources. The complete suite of instrumentation and controls are available for sputter applications such as optical coatings, dielectrics, and metallic/conductive coatings.
Although other types can be used, the most popular form of cathodes used in such systems is rectangular. Moreover, even if the cathodes can be configured for intentionally non uniform coating, most users want uniform coating of their substrates. In an in-line system, the uniformity in the direction of travel of the pallet relies on the stability of the chamber pressure/gas mixture and the cathode power, as well as the stability of the transport speed and the start/stop positions in front of and in the rear of the deposition zone.
For a single pallet, or for the first and last pallet in a tip to tail continuous run, the start as well as the stop position must be well out from directly beneath the target to prevent accruing unintentional deposition in any pre-sputter stabilization period, before beginning the scan. Any start, stop, or reversal of scan direction must occur outside the actual deposition zone and the scan must be stable and continuous through the deposition zone. Scans can be either single pass in either direction or back and forth to accrue thicker coatings.
Three and four target systems are normally used and it is possible to increase the chamber length to house additional sources when required. With different target materials on the cathodes, it is thus possible to deposit multiple layers in a single pass, or with duplicate targets, it is possible to achieve thicker coatings in a single pass. Homogeneity in the other axis that is at right angles to the scan direction of the pallet is identified by the performance of the cathode, particularly for reactive sputtering, possible gas distribution problems. Along the center of the length of the target, both homogeneity and utilization are usually good enough. However, at the ends where the ‘race track’ path turns around, the rate of deposition and accruing film thickness will decrease unless magnets are adjusted to compensate. However, if that is done target utilization is reduced because of the deepening of the erosion channel.
Tip to Tail Approach
Tip to tail processing in the larger multi pallet systems is advantageous for target material utilization. In the tip to tail approach, the gap between one tail and the next tip is very short and the material is going onto a ‘live’ pallet full of substrates once again. The new pallet enters when the leading pallet exits the deposition zone. The efficiency of the tip to tail approach in material usage can be nearly twice when compared to the single pallet.
It is possible to customize in-line sputter systems to accommodate a variety of substrate sizes and process requirements.
About Semicore Equipment
Semicore is a manufacturer and worldwide supplier for the electronics, optical, solar energy, medical, automotive, military and related high technology industries.
Our high-performance production or R&D vacuum sputtering and thin film evaporation systems provide coatings on a variety of materials including plastic films, glass, ceramics, metals and hybrid substrates.
Whether you want to take advantage of our proven industrial solutions for vacuum system automation, process control and supervisory monitoring applications or need to develop some unique new application of your own design you will find Semicore’s staff and facilities to be competent, open-minded and eager to help.
This information has been sourced, reviewed and adapted from materials provided by Semicore Equipment.
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