R&D market cluster arrangement solutions - Design and options
Introduction
Sputtering systems for universities, R&D departments and small batch coating facilities usually look very much alike: cluster tool. And there are many good reasons for this type of design and magnetron arrangement. The major advantage is its flexibility and possibilities to adjust and change the setup on the go.
This enables cluster tools to suit many different and also difficult depositions and coatings with a single system.
Design
Following we will take a closer look into two main components of vacuum chambers with cluster arrangement:
Magnetrons and
Ion sources
Figure 1: Typical arrangement of circular magnetrons in a cluster system.
1. Magnetrons
1.1. Circular Magnetrons
Problem: Many different applications, coatings, tests to be deposited with limited equipment and budget, while also achieving results that can match industry demands.
Solution: Cluster tool with multiple circular magnetron heads that can be adjusted individually.
A vacuum system with so-called cluster arrangement consists of multiple small size circular magnetron heads, typically in the size of 2” or 3” target diameters, placed confocally above an ideally rotating substrate. The small footprint magnetron head allow 3 or more cathodes in small diameter chamber. The magnetron heads can be adjusted in depth to the chamber via a mounting shaft and a tilting angle is set. With the right axial offset from the middle of rotating substrate, you can achieve uniformity in the <±3 % region.
Figure 2: Calculator for finding good parameters to achieve desired uniformity.
Figure 3: Circular magnetron head with tilt mechanism.
Many other features can be added to the magnetrons to make the depositions and handling better.
Let’s start with the magnetic array: standard magnetics work for almost every coating sometimes even ferromagnetic material. Other times you are sputtering precious material and want to achieve a higher target yield to save costs. A high yield magnetic array which uses more magnetic pole-system can achieve easily 40% target use.
Figure 4: Sputtered 4" target with a high yield magnetic array. Wide racetrack will give better yield.
A shutter will help to clean targets before sputtering onto your substrate and pre-condition the cathode. Usually, the shutter can be opened manually or via a pneumatic system and also helps to reduce contamination inside your chamber. Same as a sputter chimney, which reduces cross contamination between the multiple magnetron heads that might be fitted with different target materials.
Figure 5: Chimney and shutter mechanism for circular magnetrons.
Target change should also be as easy as possible, as you might be changing it often! An indirect target cooling is beneficial so you don’t have to deal with water inside your chamber. A one-handed mechanism for target change inside the system helps your staff to quickly rearrange your system to new depositions.
Last but not least, gas injection. Gas injection through the magnetron is a good way to keep the overall pressure low and coating quality high! Think about mean-free-path of particles.
And to round it up, what kind of power do you want to use? DC/pulsed, RF or maybe HiPIMS? Your cathode should be able to work with all of these modes to be flexible and open to new depositions and coatings.
Figure 6: Many options to configure a circular magnetron to achieve maximum flexibility and best results.
1.2. Full Face Erosion Magnetron
Problem: Need for clean depositions and/or high target utilisation in small cluster tools
Solution: Magnetron with moving magnetic array
The need for defect free and clean depositions for high end coatings is sometimes hard to achieve. Mini arcs, redeposition, flaking… you name it. To keep your coatings as cleans as possible multiple things need to be taken care of and one of them is your magnetron itself. Especially in reactive coatings the target will show redeposition of material. That will inevitably lead to small arcs on the target and later to flaking of material and maybe shorts.
The solution is similar to a rotatable magnetron, a dynamic moving magnetic array that covers the whole target area: A small diameter (3”) full-face-erosion (FFE) magnetrons, where the plasma will travel across the whole surface and no material will be redeposited. That will lead to less defects and arcing, and therefore clean coatings. Another nice benefit is an enormous target yield above 60%. The yield makes the FFE also a preferred choice for high cost and compound materials.
Figure 7: Off-center plasma due to the magnet array moving across the whole target.
Figure 8: Sputtered target of FFE magnetron.
Same as with standard magnetrons in a cluster tool, the FFE can be fitted with
- a tilt
- chimney,
- shutter,
- gas injection,
- adjustable shaft and
- different power modes for your needs and flexibility to create new and exciting coatings.
Figure 9: Internally mounted FFE with tilt, wall-mount-feedthrough and flange, motor on the back (left hand side).
2. Pre-treatment with Ion sources
Problem: Coating adhesion, stress, poor density, hardness
Solution: pre-treatment and in-situ treatment.
Figure 10: Ion source (left) and circular magnetron (right) running in simultaneous process.
Another very nice tool for any deposition is a pre-treatment by plasma sources. The pre-treatment will be a major game changer to achieve
- better adhesion,
- scratch resistance and
- denser coatings.
Many different kinds of plasma etchers and sources are available on the market, often difficult what to choose. For cluster tools there are 3” ion source heads available that can be fitted with the magnetrons side by side.
Due to its wide operating pressure range, a simultaneous use of ion source and magnetron sputtering is possible in a cluster tool. So, the ion source could not only pre treat the substrates but also densify the just deposited coatings, plasma enhanced.
Usually, Ar or O2 gases are used but you could also introduce C2H2 for PECVD coatings or similar.
The ion sources are powered by a DC voltage and typically run low current so don’t expect a lot of etching. But that also helps to minimise the contamination by the source itself. Some models run StSt targets which will be sputtered and contaminate your substrate. Materials like graphite are more suitable as they sputter very slowly. Also, there is the need to add electrons into the plasma beam to make it electrically neutral. A filament is another source for contamination and also needs maintenance. Other methods that have a self-neutralizing beam are easier to use.
And as usual in a cluster, features like a tilt, adjustable hight, gas-injection should be there to help you to maximise your potential and your coating quality.
Figure 11: Front view of ion source with graphite front. Center ring is 3" wide for the plasma jet.
Figure 12: Side view of ion source in operation.
Figure 13: Ion source with internal mounting, tilt option, wall- mount-feedthrough.
Summary
So, let’s summarise all these options and ways to configure your coating equipment:
Magnetrons with many features like GENCOA’s product portfolio can help and boost your research project and with its flexibility and competitiveness you will be able to achieve very nice and consistent results with cluster tools.
A plasma pre-treatment is the next big step and a great tool to get new and exciting results for R&D and is something that is more and more implemented also in the industry.
If you want to have a closer insight into the products, we can help you with Gencoa’s wide range for cluster arrangements and knowledge. Another helpful tool is the widely known sputter rate calculator from Gencoa. Check it out at https://www.gencoa.com/sputter-calculation to calculate deposition rates easily.
Feel free to contact us at florian.meyer@gencoa.com or tvartiainen@avaluxe.de to get in touch and talk about these interesting and fascinating ways of improving your next or existing system.