A Guide to Chuck Selection for Spincoating Success

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publication date

January 12, 2024

The chuck is a critical part of the spin coating process, providing the interface between the spin coater and the substrate being coated. Selecting the correct chuck for each substrate is key to ensuring best coating results.

Multiple chucks of different designs and sizes can be used with one spincoater making it a long term investment for any research group, and our experts within the PI-KEM Energy and Material Processing Team are available to ensure you get the most appropriate chuck for each application. Factors they will consider include the substrate material, size and shape, desired film thickness, and process requirements. As well as the make and model of spincoater you will be using.

Choosing the correct chuck for a spincoater is crucial for several reasons, all of which could impact the success and quality of your coating process:

Stability and Balance:

Substrate Security: The chuck needs to firmly hold the substrate (your sample) in place without any wobbling or vibration, even at high rotational speeds. This prevents defects in the coating film due to uneven spinning or the substrate being damaged due to becoming loose during the process.
Centering: Precise centering of the substrate ensures uniform coating thickness across its entire surface. Misalignment can lead to uneven edges or thinner areas in the film. This can also cause instability leading to substrate damage.
Rotational forces: The chuck must be able to withstand the rotational forces generated by the spincoater without warping or breaking. Improperly chosen chucks can lead to imbalances and damage to both the chuck and the spincoater itself.

Film Quality and Consistency:

Uniformity: Accurate centering and secure holding contribute to a consistent film thickness across the entire substrate. Chucks with uneven surfaces or poor gripping can cause variations in the film thickness.
Defects: Chucks with imperfections or manufactured from incompatible materials can introduce contamination or defects into the film. Choosing a chuck made from a suitable material for your specific coating process is essential.

Additional Considerations:

Substrate size, shape, and thickness: Match the chuck size and design to your substrate dimensions. Chucks for specific shapes like wafers or squares may be required.

Most chucks use vacuum to hold the substrate firmly during the coating cycle. It is vital that the substrate completely covers the entire vacuum area of the chuck, with a small overhang all the way around. E.g. for a 50mm wafer, a 44mm chuck would be ideal, having a 3mm overhang all around. This prevents loss of vacuum, causing interruption to the coating cycle, or the substrate becoming detached. It also prevents coating liquid from being pulled into the internal vacuum components of the spin coater, causing blockage and damage.
For very thin substrates then the vacuum design may need to be adjusted and heavy substrates may require additional holding pins or support to hold them securely. Using a chuck not designed for your substrate's geometry could lead to stress fractures, cracks, or warping, inconsistent coating, or the substrate becoming insecure and detaching from the chuck.

Vacuum compatibility: Some processes require vacuum chucks for optimal holding, and it is important to use a chuck compatible with your spincoater’s vacuum system. Equally some substrates may not be suited to a vacuum chuck and a non-vacuum design may need to be used.

Thin (usually less than 1mm), rigid, brittle substrates, e.g. silicon wafers, glass wafers, etc require a grooved chuck, that provides support across the full face of the chuck, and distributed vacuum evenly. Usually, stainless steel or aluminium.

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Heavy, thick rigid regular shaped substrates, e.g. glass, quartz, ceramic, metal require an O-ring chuck. The O-ring provides a firm grip and tight vacuum seal to hold these heavy substrates. Usually, stainless steel or aluminium.

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‍Custom chucks are used for special substrates, that are irregular shapes, need extra support, etc.

Microscope slide chucks are used for rectangular substrates, these chucks are custom made to suit individual requirements, ensuring the substrate is fully held and supported.

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Chucks with pins or fingers are used where the substrate is heavy. The pins or fingers provide additional security by holding the substrate in place and preventing planar movement, whilst the vacuum provides the vertical hold.

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Porous chucks are used when the substrate is flexible, e.g. metal foils, or polymer films, and would otherwise form the shape of the surface of the chuck. In place of grooves, an insert of porous aluminium is used to spread the vacuum evenly.

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‍Material compatibility: Ensure the chuck material, the substrate material and the spincoater bowl coating are all compatible with the coating material and solvent used in your process. Incompatible materials can react with each other, leading to contamination or damage.

Chucks manufactured from solid Teflon or Delrin are used for specific applications:

When the chemicals used in the coating are not compatible with standard chuck materials.
When the substrate must not contact any metallic surface (e.g. some semiconductor materials)
Where the coating is very sensitive to variation in temperature, and where a metallic chuck could conduct thermal energy at the points it contacts the substrate surface.

Teflon and Delrin chucks are limited in size due to being susceptible to plastic deformation at high rotation coating speeds.

By considering factors like stability, film quality and substrate compatibility, you can optimise your spin coating process and ensure successful results. By ensuring the best results, and preventing equipment damage, this will maximise the coating throughput as well as cost efficiency.

Selecting the right chuck for you.

This process is completely dependent on your application and at PI-KEM we work with both the manufacturers we represent and a local precision engineering partner, to ensure we supply the most appropriate solution for the work you are undertaking. We provide a wide range of chucks varying in diameter, material (aluminium, stainless steel, Delrin, etc.), and design (standard, grooved, porous, with pins and finger, etc.). For specialist applications we can offer a custom design and manufacture service to produce a suitable chuck suited to your requirements.

After asking a number of questions, our team can advise on the correct design of chuck for your process. These include:

What is the material of your substrate?
What are the dimensions of your substrate, including thickness?
What coatings will you be applying, what thickness are you looking to achieve?
Will you be applying a single coating or multiple layers?
What spincoater make and model will you be using?
Your budget and project timeline

PI-KEM have over 30 years of expertise in chuck design and are UK and European representatives for MTI Corporation, Specialty Coating Systems and Navson. By combining our diverse product portfolio, technical expertise, and dedicated support, PI-KEM is here to help you navigate the world of chucks and select the perfect solution for your specific needs.