What Is a Spin Coater?
A spin coater is a device used to apply paint to the surface of a substrate. After a drop of paint is applied to the center of the substrate, the substrate is rotated while controlling the acceleration and rotation speed to create a film with a uniform thickness using centrifugal force.
Although there are some disadvantages, such as the fact that it can only be used on smooth base materials and is not suitable for coating large areas, it can form a variety of thin films with minimal thickness error. This equipment is used for manufacturing semiconductors and displays, coating optical media, etc.
Uses of Spin Coaters
Spin coaters can be used to produce thin films of uniform thickness on smooth substrates.
Spin coaters are used in the field of photolithography. Photolithography is a technology that creates fine patterns on the surface of a substrate, such as a silicon substrate, by applying a photosensitive agent to the substrate and then irradiating it with intense light, such as ultraviolet light. This technology is indispensable for the manufacture of semiconductors and displays.
It is also widely used for coating the surface of optical media such as DVDs and Blu-ray Discs, and for applying light-dimming solutions to lenses.
Principles of Spin Coaters
A spin coater is a coating system that uses centrifugal force generated by rotation to coat the surface of a substrate. It is also known as a spinner. It is a coating method suitable for producing thin films on flat substrates, and is characterized by its uniform evenness in film thickness.
First, the substrate is set in the spin coater, and a drop of coating material is applied near the center of the substrate. Next, the substrate is rotated to apply centrifugal force to the paint and adjust it so that the paint is diffusely applied to the substrate surface. Rotation speed and acceleration can be set by the equipment and should be determined considering the paint’s liquid properties and film thickness. After the rotation is completed, the substrate is removed from the spin coater, and the coating is dried by heating or UV curing. Through these series of operations, a uniform thin film can be produced on the substrate.
The advantages of thin film coating with a spin coater include the ability to form thin films of various thicknesses by precisely setting the liquid nature of the coating, the number of revolutions, and other parameters, and the ability to use a smaller amount of coating material. On the other hand, the disadvantages include the loss of paint during coating and the limitation of coating to a small area.
How to Use Spin Coaters
A spin coater is used to generate a thin film from a compound. Here we explain how to use it.
- The base in the center of the spin coater is the rotating element. A glass or metal substrate is set on this rotor. The way to fix the substrate to the rotating body is to pull a vacuum to fix the substrate to the pedestal. If a vacuum is not desirable, use double-sided tape or other adhesive tape, but be sure to use highly adhesive tape.
- Pour the polymer or other compound solution onto the substrate. Pour the solution evenly so that the entire substrate is covered as much as possible.
- Set the rotation speed and rotation time, and press the start button. When the time is up, the rotation stops, and a uniform thin film is formed on the substrate.
Incidentally, there is a vacuum evaporation system for the same thin film creation. However, polymers and other materials may decompose in a vacuum, making a spin coater suitable in this case.
Other Information on Spin Coaters
1. Eliminating Coating Irregularities with Spin Coaters
Spin coaters produce a uniform thin film, but there are cases where unevenness in the coating occurs, resulting in invisible irregularities. The following are some conditions that can cause coating irregularities.
- Slow rotation speed (fewer revolutions over time)
- High viscosity of the compound solution
- Heaping of the solution is observed at the corners of the substrate
First, the rotational speed is an issue. In basic spin coaters, the slower the rotational speed, the thicker and more non-uniform the film is likely to be. The easiest solution is to increase the rotation speed and extend the rotation time. If you have time, fix the rotation time and measure the film thickness at each rotation speed. The best solution is to find the optimal rotation speed and time.
If the viscosity of the compound solution is high, it will be difficult to spread evenly, resulting in a non-uniform film. One way to deal with this is to dilute the solution concentration to reduce viscosity.
To address the problem of non-uniformity in the corners of the substrate, it is best to use a closed-type spin coater with an automatic drop function. The automatic drop function automatically dispenses the compound solution onto the spinning substrate. The solution spreads quickly to the substrate as soon as it is dispensed, preventing the corners from rising and enabling the formation of a uniform thin film.