The Spin Coating Theory

Spin processor solutions

Spin coating is a proven method for applying uniform thin films to flat substrates. In this process, an excess amount of coating solution is applied either manually via syringe or automatically through a dispensing unit. Subsequently, the substrate is rotated at high speed (up to 10,000 rpm). The centrifugal force spreads the fluid evenly, while volatile solvents evaporate, leaving a uniform film.

Film thickness depends on the material properties of the coating (e.g., viscosity, solid content) and the rotational speed. Consistent speed control is critical for achieving homogenous layers and reproducible results.

Typical applications

• Photolithography (photoresist layers ~1 µm thick at 1,000–4,000 rpm for 30–60 seconds)
• Fabrication of nanometric thin films (< 10 nm)
• Coating of polymers such as PMMA, PDMS, or block copolymers
• Deposition of functional thin films (e.g., self-cleaning titanium dioxide on glass or quartz)

Materials & processing

Many polymers can be spin-coated, with thickness controlled by polymer molecular weight, solvent choice, and spin speed. For example, PMMA dissolved in suitable solvents can produce coatings from a few nanometers to several micrometers. Solutions can also be doped with active compounds for optical or electronic applications.

For high-quality results, substrates must be thoroughly cleaned and the coating solution filtered to remove dust. While spin coating is often performed in cleanroom conditions, it can also be done in controlled lab environments using nitrogen or argon flow to reduce moisture absorption.

Advantages of POLOS^® Spin Coaters

• Speeds up to 12,000 rpm with ultra-fast ramp-up (0.3 s)*
• Multiple motor modes (clockwise, counterclockwise, puddle)
• Options for manual or automatic chemical dispense
• Compatibility with a wide range of substrates and sizes
• Precise, reproducible coating for research, prototyping, or production

*Depending on substrate size and chuck type.

Post-spin process

After spin coating, the substrate is typically transferred quickly to a hot plate, heated to around 100 °C, for several seconds to a few minutes. This step helps evaporate the initial solvent and solidify the coating.

Next, the substrate undergoes a longer bake-out phase — often several hours or overnight — in an oven or vacuum oven, at a temperature high enough to remove any remaining solvent.

To protect films from dust during one or both bake-out stages, plates are sometimes placed in a petri dish. However, solvent condensation on the dish lid can negatively affect film smoothness and quality. To prevent this, the lid should be left slightly ajar, allowing solvent vapors to escape.