Working Principle of Spin Coating

The spin-coating process consists of several steps, including dispensing the coating solution, high-speed rotation, and drying (solvent evaporation).

1. Static Dispensing

Static dispensing involves simply depositing photoresist onto the center of a stationary substrate. The dispensing volume typically ranges from 1 to 10 mL.

The amount of photoresist required depends on its viscosity and the size of the substrate. A higher-viscosity photoresist and/or a larger substrate generally requires a greater dispensing volume to ensure that the entire substrate surface is covered during the high-speed spinning stage.

2. Dynamic Dispensing

Dynamic dispensing involves dispensing the photoresist while the substrate is rotating at a low speed, typically around 500 rpm.

The purpose of dynamic dispensing is to help the photoresist spread more easily across the substrate surface and reduce material waste. This method allows the entire substrate surface to be wetted and covered with a relatively small amount of photoresist.

Dynamic dispensing is particularly suitable when the photoresist or substrate has poor wettability, helping to prevent the formation of pinholes.

3. High-Speed Spinning

After dispensing the photoresist, the next step is high-speed spinning. The substrate is rotated at high speed to thin the photoresist layer to the desired final film thickness.

The rotational speed during this stage typically ranges from 1,500 to 6,000 rpm. The appropriate speed depends on the properties of the photoresist, including its viscosity, solvent evaporation rate, solid content, and surface tension, as well as the size of the substrate.

The high-speed spinning duration can range from 10 seconds to several minutes.

The spin speed and spinning duration largely determine the final thickness of the photoresist film. In general, a higher spin speed and longer spinning duration result in a thinner film.

Many variable factors affect the spin-coating process. These factors often counterbalance one another and gradually reach equilibrium. Therefore, sufficient spinning time should be allowed for the various influencing factors to stabilize and achieve a uniform coating.

Application Scope

This Spin Coater equipment is widely used for coating substrates in various fields, including micro-electromechanical systems (MEMS) micromachining, biotechnology, materials science, semiconductors, photomask fabrication, new energy, thin films, optics, and surface coating. It is particularly suitable for coating small substrates or samples that are too small for conventional dip-coating or blade-coating methods.