The process of the spin coater includes the following steps:

　　Spin coater is a typical glue coating process, which includes glue dripping, high-speed rotation and drying (solvent evaporation) steps. In the glue dripping step, the photoresist is dripped onto the substrate surface, and the high-speed rotation spreads the photoresist onto the substrate to form a thin layer. In the drying step, the excess solvent in the glue layer is removed. The two commonly used glue dripping methods are static glue dripping and dynamic glue dripping.

Static glue dripping is simply dripping the photoresist onto the center of the static substrate surface, and the glue dripping amount varies from 1 to 10 ml. The amount of glue dripped should be determined according to the viscosity of the photoresist and the size of the substrate. If the viscosity is relatively high and/or the substrate is relatively large, more glue is often required to ensure that the entire substrate is coated with glue during the high-speed rotation stage. The dynamic glue dripping method is to drip glue while the substrate is rotating at a low speed (usually around 500 rpm). The role of "dynamic" is to make the photoresist easy to spread on the substrate and reduce the waste of photoresist. Dynamic glue dripping does not require a lot of photoresist to wet (spread and cover) the entire substrate surface. Especially when the wettability of the photoresist or the substrate itself is poor, dynamic glue dispensing is particularly suitable and will not produce pinholes.

After dispensing, the next step is high-speed rotation. To make the photoresist layer thinner to the required film thickness, the rotation speed at this stage is generally 1500-6000 rpm. The selection of the rotation speed also depends on the performance of the photoresist (including viscosity, solvent evaporation rate, solid content and surface tension, etc.) and the size of the substrate. The time of rapid rotation can be from 10 seconds to several minutes. The speed of the glue dispensing and the time of the glue dispensing often determine the thickness of the film.

Generally speaking, the faster the glue dispensing speed and the longer the time, the thinner the film thickness. There are many variable factors that affect the glue dispensing process, and these factors often offset each other and tend to balance during the glue dispensing. Therefore, it is necessary to give the glue dispensing process enough time to balance the many influencing factors.

The acceleration of the substrate during the glue dispensing process of the glue dispensing spin coater will also affect the performance of the glue film. Because the photoresist begins to dry (solvent evaporates) at the beginning of the substrate rotation stage. Therefore, it is important to accurately control the acceleration. In some photoresist processes, 50% of the solvent in the photoresist evaporates within a few seconds of the start of the photoresist process. When applying the photoresist on a substrate that has been photoetched with patterns, acceleration also plays an important role in the quality of the film. In many cases, the substrate already has fine patterns left from the previous process. Therefore, it is important to apply the photoresist evenly across these patterns on such a substrate.