Spincoating

Spin coating is a technique for depositing thin, uniform films on flat substrates by dispensing a liquid coating onto the substrate and then spinning it at high speed. Centrifugal forces spread the liquid outward while solvent evaporation solidifies a thin film. It is widely used in the semiconductor, microfabrication, optics, and organic electronics industries, as well as in research settings for coatings and polymer films.

Process steps include preparing a clean substrate, applying a small volume of coating solution to its center, transferring the substrate to a spin coater, and ramping to a target rotational speed with a controlled acceleration. The spin time is chosen to achieve thinning and drive off solvent; a post-spin bake or cure may follow to harden the film.

Film thickness and uniformity are governed primarily by the coating solution viscosity, spin speed and duration, solvent volatility, and ambient conditions such as temperature and humidity. Higher spin speeds and longer spin times typically yield thinner films but the relationship depends on solvent evaporation and substrate wetting. Edge beads and thickness nonuniformities near the substrate rim can occur, requiring optimization of dispense volume, ramp profile, and sometimes edge bead removal techniques.

Materials commonly used include positive and negative photoresists, PMMA, polyimides, and conductive or functional polymers such as PEDOT:PSS. Spin coating is also employed for inorganic and hybrid layers, including oxide and polymer matrices, flexible electronics, and optical coatings.

Equipment consists of a spin coater mounted on a programmable chuck, a dispense system for coating solution, and optionally a nitrogen purge or environmental enclosure. Film thickness is typically measured by ellipsometry, profilometry, or reflectometry, and quality is assessed by uniformity across the wafer or substrate.