User:BrewerScience/sandbox

Spin Coating

Spin Coating has been used for several decades for thin films. There are several critical variables that come into play when spin coating liquid resins including photosensitive materials. Additionally these variables have critical effects on the overall coating uniformity, thickness, surface quality, and device yield. These include spin speed, acceleration, repeatability, resolution, and fume exhaust control.

One of the most important factors in spin coating is repeatability. Subtle variations in the spin process can result in drastic variations in the coated film quality. Other critical factors in spin coating include overall spin speed and accuracy. The speed of the substrate (rpm) affects the degree of radial (centrifugal) force applied to the liquid resin as well as the velocity and characteristic turbulence of the air immediately above it. In particular, the high-speed spin step generally defines the final film thickness. Minor variations of 5 rpm at this stage can cause severe coating anomalies. Therefore, spin speed accuracy can have tremendous effects on consistent thickness and downstream process success.

Acceleration of the substrate toward the final spin speed can also dramatically affect the coated films properties. The resin begins to dry during the initial part of the spin cycle, it is important to accurately control acceleration. In many cases, up to 50% of the solvents in the resin will be lost to evaporation in the first few seconds. Ability to actually achieve ramp rates of ≥ 2000 with a fully loaded chuck and maintain accurate speeds (0.2) during the entire process is paramount.

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