Meniscus coating is the process of applying a liquid substance such as a photosensitive polymer onto the top of a substrate. During this process, the substrate is positioned on a vacuum chuck to hold it in place. The plate is then inverted to the coating position shown below.
The applicator has one closed end and one open end, so that
material can be pumped into the tube. The material then flows out of a
slot, located at the top of the tube, and is desposited onto the
substrate. The applicator tube moves beneath the substrate and the
coating is formed as the meniscus contacts the substrate. Unused
material is collected in a reservoir and recirculated
through the tube. The recirculation of material can limit waste to less
than 5%.
There are several adjustable process parameters involoved in meniscus
coating:
- Applicator Speed- Faster speeds produce a thicker deposited film.
- Applicator/Substrate Distance
- Pump Pressure
- Substrate Type
- Material Type
- Material Viscosity- This parameter is varied by solvent evaporation
and temperature.
- Hot-Plate Temperature- Higher temperatures cause the coating material
to be less viscous, resulting in a thinner film formed.
The film thickness after meniscus coating can be
described by the following formula:
