conformal photoresist over high aspect ratio features, coating several microns over three-dimensional structures such as V-grooves, deep trenches, silicon cavities, and through silicon vias (TSVs). Spray coating applies photoresist as a fine mist. A spray nozzle atomizes the resist into small droplets that are deposited across the wafer in one or more passes, building up the film thickness gradually. Because the droplets settle onto every exposed surface, spray coating produces a conformal layer that follows topography, coating the sidewalls and floors of features that spin coating cannot reach. A film built from mist. Droplets settle onto every exposed surface, so the resist follows the topography into and out of deep features. This conformal behavior makes spray coating the better choice for high aspect ratio features, allowing several microns of photoresist over three-dimensional structures such as V-grooves, deep trenches, silicon cavities, and through silicon vias (TSVs). Spray coating also uses resist efficiently, with little waste, and can coat fragile or perforated wafers that would not survive high speed spinning. The tradeoff is that thickness uniformity on a flat surface is not as high as spin coating, and the surface is slightly rougher. Typical Applications - Coating over deep trenches and silicon cavities - Through silicon vias (TSVs) - V-grooves and three-dimensional MEMS structures - High aspect ratio features after DRIE - Fragile, perforated, or cavity wafers - Conformal resist for topographic patterning
