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Photographic emulsion is a light-sensitive colloid used in film-based photography. Most commonly, in silver-gelatin photography , it consists of silver halide crystals dispersed in gelatin . The emulsion is usually coated onto a substrate of glass , films (of cellulose nitrate , cellulose acetate or polyester ), paper, or fabric.
For very small, dense features (< 125 or so nm), lower resist thicknesses (< 0.5 microns) are needed to overcome collapse effects at high aspect ratios; typical aspect ratios are < 4:1. The photoresist-coated wafer is then prebaked to drive off excess photoresist solvent, typically at 90 to 100 °C for 30 to 60 seconds on a hotplate. [ 24 ]
Instead, scientists would refer to photosensitizers as sensitizers used in photo-oxidation or photo-oxygenation processes. Studies during this time period involving photosensitizers utilized organic photosensitizers, consisting of aromatic hydrocarbon molecules, which could facilitate synthetic chemistry reactions.
Light can be considered to be a stream of discrete photons, and a light-sensitive emulsion is composed of discrete light-sensitive grains, usually silver halide crystals. Each grain must absorb a certain number of photons in order for the light-driven reaction to occur and the latent image to form. In particular, if the surface of the silver ...
To explain this in graphical form you may have a graph on Log exposure energy versus fraction of resist thickness remaining. The positive resist will be completely removed at the final exposure energy and the negative resist will be completely hardened and insoluble by the end of exposure energy. The slope of this graph is the contrast ratio.
For example, an emulsion rated at 250 H&D would require ten times the exposure of an emulsion rated at 2500 H&D. [7] The methods to determine the sensitivity were later modified in 1925 (in regard to the light source used) and in 1928 (regarding light source, developer and proportional factor)—this later variant was sometimes called "H&D 10".
The developer diffuses into the film emulsion to react with its layers. [10] This process happens simultaneously for all three colors of couplers in the film: cyan (in the red-sensitive layer in the film), magenta(for the green-sensitive layer), and yellow (for the blue-sensitive layer). [ 6 ]
The mask allows for precise control over the doping and etching processes used to form devices on silicon wafers. It is important for the mask to hold up to chemical attack during the etching process. Photoresists have three major components, a solvent, resin, and sensitizer (or photoactive compound).