Light-sensitive compounds, development

The main components of most commercially available positive photoresists are novolak as a binder and naphthoquinone-diazdde as a light-sensitive component. This light-sensitive compound is not base soluble and acts as a dissolution inhibitor for the novolak, which results in a very low dissolution rate of unexposed resist in aqueous base developer. Upon exposure a reaction is induced to yield indene carboxylic acid via a ketene ... 

It is fruitless to attempt detailed study of a phenomenon whose products are not well identified. It is unfortunately frequently noted in the literature, especially in cases of column chromatography, that fractions are only identified as to the chemical operations which brought them to light. Fractions are identified, for example, only by the solvent used. Speculations as to the composition of the radioactive solutes in such solutions can seldom be really reliable, and the presence of an unexpected radioactive species is in such cases undetectable. It is also important in reading the literature to watch out for cases in which the chemical yields of the carriers have not been measured. Extensive decomposition can often occur on silica gel and alumina columns, especially when photosensitive or moisture sensitive compounds are used. For these reasons much of the information now existing in the literature must be regarded as only exploratory, awaiting the development of better analytical methods for separation, purification, identification and determination of the products —known or expected. 

Silver halide grains are used as the light-sensitive component in many solution processes involving physical development. The latent images or partially developed latent images comprise the nuclei upon which the physical development reactions are catalyzed. There are many other nuclei-forming compounds, however, which find use in systems where the speed of silver halide is not required, its expense is unsuitable, or a more efficient catalyst for the physical development reaction is desired. 

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