Photochemical amplification effects

It should be said, however, that the initial light signal associated with the photoisomerization of the photochromic moiety is usually a weak effect, and requires amplification in order to construct photoswitchable devices. The greater the amplification factor, the greater is the sensitivity of the system. Substantial amplification can be achieved when the primary photochemical reaction is coupled with a subsequent event that occurs after absorption of light. 

In general, the chemical transformations associated with the chemical amplification mechanism in resists is effected through heating the exposed resist film, in a process called postexposure bake (PEB). Although, in principle, the active catalytic species (ions or radicals) could be generated from either photochemical (or radiochemical) acid or base generators, the acid generators are now used almost exclusively in advanced resist systems. ... 

A number of PAGs have been synthesized for use in chemically amplified resist systems. The choice of PAG to use for each specific application is dependent on a number of factors, including the nature of the radiation, quantum efficiency of acid generation, solubility, miscibility with resin, thermal and hydrolytic stability, plasticization effect, toxicity, strength and size of generated acid, impact on dissolution rates, cost, etc. Figure 7.10 shows classes, while Table 7.5 is a list of typical photochemical acid generators currently in use in chemical amplification resists. 

A correlation of the photosensitivities of several organic photochemical systems with this theoretical value is given in Table 1, where the sensitivity of some silver halide materials were Included for comparison. It Is trivial to state that the success of classical photographic systems, considered from the point of view of their photosensitivity, lies in the possibility of chemical amplification of the latent image. It seems therefore evident that the only chance for organic photochemical systems to realize a significant penetration Into the broad application field of silver systems with sensitivities of 10 ergs/cm and less Is to find some way to amplify the primary photochemical effect - that is, to find photochemical reactions with an overall... 

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