Chemically amplified resists CARs

It should be pointed out that the solubility change in all chemically amplified resists (CARs) occurs only in the dark reaction during the PEB. Some of the CARs such as acetal and ketal systems have low activation energy, so deprotection can occur with low-temperature PEBs or even at room temperature. In the absence of thermally driven diffusion such as in acetal and ketal resist systems, BARCs must be used for resists with such low PEB temperatures, which are significantly lower than the soft bake temperature, in order to control reflectivity issues associated with standing waves. 

Finally, it has to be discussed why certain chemically amplified resists (CARs), that are applied successfully in photolithography and function on the basis of radiation-induced acid generation, are applicable also in high-energy radiation lithography. Sulfonium and iodonium salts, such as those presented in Chart 5.14, are typical acid generators in this context. 

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