To produce the smallest possible circuitry, today's most advanced lithographic exposure systems are designed to use light of very short wavelength - deep-ultraviolet light at a wavelength below 200 nm, or soft x-rays in the region of ~ 13 nm. These exotic light sources are relatively weak, so the photoresist must be designed to utilize this light as efficiently as possible. Essentially all photoresists used today for microelectronics fabrication employ the concept of chemical amplification to enhance the efficiency of light utilization.

The principle of a chemically amplified (CA) photoresist is illustrated in the accomanying figure. The photoresist film is composed of a polymer that bears acid-sensitive groups pendant to the polymer chain. Dissolved in the solid polymer film is a small quantity of a compound that produces an acidic product when it absorbs light. A latent image of acid product is formed in the film when exposed to a pattern of light. In a subsequent heating step, this acid catalyzes the fragmentation of the groups pendant to the polymer chain (termed deprotection). The acid is not consumed in the deprotection reaction and can therefore catalyze the reaction repeatedly. Experimental measurements show that one hundred to on thousand deprotection reactions occur for every acid formed; this is the origin of "chemical amplification".

The deprotected polymer differs markedly from the original polymer int its polarity and reactivity. In a final step, the substrate is immersed in a liquid developer that selectively dissolves the deprotected polymer, producing a relief image useful for subsequent pattern transfer.

Link to a paper on "Quantitative depth profiling of photoacid generator molecules in photoresist materials by near-edge x-ray absorption fine structure spectroscopy"