Chemistry of photolithographic imaging materials based on the chemical amplification concept

This review describes the versatile chemistry of photolithographic imaging materials developed for nanofabrication of semiconductor devices. Conventional photoresists based on novolac/diazonaphthoquinone systems are not appropriate for the generation of relief images under sub-100 nm. In order to employ deep UV radiation techniques that are required for nanopattern generation, such as with 248, 193 and 157 nm excimer lasers, completely different strategies are required. Incorporation of chemical amplification concept into the design of resist systems has led to significant breakthroughs in the photolithography industry. In a chemically amplified resist system, a cascade of chemical events is promoted by photochemically generated initiating molecules. This leads to changes in the chemical or physical properties of the resist systems which typically develop during the postexposure baking procedure. Polarity change of the resist polymer along with depolymerization and crosslinking strategies has been widely employed in chemically amplified systems. Chemistry related to radiation resists using high-energy photons and charged particles, such as extreme-UV, X-ray, electron beam, ion beam has also been developed.