ABSTRACT
Photolithography is a system composed of various subsystems such as light sources, exposure tools, masks, pellicles and photoresist materials. Advanced photolithography employs an excimer laser as a light source in the exposure tools. The principle of photolithography is similar to that of photography: the exposure of mask images through an optical system produces latent images in a photosensitive resist material (photoresist), which is then developed in a developer solution to form resist patterns. The delay in the development of a photolithography system with shorter wavelengths is pushing the development of such a technological innovation. To use CaF2, the overcome its intrinsic birefringence and this problem has been investigated. Several candidates for resist materials have been proposed and developed, and relatively good patterns have been reported. Requirements for an output power of EUV light exceeding 100 W at the intermediate focus have meant that liquid-phase Xe and solid-phase Xe have been intensively investigated.
