F2 excimer laser

Water absorbs only below about 185 nm (2,3). The first absorption spectrum is continuous (145-185 nm) corresponding to the transition A -B - X -A. Photodissociation in this region has been studied in detail by Welge and Stuhl (21) and recently by Andresen et al. (22-25). The main dissociation process (99%) at 157 nm (F2 excimer laser) is... 

Positive photoresist amplifier perfluoro polymers, (IV), (V), (VI), and (VII), prepared by Kanna [4], Hohle [5], DiPietro, [6], and AUen, [7], respectively, were effective with an exposed light source of 160 nm and thus usable with an F2 excimer laser beam. ... 

M. Kuhnke, L. Cramer, J.T. Dickinson, T. Lippert, and A. Wokaun,TOF-MS study of photoreaktive polymers ablated by F2 excimer laser (157 nm). Poster at COLA, 2003, Kreta. 

With F2 excimer laser lithography at 157 nm, even polymers based on aerylates and norbonenes are too opaque to be of any useful value in resist appheations. Therefore, fluorocarbons and silanol polymers are the two main classes of polymers that have reasonable transparency at this wavelength. Again, like their 193-nm and 248-nm counterparts, the 157-nm resists employ chemical amplification in their imaging mechanism, for quite similar reasons. 

Figure 13.12 shows the UV absorption profile of typical gases found (O2, H2O) and formed (O3) in the ambient environment of exposure tools. The Schumann-Runge band (180-210-nm) and continuum (<180-nm) regions dominate the photochemistry of molecular oxygen around 193 nm (of ArF exciplex laser) and 157 nm (of F2 excimer laser), respectively. 

In addition to its indispensable role in microelectronics and optoelectronics, photoKthography has been widely utilized for versatile fields including MEMS, micro sensors and actuators, micro-chemical reactions and analytical systems, and micro-optical systems [128, 129]. Currently UV hthography has feature sizes down to 250 nm, and it is expected to be reduced to 100 nm in the near future by use of a combination of deep UV hght (for example 193 nm ArF excimer laser or 157 nm F2 excimer laser) and improved photoresists. 

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