Outlook for 157 nm resist design

We have measured the transparencies of a number of candidate resist materials for 157 nm, with an emphasis on determining which chemical platforms would allow resists to be used at maximum thicknesses while meeting requirements for optical density. Although ideal imaging is usually obtained at an optical density between 0.1 and 0.3 and values in excess of 0.5 can often result in nonvertical wall profiles, we chose to arbitrarily choose 0.4 as the maximum tolerable optical density. Using this analysis, our findings show that all existing commercially available resists would need to be <60 nm thick, whereas specialized hydrocarbon resists could be made similar to 100 nm thick, and new resists based on hydrofluorocarbons, siloxanes, and/or silsesquioxanes could be engineered to be used in thicknesses approaching 200 nm. We also assess the tradeoff between these thicknesses and what current information exists regarding defects as a function of resist thickness. (C) 1999 American Vacuum Society. [S0734-211X(99)12806-3].