Outlook for 157-nm Resist Designs

We have measured the transparencies of a number of candidate resist materials for 157nm, with an emphasis on determining which chemical platforms would allow resists to be used at maximum thicknesses while meeting requirements for optical density. Assuming an ideal resist optical density of 0.4, our findings show that all existing commercially available resists would need to be<60nm thick, whereas specialized hydrocarbon resists could be made 100nm thick, and new resists based on hydrofluorocarbons, siloxanes, and/or silsesquioxanes could be engineered to be used in thicknesses approaching 200nm. We also assess the tradeoff between these thicknesses and what current information exists regarding defects as a function of resist thickness.