Single Layer Fluoropolymer Resists for 157 nm Lithography

We have developed a family of 157 nm resists that utilize fluorinated terpolymer resins composed of 1) tetrafluoroethylene (TFE), 2) a norbornene fluoroalcohol (NBFOH), and 3) t-butyl acrylate (t-BA). TFE incorporation reduces optical absorbance at 157 nm, while the presence of a norbornene functionalized with hexafluoroisopropanol groups contributes to aqueous base (developer) solubility and etch resistance. The t-butyl acrylate is the acid-catalyzed deprotection switch that provides the necessary contrast for high resolution 157 nm imaging. 157 nm optical absorbances of these resists depend strongly upon the amount of t-BA in the polymers, with the TFE/NBFOH dipolymers (which do not contain t-BA) exhibiting an absorbance lower than 0.6 μm. The presence of greater amounts of t-BA increases the absorbance, but also enhances the dissolution rate of the polymer after deprotection, yielding higher resist contrast. Formulated resists based upon these fluorinated terpolymer resins have been imaged at International Sematech, using the 157 nm Exitech microstepper with either 0.6 NA or 0.85 NA optics. We have carefully explored the relationship between imaging performance, resist contrast, optical absorbance, and t-BA content of these terpolymer resist resins, and describe those results in this contribution.