New materials for 157-nm photoresists: characterization and properties

Abstract

The design ofan organic material satisfying all ofthe requirements for a single layer photolithography resist at 157 nm is a formidable challenge. All known resists used for optical lithography at 193 nm or longer wavelengths are too highly absorbing at 157 nm to be used at film thicknesses greater than -9O nm. Our goal has been to identify potential, new photoresist platforms that have good transparency at 157 nm (thickness normalized absorbance of2.5 rim' or less), acceptable plasma etch resistance, high Tg, and compatibility with conventional 0.26 N tetramethylammonium hydroxide developers. We have been investigating partially fluorinated resins and copolymers containing transparent acidic groups as potential 157 nm photoresist binders; a variety ofmaterials with promising initial sets ofproperties (transparency, etch resistance, solubility in aqueous TMAH) have been identified. Balancing these properties with imaging performance, however, remains a significant challenge.

Fluoropolymers for 157 nm Lithography: Performance of Single Layer Resists.

“…We [3] and others [9,10] have reported imaging results with TFE copolymers with optical absorbances in the range of 2.0 µm"1, or slightly lower, based upon terpolymers composed of TFE, hexafluoroisopropanol-functionalized NB, and a protected acid-labile carboxylate ester. Here we will describe some of those results, and then several recent imaging results with resists having formulated absorbances as low as 1.4 µm"1.…”

“…3.1.1 TFE Copolymers 3.1.1.1 Effect of TFE Incorporation on Optical Absorption Incorporating TFE into the backbone of copolymers has a powerful effect on the 157 nm absorbance of resist resins [2,3]. In Figure 3 we show two spectra, one of a VA copolymer of functionalized norbornenes, and the other of the same functionalized norbornenes but with some TFE copolymerized in the backbone.…”

“…The 157 nm absorbance has decreased signs scantly as a result of the TFE incorporation. This result initially stimulated our interest in the use of TFE copolymers as resins for 157 nm photoresists [2,3].…”

“…VA addition polymers are a second platform that has been considered for 157 nm resist resins [3,4]. As described above, these polymers have a distinct disadvantage in optical absorbance compared with TFE copolymers.…”

“…The development of increasingly more transparent fluoropolymers for 157 nm lithography is an ongoing activity in a number of research laboratories around the world [3][4][5][6][7], leading to considerable progress in that direction during the past four years.…”