Trilayer development for 193 nm immersion lithography

Abstract

Immersion technology is enabling the extension of 193 nm lithography by increasing the numerical aperture (NA) of the exposure system. The result is smaller depth of focus, subsequently requiring the use of thinner photoresists. Consequently, bottom antireflective coatings (BARCs) are required to have increased etch selectivity to thinner photoresists, as well as improved reflectivity control to minimize reflectivity from higher incident angles of hyper NA lens systems. A spin on trilayer patterning scheme has recently become a favorable approach to simultaneously address these issues. IBM and Shin Etsu have jointly developed a silicon containing BARC for the purpose of trilayer imaging. In this work, hyper NA imaging performance of the trilayer film stack is reported, at NA > 1.0. Full field, polarized 1.2 NA dipole imaging of line/space lithographic patterns is compared with both the trilayer imaging stack as well as a single layer, organic BARC stack. The process window of 1-D line/space structures was found to be significantly improved on the trilayer imaging stack. Improved profiles were observed on the trilayer film stack, with other lithography metrics showing comparable performance on both film stacks. Characterization of a solvent based rework scheme is presented for the trilayer imaging stack. Also, the chemical interaction between the silicon BARC and the photoresist was studied with an acid diffusion experiment. Within the detection limits of the experiment, it was found that acid diffusion from the silicon BARC is not a likely contributor to imaging performance. ©2007TAPJ.