Novel diffusion analysis in advanced chemically amplified DUV resists using photometric methods

Abstract

The demand for smaller device dimensions in microlithography drives the need to understand and control diffusion during photoresist processing. In advanced chemically amplified systems the lithographic performance is strongly influenced by diffusion of acid and base additives. Photoacid generation efficiencies and diffusion parameters were quantitatively evaluated using an established in situ photometric method employing a pH-sensitive organic dye. [1-3] A kinetic model for the post-exposure bake (PEB) has been proposed, transferred to molecular reaction dynamics and extanded to transport properties. The experimental data for this model liave been obtained from UV/VIS spectroscopy measurements. The UVA/IS data show that a photoacid loss reaction during post-exposure bake has to be taken into account. Rough estimations of the acid diffusion lengths are given by the rate of the diffusion-controlled neutralization reaction for blanket exposures. The acid diffusion range was minimized, as the temperature of pre baking was raised and the PEB temperature was reduced. Chemical kinetics around the glass transition temperature of the resist are discussed. Furthermore, a face-to-face contact experiment (wafer-sandwich) involving the dye was used to determine acid loss during PEB. Comprehensively, the acid diffusion within the matrix and acid evaporation out of the matrix could be quantified. Results are used to improve the lithographic performance of the dual-wavelength CARL® [4,5] resist system presently used at Infineon Technologies. © 1999 TAPJ.