Diffusivity measurements in polymers: IV. Acid diffusion in chemically amplified resists

Abstract

Many of the strategies for sub 0.25 micrometer lithography depend on chemically amplified resists to provide sensitivity. For example, glass damage limits the dose that can be delivered at 193 nm, and source brightness limits the dose that can be delivered in the EUV. However, acid diffusion, an integral part of the chemical amplification process, dramatically affects the lithographic performance of chemically amplified resists. The transport properties of Bronsted acids in glassy polymers have been estimated from a variety of indirect measurements. We have, for the first time, directly measured the diffusion coefficients of acids in polymer films. A quartz crystal microbalance (QCM) was used to make the measurements. The QCM can detect small changes in mass which is indicated by a shift in the resonant frequency of the piezoelectric quartz crystal (see the accompanying paper 'Diffusivity measurements in Polymers, Part III: Quartz Crystal Microbalance Techniques'). The experiments were conducted at different temperatures in order to establish the dependence of the diffusion coefficient on temperature. Acid diffusion in poly(hydroxystyrene) is discussed. The results obtained from the diffusion experiments have been used in lithographic simulation (PROLITH). Results of acid diffusion in poly(hydroxystyrene) are discussed.