Acid diffusion in a chemically amplified negative i-line photoresist

One of the major factors which determines the success of resist photochemistry is acid diffusion. Inadequate or excess diffusion can cause undesirable resist profiles, limit resolution and adversely impact process windows. Both formulation and process parameters effect acid diffusion. Formulation factors include such things as intrinsic properties of the acid, resin, and solvent. The process parameters which effect acid diffusion are mainly exposure dose, post-apply (PAB) and post-exposure bake (PEB). A practical study has been conducted which investigates the effect of PAB and FEB times and temperatures on acid diffusion in a chemically amplified negative i-line photoresist. Acid diffusion was measured by determining the change in linewidth of an isolated resist line. The goal of the study was to maximize acid diffusion through PAB and FEB conditions with minimal impact on profile quality and process windows. Maximum acid diffusion was required to combat a minimum light intensity at the surface of oxide wafers. Data on quantifying acid diffusion through linewidth change, maximizing acid diffusion at low light intensities as well as the role of the resist formulation will be discussed.