Imaging of photogenerated acid in a chemically amplified photoresist

Abstract

Chemically amplified photoresists are widely used throughout the semiconductor industry due to the need for high throughput in the lithography process. Knowledge of the location of acid molecules in chemically amplified resists is of paramount importance for the process control of the image formation of almost all the lithographic techniques used in the semiconductor industry today. We have demonstrated a technique based on pH-dependent fluorescence which can measure directly the spatial distribution of the photoacid in photoresist films without the need of any other subsequent process after exposure. By adding a small amount of fluorescent material to the resist, a latent image can be formed when photogenerated acid molecules quench the fluorescence in exposed areas. We demonstrate images formed after exposure of SAL605 resist films to x-ray radiation, with no post-exposure bake, and show that the optical contrast is a function of dose. We also show that the same technique can be utilized for rapid evaluation of photoacid generator efficiency.