Analytical model for ArF photoresist shrinkage under scanning electron microscopy inspection

Abstract

Linewidth slimming is a phenomenon occurring specifically in photolithography of 193 nm wavelength (ArF) radiation. Photoresists for this wavelength appear to lose volume when exposed to electron-beam radiation, as when scanned in scanning electron microscopy for critical dimension (linewidth) measurement. This work is an attempt to understand this “shrinkage” from a polymer physics point of view. More specifically, the authors try to check the applicability of free volume theory in polymer systems by calculating some relevant physical properties, assuming that the exposure to e-beam creates an external hardened shell for the material bulk, and continued exposure will deliver heat into the polymer enclosed in a confined space. The authors’ main conclusion is that the free volume loss (annealing) shows qualitative resemblance to experiment, but this effect exclusively is not a sufficient quantitative explanation for the observed shrinkage. A possible explanation for this discrepancy is that their model is limited due to unknown material parameters, or that the annealing is coupled with other effects such as “wringing” solvent out.