# Initial Stage of Nanoscale Imaging in Positive Tone Extreme UV Photoresists: The Influence of the Polymer Sequence

## TL;DR

This paper studies how polymer chain structures in EUV photoresists affect early nanoscale imaging processes, finding that polymer sequence has little impact on initial radiolytic reactions.

## Contribution

The study introduces a computational model to evaluate the influence of polymer sequence on radiolytic spur formation in EUV photoresists.

## Key findings

- Polymer sequence has no significant effect on the composition of radiolytic spurs.
- Electron thermalization predictions align with existing literature, validating the computational approach.
- Potential imaging improvements likely arise from postimaging steps rather than initial polymer structure.

## Abstract

Photolithographic patterning using extreme ultraviolet
(EUV, 92.5
eV) light is a radiolytic process that initially forms electrons,
radical cations, anions, and neutral radicals in the polymeric photoresist
matrix. These species may participate in the chemical reactions that
define the ultimate resolution of the printed image, and their concentrations
and nanometer-scale stochastic variations in their formation influence
printed image quality. Proposals have been made that polymer chain
uniformity may be advantageous in reducing stochastics due to spatial
inhomogeneities, and this aspect of radiolysis is examined in this
work. We have simulated the initial subpicosecond stages of the imaging
process for a series of photoresist films that are identical in composition
but vary in their polymer chain structures. We use detailed, physically
accurate stochastic reaction-diffusion calculations to evaluate the
influence of defined sequence and random copolymer structures on radiolytic
spur formation, i.e., a cluster of species formed by electron-polymer
interactions that defines the initial spatial characteristic of the
imaging process. Predictions of electron thermalization in the present
work are shown to be consistent with the literature, indicating that
our overall computational approach for ultrafast nanoscale processes
is sound. The computational results show that the polymer sequence
has no significant effect on the spur composition. This suggests that
any potential imaging improvements to be gained by sequence control
must originate from postimaging lithographic process steps.