Study of EB resist dissolution contrast and chemical blur impact on the ultimate resolution

Abstract

EB (electron beam) resist is widely used for the EUV (extreme ultraviolet) mask production. Tighter pitch size and smaller pattern features are required on EUV mask for the next generation EUV patterning. A novel, high dose, positive-tone chemically amplified resist (pCAR) using PHS (polyhydroxystyrene) based polymer has been developed with improved resolution performance as verified by Point-beam writer and Multi-beam mask writer (MBMW). In this study, several high dissolution contrast pCAR formulations were studied under Point-beam conditions to investigate the impact of the chemical blur and the chemical stochastics on lithographic performance. For suppressing the chemical blur in the pCAR after exposure, formulations using larger size PAG (photo acid generator) could improve the resolution performance due to reduced acid diffusivity. For reducing the chemical stochastics, higher PAG loading pCAR and the slower sensitivity pCAR were investigated. Improved resolution and LWR (line width roughness) performances were obtained by these pCAR up to approximately 200μC/cm² under Point-beam condition. On the other hand, the lithographic performance was degraded at 270μC/cm². Analytical results of PAG decomposition ratio by HPLC suggested the possibility that decreased acid generation contrast could degrade lithographic performance when the pCAR sensitivity is too slow. The investigation of different dissolution contrast pCAR showed that higher dissolution contrast pCAR with higher Rmax resulted in improved resolution performance. According to this study, efforts to minimize the chemical blur and stochastics, and to maximize the photoresist contrast were the key factors for designing high-performing, low sensitivity pCAR. The verification results of the ultimate resolution of the representative pCAR with 60nm film thickness were also described in this paper under MBMW and mask process conditions. HP21nm line and space pattern could be resolved without pattern collapse. The small ring pattern with a 10.5nm pattern width was nicely resolved as the smallest feature.