High-Performance Chain Scissionable Resists for Extreme Ultraviolet Lithography: Discovery of the Photoacid Generator Structure and Mechanism

Abstract

Extreme ultraviolet (EUV) lithography currently dominates the frontier of semiconductor fabrication. Photoresists must satisfy increasingly strict pattern fidelity requirements to realize the significant enhancements in resolution offered by EUV technology. Traditional chemically amplified resists (CARs) have hit a barrier in the form of the resolution, line edge roughness, and sensitivity trade-off. This has been compounded by a lack of understanding of the chemical mechanism associated with the EUV process. Here, we synthesize a series of novel EUV photoresists based on a self-immolative, acid-labile poly­(acetal) system. These systems are shown to be commercially viable under current EUV requirements. Careful study of the resists’ degradation pathways has enabled the identification of a remarkable photoacid generator (PAG) that functions as both an acid generator and base quencher, enabling further improvements over previous resists. density functional theory calculations reveal, for the first time, the connection between the PAG activation barrier and resist sensitivity and suggests why attempts to use electron-beam lithography to predict EUV performance have failed.

Synthesis of End-Cap Enabled Self-Immolative Photoresists For Extreme Ultraviolet Lithography

“…This resulted in PPA 3, which possessed two responsive endcaps at the head and tail of the polymer. For comparison, PPA 1 was constructed to bear a phenyl carbonate end-cap known to be inactive 22 under UV radiation. TGA analysis (SI) demonstrated that PPA 2 and 3 still enjoyed good thermal stability, with degradation temperatures of 143 and 147 °C, respectively.…”

“…Despite this undesirable effect, the doseto-clear (DTC) of 90 mJ/cm 2 for PPA 3 far exceeds recent attempts 20 to utilize PPA as a PAG free EUV photoresist where DTC measurements exceeded 10000 mJ/cm 2 . Furthermore, the absence of PAGs in this resist is likely to significantly improve the resolution and line edge roughness beyond the previously developed two component system 22 by eliminating the deleterious effects of acid diffusion.…”

“…These self-immolative resists predate the employment of PAGs but have long been neglected due to their instability and propensity to contaminate the optics of lithography tools. Recently, we reported the synthesis of a remarkably stable poly­(phthalaldehyde) (PPA) derivative that did not suffer from monomer outgassing associated with the original PPA resist. − This brominated derivative (Br-PPA) was studied with various PAGs to create a resist system that was ultimately limited by acid diffusion and the stochastics of mixing the two components. In this work, we sought to synthesize an improved resist based on Br-PPA that did not require the usage of separate small molecule PAGs to achieve high EUV sensitivity.…”

Synthesis of End-Cap Enabled Self-Immolative Photoresists for Extreme Ultraviolet Lithography

“…Recently, we reported the synthesis of a remarkably stable poly(phthalaldehyde) (PPA) derivative that did not suffer from monomer outgassing associated with the original PPA resist. [21][22][23] This brominated derivative (Br-PPA) was studied with various PAGs to create a resist system that was ultimately limited by acid diffusion and the stochastics of mixing the two components. In this work, we sought to synthesize an improved resist based on Br-PPA that did not require the usage of separate small molecule PAGs to achieve high EUV sensitivity.…”

“…This resulted in PPA 3, which possessed two responsive end-caps at the head and tail of the polymer. For comparison, PPA 1 was constructed to bear a phenyl carbonate end-cap known to be inactive 22 under UV radiation. TGA analysis (SI) demonstrated that PPA 2 and 3 still enjoyed good thermal stability, with degradation temperatures of 143 ˚C and 147 ˚C, respectively.…”