Surface hardening of extreme ultraviolet(EUV) photoresist by CS₂ plasma for highly selective and low damage patterning

Extreme ultraviolet (EUV) lithography has the advantage of implementing a finer pattern by using a wavelength of 13.5 nm light source with a higher resolution value than the existing ArF light source. However, there are several issues regarding EUV photoresist (PR), such as low etch resistance due to thin thickness and pattern mismatch during subsequent processing/deterioration of electrical characteristics of the device due to increase in line edge roughness (LER). In this study, the effect of CS₂ plasma treatment and/or followed annealing at 80 °C on the EUV PR properties was investigated to improve PR characteristics such as LER, etch resistance, etc. during the etching by CF₄ plasma. The CS₂ plasma treatment and followed annealing improved the PR characteristics such as decreased ΔLER, decreased ΔCritical dimension, and decreased ΔThickness of the PR after the etching compared to the reference and/or annealed PR. Especially, the PR treated by CS₂ plasma + annealing showed the improvement of etch resistance of ∼ 70 % compared to the reference PR. The X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy showed that the improvement of EUV PR properties were related to the formation of C[sbnd]S, O[dbnd]S bonds on the surface of PR by the CS₂ plasma treatment + annealing.