Impact of vacuum ultraviolet photons on ultrathin negative tone resists for extreme ultraviolet lithography during plasma etching

To achieve further miniaturization of semiconductor devices, extreme ultraviolet lithography is employed for patterning at the cutting-edge nodes. This technique necessitates the use of ultrathin resists (less than 50 nm thick) to maintain pattern stability and meet depth of focus requirements. Typical cold plasmas used for dry etching are rich in vacuum ultraviolet photons, which can cause unintended damage to these resists. This can further reduce the etch budget and complicate pattern transfer. Thus, understanding the impact of these plasma photons on ultrathin resists can be crucial for enabling pattern transfer of sub-10 nm features. Here, we investigate the effects of the vacuum ultraviolet photons on three different models of ultrathin negative tone chemically amplified resists along with polymethyl methacrylate as a reference positive tone baseline resist. The resists were exposed to vacuum ultraviolet photons using a deuterium lamp, to argon ions using an ion beam etch tool, and to argon plasma using an inductively coupled plasma etch tool. Using different characterization techniques, the variations in etch rate, surface roughness, and bulk chemical changes of the resists under different processing conditions were examined. The applicability of the Ohnishi number and ring parameter etch rate models to the resists and processing conditions used was also studied.