Reduction of EUV resist damage by neutral beam etching

Even though EUV lithography has the advantage of implenting a finer pattern compared to ArF immersion lithography due to the use of 13.5 nm instead of 193 nm as the wavelength of the light source, due to the low energy of EUV light source, EUV resist has a thinner thickness than conventional ArF resist. EUV resist having such a thin thickness is more vulnerable to radiation damage received during the etching because of its low etch resistance and also tends to have a problem of low etch selectivity. In this study, the radiation damage to EUV resist during etching of hardmask materials such as Si₃N₄, SiO₂, etc using CF₄gas was compared between neutral beam etching (NBE) and ion beam etching (IBE). When NBE was used, after the etching of 20 nm thick EUV resist, the line edge roughness increase and the critical dimension change of EUV resist were reduced by ∼1/3 and ∼1/2, respectively, compared to those by IBE. Also, at that EUV etch depth, the root mean square surface roughness value of EUV resist etched by NBE was ∼2/3 compared to that by IBE on the average. It was also confirmed that the etching selectivity between SiO₂, Si₃N₄, etc and EUV resist was higher for NBE compared to IBE. The less damage to the EUV resist and the higher etch selectivity of materials such as Si₃N₄and SiO₂over EUV resist for NBE compared to IBE are believed to be related to the no potential energy released by the neutralization of the ions during the etching by NBE.