Atomic layer etching process application to TaO hard-mask etching for next-generation EUV (Extreme-Ultraviolet) photomask fabrication

To achieve the minimization of etched amount variation to less than 1nm, which is quite difficult in conventional RIE (Reactive Ion Etching) processes, we optimized the ALE (Atomic Layer Etching) process using Shibaura Mechatronics ARES^TM mask etch system and applied it to an etch hard-mask material, TaO (Ta-based oxide). By setting the thickness of the modification layer to less than 1nm and suppressing physical sputtering in the etching step, we obtained experimental evidence of the self-limiting etching of TaO. Moreover, since the very small etching amount per cycle of 0.18nm was achieved, we foresee potential applications for next-generation EUV (Extreme-Ultraviolet) photomask fabrication with high precision.