Evaluation of thinner resist film in beyond EUV interference lithography tool at NewSUBARU

Beyond EUV (BEUV) lithography with 6.7 nm wavelength is expected as a potential solution to meet the rigid demands of the smaller feature sizes. To evaluate resist pattering performance under BEUV irradiation, we have developed BEUV interference lithography (BEUV-IL) tool based on our prior EUV-IL system. The original IL system installed at NewSUBARU BL09B long undulator beamline, has been used to evaluate resist EUV-pattering performance at 13.5 nm wavelength. Two spacialy coherent lights diffracted by the grating produces interference fringes at the overlap region of the first-order lights. These fringes enable formation of L/S resist patterns with half-pitches of 50, 30, 25, 20, 17.5, and 15 nm, corresponding to 1/2 grating pitch. Building upon this setup, the BEUV-IL tool incorporates a new diffraction grating optimized for BEUV irradiation. This grating, composed of Ta absorber with the thickness of 20 nm and SiC support membrane with the thickness of 70 nm, achieves sufficient BEUV diffraction efficiency. For the future lithography technology, resist film must be thinner due to the aspect ratio constraints with miniaturization and the reduced depth of focus in higher NA exposure tools. Thus, we will present BEUV patterning results focusing on thin resist films. These results demonstrate the potential of the BEUV-IL tool for next-generation resist evaluation.