Extending logic metal printing with sub-resolution grating in high and hyper NA EUV lithography

Low-n attenuated phase shift mask (Low-n mask) has been widely used in EUV lithography industry as it aligns the diffraction phases between the zeroth and first orders, enhancing exposure latitude (EL) and boosting throughput. However, it has faced challenges such as side-lobe printing due to its high reflectivity and best focus (BF) variation when used in environments with a wide range of pattern pitches. To mitigate this, conventional sub-resolution assisted features (SRAF) could be inserted, but as the main features’ pitch decreases, the space that needs to be inserted in between also decreases by nearly half or more, it will become challenging when scaling to Hyper NA dimensions. We proposed Sub-Resolution Grating (SRG) crossing the main features perpendicularly, which not only suppresses unwanted side-lobe printing but also improves the imaging quality with a better BF alignment over a broader pitch range by effectively aligning diffraction phases. The SRG helps correct issues such as Bossung tilt and critical dimension (CD) asymmetry in non-repeating n-bar patterns, which certainly contributes to CD-based process window (PW) enhancement. This paper demonstrates, through rigorous simulation, that this technology can ultimately overcome the limit