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ASML projects EUV quadruple patterning for 2nm logic node, explores High-NA potential

Fred Chen


We explore in this study imaging performance of horizontally oriented logic metal layer designs computationally, focusing on metal patterns with a pitch of 20nm (P20) and a tip-to-tip (T2T) range of 8- 35nm using 0.55 NA EUV single exposure. Simulations are performed by the method of source-mask optimization (SMO) using the TachyonTM software. The key assessed imaging parameters include the (normalized) image log-slope (NILS/ILS), overlapping depth of focus (DOF), and best focus (BF) shift. Simulation results show that traditional TaBN masks offer a reasonable overall contrast and DOF of both dense lines and through-pitch line patterns. Low-n masks offer benefits in contrast and dose. Low-n masks also show improvement in BF shift range, but such benefits vary with the extinction coefficient k as well as the pitch range and pattern selections. Other resolution enhancement techniques such as subresolution assistant features (SRAF) and bright-field imaging associated with metal-oxide-resists (MOR) also provide help to improve patterning performance. Metal designs with thick power rails have an impact on the contrast of neighboring patterns. Inner SRAF OPC and narrow power rails can effectively eliminate this impact. Patternable T2T size is type-dependent. Our study finds a flat ILS when T2T size is ≥15nm (for P20 lines) and a quick ILS drop when T2T size is < 15nm. It also reveals that complex T2T designs (e.g. staggered T2Ts) have lower contrasts. Additional care is needed in OPC other than avoiding such patterns in design. Our study confirms the potential replacement of 0.33 NA 3- to 4-time multipatterning by 0.55 NA single patterning.
This would be an optical necessity for 20 nm pitch, but already required by stochastics at 30 nm pitch (5nm).

20 nm pitch is also doable by ArFi SAQP.
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