As future patterning processes reach the limit of lithographic printability, continuous innovation in mandrel trim or shrink strategies are required to reach sub-20 nm line-space patterning. Growing concerns of lithography defectivity, mask selectivity, line edge roughness (LER), line width roughness (LWR), and critical dimension uniformity (CDU) present significant challenges towards this goal. The authors compare various alternative mandrel trim strategies to highlight potential solutions and drawbacks towards enabling successful printing of mandrels used in extreme ultraviolet (EUV) multi-patterning schemes. Through this comparison, the authors demonstrate the challenges of maintaining adequate pattern transferability while keeping aspect ratio-driven line roughness and material selectivity under control. By process partitioning, the limitations of traditional lithography and etch trimming strategies are highlighted, suggesting the need for new methods of CD reduction after the pattern has been transferred. These new trimming methods offer flexibility in CD control without negatively impacting the mandrel profile and demonstrates better tunability across different material sets, allowing for evaluation of different mask and mandrel material combinations for downstream process optimization.
TEL’s patented DCS function and conventional plasma treatment were applied on EUV PR to examine the effect of ion/radical loading and surface modification. The DCS function accelerates plasma selective deposition particularly on the top of EUV PR at 36nm pitch. The increment of EUV PR height secures etching budget and provides longer plasmas smoothing period. In addition, line roughness was also smoothed during area plasma selective deposition due to loading effect. In this study, our plasma treatment was able to improve PR roughness by 30% comparing to as-exposed litho and the performance was kept to the next oxide layer. Furthermore, an extra 13.7nm of PR was gained which enlarged the process windows of etching selectivity and plasma smoothing effect.