For 45nm and 32nm node technology, the challenges for resolution and CD control of mask patterns become the steeper
mountain path. Especially, Sub Resolution Assist Feature (SRAF) is the smallest pattern on mask and amplifies the
difficulty of mask fabrication. In order to improve the resolution of fine patterns, the influence of wet processing cannot
be neglected, because it causes the pattern collapsing. Wet processing of mask-making can be divided into resist
development and cleaning.
In this study, the root causes of pattern collapsing are investigated at each wet processing. It is confirmed that thin resist
can enhance the resolution limit of resist pattern and hard-mask blank, such as OMOG: Opaque MoSi On Glass, is
suitable for thinner resist under 1500A. The pattern collapsing of OMOG is compared with that of Att.PSM at the
cleaning before and after Cr stripping. Mask inspection finds that pattern collapsing can be suppressed by OMOG at both
cleanings. It is because OMOG has lower cleaning stress than Att.PSM due to lower aspect-ratio. This benefit is
demonstrated by cleaning stress simulation. Additionally, it is found that the SRAF size of OMOG can be wider than
Att.PSM by optical simulation. From these results, OMOG has much advantage of fine pattern fabrication and is the
optimal blank for 32nm node and beyond.