Double patterning combined with shrink technique to extend ArF lithography for contact holes to 22nm node and beyond

Lithography becomes much more challenging when CD shrinks to 22nm nodes. Since EUV is not ready, double patterning combined with Resolution Enhancement Technology (RET) such as shrink techniques seems to be the most possible solution. Companies such as TSMC[1] and IBM[2] etc. are pushing out EUV to extend immersion ArF lithography to 32nm/22nm nodes. Last year, we presented our development work on 32nm node contact (50nm hole at 100nm pitch) using dry ArF lithography by double patterning with SAFIER shrink process[3]. To continue the work, we further extend our dry litho capability towards the 22nm node. We demonstrated double patterning capability of 40nm holes at 80nm pitch using ASML XT1400E scanner. It seems difficult to print pitches below 140nm on dry scanner in single exposure which is transferred into 70nm pitch with double patterning. To push the resolution to 22nm node and beyond, we developed ArF immersion process on ASML XT1700i-P system at the College of Nanoscale Science and Engineering (Albany, NY) combined with a SAFIER process. We achieved single exposure process capability of 25nm holes at 128nm pitch after shrink. It enables us to print ~25nm holes at pitch of 64nm with double patterning. Two types of hard mask (HM), i.e. TIN and a-Si were used in both dry and immersion ArF DP processes. The double patterning process consists of two HM litho-shrink-etch steps. The dense feature is designed into two complementary parts on two masks such that the density is reduced by half and minimum pitch is increased by at least a factor of 21/2 depending on design. The complete pattern is formed after the two HM litho-shrink-etch steps are finished.