Fabrication of ultrasmooth complementary split ring resonators by an improved template stripping method on SU-8

► Template stripping method was improved to fabricate ultrasmooth hollow structures. ► SU-8 was used to peel off Au nanopatterns from silicon template. ► The pre-baking temperature and depth of nanopatterns on template were optimized. ► Nanoscale complementary split ring resonators with a gap of 30 nm were obtained. ► The RMS surface roughness of stripped surface was improved from 1.3 to 0.4 nm.