Studying the effects of chemistry and geometry on DSA hole-shrink process in three dimensions

Acquiring three-dimensional information becomes increasingly important for the development of block copolymer (BCP) directed self-assembly (DSA) lithography, as 2D imaging is no longer sufficient to describe the 3D nature of DSA morphology and probe hidden structures under the surface. In this study, using post-DSA membrane fabrication technique and STEM (scanning transmission electron microscopy) tomography we were able to characterize the 3D structures of BCP in graphoepitaxial DSA hole shrink process. Different DSA structures of singlets formed in templated holes with different surface chemistry and geometry were successfully captured and their 3D shapes were reconstructed from tomography data. The results reveal that strong PS-preferential sidewalls are necessary to create vertical DSA cylinders and that template size outside of process window could result in defective DSA results in three dimensions. Our study as well as the established 3D metrology would greatly help to develop a fundamental understanding of the key DSA factors for optimization of the graphoepitaxial hole shrink process.