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

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