New Insight into the Mechanism of Sequential Infiltration Synthesis from Infrared Spectroscopy


Sequential infiltration synthesis (SIS) has been recently demonstrated to increase the etch resistance of optical, e-beam, and block copolymer lithography resists for sub-50 nm pattern transfer. Although SIS can dramatically enhance pattern transfer relevant to device applications, the complex processes involved in SIS are not clearly understood. Fundamental knowledge of the chemistry underlying SIS is necessary to ensure a high degree of perfection in large-scale lithography. To this end, we performed in situ Fourier transform infrared (FTIR) spectroscopic measurements during the SIS of Al2O3 using trimethylaluminum (TMA) and H2O into poly(methyl methacrylate) (PMMA). The FTIR results revealed that TMA reacts quickly with PMMA to form an unstable complex. The subsequent conversion of this intermediate complex into stable Al—O linkages is slow and must compete with rapid TMA desorption. We support this interpretation of the FTIR data using density functional theory to calculate plausible structures for the unstable TMA-PMMA complex and the covalently linked species. As a consequence of this two-step reaction between TMA and PMMA, the detailed history of the TMA exposure becomes critical to achieving reliable patterns in SIS lithography. We demonstrate this using scanning electron microscopy to image the patterns resulting from SIS treatment of block copolymer films under different TMA exposure conditions. This better understanding of the SIS reaction dynamics should improve reliability in SIS lithography as well as other SIS applications.


Physics, Astronomy, and Materials Science

Document Type





thin films, precursors, fourier transform infrared spectroscopy, organic compounds, polymers

Publication Date


Journal Title

Chemistry of Materials