For the development of the most cost effective lithographic solutions for the 22nm node, the lithographic process and
relevant requirements on CDU and overlay need to be identified. In this work, 22nm logic SRAM is selected as use case
because FinFET SRAM cells are considered to be a potential successor to conventional planar transistors for 22nm node
chips. We focus on the back-end layers of FinFET SRAM, including metal and contact. Litho solutions simulated under
ideal scanner conditions with the ASML Brion TachyonTM SMO product are shown. This tool co-optimizes a pixilated
freeform source and a continuous transmission gray tone mask based on merit functions of edge placement error. Per
scenario, these simulations result in a set of preferred litho solutions with respective source and mask. These solutions
have to comply with an imaging metric characterized by MEEF and common PW based on typical fab requirements. In a
second step the previously generated solutions are evaluated for CDU analysis using realistic scanner error budget. The
purpose is to predict the CDU performance of scanner, process and reticle in order to identify the major contributors for
every scenario solution.
Double patterning is considered the most viable option for 32- and 22-nm complementary metal-oxide semiconductor (CMOS) node development and has seen a surge of interest due to the remaining challenges of next-generation lithography systems. Most double patterning approaches previously described require intermediate processing steps (e.g., hard mask etching, resist freezing, spacer material deposition, etc.). These additional steps can add significantly to the cost of producing the double pattern. Alternative litho-only double patterning processes are investigated to achieve a composite image without the need for intermediate processing steps. A comparative study between positive–negative (TArF-P6239+N3007) and positive–positive tone (TArF-P6239+PP002) imaging is described. In brief, the positive–positive tone approach is found to be a superior solution due to a variety of considerations.