LER improvement for sub-32nm pitch self-aligned quadruple patterning (SAQP) at back end of line (BEOL)

Critical back end of line (BEOL) Mx patterning at 7nm technology node and beyond requires sub-36nm pitch line/space pattern in order to meet the scaling requirements. This small pitch can be achieved by either extreme ultraviolet (EUV) lithography or 193nm-immersion-lithography based self-aligned quadruple patterning (SAQP). With enormous challenges being faced in production readiness of EUV lithography, SAQP is expected to be the front up approach for Mx grid patterning for most of industry. In contrast to the front end of line (FEOL) fin patterning, which has successfully deployed SAQP approach since 10nm node technology, BEOL Mx SAQP is challenging owing to the required usage of significantly lower temperature budgets for film stack deposition. This has an adverse impact on the material properties of the as-deposited films leading to emergence of several challenges for etch including selectivity, uniformity and roughness. In this presentation we will highlight those unique etch challenges associated with our BEOL Mx SAQP patterning strategy and summarize our efforts in optimizing the patterning stack, etch chemistries & process steps for meeting the 7nm technology node targets. We will present comparison data on both organic and in-organic mandrel stacks with respect to LER/LWR & CDU. With LER being one of the most critical targets for 7nm BEOL Mx, we will outline our actions for optimization of our stack including resist material, mandrel material, spacer material and others. Finally, we would like to update our progress on achieving the target LER of 1.5 nm for 32nm pitch BEOL SAQP pattern.