Defect characterization of EUV Self-Aligned Litho-Etch Litho-Etch (SALELE) patterning scheme for advanced nodes

In this paper, we will investigate defect modes and pattern variations for EUV (extreme ultra-violet lithography) double pattering scheme using self-aligned litho-etch-litho-etch process on final pitch 28nm test structures. As we continuously shrink device sizes towards aggressive pitches, the industry is moving towards adopting double pattering using EUV. Although we continue to push limits of 0.33NA EUV in terms of pitch and CD (critical dimensions) with novel resists and processes, stochastic defects pose greater challenge at pitches below 40 nm [1]. One of the ways to circumvent this problem is to use a multi-patterning scheme with relaxed design rule. Self-aligned litho-etch-litho-etch (SALELE) is one such scheme for early BEOL (back end of line) layers. The benefit of this patterning approach is that no dummy metal is added and blocks are needed only at tight tip-to-tip definitions, which can help to reduce parasitic capacitance. In this paper we will employ SEM inspection techniques to understand pattern variabilities, after initial optical inspection was done to discover different defect modes. We show that with analysis of SEM images we can get further insight on process variations.