Inspection of Stochastic Defects With Broadband Plasma Optical Systems for Extreme Ultraviolet (EUV) Lithography

As extreme ultraviolet (EUV) lithography enters high volume manufacturing (HVM) to enable the sub-7nm scaling roadmap, characterizing and monitoring defects that print at wafer level are of critical importance to yield. This is especially true for defects coming from the EUV mask, due to multi-layer defects or added particles or growth on mask during its use, and for defects coming from the pattern formation process itself, which are known as stochastic printing defects or simply stochastic defects. In this paper we focus on developing inspection solutions for stochastic defects, which essentially are random local variations that occur between structures that should, in principle, print identically. These defects occur at significant frequencies with current state-of-the-art processes. Specifically, we discuss the importance of detecting these defects using KLA broadband plasma (BBP) optical inspection systems and the development of useful analysis methodologies. In addition, we describe use of traditional focus-dose process window discovery methodology developed on these optical inspection systems, for a foundry N5 equivalent M2 layer with both hybrid EUV and direct EUV patterning schemes. We highlight the impact of EUV stochastics to the overall process window.