With state-of-the-art EUV lithography moving to the 3 and 2 nm nodes, yield control and connected to that particle contamination control are crucial aspect of High-Volume Manufacturing (HVM). While much progress has been made in recent years, the continuously tightening node requirements translate into ever more stringent requirements on particle contamination control. Besides for lithographic scanners, operating in a low background pressure hydrogen gas environment, particle contamination control is also important for space exploration (which also operates in low pressure environments), where particles may lead to malfunctioning moving parts, loss of solar power generation, and human health hazards. A key factor in release of particles in these low-pressure environments is the ionization of the low-pressure background gas by energetic photons (for instance EUV in lithographic scanners, and broadband energetic radiation in space), and resulting plasma with fast electrons of 25 eV and above. Experiments show that these electrons can mobilize and remove particles on most materials, and that the governing effects strongly depend on the substrate material, coating and surface finishing. This paper will discuss work on understanding and modeling these effects and describe possible solution paths to improve particle contamination control, both for lithographic scanners and for space exploration.
In the past years, EUV lithography scanner systems have entered high-volume manufacturing for state-of-the-art integrated circuits (IC), with critical dimensions down to 10 nm. This technology uses 13.5-nm EUV radiation, which is transmitted through a near-vacuum H2 background gas, imaging the pattern of a reticle onto a wafer. The energetic EUV photons excite the background gas into a low-density H2 plasma. The resulting plasma will locally change the near-vacuum into a conducting medium and can charge floating surfaces and particles, also away from the direct EUV beam. We will discuss the interaction between EUV-induced plasma and electrostatics, by modeling and experiments. We show that the EUV-induced plasma can trigger discharges well below the classical Paschen limit. Furthermore, we demonstrate the charging effect of the EUV plasma on both particles and surfaces. Uncontrolled, this can lead to unacceptably high voltages on the reticle backside and the generation and transport of particles. We demonstrate a special unloading sequence to use the EUV-induced plasma to actively solve the charging and defectivity challenges.
With the introduction of the NXE:3400B scanner, ASML has brought EUV to High-Volume Manufacturing (HVM). In this context, ASML is pursuing a dual-path approach towards zero reticle defectivity: EUVcompatible pellicle or zero particles towards reticle by advanced particle contamination control. This paper will focus primarily on the approach of advanced particle contamination control and on the understanding of EUV-induced plasma to control both release and transport of particles within the scanner. This paper will present our advancements in understanding and control of particle forces related to the EUV-induced plasma, for EUV sources up to 250W and beyond. This will combine models and simulations with off-line experiments as well as in-situ scanner tests. It will be shown that our understanding of the underlying mechanisms of plasma-induced release and transport of <1um particles enables us to manage defectivity levels down to be compatible with HVM requirements for sub-10nm node lithography.
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