Effect of deposition, sputtering, and evaporation of lithium debris buildup on EUV optics

One of the critical issues within extreme ultraviolet (EUV) lithography is that of mirror lifetime and the degradation due to debris buildup from the EUV pinch. This work experimentally measures the mitigation of Li debris from collecting on the surface of EUV-like optics through combined use of a helium secondary plasma, evaporation from optic materials at elevated temperatures, and preferential sputtering off of the optic material. This leads to sputter enhanced removal of the lithium debris. This applied research expands the current knowledge base in understanding lithium interactions with a helium plasma and optic surfaces and provides a basis for analytical model development. The ultimate goal is to improve the current state of the art knowledge in lithium-optic material interactions, experimentally test mitigation and renewal of optic materials, and develop a relevant model for the predictive capabilities of the mirror optics while expanding the knowledge base of lithium transport and interaction. Experimental results are measured through the use of profilometry and AFM to quantify the ability to keep the EUV optic in an as received state while being exposed to EUV like lithium debris.