Physical and chemical analysis of La/B4C multilayer structure with carbon barriers for ∼6.7 nm EUV application

A series of La/B₄C multilayers with different C-barriers were deposited using magnetron sputtering dedicated for a wavelength ca. 6.7 nm wavelength. Grazing incidence X-ray reflectometry, atomic force microscopy, high-resolution transmission electron microscopy, and energy-dispersive X-ray spectroscopy were used to investigate the physical structure of the multilayer with different barrier layers. It was found that 0.2 nm carbon barrier at the B₄C-on-La interface slightly improved the physical structure especially compared to adding C barrier at the other interface or with larger thickness. In-depth X-ray photoelectron spectroscopy profile measurements indicated an increased formation of C-La bond, which potentially decreased the content of the optically unfavorable B-La bond in the competitive reaction at interfaces. A reduced interlayer density was also found after the deposition of C barrier according to the fitted results of hard X-ray and EUV reflectance. It is estimated that the reduced density and different composition of the interlayer contribute to the enhanced EUV reflectance of the La/B₄C/C multilayer. The highest reflectance for the C-barrier sample is 49.4 % at 6.640 nm, while the highest reflectance for the No-barrier sample is 37.6 % at 6.616 nm.