A metallic grating is formed to include a substrate; a plurality of high aspect ratio trenches disposed in the substrate such that the high aspect ratio trenches are spaced apart from one another by a field surface of the substrate; a metallic superconformal filling formed and disposed in the high aspect ratio trenches; and a grating including a spatial arrangement of the high aspect ratio trenches that are filled with the metallic superconformal filling such that the metallic superconformal filling is void-free, and the high aspect ratio trenches are bottom-up filled with the metallic superconformal filling, wherein a height of the metallic superconformal filling is less than or equal to the height of the high aspect ratio trenches.