Test structure. (a) Scanning electron micrograph of a 500 nm thick tantalum test structure with 50 nm lines and spaces. (b) Hologram of the test structure obtained from the normalized intensity distribution recorded during 1 second total illumination time. Effective pixel sizes are 16 nm in horizontal and 11 nm in vertical direction, the field of view is 3.4 μm (h) × 2.2 μm (v). (c) Profile along the black line in (b) together with a sinusoidal fit yielding a perdiodicity of 100.7 nm, well in agreement with the 50 nm feature size.