File Name : figure_s1.pdf

Caption : fig. s1 | euv interference lithography. (a) schematic representation of the xil-ii beamline at the paul scherrer institute. euv light with tunable wavelength is generated by an undulator and gets reflected off a series of mirrors for high harmonic suppression and focusing. the beam is then focused on a pinhole (spatial filter) and the spatially coherent beam subsequently illuminates the imaging module (mask with gratings). (b) photograph of a mask with transmission gratings. the spacing between the grating sets varies with their grating period in order to get the same mask-sample spacing for the different diffraction angles. (c) the operation principle of euv-il based on transmission gratings. a silicon nitride membrane (green) is grown and released by koh-etching of the si wafer (gray). gratings with period g are formed on hsq photoresist by ebl. the metal photonstop (beige) ensures that light passes only through the gratings where it gets diffracted. the interference pattern of the 1st order diffracted beams gets recorded on the sample photoresist (red) and its period is independent of the wavelength λ.

File Name : figure_s2.pdf

Caption : fig. s2 | geometrical analysis of mil. (a) extended version of fig. 1b featuring a non-symmetrical case of the mil device. one of the mirrors has a higher angle than the other by a value δ, and the wafer is tilted at an angle θ. (b) geometrical analysis of the asymmetric case, in which the difference of the optical path lengths cex and dfx is expressed as a function of position x and the grazing angles in order to derive the interference pitch. (c) the elevation of the overlap area with respect the sample at the asymmetric case. (d) the tilted-wafer case, in which the pitch is projected at an angle θ leading to an observed pitch expanded by 1/cos⁡θ.

File Name : figure_s3.pdf

Caption : fig. s3 | surface roughness in mil. (a) afm image of the mirror surface, after ru 10 nm deposition. (b) the distribution of the corresponding height-sensor measurements that shows an rms roughness of 0.15 nm. (c) simulated reflectivity as a function of grazing angle for different roughness values.