AFM interlaboratory comparison for nanodimensional metrology on silicon nanowires

Silicon nanowires (NWs) with a cylindrical form are fabricated by means of nanospheres lithography and metal-assisted chemical etching to obtain high aspect ratio nanostructures (diameter of about 100 nm and length of more than 15 µm) on cm2 area. The nanodimensional characterization of individual NWs is performed by using several techniques, because dimensions at the nanoscale strictly relate to functional performances. In this study, we report the results of an interlaboratory comparison between measurements from a metrological atomic force microscope (AFM) and research AFMs located in different national metrology institutes (NMIs) across Europe and in a university. The purpose of this study is to characterize two measurands: (i) sidewall roughness (Ra, Rq, Rz, Rsk, Rku parameters), extracted from the top profile measured along the nanowire length, and (ii) diameter of the nanowires measured as top-height. To this goal, the nanowires are spread horizontally on a silicon substrate, which has several areas labelled with a pattern of crosses and letters facilitating the measurement of the same NW, in order to study the reproducibility due to different instruments. Measurements show a good agreement between the different NMIs, with a combined standard uncertainty of top-height diameter less than 3%, and with a combined standard uncertainty of roughness parameters well within 5% for Ra and Rq values.