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AFM benchmark for the profile characterisation of subwavelength diffractive elements within the EC Network of Excellence on Micro-Optics (NEMO)

The round robin "measurement of subwavelength diffractive elements" tackles the metrology problems related to the measurement of diffraction gratings by AFM. It aims at quantifying the absolute precision and the uncertainty of the measurement considering some features of such structures like the depth, the period, the fill factor and the shape of the profile. This round robin involved four partners within NEMO. Each partner has measured three different samples: one 2D small depth grating, one 1D small depth grating and one 1D high aspect ratio grating. In order to get rid of the samples inhomogeneity, the measurements were performed exactly at the same location on each sample by all partners. This was achieved by using a multiscale resist pattern transferred on the gratings which precisely defined a 5×5 μm2 area. The paper will sum up the experimental values obtained by all the partners, draw general conclusions and make suggestions to improve the accuracy of AFM measurements.