Uncertainty contribution of tip-sample angle to AFM lateral measurements

AFM measurements are very important for quality control in the photovoltaic, microfluidic, electronic or micro-optic industries. This work proposes an algorithm to complete the uncertainty evaluation of AFM systems along the XY-axis under conditions where tolerance of curved surfaces must be controlled. This algorithm is also tested for tilt angles between tip and sample from 0° to 9° using an experimental arrangement which consists of an AFM instrumented with an inclinometer and four step height standards.Results show good agreement between the theoretical model and experimental results for samples with larger steps TGZ03 (465 nm) and TGZ11 (1416 nm), but with poor results for the smaller samples TGZ01 (17.6 nm) and TGZ02 (73.1 nm). An angle of 9° shows an error of about 3% in the horizontal determination of the step dimension, but it could increase to 47% for a tilt angle of 30° according to the theoretical model.The angle error between tip and sample is included in the uncertainty budget using a uniform distribution. An evaluation is performed in a theoretical rolling machine for imprint lithography where a step must be measured with nominal dimensions of 3 μm—X-axis and 1 μm—Z-axis. An assumed tip-sample angle is assumed that changes from 0° to 22.5° (curved form) and produces an uncertainty contribution to the X measurement of 55.7 nm. This uncertainty is important and must be considered to guarantee tolerances in quality control of curved form products.