Single-shot method for bias-free LER/LWR evaluation with little damage

A new method of evaluating line-edge or linewidth roughness (LER/LWR) is proposed. Conventional, directly measured LER/LWR values always contain a random noise contribution called LER/LWR bias. Our method can separate this bias artifact from the true LER/LWR using a single image of the pattern. The idea is based on the dependence of calculated LER/LWR value on the image-processing parameter for noise reduction. Both the conventional and the new bias-free LER/LWR were calculated using a series of images with different signal integration times (numbers of frames) but a fixed field of view. The LER/LWR obtained by our method was independent of the number of frames, and agreed with the conventional LER/LWR as measured using an image with a sufficiently large number of frames. It is concluded that the proposed bias-free LER/LWR measurement method will be a powerful tool in lithography metrology, especially for achieving practical and accurate LER/LWR measurement with little sample damage.