Bias-free measurement of LER/LWR with low damage by CD-SEM

Abstract

We propose a new method for the evaluation of line-edge or linewidth roughness (LER/LWR). Conventional, directly measured LER/LWR values always contain a random noise contribution, which is called LER/LWR bias. Our method can separate this bias artifact from the true LER/LWR by using a single image of the sample pattern. The idea is based on the dependency of a measured LER/LWR value on the image-processing parameter for noise reduction. Both, the conventional and the new bias-free LER were calculated on series of images with different frame integration numbers but a fixed field of view. In addition, the validity of this method to the gate-LWR measurement on an ArF resist line pattern was examined. The LER/LWR obtained by our method was independent of the frame number, and agreed with the conventional LER/LWR as measured on an image with a sufficiently large frame-number. That is, our method can evaluate LER/LWR without random-noise contribution, suggesting that the method can be applied to images recorded under low-sample-damage conditions (i.e., low signal-to-noise ratio). 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 low sample damage.