Capture rate enhance method of 0.1-μm level defects by pattern-matching inspectors

In this paper, a method of enhancing the capture rate of 0.1-μm level defects by pattern-matching inspectors is studied from the viewpoint of image variances. By our method, defect inspection engineers can obtain quantitative information for enhancing the capture rate of 0.1-μm level defects on both actual devices and test element groups (TEGs). The inspection sensitivities were experimentally evaluated by using the detection rate of the defects on an actual device and on the TEG. The image noise and the defect signal of the captured charge-coupled device (CCD) images of the same defect were quantitatively analyzed. The observed image noise and the defect signal obey a normal distribution. The capture rate calculated by our model, based on normal distribution, almost agrees with the experimental data. Next, we propose a new criterion called the “practical rapture rate” by uniting the rapture rate and the false count. The threshold value optimized from the viewpoint of the practical capture rate agrees with empirical thresholds value set by our defect inspection engineers. Finally, as an example of capture rate enhancement, a unique TEG called TWICE (TEG with image contrast enhancing) for photoresist inspection is demonstrated