Image resolution monitoring technique for CD-SEM

This report presents a technique for quantifying the differences in resolution between tools from the SEM images at sub-nanometer scales. The accuracy of resolution monitoring of SEM images depends on the image noise factor and the sample shape factor. Therefore, a resolution monitoring method that is less dependent on the noise and the sample shape is highly desirable. In this study, the dependence on random noise and changes in sample shape are evaluated for three existing resolution measurement methods: the contrast-to-gradient (CG), fast Fourier transform (FFT) and auto correlation function (ACF) methods. By analyzing simulated and experimental SEM images, it was found that the CG method was the least dependent on noise and the sample, while the other two methods exhibited larger variations between samples. On the basis of these benchmarking results, the CG method appears to exhibit the best performance out of these existing resolution measurement techniques.