New detailed CD measurement method by scanning confocal laser microscope

We have developed a new CD measurement method for a chromium pattern on a photomask. Using the scanning confocal laser microscope, we can not only measure CD of a chromium pattern, but also predict width of the chromium pattern tail. Using a scanning confocal laser microscope, we can obtain a reflective intensity profile. We can observe the minima in the profile of a chromium pattern. The position of the minimum almost corresponds to the pattern edge, in spite of a little offset. As a result of our analysis, there is a correlation between the offset and the chromium tail width, and the correlation depends on wavelength of a laser. Using two profiles with two wavelengths, we can obtain the chromium bottom width and the chromium tail width by two equations. By comparing the results of our method and the results of cross-sectional SEM observation, we have confirmed they are good agreement.