Automated high-precision measurement of critical dimensions using the scanning probe microscope

We describe a computerized method to measure the geometry of regular, nanometer-scale structures. By compiling measurements of hundreds of features, we obtain statistically robust results, not only for mean values of structural parameters, but also for the standard deviations, so that process windows can be determined. On DVDs, the smallest feature are pits or bumps about 400 nm long, 320 nm wide, 120 nm high, with a track pitch of 740 nm. We measured the following parameters: track pitch, bump height, bump width and length, bump length, and four sidewall slope angles, in each case reporting mean, standard deviation and other statistics. For each 10 by 10 micron image of a DVD stamper, containing about 100 bumps, we tabulated about 1000 values. In a plot of bump width versus bump length, we found that width at half height increased from 328 nm for the shortest bumps to about 385 nm for bumps longer than 800 nm; this matches the increase seen for corresponding optical signals produced when a finished disc is played. Where sidewall angle deviated from the norm, we were able to review the image data to identify the specific nature of the defect. Thus, feature geometry will no longer be a hidden variable in the path between controlling production equipment and observing the good or bad electrical performance of a finished disc.