AFM measurement of linewidth with sub-nanometer scale precision

A critical-dimension atomic force microscope system equipped with an ultra-high resolution, three-axis laser interferometer was constructed and tested. The MIRAI (Millennium Research for Advanced Information Technology) project has been improving the precision of critical dimension measurements with atomic force microscopy (AFM) by implementing modularized laser interferometers, to meet requirements for dimensional measurement in 45 nm technology node. The stability of the cross-sectional profile of an AFM image for a rectangular cross-section was greatly improved by optimizing interferometer linearity and resolution with DSP signal processing and reducing the angular motion and mechanical vibration of the monolithic three-dimensional probe scanner with a unique parallel spring mechanism. The repeatability of linewidth measurement of a nominal 100 nm linewidth along the same scanned line showed a standard deviation of 0.5-1.0 nm (3-sigma). This shows AFM to be one of the most promising metrological tools for next-generation nanodevice fabrication processes. Instrumentation, measurement results, and precision will be discussed.