Copper/low-k process characterization for 90nm technology using SEM and TEM imaging

Artificial vertical and lateral shrinkage of different carbon-doped oxide (CDO) low-k materials is observed for electron beam exposure. The effect depends on SEM and TEM imaging conditions and sample preparation procedures. Typical artifacts include layer thinning and de-lamination of the CDO material from surrounding materials. TEM imaging is less critical compared to SEM. This is partly due to the favorable conditions during TEM sample preparation employing ion milling steps, which avoid the mechanical stress of conventional SEM sample cross-sectioning. Samples also absorb less energy from the electron beam during TEM scanning, which minimizes the impact of CDO shrink. Some artifacts are difficult to distinguish from real process issues, e.g. de-lamination caused by poor layer adhesion. Therefore, careful sample preparation and imaging are necessary to provide meaningful information.