Application of Z-contrast imaging in deep-sub-micron process optimization

With integrated circuits going into the 0.18 μm generation and below, transmission electron microscopy (TEM) is becoming more routinely used and indispensable for equipment qualification, process monitoring and optimization, technology development, and failure analysis. However, TEM analysis is required to be more sample thickness forgivable. Scanning transmission electron microscopy (STEM) is a very good candidate for these purposes, as STEM can handle thicker TEM samples. By varying the camera length, the scattered angle of electrons forming STEM images changes. At large scattering angles, the scattering cross section is strongly atomic number (Z) dependent (D.B. Williams and C.B. Carter, Transmission Electron Microscopy, Plenum Press, New York and London, p. 41, 1996). Therefore the image contrast is dominated by Z and Z-contrast imaging is thus named. In this paper, we utilize the Z-contrast imaging technique to study the influence of different pre-copper/tantalum deposition cleaning scheme on the formation of Cu dual damascene structure of 0.13 μm technology node. The results clearly show that Z-contrast STEM imaging can be applied successfully to overcome some of the difficulties encountered in normal TEM observations, and it is a very useful tool for process optimization.