Electron penetration effects in the Scanning Electron Microscope applied to Cu/Ta thin films
Current semi-conductor technology uses low-resistivity metals, as Cu, for integrated circuit conductor lines and contact structures. Copper, however, is quite mobile in silicon at elevated processing temperatures and a diffusion barrier such as Ta, is therefore required between the Si and Cu. The interdiffusion of Cu and Si with Ta as a diffusion barrier was studied in samples annealed between 500°C and 800“C, using scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Secondary electron images obtained in the SEM, from 5keV to 25keV accelerating voltages were correlated to the structural information obtained by cross-section TEM. This work showed that annealing produced a compositionally non-uniform underlayer beneath the Ta film, and that the technique of varying the accelerating voltage in the SEM provides a means of quickly obtaining such information about underlying structures.