Effects of ‘As Deposited’ and Alloying Temperatures on the Distribution of Cu in 0.5%Cu-Al Films

The Al-0.5wt%Cu alloys in Ti-TiN/Al/Ti-TiN metal interconnects were investigated using blanket and patterned films deposited on SiO2. Distribution of Cu and Ti within the Al films was determined using Resistivity (Rs), X-ray Diffraction (XRD), Rutherford Backscatter Spectroscopy (RBS), and Secondary Ion Mass Spectroscopy (SIMS). The location of Cu, Ti, Al and their intermetallics were studied in a CM300 field emission gun (FEG) TEM using Energy Filtered Transmission Electron Microscopy (EFTEM) with a Gatan Imaging Filter (GIF). No significant differences were observed with Rs or XRD textural analysis. Elemental distribution analysis from RBS and SIMS revealed relatively higher concentrations Cu at the Al/Ti-TiN barrier interface. This was attributed to sputtering bias during the start of the Al deposition and the subsequent snow plowing of Cu during the growth of the TiAl3 intermetallic. TEM imaging and elemental analysis showed that Cu is completely dissolved into solution at deposition temperatures ≥ 300°C. At temperatures ≤ 250°C some (Al2Cu) precipitates were observed on grain boundaries. Continued thermal cycling does not effectively change the elemental distribution. Therefore, it can be concluded that the solid solubility of 0.5wt%Cu in Al was not reached at these low temperatures or during the subsequent thermal cycling.