Creation mechanism of metal depression in sputtering process for aluminum interconnects

For the aluminum (Al) metal line device fabricated by sputtering process, one of the frequently seen and well-known defects was metal depression. In this paper, several experiments were performed which consisted in varying the temperature, Ar gas flow rate, thickness, and stabilization time to eliminate this defect and to find the origination of the metal depression for below 0.13 μm technology. The metal depression was significantly related to the temperature, where the less metal depression was observed in relatively low temperature. The Ar gas flow rate did not influence the creation of the metal depression. The off-state ESC also showed the good surface morphology without the metal depression. The metal depression showed the inverse tendency to the thickness of Al film, however there is a limit to the thick Al film. The stabilization time after Al deposition was a very important factor for the metal depression. The sufficient stabilization time eliminated the metal depression through the resistance ability against the thermal stress.