Low temperature gettering of Cu, Ag, and Au across a wafer of Si by Al

A set of sandwich structures consisting of a noble metal film of Cu, Ag, or Au on one side of a Si wafer (200 μm thick) and an Al film on the other side was annealed at 540°C for 100 h to study the gettering of these noble metals across the wafer by Al. Rutherford backscattering spectroscopy was used to analyze the amount of these metals in the Al. A very large quantity of Cu(∼1021 atom/cm3) in the Al film was detected after the annealing but neither Ag nor Au could be found in the Al. The solubility of Cu in Si at 540°C has been calculated to be 1.7×1014 atom/cm3.