The influence of the pre-anneal ambient on the gate oxide integrity effect of copper contamination

Three sets of wafers, the first used as delivered, the second pre-annealed in oxygen and the third pre-annealed in nitrogen, were contaminated with copper after removing any surface oxides. Wafers that did not receive a pre-anneal and wafers that were preannealed in nitrogen showed higher gate oxide defect densities than those pre-annealed in oxygen. In a second experiment, two sets of wafers again received the same pre-anneals, a gate oxide was grown and the backside of the wafer was stripped and contaminated with copper. After a post-contamination anneal, gate oxides on wafers with the pre-anneal in nitrogen showed higher defect density than those pre-annealed in oxygen. Two possible mechanisms for these effects are presented and discussed based on diffusion/interaction of copper with silicon self interstitials. Deep Level Transient Spectroscopy (DLTS) experiments are proposed to identify the responsible/dominant mechanism. No damage can be observed in tunnel current and junction leakage on a fully processed test device lot with backside copper contamination when the anneal temperature is 450°C or lower