Stress and source conditions of DC magnetron sputtered Nb films

We have studied the quality of Nb films from two different DC magnetron sources in a vein similar to previous work at Fujitsu Laboratories and NIST. In particular we are interested in the effects of target erosion on Nb film quality and on operating conditions of the magnetron sources. We find that the concept of a current-pressure (I-P) stress line of constant voltage (NIST), though giving qualitative guidance on proper source operating conditions, is not a sufficiently accurate model to set either of our magnetron source conditions over the life of the targets. In particular we find that: (1) the shape of our I-P "lines" change with target usage, (2) the stress values attributed to different points on a given I-P line at one "snapshot" in the target life are often different, and (3) the stress attributed to a given point on an I-P line may change over the life of a target. Alternative source operation strategies for maintaining stress free films will be discussed and the influence of other parameters including temperature, substrate material, source distance, substrate motion and target to target repeatability will also be examined.<>