Correlation of optical and electrical test structures for characterisation of copper self-annealing

The self-annealing properties at room temperature of electrochemically deposited copper have been investigated for the first time using test structures to simultaneously measure the spatial variation of sheet resistance and film stress with time. The phase changes associated with the self-annealing of copper on 200mm wafers have been observed over a period of 30 hours indirectly through these parameters, mapped across the wafer. In particular, this paper reports the influence of the electroplating current density on the resulting characteristics of the deposited copper.