In this work, we address the problem of identifying the
minimum temperature required to diffuse copper deposited at the silicon
surface into the bulk, and to identify a suitable method to detect the
initial stages of copper electrical activity at wafer surface. Thermal
treatments at temperatures ≥250 °C were studied. It is shown
that after an annealing at temperatures ≥250 °C a significant
copper fraction diffuses in silicon, but it is not electrically active for
carrier recombination. In addition, after these treatments copper at the
silicon surface cannot be completely removed by cleaning. A moderate
electrical activity is associated to copper at the oxide-silicon interface
in the native oxide A change in the chemical bonds of copper is detected
by XPS after annealing at 700 °C.
After a further annealing at 900 °C, copper is electrically
active for recombination both at the surface and in the bulk.