Low temperature drive-in of surface-deposited copper in silicon wafers

Abstract

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.