Detection of low-level copper contamination in p-type silicon by means of microwave photoconductive decay measurements

In order to achieve a better understanding of the behaviour of copper in p-type silicon, studies of the recombination of copper were carried out by the microwave photoconductive decay measurement method (μ PCD) using high-intensity bias light. It was observed that in the presence of small oxygen precipitates, high-intensity light could be used to activate precipitation of interstitial copper. It is suggested that high-intensity light changes the charge state of interstitial copper from positive to neutral, which enhances the precipitation. The precipitation follows Ham's kinetics and results in an increase in the recombination rate, which is detectable even with very low copper concentrations. This phenomenon can be used to detect low levels of copper contamination by the μ PCD method. In addition, it was observed that out-diffusion as well as in-diffusion of interstitial copper could be affected by an external corona charge. Thus, it is suggested that copper atoms do not form stable bonds at the Si–SiO₂ interface after out-diffusion from bulk silicon.