Sensitive copper detection in p-type CZ silicon using μ-PCD

Conventional microwave photoconductive decay method in conjunction with high-intensity bias-light has been used to study out-diffusion and precipitation of copper in p-type silicon. The high-intensity light is used to activate the precipitation of interstitial copper, which follows Ham's kinetics and results in a distinctive decrease in the excess carrier lifetime. Results indicate that Cu concentration well below 10(12) cm(-3) can be detected by this method. It is demonstrated that positive corona charge can be used to prevent out-diffusion of interstitial copper, while negative charge enables copper to freely diffuse to the wafer surfaces. It was observed that precipitation rate of copper increases significantly when the bias-light intensity is raised above certain critical level. In addition, the copper precipitation rate was discovered to be much higher in samples, which have internal gettering sites. These findings suggest that i) high-intensity light reduces the electrostatic repulsion between positively charged interstitial copper ions and copper precipitates enabling copper to precipitate in wafer bulk even at low concentration level ii) during high-intensity illumination oxygen precipitates provide effective heterogeneous nucleation sites for copper.