Effects of copper and oxygen precipitation during thermal oxidation of silicon: An electron-beam-induced current study

The effects on minority carrier diffusion length L_n of the oxidation of p-type silicon in a copper-contaminated ambient have been analyzed using an electron-beam-induced current. The experiments were carried out on Czochralski (Cz) and float-zone silicon, and on samples with damaged and undamaged surfaces, in order to evaluate the role of oxygen supersaturation in the starting material, and the influence of the formation of oxidation-induced stacking faults on oxygen and copper precipitates during the oxidation anneal. The microstructure of the interface silicon underlayers was controlled using transmission electron microscopy and secondary ion mass spectrometry. The diffusion length L_n was drastically decreased in regions free of copper colonies, showing that a noticeable concentration of copper existed in the form of pointlike recombinant defects in the bulk. This effect was more pronounced in Cz silicon, where it was assigned to the presence of oxygen-based clusters acting as copper traps, and in the cases of damaged surfaces, where it indicated that the growth of the copper-related pointlike defects occurred with the emission of silicon self-interstitials.