The anomalous depth distribution of low dose oxygen and nitrogen ions implanted into silicon

Silicon wafers have been implanted with oxygen and nitrogen ions with an energy of 150 keV in the dose range of 1016-1017 cm-2. Implantations were carried out both singly, i.e. just oxygen or just nitrogen, and also doubly i.e. combinations of oxygen and nitrogen. In the latter case, the sequence of the implantations was varied. The implanted samples were analysed using secondary ion mass spectrometry (SIMS) and the X-ray rocking curve technique. In the double implanted material, when oxygen was implanted before nitrogen, both the impurity distributions were seen to shift deeper than expected into the structure. However, when nitrogen was implanted first, no shift was observed. For the singly implanted material, the X-ray rocking curve measurements showed that the as-implanted oxygen sample was found to contain stress in the silicon lattice, whereas no stress was detected in the nitrogen sample. This stress also exists in both the doubly implanted samples. However, the amount of stress and the crystalline quality of the material is dependent on the sequence of the double implant and temperature. The anomalous impurity depth distributions can be explained by the segregation of reactive impurities on to interstitial defects created during high temperature implantation. (author)