Characterization and environmental impact of plasma products within an ion implanter

The way in which the plasma in the ion source interacts with the constituent elements of the source chamber can provide important insights into the plasma chemistry and may facilitate improvements in ion source design and operation. It is also an important parameter in determining the environmental impact of the implantation process. It is worth noting that less than 0.4% of the material placed into the ion source is actually implanted as a dopant into the target wafers; the rest remains as a solid residue or gaseous emission. As many of the materials used for dopant implantation are either highly toxic, pyrophoric, greenhouse gases or powerful ozone depleters, or combinations of the above it is imperative, that the extent, location and chemical composition of these residues are quantified and understood. This will enable their impact on the environment, economy and society, the three pillars of sustainable development to be assessed. In this study small pieces of silicon were placed at predetermined points within the source chamber of a commercial ion implantation system. Antimony was then run using SbF₃ as the feed gas. At the end of the run the silicon samples were retrieved and analysed using Rutherford Backscattering (RBS) and ion channelling. It was found that the location of the samples influenced the elemental composition of the plasma products deposited in the source chamber. A similar experiment was also conducted for BF₂ ⁺ implants using a BF₃ feed gas, again the elemental composition varied with the position of the silicon samples allowing the distribution of different elements, within the plasma products, to be mapped around the source chamber.