Dynamic SIMS Application for Characterization of Advanced Doping Schemes in Semiconductors

Secondary ion mass spectrometry has been the main technique to characterize depth distributions of dopant atoms in Silicon for more than 30 years, following the rapid technological developments in complementary metal oxide semiconductor (CMOS) miniaturization. In fact, SIMS arose among other analytical techniques because of its excellent detection limits (<ppm), depth resolution, and relatively high analytical throughput with great reproducibility/ repeatability. A virtuous circle was established between technological solutions able to provide shallower dopant distributions and SIMS instrumentation improvements. In particular, the constant reduction of junction depths required a continuous optimization of depth resolution and reduction of the sputtering initial transient width, both achievable mainly by reducing the impact energy of primary ions. Phenomena as ion beam induced topography and high concentration quantification needed to be addressed in order to grant the level of accuracy required by CMOS technology, but overall SIMS followed CMOS doping technology up to the last decade. Nowadays, new challenges are posed by the switching from planar transistors to tridimensional nanometric devices like FinFET or Trigate transistors. It is thus harder to assume that phenomena of dopant diffusion or precipitation observed in ‘SIMS-measurable’ un-patterned samples are identical in structures only few ten’s of nanometers thick. Analytical technics like atom probe tomography are gaining space in dopant characterization and it is worth asking what application field is left to SIMS. In this presentation, an overview of the SIMS application to dopant characterization in the last 10 years will be given through a summary of results collected from specific analytical cases, mainly focused on n-type dopants in Si. In particular, results obtained applying sub-keV primary beam impact energies will be summarized and examples of quantitative depth profiling will be reported for shallow distributions in silicon showing what application margins are left to SIMS and which strength points can still represent an added value of the technique. Plasma ion immersion implantation (PIII) samples will be reported as ultimate case of application of SIMS and results will be discussed with respect to other analytical techniques.