Electron holographic characterization of ultra-shallow junctions in Si for nanoscale MOSFETs

This investigation attempts quantitative characterization of ultra-shallow junctions (USJs) in Si, useful for future generations of nanoscale MOSFETs as predicted by the Semiconductor Industry Association Roadmap. The USJs were fabricated using rapid thermal diffusion (RTD) from a heavily doped n-type surface source onto a heavily doped p-type substrate. The dopant profiles were analyzed using secondary ion mass spectrometry (SIMS), and were further used to calculate the metallurgical junction depth (MJD). One-dimensional (1-D) characterization of the electrical junction depth (EJD) associated with the electrically activated fraction of the incorporated dopants was performed using off-axis electron holography in a transmission electron microscope. 1-D potential profiles were derived from the unwrapped phase of the reconstructed holograms. The EJD was derived from the measured potential distribution across the p-n junction, and quantitative comparison is made with MJD derived from the SIMS profiles. The comparison between calculated electric field and total-charge distributions from the measured potential profiles and the simulated distributions using the SIMS profiles provides a quantitative estimate of the electrical activation of dopants incorporated by the RTD process, within the accuracy limits of this technique, which is discussed herein.