Electron holographic characterization of nanoscale charge distributions for ultra shallow PN junctions in Si

This study extends electron holography as a quantitative characterization tool for nanoscale charge distributions associated with ultra shallow PN junctions in Si, which are needed for fabricating nanoscale MOSFETs, Si quantum dots and single electron transistors. The ultra shallow junctions were fabricated using rapid thermal diffusion from a heavily doped n-type surface source onto a heavily doped p-type substrate. Chemical characterization of the dopant profiles was performed using secondary ion mass spectrometry, which were analyzed to derive the metallurgical junction depth. 1-D characterization of the electrical junction depth 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 across the p–n junctions derived from electron holographic analysis were used to calculate the electric field and total charge distributions in the space charge region of the p–n junctions using numerical derivatives. Quantitative comparison between calculated electric field and total charge from the measured potential profiles and the simulated distributions using the secondary ion mass spectrometry profiles provide a reasonable estimate of the electrical activation of dopants in the ultra shallow junctions considered for this investigation.