Depth profile characterization of hydrogen implanted silicon using spectroscopic ellipsometry

Ion beam implantation of silicon with hydrogen is a method of producing thin silicon films for the manufacture of silicon on insulator (SOI) wafers. The implanted hydrogen depth profiles are traditionally measured using nuclear reaction analysis (NRA) or secondary ion mass spectrometry (SIMS) which have the disadvantages of requiring specialized equipment and, in the case of SIMS, being a destructive measurement. In the current work, a simplified method of measuring the depth profile of implanted hydrogen ions in silicon has been developed. Using a spectroscopic ellipsometer, optical data are collected from hydrogen implanted silicon wafers in a non-contact and non-destructive manner. The ellipsometric data from 600-980 nm wavelength are then analyzed by modeling the damage as a graded sub-surface layer in the silicon. By fitting this model to the experimental data, values for the depth of the implantation and the width of the implantation distribution can be extracted. This method offers the advantages of being repeatable, fast, and non-destructive, as well as using a piece of metrology equipment readily available in most semiconductor tabs. The method has been tested over a range of implant energies (24-92 keV) and hydrogen doses and shows excellent correlation to traditional NRA measurements for implant depth profile.