Nondestructive ion-implant monitoring using laser Raman spectroscopy

A new Raman technique for monitoring low-dose ion implants is described. The capability for detection of implants of 20– 50 keV B+ (or equivalent [Formula: see text] energies) at doses as low as ~1010 cm−2 is of particular interest. Currently, there are few other noncontact, nondestructive methods of evaluating implant doses below 1013 cm−2 (e.g., Vt-adjust, field, and p-well implants) in patterened production wafers. The feasibility of using the technique for monitoring Vt-adjust implants is demonstrated.Low-energy B+ and [Formula: see text] ion implants in silicon were studied to determine the detection limits of the technique. Samples were analyzed immediately after implantation, without annealing. Implant doses in the range from 3 × 1016 cm−2 to the detection limit of 3 × 1010 cm−2 were characterized in this way. The presence of a surface layer of SiO2 (≤ 100 nm thick) did not interfere with the measurements. A tunable laser was used to optimize the sensitivity to implants of different energies.Since the frequency spectrum of Raman scattering can also provide information on the structure of the damaged region or on the distribution of activated boron and residual ion damage after annealing, Raman spectroscopy shows promise in several applications for in situ process monitoring of ion implantation for very large scale integration technology.