Centroid location of implanted ions in the SiO₂ layer of MOS structures using the photo I-V technique)

Abstract

The centroids for distributions of various ions important in Si technology (Al, P, and As) implanted at energies from 5 to 100 keV and a fluence of 1×1013 cm-2 into 1300-1400-Å-thick SiO 2 layers of metal-silicon dioxide-silicon (MOS) structures have been located by using measurements of the photocurrent as a function of the gate voltae which is called the photo I-V technique. This technique senses trapped electrons on sites related to the implanted ions after charging by avalanche injection. A high-temperature (1000 °C in N2 for 30 min) premetallization anneal was used in order to minimize trapping on atomic displacement damage sites which could give a different centroid than that of the ion distribution. Good agreement of the trapped electron centroid deduced from the photo I-V technique with calculations of the ion centroid based on the theory of Lindhard, Scharff, and Schiøtt (LSS) and with independent experimental determinations of the ion centroid from profiles using secondary ion mass spectroscopy (SIMS) or He+ ion backscattering was found in most cases. The photo I-V technique is shown to have distinct advantages over most techniques which directly measure the ion distribution or centroid like SIMS and He+ ion backscattering because of its nondestructive nature, minimally perturbing effect, and extremely low detectability limit of 10 11 charges/cm2 or less. The empirical relationship observed by Chu, Crowder, Mayer, and Ziegler for ion implantation into various amorphous insulators between the LSS normalized centroid ρ and the LSS normalized energy ε of ρ=2.7ε has been shown for the first time to be valid for ε?0.4.