ENERGY LOSS OF IONS IMPLANTED IN MOS DIELECTRIC FILMS

Energy loss measurements of ions in the low kinetic energy regime have been made on as-grown SiO2(170-190nm) targets. Singly charged Na+ ions with kinetic energies of 2-5 keV and highly charged ions Ar+Q (Q=4, 8 and 11) with a kinetic energy of 1 keV were used. Excitations produced by the ion energy loss in the oxides were captured by encapsulating the irradiated oxide under a top metallic contact. The resulting Metal-Oxide-Semiconductor (MOS) devices were probed with Capacitance-Voltage (C V) measurements and extracted the flatband voltages from the C-V curves. The C-V results for singly charged ion experiments reveal that the changes in the flatband voltage and slope for implanted devices relative to the pristine devices can be used to delineate effects due to implanted ions only and ion induced damage. The data shows that the flatband voltage shifts and C-V slope changes are energy dependent. The observed changes in flatband voltage which are greater than those predicted by calculations scaled for the ion dose and implantation range (SRIM). These results, however, are consistent with a columnar recombination model, where electron-hole pairs are created due to the energy deposited by the implanted ions within the oxide. The remaining holes left after recombination losses are diffused through the oxide at the room temperature and remain present as trapped charges. Comparison of the data with the total number of the holes generated gives a fractional yield of 0.0124 which is of the same order as prior published high energy irradiation experiments. Additionally, the interface trap density, extracted from high and low frequency C-V measurements is observed to increase by one order of magnitude over our incident beam energy. These results confirm that dose- and kinetic energy -dependent effects can be recorded for singly charged ion irradiation on oxides using this method. Highly charged ion results also confirm that dose as well as and charge-dependent effects can be recorded for irradiation of oxides using this method. In particular, the results as a function of charge state indicate that there is a significant enhancement in the induced flatband voltage shift as the charge state of the beam is increased. This was quantified by measuring the flatband voltage shift across multiple ion doses for fixed incident charge states to obtain a normalized value of the shift induced per incident ion. These normalized results show an enhancement in the shift, which grows monotonically across our charge state data, from 1.14 x 10-12V/ion for Ar1+ ions to 1.12 x 10-11V/ion for Ar11+ ions. It is probable that this enhancement in the shift is due to the different potential energy for the two charge states (15 eV for Ar1+ and 2004 eV for Ar11+). For example, potential energy deposited into the oxide could produce more electron-hole pairs beyond those generated by kinetic losses such that both effects are captured in the C-V measurements of the MOS devices. If these data are interpreted as a record of the energy loss, then a near-quadratic dependence on the incident charge state emerges which is consistent with results obtained elsewhere