| AVS 58th Annual International Symposium and Exhibition | |
| Plasma Science and Technology Division | Thursday Sessions |
| Session PS+TF-ThM |
| Session: | Plasma Deposition and Plasma Enhanced ALD |
| Presenter: | Steven Vitale, MIT Lincoln Laboratory |
| Authors: | S.A. Vitale, MIT Lincoln Laboratory C. Hodson, Oxford Instruments Plasma Technology, UK |
| Correspondent: | Click to Email |
Lanthanide series oxides are being evaluated as second-generation high-k gate dielectric materials. In addition to improving transistor electrostatics by reducing the equivalent oxide thickness (EOT), using lanthanide series gate oxide capping layers allows the effective metal gate workfunctions to be tuned toward the silicon band edges, providing the correct transistor threshold voltages. However these non-traditional CMOS materials have several integration challenges that must be overcome, including depositing a thermally-stable, high quality film with low fixed charge and high-k, without damage to the underlying layers of the gate stack. In addition, in some gate-first and gate-last approaches, the oxide must be etched from the source/drain regions prior to silicidation.
In this work, plasma-enhanced atomic layer deposition (PE-ALD) of gadolinium oxide is reported for the first time. Using Gd(iPrCp)3 as the organometallic precursor and a pure O2 plasma as the oxygen source, Gd2O3 growth is observed from 150oC to 350oC, though the optical properties of the film improve at higher temperature. True layer-by-layer ALD growth of Gd2O3 does not occur under all conditions, in fact only a relatively narrow window of self-limiting ALD growth of 1.4 Å/cycle was observed at 250oC and below under certain precursor dose conditions. As the temperature increases, high-quality films are deposited, but the growth mechanism appears to become CVD-like. At 250oC, the refractive index of the film is stable at ~1.80 regardless of other deposition conditions, and the measured dispersion characteristics are comparable to those of bulk Gd2O3. The electrical characteristics of the films, such as fixed charge and dielectric constant, are extracted from C-V measurements using TiN metal gate capacitors, and will be reported.
The plasma etching rate of the ALD Gd2O3 film in a high-density helicon reactor is very low. Little difference is observed in etching rate between Cl2 and pure Ar plasmas, suggesting that physical sputtering dominates the etching at high bias power. A threshold bias power exists below which etching does not occur, thus it may be possible to etch a metal gate material and stop easily on the Gd2O3 gate dielectric. The threshold bias power is lower in a Cl2 plasma compared to an Ar plasma, which suggests there is a small ion-enhanced chemical component to the etching as well.
*This work is sponsored by the Department of the Air Force under Air Force Contract #FA8721-05-C-0002. Opinions, interpretations, conclusions and recommendations are those of the author and are not necessarily endorsed by the United States Government.