| Contact resistance is increasingly becoming an impediment to continued performance enhancement by scaling for traditional complementary metal oxide semiconductor field effect transistors (CMOSFETS). Solutions to this problem are wanting, and with decreasing con- tact area, demands on the contact properties are escalating. With ever-decreasing contact areas, specific contact resistivity has to be reduced below 1 O-mum2 to 0.1 O-mum 2 in the next 10--15 years. With dopant densities in the source and drain regions nearing the limits of solid solubility, the most likely solution will involve reducing the Schottky barrier height (phi SBH) to near zero. This dissertation focuses on a novel approach to reducing the phiSBH, with the goal of reducing specific contact resistivity. The presence of dipoles at certain oxide interfaces has been revealed by recent research into gate stack scaling. The goal is to utilize these dipoles in a contact, in order to controllably adjust the phi SBH, moving it from its pinned position near the middle of the gap closer to the conduction and/or the valence band edges. To this end, several successful experiments have been conducted. To test the feasibility of controllably adjusting the phiSBH several diodes were fabricated with tantalum nitride (TaN) metal contact and various oxide dipole layers. The ability to adjust the phiSBH to near the conduction and valence band edges is demonstrated, and improved electrical resistance compared with the standard contact metal, NiSi, is demonstrated on n-Si (Chapter 4). Deeper understanding of the dipole formation process, as well as the scalability and maximum phiSBH tuning is explored in extremely thin AlOx/SiO 2 layers using diodes with TaN metal contacts by varying deposition process techniques and parameters. The best layers are found to be extremely thin, but also with large dipole magnitudes, as evidenced by the changes in the phiSBH (Chapter 5). Applications to a real device are explored using a promising variant of the classical CMOSFET, the FinFET. A significant reduction in the parasitic source and drain series resistance is correlated with a reduction of the phiSBH due to the inclusion of dipole providing layers at the contact interface (Chapter 6). Finally, physical characterization and confirmation of the dipole mechanism is provided by in-situ fabrication and investigation of the contact interfaces using photoelectron spectroscopy and electrical characterization (Chapter 7). The directions for future research on these contacts will also be discussed (Chapter 8). |
