|Ph.D Student||Fadida Gliksman Sivan|
|Subject||The Role of Interfaces and Defects in Controlling the|
Properties of Ge Based MOS Devices
|Department||Department of Materials Science and Engineering||Supervisor||Professor Emeritus Moshe Eizenberg|
|Full Thesis text|
Si based MOS devices are reaching the limit of performance under the dimensions minimization trend. Ge is a leading candidate as channel material that might replace Si, thanks to its high carriers mobilities. However, future integration of Ge as a high mobility channel in metal-oxide-semiconductor (MOS) technology requires a thorough understanding of Ge based MOS capacitors. The objective of this research was to determine the role of interfaces and defects in controlling the properties of MOS capacitors consisting of a metal electrode, a high-k dielectric, and Ge as a high-mobility semiconductor.
The first part of this research focused on optimization of the Ge surface passivation method and annealing conditions. Since there is no consistency in reported results regarding those issues, we have decided to investigate them in our specific gate stacks. When sulfur termination of the Ge surface was compared to GeO2 passivation, a clear advantage was observed for GeO2 based on the electrical characterizations. A possible reason is poor nucleation of ALD Al2O3 on the S-terminated Ge. Next, hydrogen environment for annealing was shown to achieve the lowest trap density at the interface. A further examination showed this effect was only possible when a catalytic metal, in our case Pt, was used. This result confirms that further passivation of the Ge interface was possible due to the dissociation of the hydrogen molecule.
The reactivity of Ti as a metal gate on Ge stacks was studied in the second part of this research. The reactions were studied using synchrotron X-ray photoelectron spectroscopy measurements, with an in-situ metal deposition and HRTEM imaging. Oxygen removal from the Ge surface was observed both in direct contact as well as remotely through an Al2O3 layer (“scavenging” effect). Then, the effect of the scavenging process on the electrical properties of the Ge MOS gate stacks was investigated in the third part of the work, where a significant deterioration of the Ge/oxide interface was observed because of the oxygen removal.
The fourth part of this research was dedicated to the physical and electrical properties of the high-k/Al2O3/GeO2/p-Ge gate stacks, where the high-k was either HfO2 or alloyed HfO2 (HfZrOy, HfGdOx or HfAlOx). Electrical measurements combined with X-ray photoelectron spectroscopy chemical bonding analysis and band alignment determination were conducted in order to assess the suitability of Hafnium-based high-k for this kind of gate stacks, with emphasis on low density of interface states and border traps. HfAlOx was found to be the most promising high-k from those studied. We have also found that the current- voltage trends for the various systems studied can be explained by the band alignment of the samples obtained by our X-ray photoelectron spectroscopy analysis.