|Ph.D Student||Kornblum Lior|
|Subject||The Role of the Metal/Dielectric Interface Properties in|
Determining the Electrical Behavior of Si MOS
|Department||Department of Materials Science and Engineering||Supervisor||Professor Emeritus Moshe Eizenberg|
|Full Thesis text|
High-k dielectrics with metal gates (HKMG) were recently introduced in the metal oxide semiconductor (MOS) technology in order to allow the continuation of the scaling of the dimensions of devices. One of the most critical issues with HKMG is control of the threshold voltage, which is dictated by the effective work function (EWF) of the gate. It was found that in many cases, the metal’s Fermi level position (or EWF) at the interface with a dielectric is pinned to a different position than expected. This phenomenon is generally termed Fermi level pinning (FLP).
The goal of this work is the understanding of how the nanoscale material properties at metal-dielectric interfaces govern the EWF of Si based MOS devices. In order to understand the metal-dielectric material properties effect on the EWF of MOS devices, the metal-dielectric interface is studied from different physical directions.
In the first part of this work, metal-Al2O3 interfaces are studied with the metal side of the interface varied using different elemental metals. After ascertaining that no FLP exists with Pt and Al on Al2O3, the EWF of their alloys are studied. Five different compositions from pure Pt to pure Al are studied in three parallel levels: microstructure characterization for the determination of the crystal phases and crystal orientation; electrical characterization of the EWF and a first-principle study of the vacuum work functions (VWF) of the different phases and orientations.
In the next part of this work, the dielectric side of the interface is varied while a uniform Pt metal is used. Two systems are investigated. The first system consists of ultrathin Ta2O5 dielectrics inserted into different positions inside an Al2O3 based MOS devices. The second system consists of ultrathin Al2O3 layers inside HfO2 based MOS devices.
In the last part of this work, organic self-assembled monolayers (SAMs) are used to directly manipulate the metal-dielectric interface, with both sides kept uniform (Al-SiO2). The EWF extraction method used in this work is demonstrated as a new approach for measuring the surface potential modulation induced by SAMs.