Advanced High-k Dielectrics for MOS Transistors Based on Silicon and III-V Channels

Over the past five decades, Si-based Metal-Oxide-Semiconductor (MOS) Field Effect Transistors (FETs) have scaled according to Moore's Law. The methods of scaling involve reduction of channel length and Equivalent Oxide Thickness (EOT). Ultra-thin high-k dielectrics with EOT below 1nm are needed for the 22nm node CMOS technology and beyond. As the oxide thickness reduces, the carrier mobility in the channel suffers significant degradation due to interface issues. In the prior research in our lab at Yale University, the Si/oxide interface was engineered by the use of a high quality ultra-thin Al2O3. TiO2 was deposited on top of the Al 2O3 to reduce gate leakage current and improve the effective dielectric constant of the Al2O3-TiO2 stack. In this work, the Al2O3-TiO2 composite gate stack was studied by Inelastic Electron Tunneling Spectroscopy (IETS) that provided important information concerning chemical bonds and traps. MOSFETs with the afore-mentioned ultra-thin Al2O3-TiO2 stack demonstrated reduced mobility degradation compared to state-of-the-art HfO2-gated devices. An improved split C-V method was employed to extract carrier mobility in the channels of MOSFETs with ultra-thin gate dielectrics.;As Si-based MOSFETs decrease in size to the nanoscale, new device architectures, such as Fin-FET, and complex strain engineering are introduced. But even these methods may not be sufficient to deliver the high switching speed desired in future MOSFETs. Some III-V channel materials that have high electron mobility are being considered as promising alternatives to Si. To realize the benefit of the high mobility, the interface between III-V semiconductors and high-k dielectrics must have a low interface-trap density (Dit). MOSFETs with InGaAs channels have been demonstrated with the afore-mentioned Al 2O3 as the gate oxide. Charge pumping measurements on the MOSFETs were carried out to study Dit at the InGaAs interface. Forming gas plasma treatment of the InGaAs surface, combined with hydrogen containing ambient during Al2O3 deposition, has showed dramatic effect for depositing high quality Al2O3 with low densities of Dit. X-ray Photoelectron Spectroscopy and IETS studies of the Al2O3/InGaAs interface have helped to understand the hydrogen effects.;In addition, X-ray radiation effects on both Si and III-V MOS devices have been investigated. Conventional electrical characterizations and the IETS technique have revealed the changes in the MOS devices after X-ray radiation.