Material properties and thermal stability of hafnium and lanthanum based high-k gate dielectrics for MOSFET digital logic.

摘要

Hf and La based dielectrics have evolved into promising high- k gate dielectric candidates for the replacement of SiO2 and SiON in scaled complementary metal oxide semiconductor field effect transistor (C-MOSFET) devices due to favorable material properties. Strained Si xGe1-x(100) epilayers on Si(100) have attracted considerable interest due to hole mobility enhancement, as well as their compatibility with existing Si-based C-MOSFET technology that makes manufacturing very-large scale integrated circuits feasible. The introduction of these new material systems into the current CMOS process flow poses significant integration challenges. For example, the thermal stability of a high-k dielectric film in direct contact with the underlying Si substrate is essential because outdiffusion of metal impurity atoms into the channel region during processing can cause carrier mobility degradation and affect the electrical performance of the integrated circuit. Also, the inherent thermodynamic instability of SixGe1-xO2 offers a formidable challenge for the successful fabrication of high-k oxides on strained SixGe1-x(100). In this dissertation, the results of thermal stability studies of Hf and La based silicate and aluminate dielectrics in direct contact with Si(100) and SixGe1-x(100) is presented. The effect of nitrogen and germanium incorporation on the thermal stability is discussed. Dielectrics deposited by Sputter Deposition, Molecular Beam Deposition and Atomic Layer Deposition techniques are evaluated. X-ray Photoelectron Spectroscopy (XPS), X-ray Diffraction (XRD), High Resolution Transmission Electron Microscopy (HR-TEM), Backside Secondary Ion Mass Spectrometry (Backside SIMS), Atomic Force Microscopy (AFM) and Electrical Measurements are utilized to characterize the dielectric stacks. For Si(100), the thermal stability after a 1000°C, 10s source/drain activation anneal is evaluated. Due to strain relaxation of the SixGe1-x(100) substrates at temperatures >800°C, the stability of the dielectric - SixGe 1-x(100) stacks were evaluated at lower temperatures. In this dissertation, the suppression of crystallization and metal outdiffusion into Si(100) after the 1000°C, 10s anneal for sputter deposited LaAlON and HfAlON dielectrics is reported. The stability of the Hf-silicate dielectrics on Si xGe1-x(100) with N and Ge incorporation appears to be correlated to the stability of Ge bonding configuration at the dielectric - substrate interface. The prospects of novel dielectrics like La-scandate (LaScO 3) and Hf-germanate (HfGeO) are discussed.