Characterization of hafnium based high-k thin films for solid state transistor gate application deposited by CVD and PECVD using hafnium(IV) tert-butoxide.

摘要

Silicon dioxide, the standard gate oxide in MOS transistors for the last three decades, has reached its scaling limit due to an unacceptably high tunneling current at thicknesses 1.0 nm. Hafnium oxide (HfO 2) and hafnium silicate (HfSixOy), based on their high dielectric constants and thermodynamic stability on Si, are the two most promising materials to replace SiO2 as a gate oxide. Metalorganic chemical vapor deposition (MOCVD) of HfO2 and HfSixO y, and their characterization, has been studied to better understand their physical and chemical properties to suit their application as a high-kappa replacement to SiO2.; Hafnium oxide and HfSixOy thin films were deposited in a custom built PECVD reactor on Si (100) using hafnium (IV) tert-butoxide (HTB), oxygen and silane at substrate temperatures of 30°, 150°, 250° and 410°C. The thermally and plasma deposited HfSixOy films showed a composition of (HfO2)0.84(SiO 2)0.16 and (HfO2)0.11(SiO2) 0.88, respectively. Plasma silicates demonstrated higher silicon (∼24 at.%) incorporation due to better dissociation of SiH4 and HTB.; HfO2 and HfSixOy films were also deposited with different oxygen precursors (O2, N2O, H2O, O2 plasma, or N2O plasma). Thermally deposited HfSi xOy films using O2 and N2O showed precursor desorption at higher temperatures resulting in lower deposition rates, whereas the H2O deposited film showed a decrease in deposition rate with temperature, suggesting a different mechanism.; In situ ATR-FTIR was conducted on adsorbed and liquid HTB to study the reaction pathway of the HTB molecule during CVD reaction. By comparing experimental ATR-FTIR spectra with theoretical frequencies calculated using density functional theory, it was concluded that the HTB molecule undergoes chemisorptive adsorption at 100°C and bridges to Si via a bidentate attachment.; Angle-resolved XPS measurements were performed for HfO2/Si (100) samples placed in wet and dry environments to study the effect of H 2O on interface stability. The comparison indicated that OH species from the adsorbed moisture on the surface of HfO2 layer migrated to the interface to react with the Si substrate to form an interfacial SiO x layer. The thickness calculations from ARXPS measurements showed thicker interfacial oxide in wet sample (18 A) compared to the dry sample (12 A).