Variable-Angle Spectroscopic Ellipsometry of InAlP Native Oxide Gate Dielectric Layers for GaAs MOSFET Applications

The ability of Variable Angle Spectroscopic Ellipsometry (VASE) to determine the thickness of the thin In0.49Al0.51P (InAlP) native gate oxide ('InAlP-ox') for GaAs-based MOSFET devices has been demonstrated. The optical constants of InAlP-ox, In0.49Ga0.51P (InGaP), and InAlP have been determined by VASE measurements using a photon energy range of 1.45 to 5.45 eV at room temperature. The optical constants of InAlP and InAlP-ox are used to characterize a thick partially-oxidized InAlP epitaxial film grown on GaAs structure. The excellent agreement between the thickness values determined by Transmission Electron Microscope (TEM) imaging and by VASE supports the validity of our optical constants results. Models have also been developed to accurately fit the thickness of less than 100 ÌÄ'_ InAlP-ox gate oxides grown directly upon a multi-layer MOSFET heterostructure. The deviation of InAlP-ox thickness results determined by VASE from those determined by TEM is within 4%.