Measurement of the physical and electrical thickness of ultrathin gate oxides

Abstract

To evaluate the reliability in measurements of the thickness of ultrathin gate oxides in the range of 2–9 nm, various techniques based on different methodologies were used for comparison. The physical thickness was determined with medium energy ion scattering spectroscopy (MEIS), high-resolution transmission electron microscopy (HRTEM), and spectroscopic ellipsometry (SE). The physical thickness was compared with the electrical thickness measured with current–voltage (I–V) and capacitance–voltage (C–V) measurements with quantum effect corrections. The physical thickness of amorphous SiO2 layers in the range of 2–9 nm determined with MEIS and HRTEM is in a good agreement with the corresponding electrical thickness from C–V and I–V measurements within 0.3 nm. For SE, which is the main technique used for in-line monitoring, we observed that it can be used for 2–9 nm ultrathin gate oxides but is more sensitive to the details of the oxide characteristics.