Steady state method for measuring the thickness and the capacitance of ultra thin dielectric in the presence of substantial leakage current

Abstract

A method is described for non-contact measuring the capacitance and the equivalent oxide thickness of ultra thin dielectric layer on a silicon substrate. The surface of a dielectric layer is electrically charged by a flux on ions from a corona discharge source until a steady state is reached when the corona flux is balanced by the leakage current across a dielectric. The flux is abruptly terminated and the surface potential of a dielectric is measured versus time. The steady state value of the surface potential is obtained by extrapolation of the potential decay curve to the initial moment of ceasing the corona flux. The thickness of a dielectric layer is determined by using the steady state potential or by using the value of the surface potential after a predetermined time. The method produces highly accurate results for oxide thickness below 40 Å with a demonstrated repeatability of a 0.03 Å in a series of 10 measurements. Alternatively, the rate of surface potential decay is calculated at the initial moment providing a measure of the charge dissipation on a dielectric capacitor. The capacitance of a dielectric layer is calculated from this rate.