Electrical method of measuring physical thickness and nitrogen concentration of silicon oxynitride gate dielectric for MOSFETs

Abstract

This paper proposes an electrical method of measuring the physical thickness T-ox and the nitrogen concentration alpha(N) of the silicon oxynitride (SiON) gate dielectric for MOSFETs. The proposed method uses the facts that the gate dielectric breakdown field strength E-BD depends on alpha(N) for a given Tox and the direct tunneling (DT) current depends strongly on T-ox. Gate current I-g versus gate voltage V-g (I-g-V-g) curves at a given alpha(N) were calculated for different T(ox)s using the DT model, and measurements were compared to the curves to obtain T-ox. The alpha(N) was obtained by comparing the measured EBD at a given T x with the theoretical E-BD for a SiON gate dielectric. These two steps were iterated until the convergence error of alpha(N) was less than 1%. The I-g-V-g curves calculated using the extracted T(ox)s and alpha(N)s agreed very well with measurements when Vg was less than the gate breakdown voltage. The difference between the equivalent oxide thickness (EOT) measured using the C-V method and the EOT calculated using the extracted T-ox and alpha(N) was less than 7%, demonstrating that the proposed method can accurately determine T-ox and alpha(N) of an ultra-thin SiON gate dielectric from only the measured I-g-V-g, curve of the MOSFET. (C) 2008 Elsevier B.V. All rights reserved.