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 α 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 α N for a given T ox 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 α N were calculated for different T oxs using the DT model, and measurements were compared to the curves to obtain T ox. The α N was obtained by comparing the measured E BD at a given T ox with the theoretical E BD for a SiON gate dielectric. These two steps were iterated until the convergence error of α N was less than 1%. The I g– V g curves calculated using the extracted T oxs and α Ns agreed very well with measurements when V g 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 α N was less than 7%, demonstrating that the proposed method can accurately determine T ox and α N of an ultra-thin SiON gate dielectric from only the measured I g– V g curve of the MOSFET.