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

This paper proposes an electrical method of measuring the physical thickness Tox and the nitrogen concentration αN of the silicon oxynitride (SiON) gate dielectric for MOSFETs. The proposed method uses the facts that the gate dielectric breakdown field strength EBD depends on αN for a given Tox and the direct tunneling (DT) current depends strongly on Tox. Gate current Ig versus gate voltage Vg (Ig–Vg) curves at a given αN were calculated for different Toxs using the DT model, and measurements were compared to the curves to obtain Tox. The αN was obtained by comparing the measured EBD at a given Tox with the theoretical EBD for a SiON gate dielectric. These two steps were iterated until the convergence error of αN was less than 1%. The Ig–Vg curves calculated using the extracted Toxs and αNs 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 Tox and αN was less than 7%, demonstrating that the proposed method can accurately determine Tox and αN of an ultra-thin SiON gate dielectric from only the measured Ig–Vg curve of the MOSFET.