Gate oxide thickness measurement using Fowler-Nordheim tunneling

It is demonstrated that the use of the Fowler-Nordheim tunneling current as a monitor of gate oxide thickness is possible if precautions are made to screen out less than ideal oxides. A very effective screen is to use separate calculations of the oxide thickness from the slope and intercept of a fit of log(J/V²) versus (I/V). The thickness extracted from the slope is considered valid if the thickness calculated from the slope is approximately 2.3 times that found from the intercept. Measurements can be made either under conditions of accumulation in an MOS capacitor or under inversion in a transistor where electrical contact can be made to the inversion layer. The barrier height is, however, 0.1 to 0.2 eV higher for injection from polysilicon than for single-crystal silicon