UNGATED FET METHOD FOR MEASURING INTEGRATED CIRCUIT PASSIVATION FILM CHARGE DENSITY

摘要

An ungated FET having an annular drain surrounding a central source is formed on a test site on the same semiconductor chip with product FET devices. All FETs are covered with a passivating film whose charge level is to be determined. An off-chip operational amplifier circuit is connected to the ungated FET to provide automatically whatever source-to-substrate bias is required to cause a negligibly small source-to-drain current, e.g., 0.5 microamps to flow. The potential difference between the source and substrate is measured while the aforesaid negligibly small source-to-drain current is flowing. The charge level in the passivating material covering the product FET devices as well as the ungated FET device is calculated using the measured source-to-substrate bias.