Semiconductor device with means for verifying a hermetic seal therefor

The present invention generally relates to methods for verifying whether a cavity is hermetically sealed, such as when semiconductor wafers are bonded together to hermetically enclose a micromachined sensing structure. More particularly, this invention relates to an electrical verification technique and device for detecting moisture within a cavity enclosing a micromachine sensing structure as an indication of whether the sensing structure is hermetically sealed within the cavity. A method and device for verifying whether a cavity () enclosing a micromachined sensing structure () between a pair of wafers () is hermetically sealed by detecting the presence of moisture within the cavity (). The method entails forming a bare, unpassivated PN junction diode () in a semiconductor substrate, preferably a device wafer () with the sensing structure (). The device wafer () is then bonded to a capping wafer () to enclose the PN junction diode () and micromachine () within a cavity () defined by and between the wafers (). The reverse diode characteristics of the PN junction diode () are then determined by causing a reverse current to flow through the diode (). For this purpose, either a known voltage is applied across the diode () and the reverse leakage current measured, or a known reverse current is forced across the diode () and the voltage measured. The unpassivated junction diode () exhibits unstable current/voltage readings if sufficient moisture is present within the cavity (), thereby indicating whether or not the cavity () is hermetically sealed.