Atomic Force Probe Kelvin Measurements of Large MOSFET Devices at Contact Level for Accurate Device Threshold Characteristics

Abstract

Abstract To reconstruct discrete device threshold characteristics at tungsten contact level with atomic force probe (AFP), specific care in making drive current measurements is essential. Kelvin probing as well as the proper placement of the AFP probes themselves is an absolute requirement for insuring precise measurements. For this paper, NFET and PFET test structures employing 3 micrometer gate widths are used to simulate a sense-amp device. The results obtained using normal pad-level probing on a conventional probe station with results from an AFP nanoprober with and without Kelvin sensing are compared. These measurements are also compared with the nominal or expected design rule values. Experimental results comparing AFP Kelvin measurements at contact level on the same MOSFET test structure versus measurement obtained conventionally at pad level underscores the importance and value of AFP Kelvin measurements.