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.

Traditional micro-probing and electrical characterization at the transistor level for sub-100nm technologies has become very difficult if not virtually impossible. Scanning probe microscopy technology specifically atomic force probing was developed in response to these issues with traditional micro-probing. The case studies presented in this paper demonstrate how atomic force probing was used to characterize failing sub-100nm transistors, identify possible failure mechanisms, and allow device/process engineers to make adjustments to the wafer fabrication process to correct the problem even though physical analysis with scanning election microscope/transmission electron microscope was not able to image and identify a failure mechanism. The probable causes for the transistor level failures are being identified through test methods, computer simulations, and electrical analysis by means of the atomic force probe after the failure has been sufficiently localized to a minimum number of transistors.

This article describes a 90nm technology SRAM soft fail analysis. The bitmaps of affected wafers show a large number of wafer edge dies failing with single cell cluster fails at supply voltages below 1.0V. The fails appear in characteristic areas within a 256k dualport SRAM memory block. Nanoprobing was used for electrical localization at the cell level by means of a Multiprobe atomic force probe (AFP) system. Fail areas exhibit very weak PFET drain currents several orders of magnitude below the target values, while the drain currents of NFET cell transistors are in the expected range. For fail visualization a junction stain was applied to TEM samples to delineate areas with different doping levels. Due to differences in etch behavior between failed and reference areas, missing LDD extensions and a partially blocked source/drain (S/D) implantation were identified as the root cause of the fails.

This paper analyzes several SRAM failures using nano-probing technique. Three SRAM single bit failures with different kinds of Gox breakdown defects analyzed are gross function single bit failure, data retention single bit failure, and special data retention single bit failure. The electrical characteristics of discrete 6T-SRAM cells with soft breakdown are discussed and correlated to evidences obtained from physical analysis. The paper also verifies many previously published simulation data. It utilizes a 6T-SRAM vehicle consisting of a large number of SRAM cells fabricated by deep sub-micron, dual gate, and copper metallization processes. The data obtained from this paper indicates that Gox breakdown location within NMOS pull-down device has larger a impact on SRAM stability than magnitude of gate leakage current, which agrees with previously published simulation data.

We perform the in-situ scanning transmission electron microscopy (STEM) study of current capacity of carbon nanofibers (CNFs) suspended between two electrodes in vacuum. At an average current density of 4×10 6 A/cm 2 , CNFs show breakdown due to current stress. Current-induced failure results in many voids between graphitic layers in CNF, indicating that the structure of CNFs strongly affects their failure mechanism due to high current stress. These findings provide the insight of the failure mode of future carbon-based interconnects.