edfas.org ELECTRONIC DEV ICE FA I LURE ANALYSIS | VOLUME 25 NO . 1 10 article describes the principles of operation of sMIM, gives an overview of the low temperature configuration, and highlights applications. PRINCIPLES OF OPERATION In ScanWave, a microwave signal is transmitted to the tip of a custom cantilever with matched impedance and shielding for lownoise operation.[2] The same tip also collects the reflected signal that has been affected by the tip-sample interaction and the collected signal is then processed in the systemelectronics to provide two output signals: sMIM-C and sMIM-R (Fig. 2). The sMIM-C signal, measured in volts, corresponds to the relative capacitance of a nanoscale volume of material directly underneath the tip; and sMIM-R, also a signal in volts, corresponds to the relative resistivity of the same volume of material. As the tip scans the sample surface, driven by an AFM, sample electrical information is obtained simultaneously with topographic information. In addition to the R and C information acquired, dC/dV and dR/dV can be collected by applying an AC signal on top of the RF signal. In a semiconductor, the dC/dV phase indicates the carrier type (n or p) and the amplitude relates to the doping level. Unlike scanning capacitancemicroscopy (SCM), in sMIM one can directly measure dC/dV without sample grounding and collect R and C information. AScanWavesystemincludes thefollowingcomponents: • Shielded probe with impedance matching • Probe interface module to attach the probe to the AFM • Microwave electronics ScanWave has been designed to work on major AFM platforms and is compatible with many AFM scanning modes such as contact mode, tapping mode, and lift mode. Since sMIM is a near-field measurement, resolution below the tip diameter can be achieved. Because of its controlled periodicity, a Moiré pattern is often used to measure resolution in sMIM systems and using this technique, a resolution of about 1 nmwas recently reported.[3] Using a capacitance reference standard, the sensitivity of the system for capacitance was measured to be 0.075 aF. ROOM TEMPERATURE sMIM Room temperature sMIM is used in semiconductor FA and device characterization,[4-6] 2D material characterization, ferroelectrics, subsurface sensing, and more. In one example sMIM was used to isolate gate oxide issues as shown in Fig. 3 where a failing gate oxide test structure was compared to surrounding devices to determine if the failure was a point defect or area contamination.[6] In another study, a highly integrated monolithic silicon PIN (P-type layer, intrinsic layer, N-type layer) diode with a 3D architecture was characterized from substrate to metal using sMIM.[4] Other use cases include locating dopant level related defects that are invisible to electron and optical microscopy, nonlinear material characterization, and nano C-V. LOW TEMPERATURE sMIM Understanding the fundamental properties of materials often requires electrical measurements to be taken at ultra-low temperatures and in the presence of high magnetic fields. This is the case for quantum computing materials, super conductivity, and other materials research areas. Abig challenge inquantumcomputing has been the phenomenon of decoherence that occurs very rapidly and is irreversible; it was discovered that under highmagnetic fields, decoherence time canbe extended.[7] Studies of decoherence and other behaviors of quantum systems are increasingly being conducted at low temperature and under varying magnetic fields. PrimeNano has introduced three types of low temperature sMIM systems that are commercially available turnkey solutions and include superconducting magnets up to 12 Tesla and 3D capabilities: Fig. 3 Study to determine root cause of failing gate oxide test structure. Good vs bad devices that were buried were measured using sMIM C-V and dC/dV.
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