This work highlights the unique capabilities of time-resolved scanning nonlinear dielectric microscopy as demonstrated in the study of SiO 2 /SiC interfaces. Scanning nonlinear dielectric microscopy (SNDM) is a microwave-based scanning probe technique with high sensitivity to variations in tip-sample capacitance. Time-resolved SNDM, a modified version, is used in this study because it allows simultaneous nanoscale imaging of interface defect density ( D it ) and differential capacitance (d C /d V ), lending itself to correlation analysis and a better understanding of the relationships that influence interface quality. Through cross-correlation analysis, it is shown that D it images are not strongly correlated with simultaneously obtained d C /d V images, but rather with difference images derived from d C /d V images recorded with different voltage sweep directions. The results indicate that the d C /d V images visualize the nonuniformity of the total interface charge density and the difference images reflect that of D it at a particular energy range.

In this paper, the authors report their successful attempt to acquire the scanning nonlinear dielectric microscopy (SNDM) signals around the floating gate and channel structures of the 3D Flash memory device, utilizing the custom-built SNDM tool with a super-sharp diamond tip. The report includes details of the SNDM measurement and process involved in sample preparation. With the super-sharp diamond tips with radius of less than 5 nm to achieve the supreme spatial resolution, the authors successfully obtained the SNDM signals of floating gate in high contrast to the background in the selected areas. They deduced the minimum spatial resolution and seized a clear evidence that the diffusion length differences of the n-type impurity among the channels are less than 21 nm. Thus, they concluded that SNDM is one of the most powerful analytical techniques to evaluate the carrier distribution in the superfine three dimensionally structured memory devices.

Two-dimensional semiconductors such as atomically-thin MoS2 have recently gained much attention because of their superior material properties fascinating for the future electronic device applications. Here we investigate the nanoscale dominant carrier distribution on atomically-thin natural and Nbdoped MoS2 mechanically exfoliated on SiO2/Si substrates by using scanning nonlinear dielectric microscopy. We show that a few-layer natural MoS2 sample is an n-type semiconductor, as expected, but Nb-doped MoS2, normally considered as a p-type semiconductor, can unexpectedly become an n-type semiconductor due to strong unintentional electron doping.

The carrier distribution in solar cell is important evaluation target. Scanning nonlinear dielectric microscopy is applied to the cross section of phosphorus implanted emitter in monocrystalline silicon solar cell and visualizes the carrier distribution quantitatively. The effective diffusivities of phosphorus are estimated from the experimental results. Then, the three-dimensional carrier distribution is simulated. The experimental and simulation results show good correlation.

High resolution observation of density of interface states (Dit) at SiO2/4H-SiC interfaces was performed by time-resolved scanning nonlinear dielectric microscopy (tr-SNDM). The sizes of the non-uniform contrasts observed in the map of Dit were in the order of several tens of nanometers, which are smaller than the value reported in the previous study (>100 nm). The simulation of the tr-SNDM measurement suggested that the spatial resolution of tr-SNDM is down to the tip radius of the cantilever used for the measurement and can be smaller than the lateral spread of the depletion layer width.

The transistor structure of memory devices and other cutting-edge semiconductor devices has become extremely minute and complicated owing primarily to advances in process technology and employment of three-dimensional structures. Among the various approaches to improve the device performance and functionality, optimizing the carrier distribution is considered to be quite effective. This study focuses on scanning nonlinear dielectric microscopy (SNDM), a capacitance-based scanning probe microscopy technique. First, to evaluate SNDM's potential for high-resolution measurement, the most commonly used metal coated tip with a tip radius of 25 nm was used to measure a quite low-density impurity distribution. Then, after confirming that the SNDM's S/N ratio was sufficiently high for the smaller probe tip, an ultra-fine diamond probe tip with a nominal tip radius of lesser than 5nm as an SNDM probe tip to measure sub-20 nm node flash memory cell transistors was employed. Successful results were obtained and are reported.

Gate-bias dependent depletion layer distribution and carrier distributions in cross-section of SiC power MOSFET were measured by newly developed measurement system based on super-higher-order scanning nonlinear dielectric microscope. The results visualized gate-source voltage dependent redistribution of depletion layer and carrier.