Yuichi Naitou

High-spatial-resolution scanning capacitance microscope using all-metal probe with quartz tuning fork

The scanning capacitance microscope (SCM) reported here uses a frequency modulation (FM) technique to control the distance between the sample and an all-metal probe. The probe was attached to a quartz tuning fork in a configuration minimizing the perturbation due to the probe. The FM-SCM yields two images of ∂C∕∂V and ∂C∕∂Z signals, where C is capacitance sensed by the probe, Z the probe–sample distance, and V a bias voltage, respectively. On a cross section of a field effect transistor, the two-dimensional p–n junction locus was observed with a spatial resolution better than 5nm in the ∂C∕∂V image. The ∂C∕∂Z images of polysilicon gate electrodes and highly doped source/drain regions have higher contrast than the ∂C∕∂V images.

Shear-mode scanning capacitance microscope

Scanning capacitance microscope (SCM) is developed using an all-metallic probe, whose distance from the sample is controlled by detecting the shear-force drag on the laterally oscillating probe. The oscillatory motion of the probe is electromechanically excited and detected. Using this SCM, a set of images of topography, dC/dV, and dC/dX is simultaneously obtained, where C and V are, respectively, capacitance and applied voltage between the probe and the sample, and X is the coordinate along probe tip oscillation. The SCM developed shows sensitivity for dC/dV higher than the conventional SCM. The dC/dX image clearly indicates the built-in depletion region due to the p–n junction.

Halo Ion Implantation Effect on Extension Profile Studied by Scanning Capacitance Microscopy Using All-Metal Probe under FM Control

By using an all-metal probe under frequency modulation (FM) control, we developed a scanning capacitance microscope (FM-SCM), and applied it to a study of the halo ion implantation effect on two-dimensional (2D) extension profiles of cross-sectional p-channel metal-oxide-semiconductor field effect transistors. With the use of the all-metal probe under FM control, we attain sub-5-nm spatial resolution for the p-n junction in the ∂C/∂V image. The built-in depletion layer presumed by the ∂C/∂V image is narrower for the higher dose sample. The composition images of ∂C/∂V and topography allow us to determine extension depth XJ and extension-gate overlap length XOV, both of which decrease with increase of the halo implant dose. Furthermore, the decrease of XOV is steeper than that of XJ, clearly implying the anisotoropic effect of halo ion implantation.

Capacitive Imaging of Graphene Flakes on SiO2 Substrate

We used scanning capacitance microscopy (SCM) for the local electrical imaging of graphene flakes on a SiO2 substrate. As a result of analyzing the dependence of the SCM measurements on the area of thin graphite nanoislands together with the observed difference in contrast of SCM images related to the graphene layers thickness, we have concluded that the SCM measurements can selectively image high-conductivity few-layer graphene (FLG) flakes on an insulating substrate without having to fabricate external electrical contacts on the graphene. Our technique is a simple way to explore the conductive properties of low-dimensional systems on an insulating substrate with nanoscale resolution.

Tip-to-Sample Distance Dependence of dC/dZ Imaging in Thin Dielectric Film Measurement

We have developed scanning capacitance microscopy (SCM) with a self-sensing conductive probe that can be used to obtain static capacitance (dC/dZ) images by virtue of the vertical vibration of the probe tip. This technique for dC/dZ imaging can delineate features, such as thickness variations or fixed charge distributions, within a dielectric film and provide a lateral resolution comparable to that of simultaneously obtained topography images. In this work, we have experimentally revealed that the lateral resolution of a dC/dZ image is insensitive to the probe tip amplitude, and the sensitivity of dC/dZ images strongly depends on the distance of the gap between the probe tip and the sample surface. These results and the force–distance characteristics of the self-sensing conductive probe indicate that the dC/dZ signal is mostly determined by the probe tip–sample capacitance and also that the spatial resolution of dC/dZ imaging is not affected by the surface-adsorbed meniscus layer under a vacuum environment measurement. Finally, we have demonstrated sub-10-nm spatial resoluton in dC/dZ imaging for thin dielectric film measurement.

Demonstration of Dopant Profiling in Ultrathin Channels of Vertical-Type Double-Gate Metal-Oxide-Semiconductor Field-Effect-Transistor by Scanning Nonlinear Dielectric Microscopy

We demonstrate dopant profiling in ultrathin channels (UTCs) (Tc=18–58 nm) of vertical-type double-gate metal-oxide-semiconductor field-effect-transistors (DG MOSFET) by scanning nonlinear dielectric microscopy (SNDM). The vertical UTCs were fabricated by orientation-dependent-wet etching. Using ion implantation technology and subsequent furnace annealing, n+-p junctions, which correspond to the source/drain of the vertical-type DG MOSFET, were formed in the upper part of the UTC. To improve the accuracy of the vertical dopant profile in the UTC, the cross-section of the UTC was magnified by beveling with a small angle by chemical mechanical polishing. Using such a beveled sample, the dopant depth profile in the vertical UTC has been measured by SNDM with nanometer-scale resolution. On the basis of the measurements of the dopant profile, an effective channel length for the vertical DG MOSFET has also been estimated quantitatively.

Tip-Induced Deformation of Graphene on SiO2 Assessed by Capacitance Measurement

Tip-induced deformation of graphene on a SiO2 substrate was probed through a combination of scanning capacitance microscopy (SCM) and dynamic force microscopy (DFM). Spectroscopic analysis revealed that the resonant frequency shift (Δf) of the probe tip oscillation and the modulated capacitance (ΔC) simultaneously measured on graphene depend on the externally applied bias voltage while keeping the tip–sample distance constant. This finding is interpreted as a result of a local displacement of the graphene surface caused by the electrostatic force between the probe tip and graphene. The approach curve of the SCM tip toward graphene can be used to calibrate the observed ΔC spectra, quantitatively yielding an average deformation of approximately 0.31 nm in trilayer graphene and 0.21 nm in single-layer graphene.

Scanning Capacitance Microscopy Evaluation of Lead Zirconate Titanate Film Formed by Aerosol Deposition Method

The local electric properties of lead zirconate titanate (PZT) film prepared by the aerosol deposition method (ADM) were investigated by scanning capacitance microscopy (SCM) using a self-sensing probe. Although an obvious ferroelectric response cannot be observed from macroscopic polarization versus applied electric field (P–E) measurements for the as-deposited PZT film, capacitance images showed a distinctive contrast as the result of the spatial variation of local dielectric permittivity. The scanning capacitance spectroscopy (SCS) measurements show that there are localized regions which have poor ferroelectricity, and this is the cause of the nominal ferroelectric properties of as-deposited PZT film.

Scanning microscopy of higher harmonic capacitance response for Si device

We have devised a novel mode for delineating p-n junction in 2 dimensions using a scanning capacitance microscopy (SCM). We modulate by an ac voltage V the capacitance C of a tiny metal-oxide-semiconductor (MOS) junction comprised by a sharp metal probe tip, a thin SiO/sub 2/ layer and a sample semiconductor, and then detect 2nd harmonic response of C, namely, d/sup 2/C/dV/sup 2/. The 2nd harmonic response shows its characteristic peak at the p-n junction because of the built-in depletion layer.