Scanning Capacitance Microscopy Probe Research Articles

Nano-scale Characterization of Ultra-thin Dielectrics/Conductive Films through Scanning Capacitance Microscopy Studies

Scanning capacitance microscopy (SCM) techniques to investigate the local electronic properties of the ultra-thin films are presented. In the first part, we show the application of SCM experiments for the high-permittivity (high-k) dielectric thin films. The static capacitance (dC/dZ) images and spatially resolved dC/dZ versus sample bias spectra have revealed the charge distributions within high-k dielectrics. Moreover, the bias stress examination has clearly imaged the charge-trapped region in the high-k stacked dielectrics. In the second part, we have demonstrated that the conductance variation ascribed to the graphene thickness can be probed through SCM measurements. The UHF field transmitted from SCM probe tip induces a local accumulation of carriers just beneath the tip. This causes carrier diffusion over the effective biased area of Seff on graphene films, which can be detected as the increment of dC/dZ signal intensity. These results indicate that our SCM technique provides a valuable method to explore the electronic characteristics of low-dimensional materials with nanoscale resolution.

Scanning capacitance microscopy study of carrier depletion within grains of n‐type polycrystalline silicon

AbstractThe local electrical properties and corresponding surface topography for phosphorus‐doped n‐type polycrystalline (n‐poly) silicon layers were investigated using scanning capacitance microscopy (SCM) of chemical mechanical polishing (CMP) and backside‐etched samples. Applying negative bias stress between a sample and a scanning SCM probe tip was found to induce a depleted region within the CMP n‐ poly‐Si sample. In contrast, bias stressing does not intrinsically change the backside‐etched n‐poly‐Si sample. By combining our results with the results of energy dispersive x‐ray spectroscopy measurement, we can conclude that the active dopant concentration within n‐poly‐Si grains is inhomogeneous. Copyright © 2008 John Wiley & Sons, Ltd.

Scanning capacitance microscopy detection of charge trapping in free-standing germanium nanodots and the passivation of hole trap sites

An array of freestanding germanium (Ge) nanodots was fabricated on a highly doped silicon substrate using an anodic alumina membrane as an evaporation mask. Approximately half of the Ge nanodots exhibit contrast reversal and hole trapping characteristics during scanning capacitance microscopy (SCM) measurements, as shown by a negative peak in the SCM differential capacitance (dC∕dV) versus probe tip-to-substrate bias profile. The disappearance of the negative dC∕dV characteristic peak after forming gas anneal at 450°C show the complete passivation of the hole trap sites by hydrogen. This is a demonstration on the spectroscopic detection of hole trapping in Ge nanodots and hydrogen passivation of hole trap sites using SCM. Partial passivation of electron trap sites after the relatively low temperature forming gas anneal was also observed as compared with complete passivation of hole trap sites. This suggests that hole traps sites are possibly located at or closer to the surface of the Ge nanodots as compared to electron traps which may be located deeper within the Ge nanodots.

Correlation Between Surface Topography and Static Capacitance Image of Ultrathin SiO2 Films Evaluated by Scanning Capacitance Microscopy

We performed scanning capacitance microscopy (SCM) using a self-sensing conductive probe to investigate the relationships between the surface morphology, oxide thickness variation, and subsurface depletion layer of ultrathin SiO2 films on p--Si substrates. First, upon analyzing the two-dimensional cross-correlation between dC/dZ images and simultaneously obtained topography images, we found that the dopant concentration of the Si substrates affects the correlation, and this can be attributed to the spatial inhomogeneities in the depletion layer formed by the SCM probe tip. We considered these depletion layer inhomogeneities to reflect the individual dopant distribution within the substrates. Second, from the surface roughness and spatial deviation of the dC/dZ images as well as the cross-correlation analysis results, we concluded that the surface roughness directly corresponds to the spatial variation in SiO2 film thickness.

Analytic description of scanning capacitance microscopy

Scanning capacitance microscopy (SCM) is a doping profile extraction using a nanometric probe as a gate of a metal-oxide-semiconductor (MOS) structure and measuring the differential capacitance. Thanks to the complete MOS equations, the authors propose in this article a description of the differential capacitance calculation. This analytic presentation is based on the solution of the Poisson-Boltzmann equation in the unidimensional mode in silicon and a decomposition of the probe in elementary rings giving capacitance from the surface probe and silicon. As [dC(Vg)∕dVg]α(dΨs∕dVg), this presentation yields to the importance of the surface band bending Ψs at the oxide-semiconductor interface. The dC(Vg)∕dVg calculation shows that the contact of the probe with the sample has its main contribution over a few nanometers. Results are discussed to obtain a calibration of a SCM probe available in a large range of doping and voltage and to assess the dC(Vg)∕dVg signal after erosion of the probe by successive scans.

Accurate modeling of the effects of fringing area interface traps on scanning capacitance microscopy measurement

Scanning capacitance microscopy (SCM) is a dopant profile extraction tool with nanometer spatial resolution. While it is based on the high-frequency MOS capacitor theory, there are crucial second-order effects which make the extraction of dopant profile from SCM data a challenging task. Due to the small size of the SCM probe, the trapped charges in the interface traps at the oxide-silicon dioxide interface surrounding the probe significantly affect the measured SCM data through the fringing electric field created by the trapped charges. In this paper, we present numerical simulation results to investigate the nature of SCM dC/dV data in the presence of interface traps. The simulation takes into consideration the traps' response to the ac signal used to measure dC/dV as well as the fringing field of the trapped charge surrounding the probe tip. In this paper, we present an error estimation of experimental SCM dopant concentration extraction when the interface traps and fringing field are ignored. The trap distribution in a typical SCM sample is also investigated.

Simulation of scanning capacitance microscopy measurements on ultranarrow doping profiles in silicon

Scanning capacitance microscopy (SCM) has been performed both in cross-sectional and in angle-beveling configurations on ultranarrow B spikes with a full width at the half maximum smaller than the SCM probe diameter. A relevant improvement in the SCM response has been observed passing from the cross section to ten times magnification, but a peculiar asymmetric shape characterizes all the profiles on the beveling configuration and broadening and peak lowering are observed for the narrowest spikes. Accurate two-dimensional simulations allowed us to reproduce the experimentally observed peculiar phenomena.

Monitoring oxide quality using the spread of the dC/dV peak in scanning capacitance microscopy measurements

This article proposes a method for evaluating the quality of the overlying oxide on samples used in scanning capacitance microscopy (SCM) dopant profile extraction. The method can also be used generally as a convenient in-process method for monitoring oxide quality directly after the oxidation process without prior metallization of the oxide-semiconductor sample. The spread of the differential capacitance characteristic (dC/dV versus V plot), characterized using its full width at half maximum (FWHM), was found to be strongly dependent on the interface trap density as a consequence of the stretch-out effect of interface traps on the capacitance-voltage ( C-V) curve. Results show that the FWHM of the dC/dV characteristic is a sensitive monitor of oxide quality (in terms of interface trap density) as it is not complicated by localized oxide charging effects as in the case of the SCM probe tip voltage corresponding to maximum dC/dV. The magnitude of the dC/dV peak, at any given surface potential, was also found to be independent of the interface traps and only dependent on the substrate dopant concentration, which makes SCM dopant profile extraction possible.

Scanning capacitance microscopy on ultranarrow doping profiles in Si

Scanning capacitance microscopy (SCM) has been performed both in cross-sectional and in angle-beveling configurations on ultranarrow B spikes with a full width at half-maximum smaller than the SCM probe diameter. The dependence of the SCM response on the magnification factor has been studied, demonstrating an improvement both in terms of spatial resolution and sensitivity by angle-beveling sample preparation. The range of applicability of the direct inversion approach for the quantification of SCM profiles on ultranarrow B spikes has been assessed for high doping spikes thicker than 3 nm and measured on bevel. Two-dimensional simulations allowed the reproduction of all the main features of the experimental SCM profiles.

Dopant extraction from scanning capacitance microscopy measurements of p-n junctions using combined inverse modeling and forward simulation

This article proposes a more accurate approach to dopant extraction using combined inverse modeling and forward simulation of scanning capacitance microscopy (SCM) measurements on p-n junctions. The approach takes into account the essential physics of minority carrier response to the SCM probe tip in the presence of lateral electric fields due to a p-n junction. The effects of oxide fixed charge and interface state densities in the grown oxide layer on the p-n junction samples were considered in the proposed method. The extracted metallurgical and electrical junctions were compared to the apparent electrical junction obtained from SCM measurements.

Development of a metal patterned cantilever for scanning capacitance microscopy and its application to the observation of semiconductor devices

The performance of scanning capacitance microscopy (SCM) strongly depends on the probe used. We have developed an original probe suitable for SCM (SCM probe), which uses a pyramid-shaped metal tip and metal lead line patterned on a silicon nitride cantilever. We installed the SCM probe on a SCM based on a commercial atomic force microscope (AFM). Differences in silicon oxide thickness and differences of dopant types and densities in a silicon substrate with a thermal oxide layer were successfully imaged by SCM simultaneously with AFM using the SCM probe. Boundaries between different dopant types and densities, which were not recognizable by AFM, were clearly observed by SCM. Signal-to-noise ratio and reproducibility were improved in the SCM images obtained with the SCM probe when compared with images obtained with a metal-coated silicon nitride cantilever.