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We measured the DC and RF impedance characteristics of micrometric metal-oxide-semiconductor (MOS) capacitors and Schottky diodes using scanning microwave microscopy (SMM). The SMM consisting of an atomic force microscopy (AFM) interfaced with a vector network analyser (VNA) was used to measure the reflection S11 coefficient of the metallic MOS and Schottky contact pads at 18 GHz as a function of the tip bias voltage. By controlling the SMM biasing conditions, the AFM tip was used to bias the Schottky contacts between reverse and forward mode. In reverse bias direction, the Schottky contacts showed mostly a change in the imaginary part of the admittance while in forward bias direction the change was mostly in the real part of the admittance. Reference MOS capacitors which are next to the Schottky diodes on the same sample were used to calibrate the SMM S11 data and convert it into capacitance values. Calibrated capacitance between 1–10 fF and 1/C2 spectroscopy curves were acquired on the different Schottky diodes as a function of the DC bias voltage following a linear behavior. Additionally, measurements were done directly with the AFM-tip in contact with the silicon substrate forming a nanoscale Schottky contact. Similar capacitance-voltage curves were obtained but with smaller values (30–300 aF) due to the corresponding smaller AFM-tip diameter. Calibrated capacitance images of both the MOS and Schottky contacts were acquired with nanoscale resolution at different tip-bias voltages.

We present a comprehensive analysis of the imaging characteristics of a scanning microwave microscopy (SMM) system operated in the transmission mode. In particular, we use rigorous three-dimensional finite-element simulations to investigate the effect of varying the permittivity and depth of sub-surface constituents of samples, on the scattering parameters of probes made of a metallic nano-tip attached to a cantilever. Our results prove that one can achieve enhanced imaging sensitivity in the transmission mode SMM (TM-SMM) configuration, from twofold to as much as 5× increase, as compared to that attainable in the widely used reflection mode SMM operation. In addition, we demonstrate that the phase of the S21-parameter is much more sensitive to changes of the system parameters as compared to its magnitude, the scattering parameters being affected the most by variations in the conductivity of the substrate. Our analysis is validated by a good qualitative agreement between our modeling results and experimen...

This letter presents an algorithm for measuring the relative permittivity of thick dielectric substrates with scanning probe microscopy. Our technique does not rely on a specific type of microscopy setup and does not require expensive numerical field simulations. To demonstrate the versatility of our method, we perform measurements at high frequencies (18 GHz) with a scanning microwave microscope and at low frequencies (2 kHz) with electrostatic force microscopy. In our experiments, we study dielectric materials with epsilon values ranging from 4 (SiO2) to 300 (SrTiO3). For low epsilon values, the accuracy of the algorithm is better than 2% for tips with less than 80 nm tip radius.

We use three-dimensional finite-element numerical simulations to fully characterize the electromagnetic interactions between a metallic nano-tip and cantilever that are part of a scanning microwave microscopy (SMM) system and dielectric samples. In particular, we use this rigorous computational technique to analyze and validate a recently developed SMM calibration procedure for complex impedance measurements in reflection mode. Our simulations show that relatively small changes in the conductivity of the substrates can cause significant variations in the measured reflection coefficient. In addition, we demonstrate that the bulk systemic impedance is extremely sensitive to modifications of system parameters, namely, variations in the cantilever inclination angle as small as 1° cause changes in system impedance that can be larger than 10%. Finally, the main experimental implications of these results to SMM imaging and calibration are identified and discussed.

We report on frequency-dependent contrast in d(S11)/dV measurements of a variably doped p-type silicon sample in the frequency range from 2 GHz to 18 GHz. The measurements were conducted with a scanning microwave microscope. The measurements were done at selected frequencies while varying the DC tip voltage. The measured d(S11)/dV signal shows a maximum for doping concentrations (NA) of 1015 cm−3−1016 cm−3 at 2.3 GHz. As the microscope operating frequency is increased, this maximum sequentially “switches” through the regions of increasing dopant concentration, displaying a maximum for NA of 1017 cm−3−1018 cm−3 at 17.9 GHz. The frequency dependent “switching” is attributed to the physics of tip-to-sample interaction, particularly as related to the frequency-dependent local surface resistance and the depletion capacitance that control the RC time constant of tip-to-sample interaction. This provides a unique platform for local, frequency-selective, spatially resolved microwave spectroscopy of semiconducting ...

In this paper, an analytical model for phase and amplitude sensitive scanning microwave microscopy on metal–oxide–semiconductor structures is presented. The phase and amplitude of the microwave signals are calculated as a function of operation frequency, oxide thickness, tip radius, bias, and doping level. For doping profiling applications it is found that both the microwave amplitude and phase signals can be used. Under appropriate operation conditions, the phase signals can be larger by a factor of 40. Series resistances turn out to be problematic as they lead to non–monotonic contrast at low doping levels. The phase and amplitude behavior on a material system with a frequency dependent dielectric constant is also investigated and the possibilities of complex impedance spectroscopy are explored.

In this paper, the impact of the tip radius on dopant profiling by scanning microwave microscopy is investigated. The cantilevers are very likely to erode in such measurements, and thus, a two-dimensional Poisson solver was used to calculate the lateral spatial resolution as a function of tip radius and doping. Moreover, a strong correlation between the slope of the calibration curves and the tip diameter was found. The slope of the calibration curves increases toward −0.5 and saturates as the radius approaches values of 150 nm, which is in agreement with experimental data obtained from scanning microwave microscopy.

The scanning microwave microscope is used for calibrated capacitance spectroscopy and spatially resolved dopant profiling measurements. It consists of an atomic force microscope combined with a vector network analyzer operating between 1–20 GHz. On silicon semiconductor calibration samples with doping concentrations ranging from 1015 to 1020 atoms/cm3, calibrated capacitance-voltage curves as well as derivative dC/dV curves were acquired. The change of the capacitance and the dC/dV signal is directly related to the dopant concentration allowing for quantitative dopant profiling. The method was tested on various samples with known dopant concentration and the resolution of dopant profiling determined to 20% while the absolute accuracy is within an order of magnitude. Using a modeling approach the dopant profiling calibration curves were analyzed with respect to varying tip diameter and oxide thickness allowing for improvements of the calibration accuracy. Bipolar samples were investigated and nano-scale defect structures and p-n junction interfaces imaged showing potential applications for the study of semiconductor device performance and failure analysis.

In this paper, the dielectric constants of colloidal nanocrystals are investigated by scanning capacitance microscopy (SCM) and scanning microwave microscopy (SMM). Whereas SMM provides frequencies from 1 up to 18 GHz, conventional SCM is restricted to values below 20 kHz. With both techniques, C(V) and dC(V)/dV curves are acquired on various nanocrystalline films (Fe3O4, CoFe2O4, PbS) with monolayer thickness and on uncovered reference areas on the same samples. As we find, the dielectric constants of these nanocrystals are significantly larger as those of the bulk materials. A strong decrease of the permittivity with increasing frequency is also found.

In this paper, an analytical model for capacitance measurements by scanning microwave microscopy (SMM)/scanning microwave spectroscopy is presented. The tip-sample interactions are included by using the physics of metal-oxide-semiconductor junctions and the influence of various experimental parameters, such as the operation frequency, tip bias, tip area, oxide thickness, and sample doping are discussed. For calibrated carrier profiling it is shown that all relevant operation parameters of the SMM can be condensed into a single calibration constant and that the sample doping is obtained by using a simple analytical formula.