This paper discusses advancements that have been made in scanning microwave impedance microscopy (sMIM) and how they are being used to measure various electrical properties in semiconductor devices. It explains that sMIM has a sensitivity of less than 0.1 aF and can measure minute changes in dielectric constant (k-value) and distinguish dopant levels over a wide range of concentrations with a spatial resolution of a few nm. For dielectric films and dopant levels, measurements are conveniently given in log-linear form with a repeatability well within the typical requirements for process monitoring. This, in turn, has enabled reliable quantification, where once only qualitative information was provided. The paper presents real-device results representing a wide range of measurement scenarios.

The use of Atomic Force Microscopy (AFM) electrical measurement modes is a critical tool for the study of semiconductor devices and process development. A relatively new electrical mode, scanning microwave impedance microscopy (sMIM), measures a material’s change in permittivity and conductivity at the scale of an AFM probe tip [1]. sMIM provides the real and imaginary impedance (Re(Z) and Im(Z)) of the probe-sample interface. By measuring the reflected microwave signal as a sample of interest is imaged with an AFM, we can in parallel capture the variations in permittivity and conductivity and, for doped semiconductors, variations in the depletion-layer geometry. An existing technique for characterizing doped semiconductors, scanning capacitance microscopy, modulates the tip-sample bias and detects the tip-sample capacitance with a lock-in amplifier. A previous study compares sMIM to SCM and highlights the additional capabilities of sMIM [2], including examples of nano-scale capacitance-voltage curves. In this paper we focus on the detailed mechanisms and capabilities of the nano-scale C-V curves and the ability to extract semiconductor properties from them. This study includes analytical and finite element modeling of tip bias dependent depletion-layer geometry and impedance. These are compared to experimental results on reference samples for both doped Si and GaN doped staircases to validate the systematic response of the sMIM-C (capacitive) channel to the doping concentration.

Scanning microwave impedance microscopy was used to analyze a CMOS image sensor sample to reveal details of the dopant profiling in planar and cross-sectional samples. Sitespecific capacitance-voltage spectroscopy was performed on different regions of the samples.