Contents lists available at ScienceDirect Solid State Electronics journal homepage: www.elsevier.com/locate/sse Near-field scanning microwave microscope platform based on a coaxial cavity resonator for the characterization of semiconductor structures Bendehiba Abadlia Bagdad, Carmen Lozano, Francisco Gamiz ⁎ Nanoelectronics Research Group, CITIC, University of Granada, 18071 Granada, Spain ARTICLE INFO Keywords: Near-field scanning microwave microscopy (NSMM) Coaxial cavity resonators Non-destructive characterization Thin film semiconductor structures ABSTRACT A Near-Field Scanning Microwave Microscope (NSMM) for the characterization of semiconductor structures has been designed, simulated and fabricated. The present NSMM system is based on a home-made coaxial-cavity resonator which is fed by a Keysight N5242A PNA-X Network Analyzer. The inner conductor of the coaxial resonator is connected to a sharpened tungsten tip, which was fabricated by an electrochemical process. The reflection and transmission coefficients S 11 ,S 21 , the resonance frequency f r and the quality factor Q of the resonant cavity are measured as the semiconductor structure is scanned by the sharpened probe tip while the sample-tip distance is kept constant in the near-field region. The interaction between the probe tip and the sample under test provides variations of these parameters which are related to the topographical and dielectric properties of a very small region of the material under the probe tip. Thus, a 2D image of the evolution of the S 11 , S 21 ,f r and Q parameters on the surface of the device under test is obtained. This image can be related to space changes in the topography, dielectric properties and composition of the semiconductor structure. 1. Introduction Near-field scanning microwave microscopy (NSMM) is a technique used for the non-destructive characterization of materials at microwave frequency range. An NSMM system consists of a sharpened metallic tip, mounted on the center conductor of a high-quality coaxial resonator. The coaxial resonator is fed by a microwave signal supplied by a Vector Network Analyzer (VNA). The transmission coefficient S 21, (resp. re- flection coefficient, S 11 ) of the cavity, measured by the VNA, shows a characteristic transmission maximum (resp. reflection minimum) at the resonant frequency, f r0 , for which it was designed, and a particular quality factor, Q 0 , which also depends on the geometry of the cavity. When the probe tip is placed close enough (in the near field region) to the device under test (DUT), a shift in the resonant frequency f r and a modification of the quality factor, Q, of the coaxial-cavity resonator are produced depending on the impedance of the tip-sample interaction. These changes are continuously measured by the VNA. The shift of the resonant frequency depends on the distance between the tip and the sample and the electromagnetic properties of the sample under test, such as the conductivity, sheet resistance, or dielectric constant, and their spatial variations [1–4]. If the distance between the tip and the surface of the sample is kept constant, the shift in f r only depends on the electromagnetic properties of a very small area (of the size of the tip dimensions) of the DUT near the probe tip. The sample is then scanned by the tip of the cavity while the distance between tip-sample is kept constant and the resonant frequency of the cavity is continuously measured by the VNA. The 2D representation of the resonant frequency, f r , quality factor Q, and magnitude of the transmission |S 21 | and re- flection |S 11 | coefficients of the coaxial-cavity resonator provides a map of the electromagnetic properties of the sample under test. Therefore, the high spatial resolution of the NSMM technique allows us to non- destructively characterize semiconductor structures with high sensi- tivity and with nanoscale resolution without damaging them [5,6]. Thus, we can evaluate, for example, the quality of the interfaces, layer thickness variations, doping and concentrations, etc. [7]. Fig. 1 shows the scheme of the NSMM structure with the main parts of the system, such as the VNA that continuously feeds a coaxial-cavity resonator with a conductive tip connected at the end of its inner con- ductor. The designed coaxial-cavity resonator provides a very high-quality factor and its potential to characterize metallic materials has been al- ready demonstrated by several groups [7,8]. In this paper, the design, simulation and set up of a NSMM platform based on a coaxial-cavity resonator have been carried out. Then, the transmission and reflection coefficients S 21 ,S 11 of the resonant cavity is continuously measured and monitored by a vector network analyzer, while a sharpened tungsten tip https://doi.org/10.1016/j.sse.2019.03.052 ⁎ Corresponding author. E-mail address: fgamiz@ugr.es (F. Gamiz). Solid State Electronics xxx (xxxx) xxx–xxx 0038-1101/ © 2019 Elsevier Ltd. All rights reserved. Please cite this article as: Bendehiba Abadlia Bagdad, Carmen Lozano and Francisco Gamiz, Solid State Electronics, https://doi.org/10.1016/j.sse.2019.03.052