Advances in Quantitative Impedance Measurement and Dopant Level Profiling Using Scanning Microwave Microscopy

Scanning microwave microscopy (SMM) is a recent development in SPM technique that combines thelateral resolution of AFM and the measurement precision of microwave analysis. It consists of an AFMinterfaced with a vector network analyzer (VAN). In the reflection mode (S11 measurement), themeasured complex reflection coefficient of the microwave from the contact point directly correlates tothe impedance of the sample under test. A linear calibration procedure for SMM using a capacitancestandard has been developed and used to measure the minute capacitance difference, such as thatbetween decanethiol and octadecanthiol SAM layers[1,2]. However, the linear calibration procedure islimited to a small impedance range. A nonlinear calibration algorithm that works on all measurementobjects has been developed recently [3]. The new algorithm is valid for the measurement of quantitativecomplex impedance, and has means to discriminate between lossy and capacitive components. Resultsfrom electromagnetic simulation of the complex impedance at the tip/sample interface using EMPro willbe presented as well. The capability of measuring the capacitance of a doped structure directly poses aunique advantage for SMM over the existing scanning capacitance microscopy technique. A highthroughput C-V mapping workflow, Scanning Sawtooth C-V Spectroscopy (SSCV), was alsoestablished. This allows for nanoscale mapping of C-V curves for materials science applications. Basedon capacitance measurement, SMM can be used for doping structure characterization of semiconductordevices see Figure 1. Quantitative dopant concentration can be obtained by calibrating the measuredcapacitance, C, or dC/dV against known dopant structures such as that fabricated by IMEC.References [1] H. P. Huber, M. Moertelmaier, T. M. Wallis, C. J. Chiang, M. Hochleitner, A. Imtiaz, Y. J. Oh, K.Schilcher, M. Dieudonne, J. Smoliner,P. Hinterdorfer,S. J. Rosner, H. Tanbakuchi, P. Kabos, and F.Kienberger, Rev. Sci. Instrum. 81 (2010)113701 [2] Shijie Wu and Jing-Jiang Yu, Appl. Phys. Lett. 97 (2010)202902 [3] J. Hoffmann, M. Wollensack, M. Zeier, J Niegemann, Hans-Peter Huberand F. Kienberger, 12th IEEE International Conference on Nanotechnology (IEEENANO) Figure 1. SMM imaging of eeprom cells with different DC bias applied