J. Wittborn, R. Weiland, Infineon Technologies AG, Munich, Germany; A. J. Huber, Neaspec GmbH, Martinsried, Germany; R. Hillenbrand, CIC nanoGUNE Consolider, Donostia – San Sebastian, Spain; F. Keilmann, Max Planck Institut of Quantum Optics and Center for NanoScience, Garching, Germany

Summary: Measurement of carrier- or doping-concentration of nanostructured devices still remains a challenge for the semiconductor industry. Secondary ion mass spectroscopy (SIMS) and spreading resistance profiling (SRP) are useful methods for measuring dopant concentration and carrier concentration, respectively, but are limited to 1-dimensional depth profiles. In addition, both these methods require relatively large, laterally homogenous sample areas. Atom probe microscopy faces the opposite problem; it yields 3-dimensional measurements of the nanoscale dopant concentration but the maximum sample size limits its use for many failure analysis applications. Here we demonstrate the benefits of near-field nanoscopy. We use laser light at 2.54 THz (wavelength λ = 118µm) scattering at metallised atomic force microscope tips to achieve 2-dimensional, quantitative mapping of carrier concentration in the range 10¹⁶ to 10¹⁹ carriers/cm³ at a spatial resolution of 40 nm (λ/3000). Nanoscale resolution is achieved by THz field confinement at the very tip apex to within 30 nm. Images of 65-nm technology node CMOS transistors demonstrate the simultaneous THz recognition of materials and mobile carriers in a single nanodevice.