Subsurface nanoimaging by broadband terahertz pulse near-field microscopy.

Combined with terahertz (THz) time-domain spectroscopy, THz near-field microscopy based on an atomic force microscope is a technique that, while challenging to implement, is invaluable for probing low-energy light-matter interactions of solid-state and biomolecular nanostructures, which are usually embedded in background media. Here, we experimentally demonstrate a broadband THz pulse near-field microscope that provides subsurface nanoimaging of a metallic grating embedded in a dielectric film. The THz near-field microscope can obtain broadband nanoimaging of the subsurface grating with a nearly frequency-independent lateral resolution of 90 nm, corresponding to ∼ λ/3300, at 1 THz, while the AFM only provides a flat surface topography.

Computed terahertz near-field mapping of molecular resonances of lactose stereo-isomer impurities with sub-attomole sensitivity.

Terahertz near-field microscopy (THz-NFM) could locally probe low-energy molecular vibration dynamics below diffraction limits, showing promise to decipher intermolecular interactions of biomolecules and quantum matters with unique THz vibrational fingerprints. However, its realization has been impeded by low spatial and spectral resolutions and lack of theoretical models to quantitatively analyze near-field imaging. Here, we show that THz scattering-type scanning near-field optical microscopy (THz s-SNOM) with a theoretical model can quantitatively measure and image such low-energy molecular interactions, permitting computed spectroscopic near-field mapping of THz molecular resonance spectra. Using crystalline-lactose stereo-isomer (anomer) mixtures (i.e., α-lactose (≥95%, w/w) and ß-lactose (≤4%, w/w)), THz s-SNOM resolved local intermolecular vibrations of both anomers with enhanced spatial and spectral resolutions, yielding strong resonances to decipher conformational fingerprint of the trace ß-anomer impurity. Its estimated sensitivity was ~0.147 attomoles in ~8 × 10-4 µm3 interaction volume. Our THz s-SNOM platform offers a new path for ultrasensitive molecular fingerprinting of complex mixtures of biomolecules or organic crystals with markedly enhanced spatio-spectral resolutions. This could open up significant possibilities of THz technology in many fields, including biology, chemistry and condensed matter physics as well as semiconductor industries where accurate quantitative mappings of trace isomer impurities are critical but still challenging.

Fast, exact, and non-destructive diagnoses of contact failures in nano-scale semiconductor device using conductive AFM.

We fabricated a novel in-line conductive atomic force microscopy (C-AFM), which can analyze the resistive failures and examine process variance with an exact-positioning capability across the whole wafer scale in in-line DRAM fabrication process. Using this in-line C-AFM, we introduced a new, non-destructive diagnosis for resistive failure in mobile DRAM structures. Specially, we focused on the self-aligned contact (SAC) process, because the failure of the SAC process is one of the dominant factors that induces the degradation of yield performance, and is a physically invisible defect. We successfully suggested the accurate pass mark for resistive-failure screening in the fabrication of SAC structures and established that the cause of SAC failures is the bottom silicon oxide layer. Through the accurate pass mark for the SAC process configured by the in-line C-AFM analyses, we secured a good potential method for preventing the yield loss caused by failures in DRAM fabrication.