"Development of Near-Field Infrared Scanning Analyzing Microscope with Sub-Micro Spatial Resolution"

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Through this research project we investigated the possibility of a high-resolution infrared optical microscope which has a spatial resolution of ten to one hundred times higher than the resolution limit determined by the Abbe's diffraction limit. Although a development of infrared microscopes is strongly required for material analysis of solid-state samples with an infrared spectrometer, its spatial resolution is insufficient for material analysis of current electronic devices because of the long wavelength of infrared light. This microscope that we investigate is equipped with a probe, but not objective lens or mirror. The probe tip provides an evanescent wave of the light onto the sample surface in the near-field of the tip. The light is modulated by interacting with the local area of the sample, and the prove is scanned across the sample surface to form the image. The result through this research is as follows :1) Theoretical analysis : The diffraction effect for a small aperture wh … More ose diameter is sufficiently smaller than the infrared wavelength but is realistically achievable (approximately one-tenth of the wavelength) and the coupling between the evanescent wave and the propagating wave in the probe tip were analyzed based on the diffraction theory by Marchand and Wolf and the angular spectrum representation. Through our analyses, several new knowledges for developing the microscopy system were obtained.2) Computer simulation : The diffractions from the small aperture were calculated by computer simulation with the real parameters.3) Machining of tips : Probe tips of a ZnSe substrate and AgCl-AgBr infrared fiber were made by grinding their ends.4) Experiments : Spatial distribution of near-field diffraction by a pinhole was measured for examining the instrumentation of the microscope. A infrared CO_2 laser was used as a source and the near-field distribution of the pinhole was detected by scanning the probe tips with a 3-axis PZT stage. It was found that double lock-in detection which synchronizes with both the tip activation in axial direction and the modulation of the source is required.Multi-layer distribution of a film was measured through a small aperture using an FT-IR spectrometer which was equipped with a pair of Cassegrain objectives, a pinhole and the probe tip. The spectrum whose wavelength is longer than the pinhole diameter were measured. Less