Setup of a scanning near field infrared microscope (SNIM): Imaging of sub-surface nano-structures in gallium-doped silicon

Abstract

We have realized a scanning near-field infrared microscope in the 3–4 μm wavelength range. As a light source, a tunable high power continuous wave infrared optical parametric oscillator with an output power of up to 2.9 W in the 3–4 μm range has been set up. Using scanning near field infrared microscopy (SNIM) imaging we have been able to obtain a lateral resolution of ≤30 nm at a wavelength of 3.2 μm, which is far below the far-field resolution limit of λ/2. Using this “chemical nanoscope” we could image a sub-surface structure of implanted gallium ions in a topographically flat silicon wafer giving evidence for a near-field contrast. The observed contrast is explained in terms of the effective infrared reflection as a function of the sub-surface gallium doping concentration. The future use of the setup for nm imaging in the chemically important OH, N–H and C–H stretching vibration is discussed.