Nanometer-scale material contrast imaging with a near-field microwave microscope

The authors report topography-free material contrast imaging on a nanofabricated boron-doped silicon sample measured with a near-field scanning microwave microscope over a broad frequency range. The boron doping was performed using the focus ion beam technique on a silicon wafer with nominal resistivity of 61Ωcm. A topography-free doped region varies in sheet resistance from 1000Ω∕◻ to about 400kΩ∕◻ within a lateral distance of 4μm. The qualitative spatial resolution in sheet resistance imaging contrast is no worse than 100nm as estimated from the frequency shift signal.