Thermal Microscopy with a Microfabricated Solid Immersion Lens

The spatial resolution of infrared thermometry is limited by diffraction to dimensions close to the wavelength of the collected infrared radiation, typically 5 μm at room temperatures. Thermal properties variations, temperature gradients, and defects with dimensions smaller than the diffraction limit are inaccessible to far-field infrared thermometry. This work demonstrates a near-field method for improving the spatial resolution of infrared thermometry based on a solid immersion lens (SIL). The SIL is microfabricated from silicon and integrated with a cantilever that is scanned over the sample surface. Infrared radiation collected by the SIL is measured in a conventional infrared microscope, and we show that the SIL improves the edge response of the thermal microscope by a factor of four. This imaging approach is able to resolve differences in the radiance from a uniformly heated, patterned structure with feature sizes below the diffraction limit in air.