A novel scattering-type THz microprobe with integrated source and detector for contact-free, high-speed surface imaging at sub-μm-resolution

Terahertz (THz) Time Domain Spectroscopy (THz-TDS) provides an interesting set of possibilities for contactless wafer inspection as many used materials contain resonant features in their refractive indices within the THz-spectrum. It can be used for example to analyze electrical properties, such as sheet resistance. Even though there is a large set of advantages for THz-TDS, the wavelength of THz radiation is often in the same or higher range as geometric features of interest. The limits for the spatial resolution of THz measurements are therefore given by the THz waves while scattering effects are not limited by the wavelength. To make use of the THz scattering effect to achieve spatial resolutions in the nanometer scale, a known approach is the scattering-type Scanning Near-field Optic Microscopy (s-SNOM) is used. In s-SNOM a sharp oscillating tip, similar to the ones used in atomic force measurements (AFM), is positioned close to the surface and is radiated with THz waves to cause the scattering effect. A detector then measures those scattering waves. One major hurdle for implementing s-SNOM is the complex setup required for alignment and operation since the THz emitter, the scattering tip and the THz detector are separated. This paper presents a method where a new THz probe antenna design provides the possibility to measure THz scattering and allows high spatial resolutions by combining those components into a probe tip. As a result, not only high spatial resolutions can be achieved but also an oscillation tip can be omitted.