Transmission-Type Laser THz Emission Microscope Using a Solid Immersion Lens

A recently developed laser terahertz (THz) emission microscope (LTEM) is a new type of inspection tool for semiconductor integrated circuits by 2-D mapping of THz emission excited by femtosecond (fs) laser pulse. For high-resolution imaging, we demonstrate the combination of a hemispherical solid immersion lens (SIL) and an LTEM with transmission-type detection mode. Unlike reflective LTEM geometries, in which both the probing fs laser pulses and the generated THz emissions utilize the same optical components, the transmission system enables flexibility in the construction of both the fs laser and the THz detection optics: The optics on the incident side of the sample are used only to manipulate the fs pulses, while those on the transmission side are meant only for manipulating the THz emission. We could improve the spatial resolution by less than 1.5 mum by combining the objective lens with the hemispherical SIL with a refractive index n = 1.98 at 780 nm.