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1 mm 1 mm 1 mm
n –Si wafer
TERAHERTZ IMAGING continued
the Protemics TeraCube near-field scanning system that includes
a PC near-field probe (the Protemics TeraSpike TD-800-X-HR-
WT) for terahertz detection and imaging (see Fig. 1). 3
A computer unit controls the TDS module as well as the
near-field imaging system. During measurements, the motion control unit of the raster scanning system transmits the
current position of the sample continuously to the data acquisition unit, where it is combined with the terahertz data recorded at each position. The high sampling rate of the TDS
module enables surface-scanning operation under continuous
movement (without stop-and-go interruptions) for full tera-
hertz transient detection.
The PC near-field probe consists of a 1-µm-thin low-tem-perature-grown gallium arsenide (GaAs) cantilever featuring
a pair of tapered electrodes that form the PC switch at the tip
of the probe. It records the transmitted terahertz field close to
the sample surface. In contrast to electrooptic crystals as near-field probes, it is characterized by lower invasiveness and higher sensitivity.
Scattering-tip-based probes can only record z-fields and ap-erture-based probes only in horizontal (x, y) fields. In contrast,
our PC near-field detectors are designed to be selectively sensitive to field vector components in x-, y-, or z-directions.
With a maximum spatial resolution of 3 to 10 µm when hovering only a few microns above the surface of a sample under
FIGURE 2. Optical microscope images (a) and terahertz maps (b)
of samples are shown after local SiNx removal (“opening”) with etch
paste at three different curing temperatures (220°, 250°, and 375°C);
a schematic illustration shows the etching cross-sections (c) at the
corresponding curing temperatures.