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Submillimeter wave exclusive Fourier transform spectrophotometer

A technology gap exists in the region of 100 GHz to 10 THz (the region called the terahertz region, submillimeter wave region or far infrared region), electromagnetic wave technology in this region is attracting attention and development. Pioneering this unexplored area is very important when considering the application to information communication which will further develop in the future and application to astronomical physics (radio astronomy) etc. However, with conventional FTIR, it was difficult to measure in the low wavenumber region of less than 10 cm -1 due to the characteristics of the optical element .
FARIS-1 is a hybrid Fourier spectrophotometer of Michelson type with high efficiency on high wavenumber side and high efficiency Martin · puppet type at low wave number side. Wide range measurement from infrared to far infrared and millimeter wave range is possible by simply changing the optical element and changing the detector. Step scan specifications and polarization modulation specifications are also available, so you can build a system customized for research use.

Hardware features

Technique for supporting far infrared measurement

Use of Martin · Puppett type interferometer and Michelson type interferometer properly

Since Michelson interferometer uses multiple reflection of the beam splitter thickness, it is necessary to increase the film thickness as the wave number becomes lower.

Therefore, the absorption of the film itself becomes large, and measurement in the low wavenumber region of 10 cm -1 or less becomes difficult.

In Japan, Martin-Paplet interferometer with efficiency of less than 100 cm -1 is available.

Martin Paplette principle

Fig. 1 Martin paplet interferometer

light source

In the wave number range of 80 cm -1 or less, a high pressure mercury light source which is stronger than the ceramic light source is used as the light source of the equipment.

Various light source intensity with respect to wave number

Fig. 2 Various light source intensity with respect to wave number


As a detector, DLATGS of PE window which operates at room temperature is installed inside.

In addition, since it is designed so that a bolometer detector can be attached to the outside, measurement with higher sensitivity can be performed.

Detector sensitivity to wave number

Fig. 3 Detector sensitivity to wavenumber

Measurement example

Measurement of Z-cut Quartz

The range from 100 GHz to 10 THz exists at the boundary between light waves and radio waves, and it transmits nonmetal and nonpolar substances such as semiconductors, plastics, paper and rubber. It corresponds to reflection measurement as well as transmission measurement. Figure 1 shows an example of Z-cut Quartz measurement. In FARIS-1, emission light in the THz region can also be measured. The system is a complete vacuum enclosure.

Transmission spectrum of silicon wafers with different resistance values

Fig. 1 Spectrum of Z-cut Quartz

Evaluation method of silicon wafer using light in terahertz region

Physical properties of semiconductor wafers using light in the terahertz region are being actively evaluated.

By using the light in the terahertz region, plasma absorption of low-doped wafers can be measured, and it is possible to evaluate the resistance value of wafers normally used in LSI.

When general silicon wafers are measured with FARIS-1, absorption of only free carriers is obtained, and as a result, carrier density and resistance can be calculated from the Drude equation.

It is also possible to estimate wafer thickness and film thickness from the interference pattern of the obtained spectrum.

Transmission spectrum of silicon wafers with different resistance values

Figure 2 Transmission spectrum of silicon wafers with different resistance values

Application example

  • Electrical and optical properties of semiconductor wafers
  • The thickness of the relatively rough film
  • Crystal structure of semiconductor wafers and films
  • The terahertz measurement system FARIS-1 has a very wide range of applied power.



Model name
Measurement wavenumber range 650 to 2 cm -1
Disassembly 0.25 to 16 cm -1
Interferometer 45 ° incidence Michelson interferometer (Martin · puppet interferometer compatible)
Beam splitter Mylar film B / S, wire grid B / S
light source Water-cooled high-pressure mercury light source
Detector PE window DTGS, bolometer


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