Manufacturing technologies
Semiconductor R&D on-site analysis and defect analysis, 3D integrated circuit development, Wide bandgap semiconductor development

Laser terahertz emission microscope for semiconductor
R&D
Institute of Laser Engineering
Professor

Masayoshi Tonouchi

Researchmap https://researchmap.jp/read0051752?lang=en

Abstract
Photocarriers excited with a femtosecond laser travel with the internal electric field, and terahertz (THz) electromagnetic waves arethen emitted. We have been developing a unique technique called
laser-THz emission microscope (LTEM), which measures the locallyexcited THz waves and analyses the spatiotemporal behavior of
the photocarriers. This time, we proved that LTEM is effective as atechnology to support the development of 3D integrated circuits
and wide bandgap semiconductor devices.

of the GaN layer on the surface can be estimated with a resolutionof 10nm on a wafer scale.

Manufacturing technologies▍ Background & Results
TSV is an important element for the development of 3D integrated circuits, and its in-depth internal analysis is becoming more
and more difficult. There are still many unknown properties of widebandgap semiconductors as well, and it is important to evaluate
their physical properties at the wafer scale.
The present study is expected to provide an integrated metrology solution that enables non-contact testing in the semiconductor
manufacturing process, not only for the evaluation of through-silicon vias (TSV) and wide-gap semiconductors. Maximizing production yield is essential for saving energy and minimizing waste,
and as R&D and production become increasingly complex due to
3D and miniaturization, the LTEM, which enables non-destructive,
non-contact analysis and inspection, will be an important innovation to solve this problem.

Fig.1▍ Significance of the research and Future perspective
Japanese semiconductor industry needs breakthrough semiconductor development technologies that are far superior to catchup technologies. One of the most important keys to solving thisproblem is the development of new analysis technologies. LTEM
provides a unique technology for visualizing the spatiotemporal
dynamics of photocarriers. For the practical application of LTEM, it
is important to demonstrate how it can be used to solve problems.
Here, we examined the usefulness of LTEM for TSVs and multiple
quantum well (MQW) structures.
In TSVs, as shown in Fig. 1, metal electrodes are fabricatedthrough the Si wafer. When a photoelectric charge is excited ina part of it, THz radiation is emitted reflecting the direction of thecharge movement. In addition, the excited THz waves travel into
the Si along the electrodes and are reflected at the backside andare again emitted as terahertz waves from the surface. The time
variation of these signals is expected useful to analyze the propagation inside, i.e., the MOS structure in three dimensions.
Figure 2 shows the MQW structure. Unlike TSV, the charges
are excited inside the MQW embedded in the GaN layer. As thecharge moves through the quantum well, the strain at the interface
between GaN and InGaN is released, which excites acoustic phonons. The acoustic phonons emit the THz waves at the surface,resulting in the complex THz waves as show in Fig.3. The thickness

Fig.2

Fig.3

P a t e n t
Jacobs, K. J. P. et al. Characterization of through-silicon vias using laser terahertz emission microscopy. Nat Electron. 2021; 4: 202–207. doi: 10.1038/
s41928-021-00559-z
Mannan, A. et al. Ultrafast Terahertz Nanoseismology of GaInN/GaN Multiple Quantum Wells. ADVANCED OPTICAL MATERIALS. 2021; 9(15): 2100258.
doi: 10.1002/adom.202100258
UR
L https://www.ile.osaka-u.ac.jp/research/THP/K e y w o r d support technology for semiconductor R&D analysis, terahertz time domain spectroscopy, through silicon via, wide bandgap semiconductor, LTEM
Tr e a t i s e