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Metrology, Inspection, and Process Control XXXVI

Exploration of quantum entanglement technologies for semiconductor inspection: practical applications and future directions

Yasunori Furukawa, Tetsuya Nishimura, Masafumi Asano, Masayoshi Arai, Yu Mukai, Ryo Okamoto, Shigeki Takeuchi

Published Apr 8, 2026• 0 citations
Publisher

Abstract

This paper explores the use of photonic quantum sensing - specifically, quantum infrared spectroscopy (QIRS) - as a novel approach for inspecting devices fabricated on silicon wafers. By employing entangled photon pairs, QIRS enables infrared spectroscopy using solely a visible light source and a visible detector and is anticipated to realize substantial miniaturization and cost reduction in the future. We developed a QIRS system employing the sample as a reflector for the probe idler photons and successfully acquired the infrared reflection spectra from a single surface of a silicon wafer, demonstrating consistency with its refractive index. Furthermore, we successfully evaluated High Aspect Ratio Contact (HARC) pattern using QIRS, marking the first accurate infrared reflectivity assessment in semiconductor fabrication. This advancement paves the way for widespread practical applications.

DOI
10.1117/12.3090255

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This paper explores the use of photonic quantum sensing - specifically, quantum infrared spectroscopy (QIRS) - as a novel approach for inspecting devices fabricated on silicon wafers. By employing entangled photon pairs, QIRS enables infrared spectroscopy using solely a visible light source and a visible detector and is anticipated to realize substantial miniaturization and cost reduction in the future. We developed a QIRS system employing the sample as a reflector for the probe idler photons and successfully acquired the infrared reflection spectra from a single surface of a silicon wafer, demonstrating consistency with its refractive index. Furthermore, we successfully evaluated High Aspect Ratio Contact (HARC) pattern using QIRS, marking the first accurate infrared reflectivity assessment in semiconductor fabrication. This advancement paves the way for widespread practical applications.
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In recent years, nonlinear quantum interferometry has been widely explored for applications like spectroscopy, optical coherence tomography, and imaging [1]. Quantum infrared spectroscopy (QIRS) uses quantum interference of generation processes of frequency-entangled visible-IR photon pairs to perform infrared spectroscopy using visible light sources and silicon-based detectors [2]. This technique utilizes a nonlinear quantum interferometer configuration where the generated IR photons pass through the sample, and the correlated visible photons are detected. The change in the detected visible photon flux with and without the sample helps extract the complex transmittance of the sample in the IR region.
Quantum infrared spectroscopy (QIRS), which harnesses the quantum interference between entangled visible and infrared photon-pair-generation processes in a nonlinear quantum interferometer, has attracted considerable attention for realizing infrared spectroscopy with high-performance visible detectors and light sources. However, a shortcoming of QIRS is its vulnerability to wave-front distortion caused by the sample structure, which can degrade the quantum interference. To address this problem, we propose employing the attenuated total-reflection (ATR) method, which utilizes close contact between the sample and a prism. The ATR method is one of the most utilized methods in infrared spectroscopy since it can be used to measure various types of materials, such as liquid, film, and powder samples, and is therefore useful for real-world applications. Here, we report wavelength-tunable ATR-QIRS measurements. We constructed a Michelson-type nonlinear quantum interferometer with a CaF2{\mathrm{Ca}\mathrm{F}}_{2}CaF2​ prism, and measured the absorption of water OH-stretching (approximately $3\phantom{\rule{0.2em}{0ex}}\text{\ensuremath{\mu}}\mathrm{m}$). The transmission spectrum obtained by our ATR-QIRS system shows good agreement with a numerically calculated transmission spectrum using the Fresnel equation.
Harnessing the quantum interference of the pair generation processes, infrared quantum spectroscopy, based on nonlinear interferometers with visible-infrared photon-pair sources, enables the extraction of the infrared optical properties of a sample through visible photon detection without the need for an infrared optical source or detector. We develop a theoretical framework for quantum Fourier-transform infrared (QFTIR) spectroscopy. The proposed Fourier analysis method, which fully utilizes the phase information in the interferogram, allows us to determine the complex transmittance and optical constants for a sample in a simple setup without the use of any dispersive optics for spectral selection. In the experimental demonstrations, the transmittance spectrum of a bandpass filter and the refractive index of silica glass are measured in the near-infrared region using QFTIR operated in a low gain regime; these results agree well with the independently measured spectrum using a conventional spectrometer and an value estimated from references. These demonstrations prove the validity and great potential of QFTIR spectroscopy.
Quantum sensing and quantum communication systems rely on high-performance single- or entangled-photon sources and single-photon detectors enabling experiments based on the quantum nature of single photons. In this contribution, we discuss the development of an entangled-photon source delivering entangled photon pairs with wavelengths of about 1550 nm alongside with single-photon avalanche detectors (SPADs) for the short-wave infrared (SWIR) and for the extended SWIR (eSWIR) spectral range. The fabrication processes of such quantum-enabling technologies is highlighted. The entangled-photon source is based on AlGaAs Bragg-reflection waveguides. Very low difference in effective refractive index of TE and TM polarized photons – important for high polarization entanglement without external compensation – as well as high single and coincidence count rates were achieved. For the fabrication of InGaAs/InP SWIR SPADs, the key technology is the planar process technology via zinc diffusion to produce spatially confined p-type regions. For the zinc-diffusion process, a novel method of selective epitaxial overgrowth was developed, achieving the intended double-well diffusion profile. Experimental data of thus fabricated InGaAs/InP SPADs show the expected dark-current, photo-current, and multiplication-gain characteristics in linear-mode operation as well as breakthrough behavior in Geiger-mode operation at 240 K, which is a typical operating temperature for InGaAs/InP SPADs achievable by thermoelectric cooling. GaSb-based SPADs for the eSWIR are fabricated in a mesa approach showing the expected dark current behavior as well. All three different devices are linked by enabling quantum technologies in the (e)SWIR as well as by using our III/V-semiconductor technology facilities.
Quantum infrared spectroscopy (QIRS), which exploits quantum interference between photon-pair generation processes, enables infrared spectroscopy using only visible and near-infrared (VNIR) light sources and detectors. Extending the spectral coverage of QIRS into the long-wavelength infrared region up to 20 {\textmu}m is crucial for the identification and characterization of a broad range of materials. However, implementing QIRS beyond 10 {\textmu}m has been challenging because the nonlinear materials used to date do not provide suitable photon-pair sources in this spectral region. Here, we design a wavelength-tunable photon-pair source based on a gallium selenide crystal and develop a QIRS system covering a broad spectral range from 8.6 to 20 {\textmu}m. Using this system, we measure the transmittance spectrum of a polystyrene film and observe characteristic absorption bands beyond 10 {\textmu}m relevant to identifying polystyrene and to probing local chain conformation. These results demonstrate that QIRS is capable of covering the entire molecular fingerprint region.