A back-illuminated 6 μm SPAD depth sensor with PDE 36.5% at 940 nm via combination of dual diffraction structure and 2×2 on-chip lens

• Published in: 2023 IEEE Symposium on VLSI Technology and Circuits (VLSI Technology and Circuits) pp. 1 - 2
• Main Authors: Fujisaki, Y., Tsugawa, H., Sakai, K., Kumagai, H., Nakamura, R., Ogita, T., Endo, S., Iwase, T., Takase, H., Yokochi, K., Yoshida, S., Shimada, S., Otake, Y., Wakano, T., Hiyama, H., Hagiwara, K., Arakawal, M., Matsumotol, S., Maeda, H., Sugihara, K., Takabayashi, K., Ono, M., Ishibashi, K., Yamamoto, K.
• Format: Conference Proceeding
• Language: English
• Published: JSAP 11.06.2023
• Subjects: Crosstalk; Diffraction; Dual diffraction structureand 2 x 2 OCL; PDE; Sensitivity; Silicon; Silicon compounds; Single-photon avalanche diodes; SPAD; System-on-chip; Very large scale integration
• ISSN: 2158-9682
• DOI: 10.23919/VLSITechnologyandCir57934.2023.10185251

We present a back-illuminated 3D-stacked 6 \mu \mathrm{m} single-photon avalanche diode (SPAD) sensor with very high photon detection efficiency (PDE) performance. To enhance PDE, a dual diffraction structure was combined with 2\times 2 on-chip lens (OCL) for the first time. A dual diffraction structure comprises a pyramid surface for diffraction (PSD) and periodic uneven structures by shallow trench for diffraction formed on the Si surface of light-facing and opposite sides, respectively. Additionally, PSD pitch and SiO 2 film thickness buried in full trench isolation were optimized. Consequently, a PDE of 36.5% was achieved at \lambda=940 nm, the world's highest value. Owing to shield ring contact, crosstalk was reduced by about half compared to a conventionally plugged one.