A Wide Spectral Response Single Photon Avalanche Diode for Backside-Illumination in 55-nm CMOS Process

• Published in: IEEE transactions on electron devices 2022-09, Vol.69 (9), p.5041-5047
• Main Authors: Liu, Yang, Liu, Maliang, Ma, Rui, Hu, Jin, Li, Dong, Wang, Xiayu, Zhu, Zhangming
• Format: Article
• Language: English
• Subjects: Avalanche diodes; Backside-illuminated (BSI) technology; CMOS; CMOS image sensor (CIS); CMOS process; Crosstalk; detector; Detectors; Doping; Geiger mode; Junctions; light detection and ranging (LiDAR); Photon avalanches; Photonics; Photons; Room temperature; single photon avalanche diode (SPAD); Single-photon avalanche diodes; Spectral sensitivity; Substrates
• ISSN: 0018-9383; 1557-9646
• DOI: 10.1109/TED.2022.3194488

This article presents a wide-spectral response single photon avalanche diode (SPAD) designed and fabricated in advanced 55-nm CMOS image sensor technology. SPADs with different active areas and doping profiles are simulated by Sentaurus-TCAD to optimize their electrical and optical performances. A global well-sharing technique is employed to deliver a pixel pitch of 16.4 ~\mu \text{m} and a fill factor of 50.96% for a device with a 6 ~\mu \text{m} radius. The proposed structure is based on a p + /deep n-well (DNW) multiplication junction, extending its spectral response as much as possible. Compared to the existing BSI SPADs, a triple protection method is innovatively used to suppress premature edge breakdown and to reduce the dark count rate (DCR) through a combination of a virtual retrograde DNW, p-well guard ring, and a poly gate ring located above the shallow trench isolation. Furthermore, deep trench isolation is employed to suppress crosstalk. Samples of different radii from 2 to 6 ~\mu \text{m} are manufactured. The SPADs exhibit a low DCR below 20 cps/ \mu \text{m} 2 at room temperature and with a 2-V excess bias. The peak photon detection probability is 20.3% at 660 nm and is maintained at a high value, more than 10%, in the spectral range of 550-820 nm.