Surface passivation film optimization and electronic sensitivity characteristic test of back-illuminated CMOS

As the core component of the electron-bombarded active pixel sensor (EBAPS), the electron-sensitive CMOS (e-CMOS) can be prepared by thinning the surface layer of back-illuminated CMOS (BSI-CMOS), which was named electron sensitization. Due to the dramatic increase of dark current during the electron sensitization of BSI-CMOS, the signal-to-noise ratio and gain characteristics of the prepared EBAPS would be reduced. To solve this problem, this paper proposed a passivation strategy of SiO₂ grown by plasma-enhanced chemical vapor deposition (PECVD) to inhibit surface defects, and the optimal SiO₂ film thickness was explored through process optimization and electron bombardment system testing. As a result, the dark current was effectively suppressed (~50 e⁻¹/s/pix), and a lower electron-sensitive threshold voltage of 550V was realized. Moreover, the defect states density of SiO₂ deposited by PECVD was lower compared to Al₂O₃, which resulted from the more matched lattice coefficient of SiO₂. Finally, EBAPS based on SiO₂ passivated e-CMOS was realized, and high-quality imaging was successfully achieved at 1×10⁻⁴lx illumination. The above results showed that the SiO₂ grown by PECVD can effectively suppress dark current at a thickness of ~5 nm, and reduce the electron-sensitive threshold voltage to 550 V, which provided technical support for the subsequent development of EBAPS devices with high gain and low noise.