Curing Process for Passivation Layer of Backside-Illuminated CMOS Image Sensor

• Published in: IEEE access 2023-06, p.1-1
• Main Authors: Park, Jongseo, Choi, Kyeong-Keun, An, Jehyun, Kang, Bohyeon, You, Hyeonseo, Hong, Giryun, Ahn, Sung-Min, Baek, Rock-Hyun
• Format: Article
• Language: English
• Subjects: Capacitance-voltage characteristics; CMOS image sensor; forming gas annealing; Hafnium oxide; HfO<sub xmlns:ali="http://www.niso.org/schemas/ali/1.0/" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">2; High-k dielectric materials; Passivation; plasma-enhanced atomic layer deposition; Silicon; SiO<sub xmlns:ali="http://www.niso.org/schemas/ali/1.0/" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">2; Substrates; surface passivation
• ISSN: 2169-3536
• DOI: 10.1109/ACCESS.2023.3286976

We fabricated Al/Al 2 O 3 /SiO 2 /Si and Al/HfO 2 /Si structures to optimize the passivation layer of a backside-illuminated (BSI) complementary metal oxide semiconductor (CMOS) image sensor (CIS), with the key properties of the newly developed high- k passivation layer analyzed via border traps, interface traps, and fixed charges. In the first experiment using Al 2 O 3 /SiO 2 bilayer-based structures, different thicknesses of SiO 2 were applied from 0 to 15 nm. The improvement in their properties was confirmed by applying forming gas annealing (FGA), a type of post-treatment, to all experimental systems. The first experiment results indicated that both the SiO 2 layer and FGA were effective for chemical passivation. However, a tradeoff occurred in the degree of improvement of the interface trap density (D it ) and fixed-charge density (Q f ) according to the SiO 2 layer thickness. Subsequently, in the second experiment using HfO 2 single-layer-based structures, FGA improved the border trap to a relatively poor extent compared to the first experiment. Nevertheless, FGA improved the electrical characteristics of the HfO 2 films without any side effects and results in optimal D it and |Q f /q| values of 2.59×10 11 eV -1 cm -2 and 1.00×10 12 cm -2 , respectively, demonstrating its potential for the passivation layer in BSI CIS applications.