Curing Process on Passivation Layer for Backside-Illuminated CMOS Image Sensor Application

Jongseo Park,Kyeong-Keun Choi,Hyeonseo You,Jehyun An,Sung-Min Ahn,Giryun Hong,Rock-Hyun Baek,Bohyeon Kang

doi:10.1109/access.2023.3286976

Abstract

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- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$k$ </tex-math></inline-formula> 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 ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{D}_{\mathrm {it}}$ </tex-math></inline-formula> ) and fixed-charge density ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{Q}_{\mathrm {f}}$ </tex-math></inline-formula> ) 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{D}_{\mathrm {it}}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\vert \text{Q}_{\mathrm {f}}/\text{q}\vert $ </tex-math></inline-formula> values of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.59 \times 10^{11}$ </tex-math></inline-formula> eV <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-1}$ </tex-math></inline-formula> cm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-2}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.00 \times 10^{12}$ </tex-math></inline-formula> cm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-2}$ </tex-math></inline-formula> , respectively, demonstrating its potential for the passivation layer in BSI CIS applications.

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