Effect of ALD processes on physical and electrical properties of HfO2 dielectrics for the surface passivation of a CMOS image sensor application

• Published in: IEEE access Vol. 10; p. 1
• Main Authors: Kim, Honggyun, Chavan, Vijay D., Aziz, Jamal, Ko, Byoungsu, Lee, Jae-Sung, Rho, Junsuk, Dongale, Tukaram D., Choi, Kyeong-Keun, Kim, Deok-kee
• Format: Journal Article
• Language: English
• Published: Piscataway IEEE 2022; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Aluminum oxide; Annealing; Atomic layer deposition; Atomic layer epitaxy; Bilayers; Capacitance-voltage characteristics; Carrier lifetime; Charge density; CMOS; CMOS image sensor; Electrical properties; Finite difference time domain method; forming gas; Hafnium oxide; HfO; 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; interface trap density; Minority carriers; Passivation; Passivity; Plasma temperature; Quantum efficiency; Silicon; surface passivation; Thin films; Vacuum annealing
• ISSN: 2169-3536
• DOI: 10.1109/ACCESS.2022.3183593

The surface passivation of a CMOS image sensor (CIS) is highly beneficial for the overall improvement of a device performance. We employed the thermal atomic layer deposition (T-ALD) and plasma enhanced (PE-ALD) techniques for the deposition of 20 nm HfO 2 as well as stacked with 3 and 5 nm Al 2 O 3 thin films. The HfO 2 /Si and Al 2 O 3 /HfO 2 /Si metal-oxide-semiconductor structures were used to analyze the fixed charge density (Q f ) and interface trap density (D it ). The as-synthesized samples show high D it and Q f values (10 12 cm -2 eV -1 ) and a minority carrier lifetime of 15-300 μs. The finite-difference time-domain simulation of high-k dielectrics confirmed that the Al 2 O 3 (top)/HfO 2 stacked structures expected higher quantum efficiency for CIS application. The effect of vacuum annealing (VA) and forming gas annealing (FGA) treatments succeeded with the decomposition of the D it and increase in carrier lifetime. The H 2 ambient FGA samples showed a remarkable decrease in the D it values. To improve the overall performance of the device after passivation, we employed an Al 2 O 3 /HfO 2 bilayer structure, which showed a low D it of 10 11 cm -2 eV -1 and a minority carrier lifetime of ~3,700 μs after 400 °C and 30 min FGA. We believe that this surface passivation strategy will pave way for future CIS technology regarding the development of lower defective surface and superior performance.