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Micromachines 2019, 10(2), 119; https://doi.org/10.3390/mi10020119

Comparison of Argon and Oxygen Plasma Treatments for Ambient Room-Temperature Wafer-Scale Au–Au Bonding Using Ultrathin Au Films

1
National Institute of Advanced Industrial Science and Technology (AIST), 1-2-1 Namiki, Tsukuba, Ibaraki 305-8564, Japan
2
Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa-shi, Chiba 277-8563, Japan
3
School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
*
Authors to whom correspondence should be addressed.
Received: 20 December 2018 / Revised: 5 February 2019 / Accepted: 7 February 2019 / Published: 13 February 2019
(This article belongs to the Special Issue Heterogeneous Integration for Optical Micro and Nanosystems)
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Abstract

Au–Au surface activated bonding is promising for room-temperature bonding. The use of Ar plasma vs. O2 plasma for pretreatment was investigated for room-temperature wafer-scale Au–Au bonding using ultrathin Au films (<50 nm) in ambient air. The main difference between Ar plasma and O2 plasma is their surface activation mechanism: physical etching and chemical reaction, respectively. Destructive razor blade testing revealed that the bonding strength of samples obtained using Ar plasma treatment was higher than the strength of bulk Si (surface energy of bulk Si: 2.5 J/m2), while that of samples obtained using O2 plasma treatment was low (surface energy: 0.1–0.2 J/m2). X-ray photoelectron spectroscopy analysis revealed that a gold oxide (Au2O3) layer readily formed with O2 plasma treatment, and this layer impeded Au–Au bonding. Thermal desorption spectroscopy analysis revealed that Au2O3 thermally desorbed around 110 °C. Annealing of O2 plasma-treated samples up to 150 °C before bonding increased the bonding strength from 0.1 to 2.5 J/m2 due to Au2O3 decomposition. View Full-Text
Keywords: heterogeneous integration; wafer bonding; low-temperature bonding; Au–Au bonding; ultrathin Au films; Ar plasma treatment; O2 plasma treatment heterogeneous integration; wafer bonding; low-temperature bonding; Au–Au bonding; ultrathin Au films; Ar plasma treatment; O2 plasma treatment
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Yamamoto, M.; Matsumae, T.; Kurashima, Y.; Takagi, H.; Suga, T.; Itoh, T.; Higurashi, E. Comparison of Argon and Oxygen Plasma Treatments for Ambient Room-Temperature Wafer-Scale Au–Au Bonding Using Ultrathin Au Films. Micromachines 2019, 10, 119.

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