TY - JOUR
T1 - Role of Thin Sn Layer for Low Temperature Al-Al Thermo-compression Bonding of Wafer-Level Hermetic Sealing
AU - Satoh, Shiro
AU - Fukushi, Hideyuki
AU - Esashi, Masayoshi
AU - Tanaka, Shuji
N1 - Funding Information:
This study was subsidized by the Creation of Innovation Centers for Advanced Interdisciplinary Research Areas Program (Ministry of Education, Culture, Sports, Science and Technology). We also express our gratitude to Dr. Hirobumi Watanabe, Chief Engineer at Ricoh Institute of Future Technology as well as to Messrs. Yukito Sato and Yoshisuke Ansai from Ricoh Core Technology R&D Center for their valuable advice.
Publisher Copyright:
© 2018 Wiley Periodicals, Inc.
PY - 2018/5
Y1 - 2018/5
N2 - This paper reports low temperature hermetic wafer bonding using Al/Sn/Al/Sn/Al as a bonding layer. The Al surface of the bonding layer was oxidized in air, but hermetic sealing was demonstrated without surface treatment at 370 °C to 390 °C, which was lower than the maximum temperature of complementary metal oxide semiconductor (CMOS) backend process (400 °C). For the successfully sealed samples, the bonding layer was considerably compressed and squeezed, and the remaining thickness was only <16% of the initial one, that is, the reduction rate was >84%. On the other hand, the samples without Sn layers inserted, that is, using a pure Al bonding layer, were not hermetically sealed at similar temperatures, showing the reduction rate smaller than 70%. A clear correlation between the reduction rate and the yield of hermetic sealing was observed. Taking account of analytical results and Al-Sn phase diagram, it is suggested that Al-Sn liquid phase in Al grain boundaries enhances the grain slip deformation of the bonding layer and fractionates the surface Al oxide layer during the bonding process. The function of Sn for Al-Al bonding suggested in this paper is useful for wafer-level hermetic micro electro mechanical systems (MEMS) packaging at low temperature.
AB - This paper reports low temperature hermetic wafer bonding using Al/Sn/Al/Sn/Al as a bonding layer. The Al surface of the bonding layer was oxidized in air, but hermetic sealing was demonstrated without surface treatment at 370 °C to 390 °C, which was lower than the maximum temperature of complementary metal oxide semiconductor (CMOS) backend process (400 °C). For the successfully sealed samples, the bonding layer was considerably compressed and squeezed, and the remaining thickness was only <16% of the initial one, that is, the reduction rate was >84%. On the other hand, the samples without Sn layers inserted, that is, using a pure Al bonding layer, were not hermetically sealed at similar temperatures, showing the reduction rate smaller than 70%. A clear correlation between the reduction rate and the yield of hermetic sealing was observed. Taking account of analytical results and Al-Sn phase diagram, it is suggested that Al-Sn liquid phase in Al grain boundaries enhances the grain slip deformation of the bonding layer and fractionates the surface Al oxide layer during the bonding process. The function of Sn for Al-Al bonding suggested in this paper is useful for wafer-level hermetic micro electro mechanical systems (MEMS) packaging at low temperature.
KW - MEMS packaging
KW - aluminum (Al)
KW - low temperature bonding
KW - thermo-compression bonding
KW - tin (Sn)
KW - vacuum seal
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U2 - 10.1002/ecj.12060
DO - 10.1002/ecj.12060
M3 - Article
AN - SCOPUS:85040762739
SN - 1942-9533
VL - 101
SP - 33
EP - 40
JO - Electronics and Communications in Japan
JF - Electronics and Communications in Japan
IS - 5
ER -