Effect of Au Film Thickness and Surface Roughness on Room-Temperature Wafer Bonding and Wafer-Scale Vacuum Sealing by Au-Au Surface Activated Bonding

Michitaka Yamamoto; Takashi Matsumae; Yuichi Kurashima; Hideki Takagi; Tadatomo Suga; Seiichi Takamatsu; Toshihiro Itoh; Eiji Higurashi

doi:10.3390/mi11050454

Effect of Au Film Thickness and Surface Roughness on Room-Temperature Wafer Bonding and Wafer-Scale Vacuum Sealing by Au-Au Surface Activated Bonding

Micromachines (Basel). 2020 Apr 27;11(5):454. doi: 10.3390/mi11050454.

Authors

Michitaka Yamamoto^{1

2}, Takashi Matsumae², Yuichi Kurashima², Hideki Takagi², Tadatomo Suga³, Seiichi Takamatsu¹, Toshihiro Itoh¹, Eiji Higurashi²

Affiliations

¹ The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa-shi, Chiba 277-8563, Japan.
² National Institute of Advanced Industrial Science and Technology (AIST), 1-2-1 Namiki, Tsukuba, Ibaraki 305-8564, Japan.
³ Meisei University, 2-1-1 Hodokubo, Hino, Tokyo 191-8506, Japan.

Abstract

Au-Au surface activated bonding (SAB) using ultrathin Au films is effective for room-temperature pressureless wafer bonding. This paper reports the effect of the film thickness (15-500 nm) and surface roughness (0.3-1.6 nm) on room-temperature pressureless wafer bonding and sealing. The root-mean-square surface roughness and grain size of sputtered Au thin films on Si and glass wafers increased with the film thickness. The bonded area was more than 85% of the total wafer area when the film thickness was 100 nm or less and decreased as the thickness increased. Room-temperature wafer-scale vacuum sealing was achieved when Au thin films with a thickness of 50 nm or less were used. These results suggest that Au-Au SAB using ultrathin Au films is useful in achieving room-temperature wafer-level hermetic and vacuum packaging of microelectromechanical systems and optoelectronic devices.

Keywords: Au film thickness; Au-Au bonding; heterogeneous integration; room-temperature bonding; surface activated bonding; surface roughness; wafer bonding; wafer sealing.