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

• Published in: Micromachines (Basel) 2020-04, Vol.11 (5), p.454
• Main Authors: Yamamoto, Michitaka, Matsumae, Takashi, Kurashima, Yuichi, Takagi, Hideki, Suga, Tadatomo, Takamatsu, Seiichi, Itoh, Toshihiro, Higurashi, Eiji
• Format: Article
• Language: English
• Subjects: Au-Au bonding; heterogeneous integration; room-temperature bonding; surface activated bonding; wafer bonding; wafer sealing
• ISSN: 2072-666X; 2072-666X
• DOI: 10.3390/mi11050454

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.