Low‐temperature bonding of glasses: The role of plasma‐engrafted surface amino groups

Abstract Low‐temperature (<∼200°C) bonding of glasses is a key technology for utilizing them for microfluidics, optical applications, and microelectromechanical systems. In the present study, bonding strength of SiO 2 glasses was examined for those after several surface treatment methods. As a result, it was found that two‐step (H 2 O→ NH 3 ) plasma treatment remarkably strengthened the bonding strength (>1 J/m 2 ) at the annealing temperature of 150°C. The improvement was achieved even when only one side of the bonded surfaces was plasma‐treated. X‐ray photoelectron spectroscopy revealed that the two‐step plasma treatment generated Si–NH 2 groups on the topmost surface. Upon the annealing (<200°C), the engrafted Si–NH 2 was desorbed from the bonded interface, indicating that the Si–NH 2 effectively reacted with Si–OH on the other side to form Si–O–Si covalent bonds. This study contributes to understanding of the role of surface functional groups for bonding reaction. Furthermore, the method proposed here would be promising as a production technology because it enables glass bonding at lower temperatures with a simple plasma system.