Preliminary study on surface processing of silica glass by atmosphere inductively coupled plasma for direct bonding

The performance for some optical system strongly depends on bonding quality of multiple optic components. For heterogeneous integration of silica glass, the direct bonding contributes to a high-strength combination without contaminating the bonding interface, but the surface activation induced in vacuum leads to low efficiency and process complexity. Accordingly, surface processing by an atmosphere inductively coupled plasma (ICP) is proposed before direct bonding. The high-energy Ar-O2 ICP is generated to enhance the hydroxyl radical density and produce good surface hydrophilicity. With ICP irradiation for 10 seconds, the initial surface (contact angle of 41.8°) can be turned super hydrophilic (contact angle < 3°) which ensures high bonding strength. After ICP irradiation, the roughness and form accuracy of the silica glass substrate were well maintained. In addition, ICP irradiation can clean the surface to improve the bonding strength of samples. It is shown that ICP irradiation can improve the bond strength without degrading the surface characteristics. Therefore, direct bonding assisted by atmosphere ICP processing shows potential applicability for heterogeneous integration of high-performance optics.