Low temperature direct bonding of silica glass via wet chemical surface activation

Abstract

Silica glass pairs were directly bonded by wet chemical surface activation at a low temperature. A smooth joint interface with no voids and micro cracks was obtained with the assistance of a 250 C heat treatment and a pressure of $30 MPa, and the excellent transmittance of the bonded pair was demonstrated by UV-Vis absorptions. This new method can tolerate a silica glass surface roughness as high as 6 nm. A demo chip with a microfluidic channel was also prepared by this method. A modified model for the glass-to-glass bonding mechanism is proposed based on the surface and interface characterization. Raman scattering analysis showed that Si-O-Si linkages at the silica glass surface were broken, and colloid-like hydrolyzed layers formed on the glass surface after the activation treatment. TEM and EELS results revealed that the 3D glass structure of the Si-O-Si linkages formed again at the interface of the directly bonded silica glass pairs after low-temperature annealing.

Mechanisms for low-temperature direct bonding of Si/Si and quartz/quartz via VUV/O3 activation

“…To decrease annealing temperature, wet chemical surface activation was performed to assist bonding. 5,6 However, this process involves chemical solutions, which is incompatible for the building of high-accuracy structure.…”

Atmospheric Pressure Dielectric Barrier Discharge Plasma-Enhanced Optical Contact Bonding of Coated Glass Surfaces

“…For surface activation of uncoated optics, there are already different wet-chemical procedures established in optics manufacturing [10]. Similar to the bonding of wafers, a dilution of ammonium hydroxide, hydrogen peroxide and water [11] or a dilution of potassium hydroxide and water can be applied [12]. Furthermore activation can be achieved by plasma treatment [13].…”

“…Such direct contacting of coated elements would represent an added value for optics manufacturing. Due to the temperature sensitivity of functional coatings the annealing temperatures are lowered to a range of 100 • C up to 250 • C [11,14]. The wet-chemical processes were already performed successfully on optical components with dielectric functional coatings, whereas the use of the plasma process has turned out to be problematic due to the fact that the used DBD penetrates into the coating material [15,16].…”

Hydrophilic Direct Bonding of MgO/MgO for High-Temperature MEMS Devices

“…These reports demonstrate the importance of O 2 plasma activation and high temperature annealing in the fields of single crystal oxides bonding. Moreover, to avoid the damage of temperature-sensitive components and broaden doping profile, wet surface chemical activation was introduced to achieve wafer pre-bonding and reduce the annealing temperature [29]- [31].…”