| AVS 56th International Symposium & Exhibition | |
| Advanced Surface Engineering | Tuesday Sessions |
| Session SE-TuP |
| Session: | Advanced Surface Engineering Poster Session |
| Presenter: | T. Plach, Johannes Kepler University, Austria |
| Authors: | T. Plach, Johannes Kepler University, Austria K. Hingerl, Johannes Kepler University, Austria V. Dragoi, EV Group, Austria G. Mittendorfer, EV Group, Austria M. Wimplinger, EV Group, Austria |
| Correspondent: | Click to Email |
Low temperature plasma activated direct wafer bonding (LTPADWB) for Si-SiO2 interfaces is a process that lowers the required annealing temperatures necessary for reaching high bond strength. Bulk strength can be realized by plasma activation with subsequent annealing at 300◦C. The mechanism behind this improvement is still under discussion.
At this temperature, half of the bulk strength is reached already with conventional wafer bonding. The low temperature steps for the hydrophilic process are interpreted as follows: Up to 100°C the substrate surfaces are held together via van der Waals interaction which is mediated by a few monolayers of water. In the range of 100-200°C the water diffuses away from the interface both along the interface and through the oxide into the crystalline bulk, where it reacts with the silicon and forms oxide. The remaining half of the bond strength is usually attributed to a closing of gaps at the interface[1], which starts at the softening temperature of the thermal oxide at around 850-900°C.
To clarify the mechanism for this commercially available process, different bonding experiments were performed to evaluate the lifetime of the surface activation and the achievable bond strength when using substrates with various orientations. Interfaces of bonded wafer pairs were investigated by transmission electron microscopy (TEM). TEM images clearly show that there is no discernible interface between the native oxide on one side and the thermal oxide on the other side.
By covering half of the wafer during plasma activation, comparisons between the activated and non-activated region could be made by atomic force microscopy, by spectroscopic ellipsometry, by Auger analysis and by X-ray photoelectron spectroscopy.
It was found that the top surface stoichiometry is chemically changed, which favors bonding. Finally a model for the mechanism that explains the experimental results will be presented.
Keywords: wafer bonding; plasma; low temperature
References
[1] Q.-Y. Tong, U. Gösele, Semiconductor Wafer Bonding: Science and Technology, Wiley, (1998)