Research On The Bonding Of Si/Si And Si/GaN Using Intermediate Metal Layers

Silicon and Gallium Nitride are the representations of the first and third generation semiconductors. GaN is one of the promising materials due to its excellent electrical, optical and mechanical properties. The epitaxial technique of GaN film on Si has been greatly improved, but the large thermal mismatch between GaN and Si leads to the formation of cracks in the GaN films. In this thesis, Si/Si and Si/GaN wafer bonding technology using intermediate metal layers were investigated for integrated at optoelectronics in the future.1. By analyzing and summarizing the wafer bonding technology, low–temperature wafer to wafer bonding using intermediate metals was studied. The wafers were bonded at the gradually reducing temperature.2. The influence of bonding temperature and intermediate metal layers on the bonding quality were investigated by various methods. It is found that the bonding strength was 1.27 MPa at the bonding temperature of 414℃. The I-V characteristics showed that the interface of Si/Ti/Au/Ti/Si is ohmic contact; and XPS indicated that the interface was mainly composed of Si-Au eutectic alloy.3. Si/GaN wafers were bonded using intermediate Ni/Au/Ti layers. The GaN material was successfully transferred from sapphire substrate to the Si substrate with lift off technique by the KrF excimer laser.4. The influence of bonding temperature and energy density of the excimer laser on the structure and optical properties of GaN film were investigated systemically. The AFM, XRD and PL measurements showed that i) the surface of the GaN by laser lift-off was not flat and the root-mean-square (RMS) roughness of the GaN on Si was approximately 50nm at the bonding temperature of 400℃; ii) the quality of the GaN film was higher at the lower bonding temperature; iii) the threshold of the energy density of the excimer laser lift off GaN was 300mJ/cm2.The main innovations of this paper are as follows: 1. Low-temperature Si/Si bonding has been realized using intermediate metals Ti/Au by prebonding and annealing at gradually changing temperature. The method has some merits, such as simple technology, low-temperature and high bonding strength.2. The bonding of Si/GaN using intermediate Ti/Au and Ni/Au layers has been realized. The GaN films grown on sapphire substrate were successfully bonded and transferred onto Si substrates. It was shown that the quality of the transferred GaN film was slightly degraded.